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* [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2]
@ 2019-06-04 16:34 David Howells
  2019-06-04 16:35 ` [PATCH 1/8] security: Override creds in __fput() with last fputter's creds " David Howells
                   ` (9 more replies)
  0 siblings, 10 replies; 32+ messages in thread
From: David Howells @ 2019-06-04 16:34 UTC (permalink / raw)
  To: viro
  Cc: Casey Schaufler, dhowells, raven, linux-fsdevel, linux-api,
	linux-block, keyrings, linux-security-module, linux-kernel


Hi Al,

Here's a set of patches to add a general variable-length notification queue
concept and to add sources of events for:

 (1) Mount topology events, such as mounting, unmounting, mount expiry,
     mount reconfiguration.

 (2) Superblock events, such as R/W<->R/O changes, quota overrun and I/O
     errors (not complete yet).

 (3) Block layer events, such as I/O errors.

 (4) Key/keyring events, such as creating, linking and removal of keys.

One of the reasons for this is so that we can remove the issue of processes
having to repeatedly and regularly scan /proc/mounts, which has proven to
be a system performance problem.  To further aid this, the fsinfo() syscall
on which this patch series depends, provides a way to access superblock and
mount information in binary form without the need to parse /proc/mounts.


LSM support is included:

 (1) The creds of the process that did the fput() that reduced the refcount
     to zero are cached in the file struct.

 (2) __fput() overrides the current creds with the creds from (1) whilst
     doing the cleanup, thereby making sure that the creds seen by the
     destruction notification generated by mntput() appears to come from
     the last fputter.

 (3) security_post_notification() is called for each queue that we might
     want to post a notification into, thereby allowing the LSM to prevent
     covert communications.

 (?) Do I need to add security_set_watch(), say, to rule on whether a watch
     may be set in the first place?  I might need to add a variant per
     watch-type.

 (?) Do I really need to keep track of the process creds in which an
     implicit object destruction happened?  For example, imagine you create
     an fd with fsopen()/fsmount().  It is marked to dissolve the mount it
     refers to on close unless move_mount() clears that flag.  Now, imagine
     someone looking at that fd through procfs at the same time as you exit
     due to an error.  The LSM sees the destruction notification come from
     the looker if they happen to do their fput() after yours.


Design decisions:

 (1) A misc chardev is used to create and open a ring buffer:

	fd = open("/dev/watch_queue", O_RDWR);

     which is then configured and mmap'd into userspace:

	ioctl(fd, IOC_WATCH_QUEUE_SET_SIZE, BUF_SIZE);
	ioctl(fd, IOC_WATCH_QUEUE_SET_FILTER, &filter);
	buf = mmap(NULL, BUF_SIZE * page_size, PROT_READ | PROT_WRITE,
		   MAP_SHARED, fd, 0);

     The fd cannot be read or written (though there is a facility to use
     write to inject records for debugging) and userspace just pulls data
     directly out of the buffer.

 (2) The ring index pointers are stored inside the ring and are thus
     accessible to userspace.  Userspace should only update the tail
     pointer and never the head pointer or risk breaking the buffer.  The
     kernel checks that the pointers appear valid before trying to use
     them.  A 'skip' record is maintained around the pointers.

 (3) poll() can be used to wait for data to appear in the buffer.

 (4) Records in the buffer are binary, typed and have a length so that they
     can be of varying size.

     This means that multiple heterogeneous sources can share a common
     buffer.  Tags may be specified when a watchpoint is created to help
     distinguish the sources.

 (5) The queue is reusable as there are 16 million types available, of
     which I've used 4, so there is scope for others to be used.

 (6) Records are filterable as types have up to 256 subtypes that can be
     individually filtered.  Other filtration is also available.

 (7) Each time the buffer is opened, a new buffer is created - this means
     that there's no interference between watchers.

 (8) When recording a notification, the kernel will not sleep, but will
     rather mark a queue as overrun if there's insufficient space, thereby
     avoiding userspace causing the kernel to hang.

 (9) The 'watchpoint' should be specific where possible, meaning that you
     specify the object that you want to watch.

(10) The buffer is created and then watchpoints are attached to it, using
     one of:

	keyctl_watch_key(KEY_SPEC_SESSION_KEYRING, fd, 0x01);
	mount_notify(AT_FDCWD, "/", 0, fd, 0x02);
	sb_notify(AT_FDCWD, "/mnt", 0, fd, 0x03);

     where in all three cases, fd indicates the queue and the number after
     is a tag between 0 and 255.

(11) The watch must be removed if either the watch buffer is destroyed or
     the watched object is destroyed.


Things I want to avoid:

 (1) Introducing features that make the core VFS dependent on the network
     stack or networking namespaces (ie. usage of netlink).

 (2) Dumping all this stuff into dmesg and having a daemon that sits there
     parsing the output and distributing it as this then puts the
     responsibility for security into userspace and makes handling
     namespaces tricky.  Further, dmesg might not exist or might be
     inaccessible inside a container.

 (3) Letting users see events they shouldn't be able to see.


Further things that could be considered:

 (1) Adding a keyctl call to allow a watch on a keyring to be extended to
     "children" of that keyring, such that the watch is removed from the
     child if it is unlinked from the keyring.

 (2) Adding global superblock event queue.

 (3) Propagating watches to child superblock over automounts.


The patches can be found here also:

	http://git.kernel.org/cgit/linux/kernel/git/dhowells/linux-fs.git/log/?h=notifications

Changes:

 v2: I've fixed various issues raised by Jann Horn and GregKH and moved to
     krefs for refcounting.  I've added some security features to try and
     give Casey Schaufler the LSM control he wants.

David
---
David Howells (8):
      security: Override creds in __fput() with last fputter's creds
      General notification queue with user mmap()'able ring buffer
      keys: Add a notification facility
      vfs: Add a mount-notification facility
      vfs: Add superblock notifications
      fsinfo: Export superblock notification counter
      block: Add block layer notifications
      Add sample notification program


 Documentation/security/keys/core.rst   |   58 ++
 Documentation/watch_queue.rst          |  328 ++++++++++++
 arch/x86/entry/syscalls/syscall_32.tbl |    3 
 arch/x86/entry/syscalls/syscall_64.tbl |    3 
 block/Kconfig                          |    9 
 block/Makefile                         |    1 
 block/blk-core.c                       |   29 +
 block/blk-notify.c                     |   83 +++
 drivers/misc/Kconfig                   |   13 
 drivers/misc/Makefile                  |    1 
 drivers/misc/watch_queue.c             |  895 ++++++++++++++++++++++++++++++++
 fs/Kconfig                             |   21 +
 fs/Makefile                            |    1 
 fs/file_table.c                        |   12 
 fs/fsinfo.c                            |   12 
 fs/mount.h                             |   33 +
 fs/mount_notify.c                      |  186 +++++++
 fs/namespace.c                         |    9 
 fs/super.c                             |  117 ++++
 include/linux/blkdev.h                 |   10 
 include/linux/dcache.h                 |    1 
 include/linux/fs.h                     |   79 +++
 include/linux/key.h                    |    4 
 include/linux/lsm_hooks.h              |   15 +
 include/linux/security.h               |   14 +
 include/linux/syscalls.h               |    5 
 include/linux/watch_queue.h            |   87 +++
 include/uapi/linux/fsinfo.h            |   10 
 include/uapi/linux/keyctl.h            |    1 
 include/uapi/linux/watch_queue.h       |  185 +++++++
 kernel/sys_ni.c                        |    7 
 mm/interval_tree.c                     |    2 
 mm/memory.c                            |    1 
 samples/Kconfig                        |    6 
 samples/Makefile                       |    1 
 samples/vfs/test-fsinfo.c              |   13 
 samples/watch_queue/Makefile           |    9 
 samples/watch_queue/watch_test.c       |  284 ++++++++++
 security/keys/Kconfig                  |   10 
 security/keys/compat.c                 |    2 
 security/keys/gc.c                     |    5 
 security/keys/internal.h               |   30 +
 security/keys/key.c                    |   37 +
 security/keys/keyctl.c                 |   89 +++
 security/keys/keyring.c                |   17 -
 security/keys/request_key.c            |    4 
 security/security.c                    |    9 
 47 files changed, 2713 insertions(+), 38 deletions(-)
 create mode 100644 Documentation/watch_queue.rst
 create mode 100644 block/blk-notify.c
 create mode 100644 drivers/misc/watch_queue.c
 create mode 100644 fs/mount_notify.c
 create mode 100644 include/linux/watch_queue.h
 create mode 100644 include/uapi/linux/watch_queue.h
 create mode 100644 samples/watch_queue/Makefile
 create mode 100644 samples/watch_queue/watch_test.c


^ permalink raw reply	[flat|nested] 32+ messages in thread

* [PATCH 1/8] security: Override creds in __fput() with last fputter's creds [ver #2]
  2019-06-04 16:34 [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2] David Howells
@ 2019-06-04 16:35 ` David Howells
  2019-06-04 18:15   ` Andy Lutomirski
  2019-06-04 16:35 ` [PATCH 2/8] General notification queue with user mmap()'able ring buffer " David Howells
                   ` (8 subsequent siblings)
  9 siblings, 1 reply; 32+ messages in thread
From: David Howells @ 2019-06-04 16:35 UTC (permalink / raw)
  To: viro
  Cc: Casey Schaufler, Casey Schaufler, dhowells, raven, linux-fsdevel,
	linux-api, linux-block, keyrings, linux-security-module,
	linux-kernel

So that the LSM can see the credentials of the last process to do an fput()
on a file object when the file object is being dismantled, do the following
steps:

 (1) Cache the current credentials in file->f_fput_cred at the point the
     file object's reference count reaches zero.

 (2) In __fput(), use override_creds() to apply those credentials to the
     dismantling process.  This is necessary so that if we're dismantling a
     unix socket that has semi-passed fds still in it, their fputs will
     pick up the same credentials if they're reduced to zero at that point.

     Note that it's probably not strictly necessary to take an extra ref on
     the creds here (which override_creds() does).

 (3) Destroy the fput creds in file_free_rcu().

This additionally makes the creds available to:

	fsnotify
	eventpoll
	file locking
	->fasync, ->release file ops
	superblock destruction
	mountpoint destruction

This allows various notifications about object cleanups/destructions to
carry appropriate credentials for the LSM to approve/disapprove them based
on the process that caused them, even if indirectly.

Note that this means that someone looking at /proc/<pid>/fd/<n> may end up
being inadvertently noted as the subject of a cleanup message if the
process they're looking at croaks whilst they're looking at it.

Further, kernel services like nfsd and cachefiles may be seen as the
fputter and may not have a system credential.  In cachefiles's case, it may
appear that cachefilesd caused the notification.

Suggested-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Casey Schaufler <casey@schaufler-ca.com>
---

 fs/file_table.c    |   12 ++++++++++++
 include/linux/fs.h |    1 +
 2 files changed, 13 insertions(+)

diff --git a/fs/file_table.c b/fs/file_table.c
index 3f9c1b452c1d..9bf2be45b7f9 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -46,6 +46,7 @@ static void file_free_rcu(struct rcu_head *head)
 	struct file *f = container_of(head, struct file, f_u.fu_rcuhead);
 
 	put_cred(f->f_cred);
+	put_cred(f->f_fput_cred);
 	kmem_cache_free(filp_cachep, f);
 }
 
@@ -252,6 +253,7 @@ struct file *alloc_file_clone(struct file *base, int flags,
  */
 static void __fput(struct file *file)
 {
+	const struct cred *saved_cred;
 	struct dentry *dentry = file->f_path.dentry;
 	struct vfsmount *mnt = file->f_path.mnt;
 	struct inode *inode = file->f_inode;
@@ -262,6 +264,12 @@ static void __fput(struct file *file)
 
 	might_sleep();
 
+	/* Set the creds of whoever triggered the last fput for the LSM.  Note
+	 * that this has to be made available to further fputs, say on fds
+	 * trapped in a unix socket.
+	 */
+	saved_cred = override_creds(file->f_fput_cred);
+
 	fsnotify_close(file);
 	/*
 	 * The function eventpoll_release() should be the first called
@@ -293,6 +301,8 @@ static void __fput(struct file *file)
 	if (unlikely(mode & FMODE_NEED_UNMOUNT))
 		dissolve_on_fput(mnt);
 	mntput(mnt);
+
+	revert_creds(saved_cred);
 out:
 	file_free(file);
 }
@@ -334,6 +344,7 @@ void fput_many(struct file *file, unsigned int refs)
 	if (atomic_long_sub_and_test(refs, &file->f_count)) {
 		struct task_struct *task = current;
 
+		file->f_fput_cred = get_current_cred();
 		if (likely(!in_interrupt() && !(task->flags & PF_KTHREAD))) {
 			init_task_work(&file->f_u.fu_rcuhead, ____fput);
 			if (!task_work_add(task, &file->f_u.fu_rcuhead, true))
@@ -368,6 +379,7 @@ void __fput_sync(struct file *file)
 	if (atomic_long_dec_and_test(&file->f_count)) {
 		struct task_struct *task = current;
 		BUG_ON(!(task->flags & PF_KTHREAD));
+		file->f_fput_cred = get_current_cred();
 		__fput(file);
 	}
 }
diff --git a/include/linux/fs.h b/include/linux/fs.h
index f1c74596cd77..db05738b1951 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -943,6 +943,7 @@ struct file {
 	loff_t			f_pos;
 	struct fown_struct	f_owner;
 	const struct cred	*f_cred;
+	const struct cred	*f_fput_cred;	/* Who did the last fput() (for LSM) */
 	struct file_ra_state	f_ra;
 
 	u64			f_version;


^ permalink raw reply	[flat|nested] 32+ messages in thread

* [PATCH 2/8] General notification queue with user mmap()'able ring buffer [ver #2]
  2019-06-04 16:34 [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2] David Howells
  2019-06-04 16:35 ` [PATCH 1/8] security: Override creds in __fput() with last fputter's creds " David Howells
@ 2019-06-04 16:35 ` David Howells
  2019-06-04 16:35 ` [PATCH 3/8] keys: Add a notification facility " David Howells
                   ` (7 subsequent siblings)
  9 siblings, 0 replies; 32+ messages in thread
From: David Howells @ 2019-06-04 16:35 UTC (permalink / raw)
  To: viro
  Cc: dhowells, raven, linux-fsdevel, linux-api, linux-block, keyrings,
	linux-security-module, linux-kernel

Implement a misc device that implements a general notification queue as a
ring buffer that can be mmap()'d from userspace.

The way this is done is:

 (1) An application opens the device and indicates the size of the ring
     buffer that it wants to reserve in pages (this can only be set once):

	fd = open("/dev/watch_queue", O_RDWR);
	ioctl(fd, IOC_WATCH_QUEUE_NR_PAGES, nr_of_pages);

 (2) The application should then map the pages that the device has
     reserved.  Each instance of the device created by open() allocates
     separate pages so that maps of different fds don't interfere with one
     another.  Multiple mmap() calls on the same fd, however, will all work
     together.

	page_size = sysconf(_SC_PAGESIZE);
	mapping_size = nr_of_pages * page_size;
	char *buf = mmap(NULL, mapping_size, PROT_READ|PROT_WRITE,
			 MAP_SHARED, fd, 0);

The ring is divided into 8-byte slots.  Entries written into the ring are
variable size and can use between 1 and 63 slots.  A special entry is
maintained in the first two slots of the ring that contains the head and
tail pointers.  This is skipped when the ring wraps round.  Note that
multislot entries, therefore, aren't allowed to be broken over the end of
the ring, but instead "skip" entries are inserted to pad out the buffer.

Each entry has a 1-slot header that describes it:

	struct watch_notification {
		__u32	type:24;
		__u32	subtype:8;
		__u32	info;
	};

The type indicates the source (eg. mount tree changes, superblock events,
keyring changes, block layer events) and the subtype indicates the event
type (eg. mount, unmount; EIO, EDQUOT; link, unlink).  The info field
indicates a number of things, including the entry length, an ID assigned to
a watchpoint contributing to this buffer, type-specific flags and meta
flags, such as an overrun indicator.

Supplementary data, such as the key ID that generated an event, are
attached in additional slots.

Signed-off-by: David Howells <dhowells@redhat.com>
---

 Documentation/watch_queue.rst    |  328 ++++++++++++++
 drivers/misc/Kconfig             |   13 +
 drivers/misc/Makefile            |    1 
 drivers/misc/watch_queue.c       |  895 ++++++++++++++++++++++++++++++++++++++
 include/linux/lsm_hooks.h        |   15 +
 include/linux/security.h         |   14 +
 include/linux/watch_queue.h      |   87 ++++
 include/uapi/linux/watch_queue.h |   82 +++
 mm/interval_tree.c               |    2 
 mm/memory.c                      |    1 
 security/security.c              |    9 
 11 files changed, 1447 insertions(+)
 create mode 100644 Documentation/watch_queue.rst
 create mode 100644 drivers/misc/watch_queue.c
 create mode 100644 include/linux/watch_queue.h
 create mode 100644 include/uapi/linux/watch_queue.h

diff --git a/Documentation/watch_queue.rst b/Documentation/watch_queue.rst
new file mode 100644
index 000000000000..7c7d299d1dee
--- /dev/null
+++ b/Documentation/watch_queue.rst
@@ -0,0 +1,328 @@
+============================
+Mappable notifications queue
+============================
+
+This is a misc device that acts as a mapped ring buffer by which userspace can
+receive notifications from the kernel.  This can be used in conjunction with::
+
+  * Key/keyring notifications
+
+  * Mount topology change notifications
+
+  * Superblock event notifications
+
+  * Block layer event notifications
+
+
+The notifications buffers can be enabled by:
+
+	"Device Drivers"/"Misc devices"/"Mappable notification queue"
+	(CONFIG_WATCH_QUEUE)
+
+This document has the following sections:
+
+.. contents:: :local:
+
+
+Overview
+========
+
+This facility appears as a misc device file that is opened and then mapped and
+polled.  Each time it is opened, it creates a new buffer specific to the
+returned file descriptor.  Then, when the opening process sets watches, it
+indicates the particular buffer it wants notifications from that watch to be
+written into.  Note that there are no read() and write() methods (except for
+debugging).  The user is expected to access the ring directly and to use poll
+to wait for new data.
+
+If a watch is in place, notifications are only written into the buffer if the
+filter criteria are passed and if there's sufficient space available in the
+ring.  If neither of those is so, a notification will be discarded.  In the
+latter case, an overrun indicator will also be set.
+
+Note that when producing a notification, the kernel does not wait for the
+consumers to collect it, but rather just continues on.  This means that
+notifications can be generated whilst spinlocks are held and also protects the
+kernel from being held up indefinitely by a userspace malfunction.
+
+As far as the ring goes, the head index belongs to the kernel and the tail
+index belongs to userspace.  The kernel will refuse to write anything if the
+tail index becomes invalid.  Userspace *must* use appropriate memory barriers
+between reading or updating the tail index and reading the ring.
+
+
+Record Structure
+================
+
+Notification records in the ring may occupy a variable number of slots within
+the buffer, beginning with a 1-slot header::
+
+	struct watch_notification {
+		__u32	type:24;
+		__u32	subtype:8;
+		__u32	info;
+	};
+
+"type" indicates the source of the notification record and "subtype" indicates
+the type of record from that source (see the Watch Sources section below).  The
+type may also be "WATCH_TYPE_META".  This is a special record type generated
+internally by the watch queue driver itself.  There are two subtypes, one of
+which indicates records that should be just skipped (padding or metadata):
+
+  * WATCH_META_SKIP_NOTIFICATION
+  * WATCH_META_REMOVAL_NOTIFICATION
+
+The former indicates a record that should just be skipped and the latter
+indicates that an object on which a watchpoint was installed was removed or
+destroyed.
+
+"info" indicates a bunch of things, including:
+
+  * The length of the record (mask with WATCH_INFO_LENGTH).  This indicates the
+    size of the record, which may be between 1 and 63 slots.  Note that this is
+    placed appropriately within the info value so that no shifting is required
+    to convert number of occupied slots to byte length.
+
+  * The watchpoint ID (mask with WATCH_INFO_ID).  This indicates that caller's
+    ID of the watchpoint, which may be between 0 and 255.  Multiple watchpoints
+    may share a queue, and this provides a means to distinguish them.
+
+  * A buffer overrun flag (WATCH_INFO_OVERRUN flag).  If this is set in a
+    notification record, some of the preceding records were discarded.
+
+  * An ENOMEM-loss flag (WATCH_INFO_ENOMEM flag).  This is set to indicate that
+    an event was lost to ENOMEM.
+
+  * A recursive-change flag (WATCH_INFO_RECURSIVE flag).  This is set to
+    indicate that the change that happened was recursive - for instance
+    changing the attributes on an entire mount subtree.
+
+  * An exact-match flag (WATCH_INFO_IN_SUBTREE flag).  This is set if the event
+    didn't happen exactly at the watchpoint, but rather somewhere in the
+    subtree thereunder.
+
+  * Some type-specific flags (WATCH_INFO_TYPE_FLAGS).  These are set by the
+    notification producer to indicate some meaning specific to the type and
+    subtype.
+
+Everything in info apart from the length can be used for filtering.
+
+
+Ring Structure
+==============
+
+The ring is divided into 8-byte slots.  The caller uses an ioctl() to set the
+size of the ring after opening and this must be a power-of-2 multiple of the
+system page size (so that the mask can be used with AND).
+
+The head and tail indices are stored in the first two slots in the ring, which
+are marked out as a skippable entry::
+
+	struct watch_queue_buffer {
+		union {
+			struct {
+				struct watch_notification watch;
+				volatile __u32	head;
+				volatile __u32	tail;
+				__u32		mask;
+			} meta;
+			struct watch_notification slots[0];
+		};
+	};
+
+In "meta.watch", type will be set to WATCH_TYPE_META and subtype to
+WATCH_META_SKIP_NOTIFICATION so that anyone processing the buffer will just
+skip this record.  Also, because this record is here, records cannot wrap round
+the end of the buffer, so a skippable padding element will be inserted at the
+end of the buffer if needed.  Thus the contents of a notification record in the
+buffer are always contiguous.
+
+"meta.mask" is an AND'able mask to turn the index counters into slots array
+indices.
+
+The buffer is empty if "meta.head" == "meta.tail".
+
+[!] NOTE that the ring indices "meta.head" and "meta.tail" are indices into
+"slots[]" not byte offsets into the buffer.
+
+[!] NOTE that userspace must never change the head pointer.  This belongs to
+the kernel and will be updated by that.  The kernel will never change the tail
+pointer.
+
+[!] NOTE that userspace must never AND-off the tail pointer before updating it,
+but should just keep adding to it and letting it wrap naturally.  The value
+*should* be masked off when used as an index into slots[].
+
+[!] NOTE that if the distance between head and tail becomes too great, the
+kernel will assume the buffer is full and write no more until the issue is
+resolved.
+
+
+Watch Sources
+=============
+
+Any particular buffer can be fed from multiple sources.  Sources include:
+
+  * WATCH_TYPE_MOUNT_NOTIFY
+
+    Notifications of this type indicate mount tree topology changes and mount
+    attribute changes.  A watchpoint can be set on a particular file or
+    directory and notifications from the path subtree rooted at that point will
+    be intercepted.
+
+  * WATCH_TYPE_SB_NOTIFY
+
+    Notifications of this type indicate superblock events, such as quota limits
+    being hit, I/O errors being produced or network server loss/reconnection.
+    Watchpoints of this type are set directly on superblocks.
+
+  * WATCH_TYPE_KEY_NOTIFY
+
+    Notifications of this type indicate changes to keys and keyrings, including
+    the changes of keyring contents or the attributes of keys.
+
+    See Documentation/security/keys/core.rst for more information.
+
+  * WATCH_TYPE_BLOCK_NOTIFY
+
+    Notifications of this type indicate block layer events, such as I/O errors
+    or temporary link loss.  Watchpoints of this type are set on a global
+    queue.
+
+
+Event Filtering
+===============
+
+Once a watch queue has been created, a set of filters can be applied to limit
+the events that are received using::
+
+	struct watch_notification_filter filter = {
+		...
+	};
+	ioctl(fd, IOC_WATCH_QUEUE_SET_FILTER, &filter)
+
+The filter description is a variable of type::
+
+	struct watch_notification_filter {
+		__u32	nr_filters;
+		__u32	__reserved;
+		struct watch_notification_type_filter filters[];
+	};
+
+Where "nr_filters" is the number of filters in filters[] and "__reserved"
+should be 0.  The "filters" array has elements of the following type::
+
+	struct watch_notification_type_filter {
+		__u32	type;
+		__u32	info_filter;
+		__u32	info_mask;
+		__u32	subtype_filter[8];
+	};
+
+Where:
+
+  * ``type`` is the event type to filter for and should be something like
+    "WATCH_TYPE_MOUNT_NOTIFY"
+
+  * ``info_filter`` and ``info_mask`` act as a filter on the info field of the
+    notification record.  The notification is only written into the buffer if::
+
+	(watch.info & info_mask) == info_filter
+
+    This can be used, for example, to ignore events that are not exactly on the
+    watched point in a mount tree by specifying WATCH_INFO_IN_SUBTREE must
+    be 0.
+
+  * ``subtype_filter`` is a bitmask indicating the subtypes that are of
+    interest.  Bit 0 of subtype_filter[0] corresponds to subtype 0, bit 1 to
+    subtype 1, and so on.
+
+If the argument to the ioctl() is NULL, then the filters will be removed and
+all events from the watched sources will come through.
+
+
+Polling
+=======
+
+The file descriptor that holds the buffer may be used with poll() and similar.
+POLLIN and POLLRDNORM are set if the buffer indices differ.  POLLERR is set if
+the buffer indices are further apart than the size of the buffer.  Wake-up
+events are only generated if the buffer is transitioned from an empty state.
+
+
+Example
+=======
+
+A buffer is created with something like the following::
+
+	fd = open("/dev/watch_queue", O_RDWR);
+
+	#define BUF_SIZE 4
+	ioctl(fd, IOC_WATCH_QUEUE_SET_SIZE, BUF_SIZE);
+
+	page_size = sysconf(_SC_PAGESIZE);
+	buf = mmap(NULL, BUF_SIZE * page_size,
+		   PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+
+It can then be set to receive mount topology change notifications, keyring
+change notifications and superblock notifications::
+
+	memset(&filter, 0, sizeof(filter));
+	filter.subtype_filter[0] = ~0ULL;
+	filter.info_mask	 = WATCH_INFO_IN_SUBTREE;
+	filter.info_filter	 = 0;
+	filter.info_id		 = 0x01000000;
+
+	keyctl(KEYCTL_WATCH_KEY, KEY_SPEC_SESSION_KEYRING, fd, &filter);
+
+	mount_notify(AT_FDCWD, "/", 0, fd, &filter);
+
+	sb_notify(AT_FDCWD, "/", 0, fd, &filter);
+
+The notifications can then be consumed by something like the following::
+
+	extern void saw_mount_change(struct watch_notification *n);
+	extern void saw_key_change(struct watch_notification *n);
+
+	static int consumer(int fd, struct watch_queue_buffer *buf)
+	{
+		struct watch_notification *n;
+		struct pollfd p[1];
+		unsigned int head, tail, mask = buf->meta.mask;
+
+		for (;;) {
+			p[0].fd = fd;
+			p[0].events = POLLIN | POLLERR;
+			p[0].revents = 0;
+
+			if (poll(p, 1, -1) == -1 || p[0].revents & POLLERR)
+				goto went_wrong;
+
+			while (head = _atomic_load_acquire(buf->meta.head),
+			       tail = buf->meta.tail,
+			       tail != head
+			       ) {
+				n = &buf->slots[tail & mask];
+				if ((n->info & WATCH_INFO_LENGTH) == 0)
+					goto went_wrong;
+
+				switch (n->type) {
+				case WATCH_TYPE_MOUNT_NOTIFY:
+					saw_mount_change(n);
+					break;
+				case WATCH_TYPE_KEY_NOTIFY:
+					saw_key_change(n);
+					break;
+				}
+
+				tail += (n->info & WATCH_INFO_LENGTH) >> WATCH_LENGTH_SHIFT;
+				_atomic_store_release(buf->meta.tail, tail);
+			}
+		}
+
+	went_wrong:
+		return 0;
+	}
+
+Note the memory barriers when loading the head pointer and storing the tail
+pointer!
diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
index 6a0365b2332c..19668c0ebe03 100644
--- a/drivers/misc/Kconfig
+++ b/drivers/misc/Kconfig
@@ -4,6 +4,19 @@
 
 menu "Misc devices"
 
+config WATCH_QUEUE
+	bool "Mappable notification queue"
+	default n
+	depends on MMU
+	help
+	  This is a general notification queue for the kernel to pass events to
+	  userspace through a mmap()'able ring buffer.  It can be used in
+	  conjunction with watches for mount topology change notifications,
+	  superblock change notifications and key/keyring change notifications.
+
+	  Note that in theory this should work fine with NOMMU, but I'm not
+	  sure how to make that work.
+
 config SENSORS_LIS3LV02D
 	tristate
 	depends on INPUT
diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
index b9affcdaa3d6..bf16acd9f8cc 100644
--- a/drivers/misc/Makefile
+++ b/drivers/misc/Makefile
@@ -3,6 +3,7 @@
 # Makefile for misc devices that really don't fit anywhere else.
 #
 
+obj-$(CONFIG_WATCH_QUEUE)	+= watch_queue.o
 obj-$(CONFIG_IBM_ASM)		+= ibmasm/
 obj-$(CONFIG_IBMVMC)		+= ibmvmc.o
 obj-$(CONFIG_AD525X_DPOT)	+= ad525x_dpot.o
diff --git a/drivers/misc/watch_queue.c b/drivers/misc/watch_queue.c
new file mode 100644
index 000000000000..c8242eab4c71
--- /dev/null
+++ b/drivers/misc/watch_queue.c
@@ -0,0 +1,895 @@
+/* User-mappable watch queue
+ *
+ * Copyright (C) 2018 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ *
+ * See Documentation/watch_queue.rst
+ */
+
+#define pr_fmt(fmt) "watchq: " fmt
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/printk.h>
+#include <linux/miscdevice.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/pagemap.h>
+#include <linux/poll.h>
+#include <linux/uaccess.h>
+#include <linux/vmalloc.h>
+#include <linux/file.h>
+#include <linux/security.h>
+#include <linux/cred.h>
+#include <linux/watch_queue.h>
+
+#undef DEBUG_WITH_WRITE /* Allow use of write() to record notifications */
+
+MODULE_DESCRIPTION("Watch queue");
+MODULE_AUTHOR("Red Hat, Inc.");
+MODULE_LICENSE("GPL");
+
+struct watch_type_filter {
+	enum watch_notification_type type;
+	__u32		subtype_filter[1];	/* Bitmask of subtypes to filter on */
+	__u32		info_filter;		/* Filter on watch_notification::info */
+	__u32		info_mask;		/* Mask of relevant bits in info_filter */
+};
+
+struct watch_filter {
+	union {
+		struct rcu_head	rcu;
+		unsigned long	type_filter[2];	/* Bitmask of accepted types */
+	};
+	u32		nr_filters;		/* Number of filters */
+	struct watch_type_filter filters[];
+};
+
+struct watch_queue {
+	struct rcu_head		rcu;
+	struct address_space	mapping;
+	const struct cred	*cred;		/* Creds of the owner of the queue */
+	struct watch_filter __rcu *filter;
+	wait_queue_head_t	waiters;
+	struct hlist_head	watches;	/* Contributory watches */
+	struct kref		usage;		/* Object usage count */
+	spinlock_t		lock;
+	bool			defunct;	/* T when queues closed */
+	u8			nr_pages;	/* Size of pages[] */
+	u8			flag_next;	/* Flag to apply to next item */
+#ifdef DEBUG_WITH_WRITE
+	u8			debug;
+#endif
+	u32			size;
+	struct watch_queue_buffer *buffer;	/* Pointer to first record */
+
+	/* The mappable pages.  The zeroth page holds the ring pointers. */
+	struct page		**pages;
+};
+
+/**
+ * post_one_notification - Post an event notification to one queue
+ * @wqueue: The watch queue to add the event to.
+ * @n: The notification record to post.
+ * @cred: The credentials to use in security checks.
+ *
+ * Post a notification of an event into an mmap'd queue and let the user know.
+ * Returns true if successful and false on failure (eg. buffer overrun or
+ * userspace mucked up the ring indices).
+ *
+ *
+ * The size of the notification should be set in n->flags & WATCH_LENGTH and
+ * should be in units of sizeof(*n).
+ */
+static bool post_one_notification(struct watch_queue *wqueue,
+				  struct watch_notification *n,
+				  const struct cred *cred)
+{
+	struct watch_queue_buffer *buf = wqueue->buffer;
+	unsigned int metalen = sizeof(buf->meta) / sizeof(buf->slots[0]);
+	unsigned int size = wqueue->size, mask = size - 1;
+	unsigned int len;
+	unsigned int ring_tail, tail, head, used, segment, h;
+
+	if (!buf)
+		return false;
+
+	len = (n->info & WATCH_INFO_LENGTH) >> WATCH_LENGTH_SHIFT;
+	if (len == 0)
+		return false;
+
+	spin_lock_bh(&wqueue->lock); /* Protect head pointer */
+
+	if (wqueue->defunct ||
+	    security_post_notification(wqueue->cred, cred, n) < 0)
+		goto out;
+
+	ring_tail = READ_ONCE(buf->meta.tail);
+	head = READ_ONCE(buf->meta.head);
+	used = head - ring_tail;
+
+	/* Check to see if userspace mucked up the pointers */
+	if (used >= size)
+		goto overrun;
+	tail = ring_tail & mask;
+	if (tail > 0 && tail < metalen)
+		goto overrun;
+
+	h = head & mask;
+	if (h >= tail) {
+		/* Head is at or after tail in the buffer.  There may then be
+		 * two segments: one to the end of buffer and one at the
+		 * beginning of the buffer between the metadata block and the
+		 * tail pointer.
+		 */
+		segment = size - h;
+		if (len > segment) {
+			/* Not enough space in the post-head segment; we need
+			 * to wrap.  When wrapping, we will have to skip the
+			 * metadata at the beginning of the buffer.
+			 */
+			if (len > tail - metalen)
+				goto overrun;
+
+			/* Fill the space at the end of the page */
+			buf->slots[h].type	= WATCH_TYPE_META;
+			buf->slots[h].subtype	= WATCH_META_SKIP_NOTIFICATION;
+			buf->slots[h].info	= segment << WATCH_LENGTH_SHIFT;
+			head += segment;
+			h = 0;
+			if (h >= tail)
+				goto overrun;
+		}
+	}
+
+	if (h == 0) {
+		/* Reset and skip the header metadata */
+		buf->meta.watch.type = WATCH_TYPE_META;
+		buf->meta.watch.subtype = WATCH_META_SKIP_NOTIFICATION;
+		buf->meta.watch.info = metalen << WATCH_LENGTH_SHIFT;
+		head += metalen;
+		h = metalen;
+		if (h >= tail)
+			goto overrun;
+	}
+
+	if (h < tail) {
+		/* Head is before tail in the buffer.  There may be one segment
+		 * between the two, but we may need to skip the metadata block.
+		 */
+		segment = tail - h;
+		if (len > segment)
+			goto overrun;
+	}
+
+	n->info |= wqueue->flag_next;
+	wqueue->flag_next = 0;
+	memcpy(buf->slots + h, n, len * sizeof(buf->slots[0]));
+	head += len;
+
+	smp_store_release(&buf->meta.head, head);
+	spin_unlock_bh(&wqueue->lock);
+	if (used == 0)
+		wake_up(&wqueue->waiters);
+	return true;
+
+overrun:
+	wqueue->flag_next = WATCH_INFO_OVERRUN;
+out:
+	spin_unlock_bh(&wqueue->lock);
+	return false;
+}
+
+/*
+ * Apply filter rules to a notification.
+ */
+static bool filter_watch_notification(const struct watch_filter *wf,
+				      const struct watch_notification *n)
+{
+	const struct watch_type_filter *wt;
+	int i;
+
+	if (!test_bit(n->type, wf->type_filter))
+		return false;
+
+	for (i = 0; i < wf->nr_filters; i++) {
+		wt = &wf->filters[i];
+		if (n->type == wt->type &&
+		    ((1U << n->subtype) & wt->subtype_filter[0]) &&
+		    (n->info & wt->info_mask) == wt->info_filter)
+			return true;
+	}
+
+	return false; /* If there is a filter, the default is to reject. */
+}
+
+/**
+ * __post_watch_notification - Post an event notification
+ * @wlist: The watch list to post the event to.
+ * @n: The notification record to post.
+ * @cred: The creds of the process that triggered the notification.
+ * @id: The ID to match on the watch.
+ *
+ * Post a notification of an event into a set of watch queues and let the users
+ * know.
+ *
+ * If @n is NULL then WATCH_INFO_LENGTH will be set on the next event posted.
+ *
+ * The size of the notification should be set in n->info & WATCH_INFO_LENGTH and
+ * should be in units of sizeof(*n).
+ */
+void __post_watch_notification(struct watch_list *wlist,
+			       struct watch_notification *n,
+			       const struct cred *cred,
+			       u64 id)
+{
+	const struct watch_filter *wf;
+	struct watch_queue *wqueue;
+	struct watch *watch;
+
+	rcu_read_lock();
+
+	hlist_for_each_entry_rcu(watch, &wlist->watchers, list_node) {
+		if (watch->id != id)
+			continue;
+		n->info &= ~(WATCH_INFO_ID | WATCH_INFO_OVERRUN);
+		n->info |= watch->info_id;
+
+		wqueue = rcu_dereference(watch->queue);
+		wf = rcu_dereference(wqueue->filter);
+		if (wf && !filter_watch_notification(wf, n))
+			continue;
+
+		post_one_notification(wqueue, n, cred);
+	}
+
+	rcu_read_unlock();
+}
+EXPORT_SYMBOL(__post_watch_notification);
+
+/*
+ * Allow the queue to be polled.
+ */
+static __poll_t watch_queue_poll(struct file *file, poll_table *wait)
+{
+	struct watch_queue *wqueue = file->private_data;
+	struct watch_queue_buffer *buf = wqueue->buffer;
+	unsigned int head, tail;
+	__poll_t mask = 0;
+
+	poll_wait(file, &wqueue->waiters, wait);
+
+	head = READ_ONCE(buf->meta.head);
+	tail = READ_ONCE(buf->meta.tail);
+	if (head != tail)
+		mask |= EPOLLIN | EPOLLRDNORM;
+	if (head - tail > wqueue->size)
+		mask |= EPOLLERR;
+	return mask;
+}
+
+static int watch_queue_set_page_dirty(struct page *page)
+{
+	SetPageDirty(page);
+	return 0;
+}
+
+static const struct address_space_operations watch_queue_aops = {
+	.set_page_dirty	= watch_queue_set_page_dirty,
+};
+
+static vm_fault_t watch_queue_fault(struct vm_fault *vmf)
+{
+	struct watch_queue *wqueue = vmf->vma->vm_file->private_data;
+	struct page *page;
+
+	page = wqueue->pages[vmf->pgoff];
+	get_page(page);
+	if (!lock_page_or_retry(page, vmf->vma->vm_mm, vmf->flags)) {
+		put_page(page);
+		return VM_FAULT_RETRY;
+	}
+	vmf->page = page;
+	return VM_FAULT_LOCKED;
+}
+
+static void watch_queue_map_pages(struct vm_fault *vmf,
+				  pgoff_t start_pgoff, pgoff_t end_pgoff)
+{
+	struct watch_queue *wqueue = vmf->vma->vm_file->private_data;
+	struct page *page;
+
+	rcu_read_lock();
+
+	do {
+		page = wqueue->pages[start_pgoff];
+		if (trylock_page(page)) {
+			vm_fault_t ret;
+			get_page(page);
+			ret = alloc_set_pte(vmf, NULL, page);
+			if (ret != 0)
+				put_page(page);
+
+			unlock_page(page);
+		}
+	} while (++start_pgoff < end_pgoff);
+
+	rcu_read_unlock();
+}
+
+static const struct vm_operations_struct watch_queue_vm_ops = {
+	.fault		= watch_queue_fault,
+	.map_pages	= watch_queue_map_pages,
+};
+
+/*
+ * Map the buffer.
+ */
+static int watch_queue_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	struct watch_queue *wqueue = file->private_data;
+	struct inode *inode = file_inode(file);
+	u8 nr_pages;
+
+	inode_lock(inode);
+	nr_pages = wqueue->nr_pages;
+	inode_unlock(inode);
+
+	if (nr_pages == 0 ||
+	    vma->vm_pgoff != 0 ||
+	    vma->vm_end - vma->vm_start > nr_pages * PAGE_SIZE ||
+	    !(pgprot_val(vma->vm_page_prot) & pgprot_val(PAGE_SHARED)))
+		return -EINVAL;
+
+	vma->vm_flags |= VM_DONTEXPAND;
+	vma->vm_ops = &watch_queue_vm_ops;
+
+	vma_interval_tree_insert(vma, &wqueue->mapping.i_mmap);
+	return 0;
+}
+
+/*
+ * Allocate the required number of pages.
+ */
+static long watch_queue_set_size(struct watch_queue *wqueue, unsigned long nr_pages)
+{
+	struct watch_queue_buffer *buf;
+	u32 len;
+	int i;
+
+	if (wqueue->buffer)
+		return -EBUSY;
+
+	if (nr_pages == 0 ||
+	    nr_pages > 16 || /* TODO: choose a better hard limit */
+	    !is_power_of_2(nr_pages))
+		return -EINVAL;
+
+	wqueue->pages = kcalloc(nr_pages, sizeof(struct page *), GFP_KERNEL);
+	if (!wqueue->pages)
+		goto err;
+
+	for (i = 0; i < nr_pages; i++) {
+		wqueue->pages[i] = alloc_page(GFP_KERNEL | __GFP_ZERO);
+		if (!wqueue->pages[i])
+			goto err_some_pages;
+		wqueue->pages[i]->mapping = &wqueue->mapping;
+		SetPageUptodate(wqueue->pages[i]);
+	}
+
+	buf = vmap(wqueue->pages, nr_pages, VM_MAP, PAGE_SHARED);
+	if (!buf)
+		goto err_some_pages;
+
+	wqueue->buffer = buf;
+	wqueue->nr_pages = nr_pages;
+	wqueue->size = ((nr_pages * PAGE_SIZE) / sizeof(struct watch_notification));
+
+	/* The first four slots in the buffer contain metadata about the ring,
+	 * including the head and tail indices and mask.
+	 */
+	len = sizeof(buf->meta) / sizeof(buf->slots[0]);
+	buf->meta.watch.info	= len << WATCH_LENGTH_SHIFT;
+	buf->meta.watch.type	= WATCH_TYPE_META;
+	buf->meta.watch.subtype	= WATCH_META_SKIP_NOTIFICATION;
+	buf->meta.mask		= wqueue->size - 1;
+	buf->meta.head		= len;
+	buf->meta.tail		= len;
+	return 0;
+
+err_some_pages:
+	for (i--; i >= 0; i--) {
+		ClearPageUptodate(wqueue->pages[i]);
+		wqueue->pages[i]->mapping = NULL;
+		put_page(wqueue->pages[i]);
+	}
+
+	kfree(wqueue->pages);
+	wqueue->pages = NULL;
+err:
+	return -ENOMEM;
+}
+
+/*
+ * Set the filter on a watch queue.
+ */
+static long watch_queue_set_filter(struct inode *inode,
+				   struct watch_queue *wqueue,
+				   struct watch_notification_filter __user *_filter)
+{
+	struct watch_notification_type_filter *tf;
+	struct watch_notification_filter filter;
+	struct watch_type_filter *q;
+	struct watch_filter *wfilter;
+	int ret, nr_filter = 0, i;
+
+	if (!_filter) {
+		/* Remove the old filter */
+		wfilter = NULL;
+		goto set;
+	}
+
+	/* Grab the user's filter specification */
+	if (copy_from_user(&filter, _filter, sizeof(filter)) != 0)
+		return -EFAULT;
+	if (filter.nr_filters == 0 ||
+	    filter.nr_filters > 16 ||
+	    filter.__reserved != 0)
+		return -EINVAL;
+
+	tf = memdup_user(_filter->filters, filter.nr_filters * sizeof(*tf));
+	if (IS_ERR(tf))
+		return PTR_ERR(tf);
+
+	ret = -EINVAL;
+	for (i = 0; i < filter.nr_filters; i++) {
+		if ((tf[i].info_filter & ~tf[i].info_mask) ||
+		    tf[i].info_mask & WATCH_INFO_LENGTH)
+			goto err_filter;
+		/* Ignore any unknown types */
+		if (tf[i].type >= sizeof(wfilter->type_filter) * 8)
+			continue;
+		nr_filter++;
+	}
+
+	/* Now we need to build the internal filter from only the relevant
+	 * user-specified filters.
+	 */
+	ret = -ENOMEM;
+	wfilter = kzalloc(struct_size(wfilter, filters, nr_filter), GFP_KERNEL);
+	if (!wfilter)
+		goto err_filter;
+	wfilter->nr_filters = nr_filter;
+
+	q = wfilter->filters;
+	for (i = 0; i < filter.nr_filters; i++) {
+		if (tf[i].type >= sizeof(wfilter->type_filter) * BITS_PER_LONG)
+			continue;
+
+		q->type			= tf[i].type;
+		q->info_filter		= tf[i].info_filter;
+		q->info_mask		= tf[i].info_mask;
+		q->subtype_filter[0]	= tf[i].subtype_filter[0];
+		__set_bit(q->type, wfilter->type_filter);
+		q++;
+	}
+
+	kfree(tf);
+set:
+	inode_lock(inode);
+	rcu_swap_protected(wqueue->filter, wfilter,
+			   lockdep_is_held(&inode->i_rwsem));
+	inode_unlock(inode);
+	if (wfilter)
+		kfree_rcu(wfilter, rcu);
+	return 0;
+
+err_filter:
+	kfree(tf);
+	return ret;
+}
+
+/*
+ * Set parameters.
+ */
+static long watch_queue_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
+{
+	struct watch_queue *wqueue = file->private_data;
+	struct inode *inode = file_inode(file);
+	long ret;
+
+	switch (cmd) {
+	case IOC_WATCH_QUEUE_SET_SIZE:
+		inode_lock(inode);
+		ret = watch_queue_set_size(wqueue, arg);
+		inode_unlock(inode);
+		return ret;
+
+	case IOC_WATCH_QUEUE_SET_FILTER:
+		ret = watch_queue_set_filter(
+			inode, wqueue,
+			(struct watch_notification_filter __user *)arg);
+		return ret;
+
+	default:
+		return -ENOTTY;
+	}
+}
+
+/*
+ * Open the file.
+ */
+static int watch_queue_open(struct inode *inode, struct file *file)
+{
+	struct watch_queue *wqueue;
+
+	wqueue = kzalloc(sizeof(*wqueue), GFP_KERNEL);
+	if (!wqueue)
+		return -ENOMEM;
+
+	wqueue->mapping.a_ops = &watch_queue_aops;
+	wqueue->mapping.i_mmap = RB_ROOT_CACHED;
+	init_rwsem(&wqueue->mapping.i_mmap_rwsem);
+	spin_lock_init(&wqueue->mapping.private_lock);
+
+	kref_init(&wqueue->usage);
+	spin_lock_init(&wqueue->lock);
+	init_waitqueue_head(&wqueue->waiters);
+	wqueue->cred = get_cred(file->f_cred);
+
+	file->private_data = wqueue;
+	return 0;
+}
+
+static void __put_watch_queue(struct kref *kref)
+{
+	struct watch_queue *wqueue =
+		container_of(kref, struct watch_queue, usage);
+
+	kfree_rcu(wqueue, rcu);
+}
+
+/**
+ * put_watch_queue - Dispose of a ref on a watchqueue.
+ * @wqueue: The watch queue to unref.
+ */
+void put_watch_queue(struct watch_queue *wqueue)
+{
+	kref_put(&wqueue->usage, __put_watch_queue);
+}
+EXPORT_SYMBOL(put_watch_queue);
+
+static void free_watch(struct rcu_head *rcu)
+{
+	struct watch *watch = container_of(rcu, struct watch, rcu);
+
+	put_watch_queue(rcu_access_pointer(watch->queue));
+}
+
+static void __put_watch(struct kref *kref)
+{
+	struct watch *watch = container_of(kref, struct watch, usage);
+
+	call_rcu(&watch->rcu, free_watch);
+}
+
+/*
+ * Discard a watch.
+ */
+static void put_watch(struct watch *watch)
+{
+	kref_put(&watch->usage, __put_watch);
+}
+
+/**
+ * init_watch_queue - Initialise a watch
+ * @watch: The watch to initialise.
+ * @wqueue: The queue to assign.
+ *
+ * Initialise a watch and set the watch queue.
+ */
+void init_watch(struct watch *watch, struct watch_queue *wqueue)
+{
+	kref_init(&watch->usage);
+	INIT_HLIST_NODE(&watch->list_node);
+	INIT_HLIST_NODE(&watch->queue_node);
+	rcu_assign_pointer(watch->queue, wqueue);
+}
+
+/**
+ * add_watch_to_object - Add a watch on an object to a watch list
+ * @watch: The watch to add
+ * @wlist: The watch list to add to
+ *
+ * @watch->queue must have been set to point to the queue to post notifications
+ * to and the watch list of the object to be watched.
+ *
+ * The caller must pin the queue and the list both and must hold the list
+ * locked against racing watch additions/removals.
+ */
+int add_watch_to_object(struct watch *watch, struct watch_list *wlist)
+{
+	struct watch_queue *wqueue = rcu_access_pointer(watch->queue);
+	struct watch *w;
+
+	hlist_for_each_entry(w, &wlist->watchers, list_node) {
+		if (watch->id == w->id)
+			return -EBUSY;
+	}
+
+	rcu_assign_pointer(watch->watch_list, wlist);
+
+	spin_lock_bh(&wqueue->lock);
+	kref_get(&wqueue->usage);
+	hlist_add_head(&watch->queue_node, &wqueue->watches);
+	spin_unlock_bh(&wqueue->lock);
+
+	hlist_add_head(&watch->list_node, &wlist->watchers);
+	return 0;
+}
+EXPORT_SYMBOL(add_watch_to_object);
+
+/**
+ * remove_watch_from_object - Remove a watch or all watches from an object.
+ * @wlist: The watch list to remove from
+ * @wq: The watch queue of interest (ignored if @all is true)
+ * @id: The ID of the watch to remove (ignored if @all is true)
+ * @all: True to remove all objects
+ *
+ * Remove a specific watch or all watches from an object.  A notification is
+ * sent to the watcher to tell them that this happened.
+ */
+int remove_watch_from_object(struct watch_list *wlist, struct watch_queue *wq,
+			     u64 id, bool all)
+{
+	struct watch_notification n;
+	struct watch_queue *wqueue;
+	struct watch *watch;
+	int ret = -EBADSLT;
+
+	rcu_read_lock();
+
+again:
+	spin_lock(&wlist->lock);
+	hlist_for_each_entry(watch, &wlist->watchers, list_node) {
+		if (all ||
+		    (watch->id == id && rcu_access_pointer(watch->queue) == wq))
+			goto found;
+	}
+	spin_unlock(&wlist->lock);
+	goto out;
+
+found:
+	ret = 0;
+	hlist_del_init_rcu(&watch->list_node);
+	rcu_assign_pointer(watch->watch_list, NULL);
+	spin_unlock(&wlist->lock);
+
+	/* We now own the reference on watch that used to belong to wlist. */
+
+	n.type = WATCH_TYPE_META;
+	n.subtype = WATCH_META_REMOVAL_NOTIFICATION;
+	n.info = watch->info_id | sizeof(n);
+
+	wqueue = rcu_dereference(watch->queue);
+
+	/* We don't need the watch list lock for the next bit as RCU is
+	 * protecting *wqueue from deallocation.
+	 */
+	if (wqueue) {
+		post_one_notification(wqueue, &n, wq ? wq->cred : NULL);
+
+		spin_lock_bh(&wqueue->lock);
+
+		if (!hlist_unhashed(&watch->queue_node)) {
+			hlist_del_init_rcu(&watch->queue_node);
+			put_watch(watch);
+		}
+
+		spin_unlock_bh(&wqueue->lock);
+	}
+
+	if (wlist->release_watch) {
+		void (*release_watch)(struct watch *);
+
+		release_watch = wlist->release_watch;
+		rcu_read_unlock();
+		(*release_watch)(watch);
+		rcu_read_lock();
+	}
+	put_watch(watch);
+
+	if (all && !hlist_empty(&wlist->watchers))
+		goto again;
+out:
+	rcu_read_unlock();
+	return ret;
+}
+EXPORT_SYMBOL(remove_watch_from_object);
+
+/*
+ * Remove all the watches that are contributory to a queue.  This has the
+ * potential to race with removal of the watches by the destruction of the
+ * objects being watched or with the distribution of notifications.
+ */
+static void watch_queue_clear(struct watch_queue *wqueue)
+{
+	struct watch_list *wlist;
+	struct watch *watch;
+	bool release;
+
+	rcu_read_lock();
+	spin_lock_bh(&wqueue->lock);
+
+	/* Prevent new additions and prevent notifications from happening */
+	wqueue->defunct = true;
+
+	while (!hlist_empty(&wqueue->watches)) {
+		watch = hlist_entry(wqueue->watches.first, struct watch, queue_node);
+		hlist_del_init_rcu(&watch->queue_node);
+		/* We now own a ref on the watch. */
+		spin_unlock_bh(&wqueue->lock);
+
+		/* We can't do the next bit under the queue lock as we need to
+		 * get the list lock - which would cause a deadlock if someone
+		 * was removing from the opposite direction at the same time or
+		 * posting a notification.
+		 */
+		wlist = rcu_dereference(watch->watch_list);
+		if (wlist) {
+			void (*release_watch)(struct watch *);
+
+			spin_lock(&wlist->lock);
+
+			release = !hlist_unhashed(&watch->list_node);
+			if (release) {
+				hlist_del_init_rcu(&watch->list_node);
+				rcu_assign_pointer(watch->watch_list, NULL);
+
+				/* We now own a second ref on the watch. */
+			}
+
+			release_watch = wlist->release_watch;
+			spin_unlock(&wlist->lock);
+
+			if (release) {
+				if (release_watch) {
+					rcu_read_unlock();
+					/* This might need to call dput(), so
+					 * we have to drop all the locks.
+					 */
+					(*release_watch)(watch);
+					rcu_read_lock();
+				}
+				put_watch(watch);
+			}
+		}
+
+		put_watch(watch);
+		spin_lock_bh(&wqueue->lock);
+	}
+
+	spin_unlock_bh(&wqueue->lock);
+	rcu_read_unlock();
+}
+
+/*
+ * Release the file.
+ */
+static int watch_queue_release(struct inode *inode, struct file *file)
+{
+	struct watch_filter *wfilter;
+	struct watch_queue *wqueue = file->private_data;
+	int i, pgref;
+
+	watch_queue_clear(wqueue);
+
+	if (wqueue->pages && wqueue->pages[0])
+		WARN_ON(page_ref_count(wqueue->pages[0]) != 1);
+
+	if (wqueue->buffer)
+		vfree(wqueue->buffer);
+	for (i = 0; i < wqueue->nr_pages; i++) {
+		ClearPageUptodate(wqueue->pages[i]);
+		wqueue->pages[i]->mapping = NULL;
+		pgref = page_ref_count(wqueue->pages[i]);
+		WARN(pgref != 1,
+		     "FREE PAGE[%d] refcount %d\n", i, page_ref_count(wqueue->pages[i]));
+		__free_page(wqueue->pages[i]);
+	}
+
+	wfilter = rcu_dereference_protected(wqueue->filter, true);
+	if (wfilter)
+		kfree_rcu(wfilter, rcu);
+	kfree(wqueue->pages);
+	put_cred(wqueue->cred);
+	put_watch_queue(wqueue);
+	return 0;
+}
+
+#ifdef DEBUG_WITH_WRITE
+static ssize_t watch_queue_write(struct file *file,
+				 const char __user *_buf, size_t len, loff_t *pos)
+{
+	struct watch_notification *n;
+	struct watch_queue *wqueue = file->private_data;
+	ssize_t ret;
+
+	if (!wqueue->buffer)
+		return -ENOBUFS;
+
+	if (len & ~WATCH_INFO_LENGTH || len == 0 || !_buf)
+		return -EINVAL;
+
+	n = memdup_user(_buf, len);
+	if (IS_ERR(n))
+		return PTR_ERR(n);
+
+	ret = -EINVAL;
+	if ((n->info & WATCH_INFO_LENGTH) != len)
+		goto error;
+	n->info &= (WATCH_INFO_LENGTH | WATCH_INFO_TYPE_FLAGS | WATCH_INFO_ID);
+
+	if (post_one_notification(wqueue, n, file->f_cred))
+		wqueue->debug = 0;
+	else
+		wqueue->debug++;
+	ret = len;
+	if (wqueue->debug > 20)
+		ret = -EIO;
+
+error:
+	kfree(n);
+	return ret;
+}
+#endif
+
+static const struct file_operations watch_queue_fops = {
+	.owner		= THIS_MODULE,
+	.open		= watch_queue_open,
+	.release	= watch_queue_release,
+	.unlocked_ioctl	= watch_queue_ioctl,
+	.poll		= watch_queue_poll,
+	.mmap		= watch_queue_mmap,
+#ifdef DEBUG_WITH_WRITE
+	.write		= watch_queue_write,
+#endif
+	.llseek		= no_llseek,
+};
+
+/**
+ * get_watch_queue - Get a watch queue from its file descriptor.
+ * @fd: The fd to query.
+ */
+struct watch_queue *get_watch_queue(int fd)
+{
+	struct watch_queue *wqueue = ERR_PTR(-EBADF);
+	struct fd f;
+
+	f = fdget(fd);
+	if (f.file) {
+		wqueue = ERR_PTR(-EINVAL);
+		if (f.file->f_op == &watch_queue_fops) {
+			wqueue = f.file->private_data;
+			kref_get(&wqueue->usage);
+		}
+		fdput(f);
+	}
+
+	return wqueue;
+}
+EXPORT_SYMBOL(get_watch_queue);
+
+static struct miscdevice watch_queue_dev = {
+	.minor	= MISC_DYNAMIC_MINOR,
+	.name	= "watch_queue",
+	.fops	= &watch_queue_fops,
+	.mode	= 0666,
+};
+builtin_misc_device(watch_queue_dev);
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 2474c3f785ca..2f72ea80d4fe 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -1420,6 +1420,13 @@
  *	@ctx is a pointer in which to place the allocated security context.
  *	@ctxlen points to the place to put the length of @ctx.
  *
+ * @post_notification:
+ *	Check to see if a watch notification can be posted to a particular
+ *	queue.
+ *	@q_cred: The credentials of the target watch queue.
+ *	@cred: The event-triggerer's credentials
+ *	@n: The notification being posted
+ *
  * Security hooks for using the eBPF maps and programs functionalities through
  * eBPF syscalls.
  *
@@ -1698,6 +1705,11 @@ union security_list_options {
 	int (*inode_notifysecctx)(struct inode *inode, void *ctx, u32 ctxlen);
 	int (*inode_setsecctx)(struct dentry *dentry, void *ctx, u32 ctxlen);
 	int (*inode_getsecctx)(struct inode *inode, void **ctx, u32 *ctxlen);
+#ifdef CONFIG_WATCH_QUEUE
+	int (*post_notification)(const struct cred *q_cred,
+				 const struct cred *cred,
+				 struct watch_notification *n);
+#endif
 
 #ifdef CONFIG_SECURITY_NETWORK
 	int (*unix_stream_connect)(struct sock *sock, struct sock *other,
@@ -1977,6 +1989,9 @@ struct security_hook_heads {
 	struct hlist_head inode_notifysecctx;
 	struct hlist_head inode_setsecctx;
 	struct hlist_head inode_getsecctx;
+#ifdef CONFIG_WATCH_QUEUE
+	struct hlist_head post_notification;
+#endif
 #ifdef CONFIG_SECURITY_NETWORK
 	struct hlist_head unix_stream_connect;
 	struct hlist_head unix_may_send;
diff --git a/include/linux/security.h b/include/linux/security.h
index 23c8b602c0ab..1df8d55de8da 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -58,6 +58,7 @@ struct fs_context;
 struct fs_parameter;
 enum fs_value_type;
 struct fsinfo_kparams;
+struct watch_notification;
 
 /* Default (no) options for the capable function */
 #define CAP_OPT_NONE 0x0
@@ -396,6 +397,11 @@ void security_inode_invalidate_secctx(struct inode *inode);
 int security_inode_notifysecctx(struct inode *inode, void *ctx, u32 ctxlen);
 int security_inode_setsecctx(struct dentry *dentry, void *ctx, u32 ctxlen);
 int security_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen);
+#ifdef CONFIG_WATCH_QUEUE
+int security_post_notification(const struct cred *q_cred,
+			       const struct cred *cred,
+			       struct watch_notification *n);
+#endif
 #else /* CONFIG_SECURITY */
 
 static inline int call_lsm_notifier(enum lsm_event event, void *data)
@@ -1215,6 +1221,14 @@ static inline int security_inode_getsecctx(struct inode *inode, void **ctx, u32
 {
 	return -EOPNOTSUPP;
 }
+#ifdef CONFIG_WATCH_QUEUE
+static inline int security_post_notification(const struct cred *q_cred,
+					     const struct cred *cred,
+					     struct watch_notification *n)
+{
+	return 0;
+}
+#endif
 #endif	/* CONFIG_SECURITY */
 
 #ifdef CONFIG_SECURITY_NETWORK
diff --git a/include/linux/watch_queue.h b/include/linux/watch_queue.h
new file mode 100644
index 000000000000..18e0834e8aa7
--- /dev/null
+++ b/include/linux/watch_queue.h
@@ -0,0 +1,87 @@
+/* User-mappable watch queue
+ *
+ * Copyright (C) 2018 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ *
+ * See Documentation/watch_queue.rst
+ */
+
+#ifndef _LINUX_WATCH_QUEUE_H
+#define _LINUX_WATCH_QUEUE_H
+
+#include <uapi/linux/watch_queue.h>
+#include <linux/kref.h>
+
+#ifdef CONFIG_WATCH_QUEUE
+
+struct watch_queue;
+
+/*
+ * Representation of a watch on an object.
+ */
+struct watch {
+	union {
+		struct rcu_head	rcu;
+		u32		info_id;	/* ID to be OR'd in to info field */
+	};
+	struct watch_queue __rcu *queue;	/* Queue to post events to */
+	struct hlist_node	queue_node;	/* Link in queue->watches */
+	struct watch_list __rcu	*watch_list;
+	struct hlist_node	list_node;	/* Link in watch_list->watchers */
+	void			*private;	/* Private data for the watched object */
+	u64			id;		/* Internal identifier */
+	struct kref		usage;		/* Object usage count */
+};
+
+/*
+ * List of watches on an object.
+ */
+struct watch_list {
+	struct rcu_head		rcu;
+	struct hlist_head	watchers;
+	void (*release_watch)(struct watch *);
+	spinlock_t		lock;
+};
+
+extern void __post_watch_notification(struct watch_list *,
+				      struct watch_notification *,
+				      const struct cred *,
+				      u64);
+extern struct watch_queue *get_watch_queue(int);
+extern void put_watch_queue(struct watch_queue *);
+extern void put_watch_list(struct watch_list *);
+extern void init_watch(struct watch *, struct watch_queue *);
+extern int add_watch_to_object(struct watch *, struct watch_list *);
+extern int remove_watch_from_object(struct watch_list *, struct watch_queue *, u64, bool);
+
+static inline void init_watch_list(struct watch_list *wlist)
+{
+	INIT_HLIST_HEAD(&wlist->watchers);
+	spin_lock_init(&wlist->lock);
+}
+
+static inline void post_watch_notification(struct watch_list *wlist,
+					   struct watch_notification *n,
+					   const struct cred *cred,
+					   u64 id)
+{
+	if (unlikely(wlist))
+		__post_watch_notification(wlist, n, cred, id);
+}
+
+static inline void remove_watch_list(struct watch_list *wlist)
+{
+	if (wlist) {
+		remove_watch_from_object(wlist, NULL, 0, true);
+		kfree_rcu(wlist, rcu);
+	}
+}
+
+#endif
+
+#endif /* _LINUX_WATCH_QUEUE_H */
diff --git a/include/uapi/linux/watch_queue.h b/include/uapi/linux/watch_queue.h
new file mode 100644
index 000000000000..4a7e0f735f4f
--- /dev/null
+++ b/include/uapi/linux/watch_queue.h
@@ -0,0 +1,82 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _UAPI_LINUX_WATCH_QUEUE_H
+#define _UAPI_LINUX_WATCH_QUEUE_H
+
+#include <linux/types.h>
+#include <linux/ioctl.h>
+
+#define IOC_WATCH_QUEUE_SET_SIZE	_IO('s', 0x01)	/* Set the size in pages */
+#define IOC_WATCH_QUEUE_SET_FILTER	_IO('s', 0x02)	/* Set the filter */
+
+enum watch_notification_type {
+	WATCH_TYPE_META		= 0,	/* Special record */
+	WATCH_TYPE_MOUNT_NOTIFY	= 1,	/* Mount notification record */
+	WATCH_TYPE_SB_NOTIFY	= 2,	/* Superblock notification */
+	WATCH_TYPE_KEY_NOTIFY	= 3,	/* Key/keyring change notification */
+	WATCH_TYPE_BLOCK_NOTIFY	= 4,	/* Block layer notifications */
+#define WATCH_TYPE___NR 5
+};
+
+enum watch_meta_notification_subtype {
+	WATCH_META_SKIP_NOTIFICATION	= 0,	/* Just skip this record */
+	WATCH_META_REMOVAL_NOTIFICATION	= 1,	/* Watched object was removed */
+};
+
+/*
+ * Notification record
+ */
+struct watch_notification {
+	__u32			type:24;	/* enum watch_notification_type */
+	__u32			subtype:8;	/* Type-specific subtype (filterable) */
+	__u32			info;
+#define WATCH_INFO_OVERRUN	0x00000001	/* Event(s) lost due to overrun */
+#define WATCH_INFO_ENOMEM	0x00000002	/* Event(s) lost due to ENOMEM */
+#define WATCH_INFO_RECURSIVE	0x00000004	/* Change was recursive */
+#define WATCH_INFO_LENGTH	0x000001f8	/* Length of record / sizeof(watch_notification) */
+#define WATCH_INFO_IN_SUBTREE	0x00000200	/* Change was not at watched root */
+#define WATCH_INFO_TYPE_FLAGS	0x00ff0000	/* Type-specific flags */
+#define WATCH_INFO_FLAG_0	0x00010000
+#define WATCH_INFO_FLAG_1	0x00020000
+#define WATCH_INFO_FLAG_2	0x00040000
+#define WATCH_INFO_FLAG_3	0x00080000
+#define WATCH_INFO_FLAG_4	0x00100000
+#define WATCH_INFO_FLAG_5	0x00200000
+#define WATCH_INFO_FLAG_6	0x00400000
+#define WATCH_INFO_FLAG_7	0x00800000
+#define WATCH_INFO_ID		0xff000000	/* ID of watchpoint */
+};
+
+#define WATCH_LENGTH_SHIFT	3
+
+struct watch_queue_buffer {
+	union {
+		/* The first few entries are special, containing the
+		 * ring management variables.
+		 */
+		struct {
+			struct watch_notification watch; /* WATCH_TYPE_META */
+			__u32		head;		/* Ring head index */
+			__u32		tail;		/* Ring tail index */
+			__u32		mask;		/* Ring index mask */
+		} meta;
+		struct watch_notification slots[0];
+	};
+};
+
+/*
+ * Notification filtering rules (IOC_WATCH_QUEUE_SET_FILTER).
+ */
+struct watch_notification_type_filter {
+	__u32	type;			/* Type to apply filter to */
+	__u32	info_filter;		/* Filter on watch_notification::info */
+	__u32	info_mask;		/* Mask of relevant bits in info_filter */
+	__u32	subtype_filter[8];	/* Bitmask of subtypes to filter on */
+};
+
+struct watch_notification_filter {
+	__u32	nr_filters;		/* Number of filters */
+	__u32	__reserved;		/* Must be 0 */
+	struct watch_notification_type_filter filters[];
+};
+
+#endif /* _UAPI_LINUX_WATCH_QUEUE_H */
diff --git a/mm/interval_tree.c b/mm/interval_tree.c
index 27ddfd29112a..9a53ddf4bd62 100644
--- a/mm/interval_tree.c
+++ b/mm/interval_tree.c
@@ -25,6 +25,8 @@ INTERVAL_TREE_DEFINE(struct vm_area_struct, shared.rb,
 		     unsigned long, shared.rb_subtree_last,
 		     vma_start_pgoff, vma_last_pgoff,, vma_interval_tree)
 
+EXPORT_SYMBOL_GPL(vma_interval_tree_insert);
+
 /* Insert node immediately after prev in the interval tree */
 void vma_interval_tree_insert_after(struct vm_area_struct *node,
 				    struct vm_area_struct *prev,
diff --git a/mm/memory.c b/mm/memory.c
index 96f1d473c89a..9f2fa2138287 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3360,6 +3360,7 @@ vm_fault_t alloc_set_pte(struct vm_fault *vmf, struct mem_cgroup *memcg,
 
 	return 0;
 }
+EXPORT_SYMBOL_GPL(alloc_set_pte);
 
 
 /**
diff --git a/security/security.c b/security/security.c
index 3af886e8fced..af758dc71e24 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1929,6 +1929,15 @@ int security_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen)
 }
 EXPORT_SYMBOL(security_inode_getsecctx);
 
+#ifdef CONFIG_WATCH_QUEUE
+int security_post_notification(const struct cred *q_cred,
+			       const struct cred *cred,
+			       struct watch_notification *n)
+{
+	return call_int_hook(post_notification, 0, q_cred, cred, n);
+}
+#endif
+
 #ifdef CONFIG_SECURITY_NETWORK
 
 int security_unix_stream_connect(struct sock *sock, struct sock *other, struct sock *newsk)


^ permalink raw reply	[flat|nested] 32+ messages in thread

* [PATCH 3/8] keys: Add a notification facility [ver #2]
  2019-06-04 16:34 [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2] David Howells
  2019-06-04 16:35 ` [PATCH 1/8] security: Override creds in __fput() with last fputter's creds " David Howells
  2019-06-04 16:35 ` [PATCH 2/8] General notification queue with user mmap()'able ring buffer " David Howells
@ 2019-06-04 16:35 ` David Howells
  2019-06-04 16:35 ` [PATCH 4/8] vfs: Add a mount-notification " David Howells
                   ` (6 subsequent siblings)
  9 siblings, 0 replies; 32+ messages in thread
From: David Howells @ 2019-06-04 16:35 UTC (permalink / raw)
  To: viro
  Cc: dhowells, raven, linux-fsdevel, linux-api, linux-block, keyrings,
	linux-security-module, linux-kernel

Add a key/keyring change notification facility whereby notifications about
changes in key and keyring content and attributes can be received.

Firstly, an event queue needs to be created:

	fd = open("/dev/event_queue", O_RDWR);
	ioctl(fd, IOC_WATCH_QUEUE_SET_SIZE, page_size << n);

then a notification can be set up to report notifications via that queue:

	struct watch_notification_filter filter = {
		.nr_filters = 1,
		.filters = {
			[0] = {
				.type = WATCH_TYPE_KEY_NOTIFY,
				.subtype_filter[0] = UINT_MAX,
			},
		},
	};
	ioctl(fd, IOC_WATCH_QUEUE_SET_FILTER, &filter);
	keyctl_watch_key(KEY_SPEC_SESSION_KEYRING, fd, 0x01);

After that, records will be placed into the queue when events occur in
which keys are changed in some way.  Records are of the following format:

	struct key_notification {
		struct watch_notification watch;
		__u32	key_id;
		__u32	aux;
	} *n;

Where:

	n->watch.type will be WATCH_TYPE_KEY_NOTIFY.

	n->watch.subtype will indicate the type of event, such as
	NOTIFY_KEY_REVOKED.

	n->watch.info & WATCH_INFO_LENGTH will indicate the length of the
	record.

	n->watch.info & WATCH_INFO_ID will be the second argument to
	keyctl_watch_key(), shifted.

	n->key will be the ID of the affected key.

	n->aux will hold subtype-dependent information, such as the key
	being linked into the keyring specified by n->key in the case of
	NOTIFY_KEY_LINKED.

Note that it is permissible for event records to be of variable length -
or, at least, the length may be dependent on the subtype.  Note also that
the queue can be shared between multiple notifications of various types.

Signed-off-by: David Howells <dhowells@redhat.com>
---

 Documentation/security/keys/core.rst |   58 ++++++++++++++++++++++
 include/linux/key.h                  |    4 ++
 include/uapi/linux/keyctl.h          |    1 
 include/uapi/linux/watch_queue.h     |   25 ++++++++++
 security/keys/Kconfig                |   10 ++++
 security/keys/compat.c               |    2 +
 security/keys/gc.c                   |    5 ++
 security/keys/internal.h             |   30 +++++++++++
 security/keys/key.c                  |   37 +++++++++-----
 security/keys/keyctl.c               |   89 +++++++++++++++++++++++++++++++++-
 security/keys/keyring.c              |   17 +++++-
 security/keys/request_key.c          |    4 +-
 12 files changed, 258 insertions(+), 24 deletions(-)

diff --git a/Documentation/security/keys/core.rst b/Documentation/security/keys/core.rst
index 9521c4207f01..05ef58c753f3 100644
--- a/Documentation/security/keys/core.rst
+++ b/Documentation/security/keys/core.rst
@@ -808,6 +808,7 @@ The keyctl syscall functions are:
      A process must have search permission on the key for this function to be
      successful.
 
+
   *  Compute a Diffie-Hellman shared secret or public key::
 
 	long keyctl(KEYCTL_DH_COMPUTE, struct keyctl_dh_params *params,
@@ -1001,6 +1002,63 @@ The keyctl syscall functions are:
      written into the output buffer.  Verification returns 0 on success.
 
 
+  *  Watch a key or keyring for changes::
+
+	long keyctl(KEYCTL_WATCH_KEY, key_serial_t key, int queue_fd,
+		    const struct watch_notification_filter *filter);
+
+     This will set or remove a watch for changes on the specified key or
+     keyring.
+
+     "key" is the ID of the key to be watched.
+
+     "queue_fd" is a file descriptor referring to an open "/dev/watch_queue"
+     which manages the buffer into which notifications will be delivered.
+
+     "filter" is either NULL to remove a watch or a filter specification to
+     indicate what events are required from the key.
+
+     See Documentation/watch_queue.rst for more information.
+
+     Note that only one watch may be emplaced for any particular { key,
+     queue_fd } combination.
+
+     Notification records look like::
+
+	struct key_notification {
+		struct watch_notification watch;
+		__u32	key_id;
+		__u32	aux;
+	};
+
+     In this, watch::type will be "WATCH_TYPE_KEY_NOTIFY" and subtype will be
+     one of::
+
+	NOTIFY_KEY_INSTANTIATED
+	NOTIFY_KEY_UPDATED
+	NOTIFY_KEY_LINKED
+	NOTIFY_KEY_UNLINKED
+	NOTIFY_KEY_CLEARED
+	NOTIFY_KEY_REVOKED
+	NOTIFY_KEY_INVALIDATED
+	NOTIFY_KEY_SETATTR
+
+     Where these indicate a key being instantiated/rejected, updated, a link
+     being made in a keyring, a link being removed from a keyring, a keyring
+     being cleared, a key being revoked, a key being invalidated or a key
+     having one of its attributes changed (user, group, perm, timeout,
+     restriction).
+
+     If a watched key is deleted, a basic watch_notification will be issued
+     with "type" set to WATCH_TYPE_META and "subtype" set to
+     watch_meta_removal_notification.  The watchpoint ID will be set in the
+     "info" field.
+
+     This needs to be configured by enabling:
+
+	"Provide key/keyring change notifications" (KEY_NOTIFICATIONS)
+
+
 Kernel Services
 ===============
 
diff --git a/include/linux/key.h b/include/linux/key.h
index 7099985e35a9..f1c43852c0c6 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -159,6 +159,9 @@ struct key {
 		struct list_head graveyard_link;
 		struct rb_node	serial_node;
 	};
+#ifdef CONFIG_KEY_NOTIFICATIONS
+	struct watch_list	*watchers;	/* Entities watching this key for changes */
+#endif
 	struct rw_semaphore	sem;		/* change vs change sem */
 	struct key_user		*user;		/* owner of this key */
 	void			*security;	/* security data for this key */
@@ -193,6 +196,7 @@ struct key {
 #define KEY_FLAG_ROOT_CAN_INVAL	7	/* set if key can be invalidated by root without permission */
 #define KEY_FLAG_KEEP		8	/* set if key should not be removed */
 #define KEY_FLAG_UID_KEYRING	9	/* set if key is a user or user session keyring */
+#define KEY_FLAG_SET_WATCH_PROXY 10	/* Set if watch_proxy should be set on added keys */
 
 	/* the key type and key description string
 	 * - the desc is used to match a key against search criteria
diff --git a/include/uapi/linux/keyctl.h b/include/uapi/linux/keyctl.h
index f45ee0f69c0c..e9e7da849619 100644
--- a/include/uapi/linux/keyctl.h
+++ b/include/uapi/linux/keyctl.h
@@ -67,6 +67,7 @@
 #define KEYCTL_PKEY_SIGN		27	/* Create a public key signature */
 #define KEYCTL_PKEY_VERIFY		28	/* Verify a public key signature */
 #define KEYCTL_RESTRICT_KEYRING		29	/* Restrict keys allowed to link to a keyring */
+#define KEYCTL_WATCH_KEY		30	/* Watch a key or ring of keys for changes */
 
 /* keyctl structures */
 struct keyctl_dh_params {
diff --git a/include/uapi/linux/watch_queue.h b/include/uapi/linux/watch_queue.h
index 4a7e0f735f4f..652fbe27a876 100644
--- a/include/uapi/linux/watch_queue.h
+++ b/include/uapi/linux/watch_queue.h
@@ -79,4 +79,29 @@ struct watch_notification_filter {
 	struct watch_notification_type_filter filters[];
 };
 
+/*
+ * Type of key/keyring change notification.
+ */
+enum key_notification_subtype {
+	NOTIFY_KEY_INSTANTIATED	= 0, /* Key was instantiated (aux is error code) */
+	NOTIFY_KEY_UPDATED	= 1, /* Key was updated */
+	NOTIFY_KEY_LINKED	= 2, /* Key (aux) was added to watched keyring */
+	NOTIFY_KEY_UNLINKED	= 3, /* Key (aux) was removed from watched keyring */
+	NOTIFY_KEY_CLEARED	= 4, /* Keyring was cleared */
+	NOTIFY_KEY_REVOKED	= 5, /* Key was revoked */
+	NOTIFY_KEY_INVALIDATED	= 6, /* Key was invalidated */
+	NOTIFY_KEY_SETATTR	= 7, /* Key's attributes got changed */
+};
+
+/*
+ * Key/keyring notification record.
+ * - watch.type = WATCH_TYPE_KEY_NOTIFY
+ * - watch.subtype = enum key_notification_type
+ */
+struct key_notification {
+	struct watch_notification watch;
+	__u32	key_id;		/* The key/keyring affected */
+	__u32	aux;		/* Per-type auxiliary data */
+};
+
 #endif /* _UAPI_LINUX_WATCH_QUEUE_H */
diff --git a/security/keys/Kconfig b/security/keys/Kconfig
index 6462e6654ccf..fbe064fa0a17 100644
--- a/security/keys/Kconfig
+++ b/security/keys/Kconfig
@@ -101,3 +101,13 @@ config KEY_DH_OPERATIONS
 	 in the kernel.
 
 	 If you are unsure as to whether this is required, answer N.
+
+config KEY_NOTIFICATIONS
+	bool "Provide key/keyring change notifications"
+	depends on KEYS
+	select WATCH_QUEUE
+	help
+	  This option provides support for getting change notifications on keys
+	  and keyrings on which the caller has View permission.  This makes use
+	  of the /dev/watch_queue misc device to handle the notification
+	  buffer and provides KEYCTL_WATCH_KEY to enable/disable watches.
diff --git a/security/keys/compat.c b/security/keys/compat.c
index 9482df601dc3..021d8e1c9233 100644
--- a/security/keys/compat.c
+++ b/security/keys/compat.c
@@ -158,6 +158,8 @@ COMPAT_SYSCALL_DEFINE5(keyctl, u32, option,
 	case KEYCTL_PKEY_VERIFY:
 		return keyctl_pkey_verify(compat_ptr(arg2), compat_ptr(arg3),
 					  compat_ptr(arg4), compat_ptr(arg5));
+	case KEYCTL_WATCH_KEY:
+		return keyctl_watch_key(arg2, arg3, arg4);
 
 	default:
 		return -EOPNOTSUPP;
diff --git a/security/keys/gc.c b/security/keys/gc.c
index 634e96b380e8..b685b9a85a9e 100644
--- a/security/keys/gc.c
+++ b/security/keys/gc.c
@@ -135,6 +135,11 @@ static noinline void key_gc_unused_keys(struct list_head *keys)
 		kdebug("- %u", key->serial);
 		key_check(key);
 
+#ifdef CONFIG_KEY_NOTIFICATIONS
+		remove_watch_list(key->watchers);
+		key->watchers = NULL;
+#endif
+
 		/* Throw away the key data if the key is instantiated */
 		if (state == KEY_IS_POSITIVE && key->type->destroy)
 			key->type->destroy(key);
diff --git a/security/keys/internal.h b/security/keys/internal.h
index 8f533c81aa8d..a7ac0f823ade 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -19,6 +19,7 @@
 #include <linux/task_work.h>
 #include <linux/keyctl.h>
 #include <linux/refcount.h>
+#include <linux/watch_queue.h>
 #include <linux/compat.h>
 
 struct iovec;
@@ -97,7 +98,8 @@ extern int __key_link_begin(struct key *keyring,
 			    const struct keyring_index_key *index_key,
 			    struct assoc_array_edit **_edit);
 extern int __key_link_check_live_key(struct key *keyring, struct key *key);
-extern void __key_link(struct key *key, struct assoc_array_edit **_edit);
+extern void __key_link(struct key *keyring, struct key *key,
+		       struct assoc_array_edit **_edit);
 extern void __key_link_end(struct key *keyring,
 			   const struct keyring_index_key *index_key,
 			   struct assoc_array_edit *edit);
@@ -178,6 +180,23 @@ extern int key_task_permission(const key_ref_t key_ref,
 			       const struct cred *cred,
 			       key_perm_t perm);
 
+static inline void notify_key(struct key *key,
+			      enum key_notification_subtype subtype, u32 aux)
+{
+#ifdef CONFIG_KEY_NOTIFICATIONS
+	struct key_notification n = {
+		.watch.type	= WATCH_TYPE_KEY_NOTIFY,
+		.watch.subtype	= subtype,
+		.watch.info	= sizeof(n),
+		.key_id		= key_serial(key),
+		.aux		= aux,
+	};
+
+	post_watch_notification(key->watchers, &n.watch, current_cred(),
+				n.key_id);
+#endif
+}
+
 /*
  * Check to see whether permission is granted to use a key in the desired way.
  */
@@ -324,6 +343,15 @@ static inline long keyctl_pkey_e_d_s(int op,
 }
 #endif
 
+#ifdef CONFIG_KEY_NOTIFICATIONS
+extern long keyctl_watch_key(key_serial_t, int, int);
+#else
+static inline long keyctl_watch_key(key_serial_t key_id, int watch_fd, int watch_id)
+{
+	return -EOPNOTSUPP;
+}
+#endif
+
 /*
  * Debugging key validation
  */
diff --git a/security/keys/key.c b/security/keys/key.c
index 696f1c092c50..9d9f94992470 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -412,6 +412,7 @@ static void mark_key_instantiated(struct key *key, int reject_error)
 	 */
 	smp_store_release(&key->state,
 			  (reject_error < 0) ? reject_error : KEY_IS_POSITIVE);
+	notify_key(key, NOTIFY_KEY_INSTANTIATED, reject_error);
 }
 
 /*
@@ -454,7 +455,7 @@ static int __key_instantiate_and_link(struct key *key,
 				if (test_bit(KEY_FLAG_KEEP, &keyring->flags))
 					set_bit(KEY_FLAG_KEEP, &key->flags);
 
-				__key_link(key, _edit);
+				__key_link(keyring, key, _edit);
 			}
 
 			/* disable the authorisation key */
@@ -603,7 +604,7 @@ int key_reject_and_link(struct key *key,
 
 		/* and link it into the destination keyring */
 		if (keyring && link_ret == 0)
-			__key_link(key, &edit);
+			__key_link(keyring, key, &edit);
 
 		/* disable the authorisation key */
 		if (authkey)
@@ -756,9 +757,11 @@ static inline key_ref_t __key_update(key_ref_t key_ref,
 	down_write(&key->sem);
 
 	ret = key->type->update(key, prep);
-	if (ret == 0)
+	if (ret == 0) {
 		/* Updating a negative key positively instantiates it */
 		mark_key_instantiated(key, 0);
+		notify_key(key, NOTIFY_KEY_UPDATED, 0);
+	}
 
 	up_write(&key->sem);
 
@@ -999,9 +1002,11 @@ int key_update(key_ref_t key_ref, const void *payload, size_t plen)
 	down_write(&key->sem);
 
 	ret = key->type->update(key, &prep);
-	if (ret == 0)
+	if (ret == 0) {
 		/* Updating a negative key positively instantiates it */
 		mark_key_instantiated(key, 0);
+		notify_key(key, NOTIFY_KEY_UPDATED, 0);
+	}
 
 	up_write(&key->sem);
 
@@ -1033,15 +1038,17 @@ void key_revoke(struct key *key)
 	 *   instantiated
 	 */
 	down_write_nested(&key->sem, 1);
-	if (!test_and_set_bit(KEY_FLAG_REVOKED, &key->flags) &&
-	    key->type->revoke)
-		key->type->revoke(key);
-
-	/* set the death time to no more than the expiry time */
-	time = ktime_get_real_seconds();
-	if (key->revoked_at == 0 || key->revoked_at > time) {
-		key->revoked_at = time;
-		key_schedule_gc(key->revoked_at + key_gc_delay);
+	if (!test_and_set_bit(KEY_FLAG_REVOKED, &key->flags)) {
+		notify_key(key, NOTIFY_KEY_REVOKED, 0);
+		if (key->type->revoke)
+			key->type->revoke(key);
+
+		/* set the death time to no more than the expiry time */
+		time = ktime_get_real_seconds();
+		if (key->revoked_at == 0 || key->revoked_at > time) {
+			key->revoked_at = time;
+			key_schedule_gc(key->revoked_at + key_gc_delay);
+		}
 	}
 
 	up_write(&key->sem);
@@ -1063,8 +1070,10 @@ void key_invalidate(struct key *key)
 
 	if (!test_bit(KEY_FLAG_INVALIDATED, &key->flags)) {
 		down_write_nested(&key->sem, 1);
-		if (!test_and_set_bit(KEY_FLAG_INVALIDATED, &key->flags))
+		if (!test_and_set_bit(KEY_FLAG_INVALIDATED, &key->flags)) {
+			notify_key(key, NOTIFY_KEY_INVALIDATED, 0);
 			key_schedule_gc_links();
+		}
 		up_write(&key->sem);
 	}
 }
diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index 3e4053a217c3..c644bf23ed14 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -914,6 +914,7 @@ long keyctl_chown_key(key_serial_t id, uid_t user, gid_t group)
 	if (group != (gid_t) -1)
 		key->gid = gid;
 
+	notify_key(key, NOTIFY_KEY_SETATTR, 0);
 	ret = 0;
 
 error_put:
@@ -964,6 +965,7 @@ long keyctl_setperm_key(key_serial_t id, key_perm_t perm)
 	/* if we're not the sysadmin, we can only change a key that we own */
 	if (capable(CAP_SYS_ADMIN) || uid_eq(key->uid, current_fsuid())) {
 		key->perm = perm;
+		notify_key(key, NOTIFY_KEY_SETATTR, 0);
 		ret = 0;
 	}
 
@@ -1355,10 +1357,12 @@ long keyctl_set_timeout(key_serial_t id, unsigned timeout)
 okay:
 	key = key_ref_to_ptr(key_ref);
 	ret = 0;
-	if (test_bit(KEY_FLAG_KEEP, &key->flags))
+	if (test_bit(KEY_FLAG_KEEP, &key->flags)) {
 		ret = -EPERM;
-	else
+	} else {
 		key_set_timeout(key, timeout);
+		notify_key(key, NOTIFY_KEY_SETATTR, 0);
+	}
 	key_put(key);
 
 error:
@@ -1631,6 +1635,84 @@ long keyctl_restrict_keyring(key_serial_t id, const char __user *_type,
 	return ret;
 }
 
+#ifdef CONFIG_KEY_NOTIFICATIONS
+/*
+ * Watch for changes to a key.
+ *
+ * The caller must have View permission to watch a key or keyring.
+ */
+long keyctl_watch_key(key_serial_t id, int watch_queue_fd, int watch_id)
+{
+	struct watch_queue *wqueue;
+	struct watch_list *wlist = NULL;
+	struct watch *watch;
+	struct key *key;
+	key_ref_t key_ref;
+	long ret = -ENOMEM;
+
+	if (watch_id < -1 || watch_id > 0xff)
+		return -EINVAL;
+
+	key_ref = lookup_user_key(id, KEY_LOOKUP_CREATE, KEY_NEED_VIEW);
+	if (IS_ERR(key_ref))
+		return PTR_ERR(key_ref);
+	key = key_ref_to_ptr(key_ref);
+
+	wqueue = get_watch_queue(watch_queue_fd);
+	if (IS_ERR(wqueue)) {
+		ret = PTR_ERR(wqueue);
+		goto err_key;
+	}
+
+	if (watch_id >= 0) {
+		if (!key->watchers) {
+			wlist = kzalloc(sizeof(*wlist), GFP_KERNEL);
+			if (!wlist)
+				goto err_wqueue;
+			INIT_HLIST_HEAD(&wlist->watchers);
+			spin_lock_init(&wlist->lock);
+		}
+
+		watch = kzalloc(sizeof(*watch), GFP_KERNEL);
+		if (!watch)
+			goto err_wlist;
+
+		init_watch(watch, wqueue);
+		watch->id	= key->serial;
+		watch->info_id	= (u32)watch_id << 24;
+
+		down_write(&key->sem);
+		if (!key->watchers) {
+			key->watchers = wlist;
+			wlist = NULL;
+		}
+
+		ret = add_watch_to_object(watch, key->watchers);
+		up_write(&key->sem);
+
+		if (ret < 0)
+			kfree(watch);
+	} else {
+		ret = -EBADSLT;
+		if (key->watchers) {
+			down_write(&key->sem);
+			ret = remove_watch_from_object(key->watchers,
+						       wqueue, key_serial(key),
+						       false);
+			up_write(&key->sem);
+		}
+	}
+
+err_wlist:
+	kfree(wlist);
+err_wqueue:
+	put_watch_queue(wqueue);
+err_key:
+	key_put(key);
+	return ret;
+}
+#endif /* CONFIG_KEY_NOTIFICATIONS */
+
 /*
  * The key control system call
  */
@@ -1771,6 +1853,9 @@ SYSCALL_DEFINE5(keyctl, int, option, unsigned long, arg2, unsigned long, arg3,
 			(const void __user *)arg4,
 			(const void __user *)arg5);
 
+	case KEYCTL_WATCH_KEY:
+		return keyctl_watch_key((key_serial_t)arg2, (int)arg3, (int)arg4);
+
 	default:
 		return -EOPNOTSUPP;
 	}
diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index e14f09e3a4b0..f0f9ab3c5587 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -1018,12 +1018,14 @@ int keyring_restrict(key_ref_t keyring_ref, const char *type,
 	down_write(&keyring->sem);
 	down_write(&keyring_serialise_restrict_sem);
 
-	if (keyring->restrict_link)
+	if (keyring->restrict_link) {
 		ret = -EEXIST;
-	else if (keyring_detect_restriction_cycle(keyring, restrict_link))
+	} else if (keyring_detect_restriction_cycle(keyring, restrict_link)) {
 		ret = -EDEADLK;
-	else
+	} else {
 		keyring->restrict_link = restrict_link;
+		notify_key(keyring, NOTIFY_KEY_SETATTR, 0);
+	}
 
 	up_write(&keyring_serialise_restrict_sem);
 	up_write(&keyring->sem);
@@ -1286,12 +1288,14 @@ int __key_link_check_live_key(struct key *keyring, struct key *key)
  * holds at most one link to any given key of a particular type+description
  * combination.
  */
-void __key_link(struct key *key, struct assoc_array_edit **_edit)
+void __key_link(struct key *keyring, struct key *key,
+		struct assoc_array_edit **_edit)
 {
 	__key_get(key);
 	assoc_array_insert_set_object(*_edit, keyring_key_to_ptr(key));
 	assoc_array_apply_edit(*_edit);
 	*_edit = NULL;
+	notify_key(keyring, NOTIFY_KEY_LINKED, key_serial(key));
 }
 
 /*
@@ -1369,7 +1373,7 @@ int key_link(struct key *keyring, struct key *key)
 		if (ret == 0)
 			ret = __key_link_check_live_key(keyring, key);
 		if (ret == 0)
-			__key_link(key, &edit);
+			__key_link(keyring, key, &edit);
 		__key_link_end(keyring, &key->index_key, edit);
 	}
 
@@ -1398,6 +1402,7 @@ EXPORT_SYMBOL(key_link);
 int key_unlink(struct key *keyring, struct key *key)
 {
 	struct assoc_array_edit *edit;
+	key_serial_t target = key_serial(key);
 	int ret;
 
 	key_check(keyring);
@@ -1419,6 +1424,7 @@ int key_unlink(struct key *keyring, struct key *key)
 		goto error;
 
 	assoc_array_apply_edit(edit);
+	notify_key(keyring, NOTIFY_KEY_UNLINKED, target);
 	key_payload_reserve(keyring, keyring->datalen - KEYQUOTA_LINK_BYTES);
 	ret = 0;
 
@@ -1452,6 +1458,7 @@ int keyring_clear(struct key *keyring)
 	} else {
 		if (edit)
 			assoc_array_apply_edit(edit);
+		notify_key(keyring, NOTIFY_KEY_CLEARED, 0);
 		key_payload_reserve(keyring, 0);
 		ret = 0;
 	}
diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index 75d87f9e0f49..5f474d0e8620 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -387,7 +387,7 @@ static int construct_alloc_key(struct keyring_search_context *ctx,
 		goto key_already_present;
 
 	if (dest_keyring)
-		__key_link(key, &edit);
+		__key_link(dest_keyring, key, &edit);
 
 	mutex_unlock(&key_construction_mutex);
 	if (dest_keyring)
@@ -406,7 +406,7 @@ static int construct_alloc_key(struct keyring_search_context *ctx,
 	if (dest_keyring) {
 		ret = __key_link_check_live_key(dest_keyring, key);
 		if (ret == 0)
-			__key_link(key, &edit);
+			__key_link(dest_keyring, key, &edit);
 		__key_link_end(dest_keyring, &ctx->index_key, edit);
 		if (ret < 0)
 			goto link_check_failed;


^ permalink raw reply	[flat|nested] 32+ messages in thread

* [PATCH 4/8] vfs: Add a mount-notification facility [ver #2]
  2019-06-04 16:34 [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2] David Howells
                   ` (2 preceding siblings ...)
  2019-06-04 16:35 ` [PATCH 3/8] keys: Add a notification facility " David Howells
@ 2019-06-04 16:35 ` David Howells
  2019-06-04 16:35 ` [PATCH 5/8] vfs: Add superblock notifications " David Howells
                   ` (5 subsequent siblings)
  9 siblings, 0 replies; 32+ messages in thread
From: David Howells @ 2019-06-04 16:35 UTC (permalink / raw)
  To: viro
  Cc: dhowells, raven, linux-fsdevel, linux-api, linux-block, keyrings,
	linux-security-module, linux-kernel

Add a mount notification facility whereby notifications about changes in
mount topology and configuration can be received.  Note that this only
covers vfsmount topology changes and not superblock events.  A separate
facility will be added for that.

Firstly, an event queue needs to be created:

	fd = open("/dev/event_queue", O_RDWR);
	ioctl(fd, IOC_WATCH_QUEUE_SET_SIZE, page_size << n);

then a notification can be set up to report notifications via that queue:

	struct watch_notification_filter filter = {
		.nr_filters = 1,
		.filters = {
			[0] = {
				.type = WATCH_TYPE_MOUNT_NOTIFY,
				.subtype_filter[0] = UINT_MAX,
			},
		},
	};
	ioctl(fd, IOC_WATCH_QUEUE_SET_FILTER, &filter);
	mount_notify(AT_FDCWD, "/", 0, fd, 0x02);

In this case, it would let me monitor the mount topology subtree rooted at
"/" for events.  Mount notifications propagate up the tree towards the
root, so a watch will catch all of the events happening in the subtree
rooted at the watch.

After setting the watch, records will be placed into the queue when, for
example, as superblock switches between read-write and read-only.  Records
are of the following format:

	struct mount_notification {
		struct watch_notification watch;
		__u32	triggered_on;
		__u32	changed_mount;
	} *n;

Where:

	n->watch.type will be WATCH_TYPE_MOUNT_NOTIFY.

	n->watch.subtype will indicate the type of event, such as
	NOTIFY_MOUNT_NEW_MOUNT.

	n->watch.info & WATCH_INFO_LENGTH will indicate the length of the
	record.

	n->watch.info & WATCH_INFO_ID will be the fifth argument to
	mount_notify(), shifted.

	n->watch.info & WATCH_INFO_FLAG_0 will be used for
	NOTIFY_MOUNT_READONLY, being set if the superblock becomes R/O, and
	being cleared otherwise, and for NOTIFY_MOUNT_NEW_MOUNT, being set
	if the new mount is a submount (e.g. an automount).

	n->triggered_on indicates the ID of the mount on which the watch
	was installed.

	n->changed_mount indicates the ID of the mount that was affected.

The mount IDs can be retrieved with the fsinfo() syscall, using the
fsinfo_mount_info and fsinfo_mount_child attributes.  There are
notification counters there too for when a buffer overrun occurs, thereby
allowing the mount tree to be quickly rescanned.

Note that it is permissible for event records to be of variable length -
or, at least, the length may be dependent on the subtype.  Note also that
the queue can be shared between multiple notifications of various types.

Signed-off-by: David Howells <dhowells@redhat.com>
---

 arch/x86/entry/syscalls/syscall_32.tbl |    1 
 arch/x86/entry/syscalls/syscall_64.tbl |    1 
 fs/Kconfig                             |    9 ++
 fs/Makefile                            |    1 
 fs/mount.h                             |   33 ++++--
 fs/mount_notify.c                      |  186 ++++++++++++++++++++++++++++++++
 fs/namespace.c                         |    9 +-
 include/linux/dcache.h                 |    1 
 include/linux/syscalls.h               |    2 
 include/uapi/linux/watch_queue.h       |   24 ++++
 kernel/sys_ni.c                        |    3 +
 11 files changed, 256 insertions(+), 14 deletions(-)
 create mode 100644 fs/mount_notify.c

diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index 03decae51513..a8416a9a0ccb 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -439,3 +439,4 @@
 432	i386	fsmount			sys_fsmount			__ia32_sys_fsmount
 433	i386	fspick			sys_fspick			__ia32_sys_fspick
 434	i386	fsinfo			sys_fsinfo			__ia32_sys_fsinfo
+435	i386	mount_notify		sys_mount_notify		__ia32_sys_mount_notify
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index ea63df9a1020..ea052a94eb97 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -356,6 +356,7 @@
 432	common	fsmount			__x64_sys_fsmount
 433	common	fspick			__x64_sys_fspick
 434	common	fsinfo			__x64_sys_fsinfo
+435	common	mount_notify		__x64_sys_mount_notify
 
 #
 # x32-specific system call numbers start at 512 to avoid cache impact
diff --git a/fs/Kconfig b/fs/Kconfig
index 9e7d2f2c0111..a26bbe27a791 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -121,6 +121,15 @@ source "fs/crypto/Kconfig"
 
 source "fs/notify/Kconfig"
 
+config MOUNT_NOTIFICATIONS
+	bool "Mount topology change notifications"
+	select WATCH_QUEUE
+	help
+	  This option provides support for getting change notifications on the
+	  mount tree topology.  This makes use of the /dev/watch_queue misc
+	  device to handle the notification buffer and provides the
+	  mount_notify() system call to enable/disable watchpoints.
+
 source "fs/quota/Kconfig"
 
 source "fs/autofs/Kconfig"
diff --git a/fs/Makefile b/fs/Makefile
index 26eaeae4b9a1..c6a71daf2464 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -131,3 +131,4 @@ obj-$(CONFIG_F2FS_FS)		+= f2fs/
 obj-$(CONFIG_CEPH_FS)		+= ceph/
 obj-$(CONFIG_PSTORE)		+= pstore/
 obj-$(CONFIG_EFIVAR_FS)		+= efivarfs/
+obj-$(CONFIG_MOUNT_NOTIFICATIONS) += mount_notify.o
diff --git a/fs/mount.h b/fs/mount.h
index 47795802f78e..a95b805d00d8 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -4,6 +4,7 @@
 #include <linux/poll.h>
 #include <linux/ns_common.h>
 #include <linux/fs_pin.h>
+#include <linux/watch_queue.h>
 
 struct mnt_namespace {
 	atomic_t		count;
@@ -67,9 +68,13 @@ struct mount {
 	int mnt_id;			/* mount identifier */
 	int mnt_group_id;		/* peer group identifier */
 	int mnt_expiry_mark;		/* true if marked for expiry */
+	int mnt_nr_watchers;		/* The number of subtree watches tracking this */
 	struct hlist_head mnt_pins;
 	struct fs_pin mnt_umount;
 	struct dentry *mnt_ex_mountpoint;
+#ifdef CONFIG_MOUNT_NOTIFICATIONS
+	struct watch_list *mnt_watchers; /* Watches on dentries within this mount */
+#endif
 	atomic_t mnt_notify_counter;	/* Number of notifications generated */
 } __randomize_layout;
 
@@ -153,18 +158,8 @@ static inline bool is_anon_ns(struct mnt_namespace *ns)
 	return ns->seq == 0;
 }
 
-/*
- * Type of mount topology change notification.
- */
-enum mount_notification_subtype {
-	NOTIFY_MOUNT_NEW_MOUNT	= 0, /* New mount added */
-	NOTIFY_MOUNT_UNMOUNT	= 1, /* Mount removed manually */
-	NOTIFY_MOUNT_EXPIRY	= 2, /* Automount expired */
-	NOTIFY_MOUNT_READONLY	= 3, /* Mount R/O state changed */
-	NOTIFY_MOUNT_SETATTR	= 4, /* Mount attributes changed */
-	NOTIFY_MOUNT_MOVE_FROM	= 5, /* Mount moved from here */
-	NOTIFY_MOUNT_MOVE_TO	= 6, /* Mount moved to here (compare op_id) */
-};
+extern void post_mount_notification(struct mount *changed,
+				    struct mount_notification *notify);
 
 static inline void notify_mount(struct mount *changed,
 				struct mount *aux,
@@ -172,4 +167,18 @@ static inline void notify_mount(struct mount *changed,
 				u32 info_flags)
 {
 	atomic_inc(&changed->mnt_notify_counter);
+
+#ifdef CONFIG_MOUNT_NOTIFICATIONS
+	{
+		struct mount_notification n = {
+			.watch.type	= WATCH_TYPE_MOUNT_NOTIFY,
+			.watch.subtype	= subtype,
+			.watch.info	= info_flags | sizeof(n),
+			.triggered_on	= changed->mnt_id,
+			.changed_mount	= aux ? aux->mnt_id : 0,
+		};
+
+		post_mount_notification(changed, &n);
+	}
+#endif
 }
diff --git a/fs/mount_notify.c b/fs/mount_notify.c
new file mode 100644
index 000000000000..46806c2764d2
--- /dev/null
+++ b/fs/mount_notify.c
@@ -0,0 +1,186 @@
+/* Provide mount topology/attribute change notifications.
+ *
+ * Copyright (C) 2018 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#include <linux/fs.h>
+#include <linux/namei.h>
+#include <linux/syscalls.h>
+#include <linux/slab.h>
+#include "mount.h"
+
+/*
+ * Post mount notifications to all watches going rootwards along the tree.
+ *
+ * Must be called with the mount_lock held.
+ */
+void post_mount_notification(struct mount *changed,
+			     struct mount_notification *notify)
+{
+	const struct cred *cred = current_cred();
+	struct path cursor;
+	struct mount *mnt;
+	unsigned seq;
+
+	seq = 0;
+	rcu_read_lock();
+restart:
+	cursor.mnt = &changed->mnt;
+	cursor.dentry = changed->mnt.mnt_root;
+	mnt = real_mount(cursor.mnt);
+	notify->watch.info &= ~WATCH_INFO_IN_SUBTREE;
+
+	read_seqbegin_or_lock(&rename_lock, &seq);
+	for (;;) {
+		if (mnt->mnt_watchers &&
+		    !hlist_empty(&mnt->mnt_watchers->watchers)) {
+			if (cursor.dentry->d_flags & DCACHE_MOUNT_WATCH)
+				post_watch_notification(mnt->mnt_watchers,
+							&notify->watch, cred,
+							(unsigned long)cursor.dentry);
+		} else {
+			cursor.dentry = mnt->mnt.mnt_root;
+		}
+		notify->watch.info |= WATCH_INFO_IN_SUBTREE;
+
+		if (cursor.dentry == cursor.mnt->mnt_root ||
+		    IS_ROOT(cursor.dentry)) {
+			struct mount *parent = READ_ONCE(mnt->mnt_parent);
+
+			/* Escaped? */
+			if (cursor.dentry != cursor.mnt->mnt_root)
+				break;
+
+			/* Global root? */
+			if (mnt == parent)
+				break;
+
+			cursor.dentry = READ_ONCE(mnt->mnt_mountpoint);
+			mnt = parent;
+			cursor.mnt = &mnt->mnt;
+		} else {
+			cursor.dentry = cursor.dentry->d_parent;
+		}
+	}
+
+	if (need_seqretry(&rename_lock, seq)) {
+		seq = 1;
+		goto restart;
+	}
+
+	done_seqretry(&rename_lock, seq);
+	rcu_read_unlock();
+}
+
+static void release_mount_watch(struct watch *watch)
+{
+	struct vfsmount *mnt = watch->private;
+	struct dentry *dentry = (struct dentry *)(unsigned long)watch->id;
+
+	dput(dentry);
+	mntput(mnt);
+}
+
+/**
+ * sys_mount_notify - Watch for mount topology/attribute changes
+ * @dfd: Base directory to pathwalk from or fd referring to mount.
+ * @filename: Path to mount to place the watch upon
+ * @at_flags: Pathwalk control flags
+ * @watch_fd: The watch queue to send notifications to.
+ * @watch_id: The watch ID to be placed in the notification (-1 to remove watch)
+ */
+SYSCALL_DEFINE5(mount_notify,
+		int, dfd,
+		const char __user *, filename,
+		unsigned int, at_flags,
+		int, watch_fd,
+		int, watch_id)
+{
+	struct watch_queue *wqueue;
+	struct watch_list *wlist = NULL;
+	struct watch *watch;
+	struct mount *m;
+	struct path path;
+	unsigned int lookup_flags =
+		LOOKUP_DIRECTORY | LOOKUP_FOLLOW | LOOKUP_AUTOMOUNT;
+	int ret;
+
+	if (watch_id < -1 || watch_id > 0xff)
+		return -EINVAL;
+	if ((at_flags & ~(AT_NO_AUTOMOUNT | AT_EMPTY_PATH)) != 0)
+		return -EINVAL;
+	if (at_flags & AT_NO_AUTOMOUNT)
+		lookup_flags &= ~LOOKUP_AUTOMOUNT;
+	if (at_flags & AT_EMPTY_PATH)
+		lookup_flags |= LOOKUP_EMPTY;
+
+	ret = user_path_at(dfd, filename, lookup_flags, &path);
+	if (ret)
+		return ret;
+
+	wqueue = get_watch_queue(watch_fd);
+	if (IS_ERR(wqueue))
+		goto err_path;
+
+	m = real_mount(path.mnt);
+
+	if (watch_id >= 0) {
+		if (!m->mnt_watchers) {
+			wlist = kzalloc(sizeof(*wlist), GFP_KERNEL);
+			if (!wlist)
+				goto err_wqueue;
+			INIT_HLIST_HEAD(&wlist->watchers);
+			spin_lock_init(&wlist->lock);
+			wlist->release_watch = release_mount_watch;
+		}
+
+		watch = kzalloc(sizeof(*watch), GFP_KERNEL);
+		if (!watch)
+			goto err_wlist;
+
+		init_watch(watch, wqueue);
+		watch->id		= (unsigned long)path.dentry;
+		watch->private		= path.mnt;
+		watch->info_id		= (u32)watch_id << 24;
+
+		down_write(&m->mnt.mnt_sb->s_umount);
+		if (!m->mnt_watchers) {
+			m->mnt_watchers = wlist;
+			wlist = NULL;
+		}
+
+		ret = add_watch_to_object(watch, m->mnt_watchers);
+		if (ret == 0) {
+			spin_lock(&path.dentry->d_lock);
+			path.dentry->d_flags |= DCACHE_MOUNT_WATCH;
+			spin_unlock(&path.dentry->d_lock);
+			path_get(&path);
+		}
+		up_write(&m->mnt.mnt_sb->s_umount);
+		if (ret < 0)
+			kfree(watch);
+	} else {
+		ret = -EBADSLT;
+		if (m->mnt_watchers) {
+			down_write(&m->mnt.mnt_sb->s_umount);
+			ret = remove_watch_from_object(m->mnt_watchers, wqueue,
+						       (unsigned long)path.dentry,
+						       false);
+			up_write(&m->mnt.mnt_sb->s_umount);
+		}
+	}
+
+err_wlist:
+	kfree(wlist);
+err_wqueue:
+	put_watch_queue(wqueue);
+err_path:
+	path_put(&path);
+	return ret;
+}
diff --git a/fs/namespace.c b/fs/namespace.c
index ae03066b2d9b..de778b2e8ec4 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -515,7 +515,8 @@ static int mnt_make_readonly(struct mount *mnt)
 	mnt->mnt.mnt_flags &= ~MNT_WRITE_HOLD;
 	unlock_mount_hash();
 	if (ret == 0)
-		notify_mount(mnt, NULL, NOTIFY_MOUNT_READONLY, 0x10000);
+		notify_mount(mnt, NULL, NOTIFY_MOUNT_READONLY,
+			     WATCH_INFO_FLAG_0);
 	return ret;
 }
 
@@ -1478,6 +1479,10 @@ static void umount_tree(struct mount *mnt, enum umount_tree_flags how)
 		list_del_init(&p->mnt_expire);
 		list_del_init(&p->mnt_list);
 
+#ifdef CONFIG_MOUNT_NOTIFICATIONS
+		if (p->mnt_watchers)
+			remove_watch_list(p->mnt_watchers);
+#endif
 		ns = p->mnt_ns;
 		if (ns) {
 			ns->mounts--;
@@ -2115,7 +2120,7 @@ static int attach_recursive_mnt(struct mount *source_mnt,
 		mnt_set_mountpoint(dest_mnt, dest_mp, source_mnt);
 		notify_mount(dest_mnt, source_mnt, NOTIFY_MOUNT_NEW_MOUNT,
 			     source_mnt->mnt.mnt_sb->s_flags & SB_SUBMOUNT ?
-			     0x10000 : 0);
+			     WATCH_INFO_FLAG_0 : 0);
 		commit_tree(source_mnt);
 	}
 
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 361305ddd75e..5db8e244d9a0 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -217,6 +217,7 @@ struct dentry_operations {
 #define DCACHE_PAR_LOOKUP		0x10000000 /* being looked up (with parent locked shared) */
 #define DCACHE_DENTRY_CURSOR		0x20000000
 #define DCACHE_NORCU			0x40000000 /* No RCU delay for freeing */
+#define DCACHE_MOUNT_WATCH		0x80000000 /* There's a mount watch here */
 
 extern seqlock_t rename_lock;
 
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 217d25b62b4f..7c2b66175f3c 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -1001,6 +1001,8 @@ asmlinkage long sys_pidfd_send_signal(int pidfd, int sig,
 asmlinkage long sys_fsinfo(int dfd, const char __user *path,
 			   struct fsinfo_params __user *params,
 			   void __user *buffer, size_t buf_size);
+asmlinkage long sys_mount_notify(int dfd, const char __user *path,
+				 unsigned int at_flags, int watch_fd, int watch_id);
 
 /*
  * Architecture-specific system calls
diff --git a/include/uapi/linux/watch_queue.h b/include/uapi/linux/watch_queue.h
index 652fbe27a876..6cb923f3454e 100644
--- a/include/uapi/linux/watch_queue.h
+++ b/include/uapi/linux/watch_queue.h
@@ -104,4 +104,28 @@ struct key_notification {
 	__u32	aux;		/* Per-type auxiliary data */
 };
 
+/*
+ * Type of mount topology change notification.
+ */
+enum mount_notification_subtype {
+	NOTIFY_MOUNT_NEW_MOUNT	= 0, /* New mount added */
+	NOTIFY_MOUNT_UNMOUNT	= 1, /* Mount removed manually */
+	NOTIFY_MOUNT_EXPIRY	= 2, /* Automount expired */
+	NOTIFY_MOUNT_READONLY	= 3, /* Mount R/O state changed */
+	NOTIFY_MOUNT_SETATTR	= 4, /* Mount attributes changed */
+	NOTIFY_MOUNT_MOVE_FROM	= 5, /* Mount moved from here */
+	NOTIFY_MOUNT_MOVE_TO	= 6, /* Mount moved to here (compare op_id) */
+};
+
+/*
+ * Mount topology/configuration change notification record.
+ * - watch.type = WATCH_TYPE_MOUNT_NOTIFY
+ * - watch.subtype = enum mount_notification_subtype
+ */
+struct mount_notification {
+	struct watch_notification watch; /* WATCH_TYPE_MOUNT_NOTIFY */
+	__u32	triggered_on;		/* The mount that the notify was on */
+	__u32	changed_mount;		/* The mount that got changed */
+};
+
 #endif /* _UAPI_LINUX_WATCH_QUEUE_H */
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index d1d9d76cae1e..97b025e7863c 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -88,6 +88,9 @@ COND_SYSCALL(ioprio_get);
 /* fs/locks.c */
 COND_SYSCALL(flock);
 
+/* fs/mount_notify.c */
+COND_SYSCALL(mount_notify);
+
 /* fs/namei.c */
 
 /* fs/namespace.c */


^ permalink raw reply	[flat|nested] 32+ messages in thread

* [PATCH 5/8] vfs: Add superblock notifications [ver #2]
  2019-06-04 16:34 [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2] David Howells
                   ` (3 preceding siblings ...)
  2019-06-04 16:35 ` [PATCH 4/8] vfs: Add a mount-notification " David Howells
@ 2019-06-04 16:35 ` David Howells
  2019-06-04 16:36 ` [PATCH 6/8] fsinfo: Export superblock notification counter " David Howells
                   ` (4 subsequent siblings)
  9 siblings, 0 replies; 32+ messages in thread
From: David Howells @ 2019-06-04 16:35 UTC (permalink / raw)
  To: viro
  Cc: dhowells, raven, linux-fsdevel, linux-api, linux-block, keyrings,
	linux-security-module, linux-kernel

Add a superblock event notification facility whereby notifications about
superblock events, such as I/O errors (EIO), quota limits being hit
(EDQUOT) and running out of space (ENOSPC) can be reported to a monitoring
process asynchronously.  Note that this does not cover vfsmount topology
changes.  mount_notify() is used for that.

Firstly, an event queue needs to be created:

	fd = open("/dev/event_queue", O_RDWR);
	ioctl(fd, IOC_WATCH_QUEUE_SET_SIZE, page_size << n);

then a notification can be set up to report notifications via that queue:

	struct watch_notification_filter filter = {
		.nr_filters = 1,
		.filters = {
			[0] = {
				.type = WATCH_TYPE_SB_NOTIFY,
				.subtype_filter[0] = UINT_MAX,
			},
		},
	};
	ioctl(fd, IOC_WATCH_QUEUE_SET_FILTER, &filter);
	sb_notify(AT_FDCWD, "/home/dhowells", 0, fd, 0x03);

In this case, it would let me monitor my own homedir for events.  After
setting the watch, records will be placed into the queue when, for example,
as superblock switches between read-write and read-only.  Records are of
the following format:

	struct superblock_notification {
		struct watch_notification watch;
		__u64	sb_id;
	} *n;

Where:

	n->watch.type will be WATCH_TYPE_SB_NOTIFY.

	n->watch.subtype will indicate the type of event, such as
	NOTIFY_SUPERBLOCK_READONLY.

	n->watch.info & WATCH_INFO_LENGTH will indicate the length of the
	record.

	n->watch.info & WATCH_INFO_ID will be the fifth argument to
	sb_notify(), shifted.

	n->watch.info & WATCH_INFO_FLAG_0 will be used for
	NOTIFY_SUPERBLOCK_READONLY, being set if the superblock becomes
	R/O, and being cleared otherwise.

	n->sb_id will be the ID of the superblock, as can be retrieved with
	the fsinfo() syscall, as part of the fsinfo_sb_notifications
	attribute in the the watch_id field.

Note that it is permissible for event records to be of variable length -
or, at least, the length may be dependent on the subtype.  Note also that
the queue can be shared between multiple notifications of various types.

[*] QUESTION: Does this want to be per-sb, per-mount_namespace,
    per-some-new-notify-ns or per-system?  Or do multiple options make
    sense?

[*] QUESTION: I've done it this way so that anyone could theoretically
    monitor the superblock of any filesystem they can pathwalk to, but do
    we need other security controls?

[*] QUESTION: Should the LSM be able to filter the events a queue can
    receive?  For instance the opener of the queue would grant that queue
    subject creds (by ->f_cred) that could be used to govern what events
    could be seen, assuming the target superblock to have some object
    creds, based on, say, the mounter.

Signed-off-by: David Howells <dhowells@redhat.com>
---

 arch/x86/entry/syscalls/syscall_32.tbl |    1 
 arch/x86/entry/syscalls/syscall_64.tbl |    1 
 fs/Kconfig                             |   12 +++
 fs/super.c                             |  116 ++++++++++++++++++++++++++++++++
 include/linux/fs.h                     |   77 +++++++++++++++++++++
 include/linux/syscalls.h               |    2 +
 include/uapi/linux/watch_queue.h       |   26 +++++++
 kernel/sys_ni.c                        |    3 +
 8 files changed, 238 insertions(+)

diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index a8416a9a0ccb..429416ce60e1 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -440,3 +440,4 @@
 433	i386	fspick			sys_fspick			__ia32_sys_fspick
 434	i386	fsinfo			sys_fsinfo			__ia32_sys_fsinfo
 435	i386	mount_notify		sys_mount_notify		__ia32_sys_mount_notify
+436	i386	sb_notify		sys_sb_notify			__ia32_sys_sb_notify
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index ea052a94eb97..4ae146e472db 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -357,6 +357,7 @@
 433	common	fspick			__x64_sys_fspick
 434	common	fsinfo			__x64_sys_fsinfo
 435	common	mount_notify		__x64_sys_mount_notify
+436	common	sb_notify		__x64_sys_sb_notify
 
 #
 # x32-specific system call numbers start at 512 to avoid cache impact
diff --git a/fs/Kconfig b/fs/Kconfig
index a26bbe27a791..fc0fa4b35f3c 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -130,6 +130,18 @@ config MOUNT_NOTIFICATIONS
 	  device to handle the notification buffer and provides the
 	  mount_notify() system call to enable/disable watchpoints.
 
+config SB_NOTIFICATIONS
+	bool "Superblock event notifications"
+	select WATCH_QUEUE
+	help
+	  This option provides support for receiving superblock event
+	  notifications.  This makes use of the /dev/watch_queue misc device to
+	  handle the notification buffer and provides the sb_notify() system
+	  call to enable/disable watches.
+
+	  Events can include things like changing between R/W and R/O, EIO
+	  generation, ENOSPC generation and EDQUOT generation.
+
 source "fs/quota/Kconfig"
 
 source "fs/autofs/Kconfig"
diff --git a/fs/super.c b/fs/super.c
index 61819e8e5469..ae44745e6e2c 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -36,6 +36,8 @@
 #include <linux/lockdep.h>
 #include <linux/user_namespace.h>
 #include <linux/fs_context.h>
+#include <linux/syscalls.h>
+#include <linux/namei.h>
 #include <uapi/linux/mount.h>
 #include "internal.h"
 
@@ -350,6 +352,10 @@ void deactivate_locked_super(struct super_block *s)
 {
 	struct file_system_type *fs = s->s_type;
 	if (atomic_dec_and_test(&s->s_active)) {
+#ifdef CONFIG_SB_NOTIFICATIONS
+		if (s->s_watchers)
+			remove_watch_list(s->s_watchers);
+#endif
 		cleancache_invalidate_fs(s);
 		unregister_shrinker(&s->s_shrink);
 		fs->kill_sb(s);
@@ -990,6 +996,8 @@ int reconfigure_super(struct fs_context *fc)
 	/* Needs to be ordered wrt mnt_is_readonly() */
 	smp_wmb();
 	sb->s_readonly_remount = 0;
+	notify_sb(sb, NOTIFY_SUPERBLOCK_READONLY,
+		  remount_ro ? WATCH_INFO_FLAG_0 : 0);
 
 	/*
 	 * Some filesystems modify their metadata via some other path than the
@@ -1808,3 +1816,111 @@ int thaw_super(struct super_block *sb)
 	return thaw_super_locked(sb);
 }
 EXPORT_SYMBOL(thaw_super);
+
+#ifdef CONFIG_SB_NOTIFICATIONS
+/*
+ * Post superblock notifications.
+ */
+void post_sb_notification(struct super_block *s, struct superblock_notification *n)
+{
+	post_watch_notification(s->s_watchers, &n->watch, current_cred(),
+				s->s_unique_id);
+}
+
+/**
+ * sys_sb_notify - Watch for superblock events.
+ * @dfd: Base directory to pathwalk from or fd referring to superblock.
+ * @filename: Path to superblock to place the watch upon
+ * @at_flags: Pathwalk control flags
+ * @watch_fd: The watch queue to send notifications to.
+ * @watch_id: The watch ID to be placed in the notification (-1 to remove watch)
+ */
+SYSCALL_DEFINE5(sb_notify,
+		int, dfd,
+		const char __user *, filename,
+		unsigned int, at_flags,
+		int, watch_fd,
+		int, watch_id)
+{
+	struct watch_queue *wqueue;
+	struct super_block *s;
+	struct watch_list *wlist = NULL;
+	struct watch *watch;
+	struct path path;
+	unsigned int lookup_flags =
+		LOOKUP_DIRECTORY | LOOKUP_FOLLOW | LOOKUP_AUTOMOUNT;
+	int ret;
+
+	if (watch_id < -1 || watch_id > 0xff)
+		return -EINVAL;
+	if ((at_flags & ~(AT_NO_AUTOMOUNT | AT_EMPTY_PATH)) != 0)
+		return -EINVAL;
+	if (at_flags & AT_NO_AUTOMOUNT)
+		lookup_flags &= ~LOOKUP_AUTOMOUNT;
+	if (at_flags & AT_EMPTY_PATH)
+		lookup_flags |= LOOKUP_EMPTY;
+
+	ret = user_path_at(dfd, filename, at_flags, &path);
+	if (ret)
+		return ret;
+
+	wqueue = get_watch_queue(watch_fd);
+	if (IS_ERR(wqueue))
+		goto err_path;
+
+	s = path.dentry->d_sb;
+	if (watch_id >= 0) {
+		if (!s->s_watchers) {
+			wlist = kzalloc(sizeof(*wlist), GFP_KERNEL);
+			if (!wlist)
+				goto err_wqueue;
+			INIT_HLIST_HEAD(&wlist->watchers);
+			spin_lock_init(&wlist->lock);
+		}
+
+		watch = kzalloc(sizeof(*watch), GFP_KERNEL);
+		if (!watch)
+			goto err_wlist;
+
+		init_watch(watch, wqueue);
+		watch->id		= s->s_unique_id;
+		watch->private		= s;
+		watch->info_id		= (u32)watch_id << 24;
+
+		down_write(&s->s_umount);
+		ret = -EIO;
+		if (atomic_read(&s->s_active)) {
+			if (!s->s_watchers) {
+				s->s_watchers = wlist;
+				wlist = NULL;
+			}
+
+			ret = add_watch_to_object(watch, s->s_watchers);
+			if (ret == 0) {
+				spin_lock(&sb_lock);
+				s->s_count++;
+				spin_unlock(&sb_lock);
+			}
+		}
+		up_write(&s->s_umount);
+		if (ret < 0)
+			kfree(watch);
+	} else {
+		ret = -EBADSLT;
+		if (READ_ONCE(s->s_watchers)) {
+			down_write(&s->s_umount);
+			ret = remove_watch_from_object(s->s_watchers, wqueue,
+						       s->s_unique_id, false);
+			up_write(&s->s_umount);
+		}
+	}
+
+err_wlist:
+	kfree(wlist);
+err_wqueue:
+	put_watch_queue(wqueue);
+err_path:
+	path_put(&path);
+	return ret;
+}
+#endif
diff --git a/include/linux/fs.h b/include/linux/fs.h
index db05738b1951..02ba4bfb9cc3 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -40,6 +40,7 @@
 #include <linux/fs_types.h>
 #include <linux/build_bug.h>
 #include <linux/stddef.h>
+#include <linux/watch_queue.h>
 
 #include <asm/byteorder.h>
 #include <uapi/linux/fs.h>
@@ -1531,6 +1532,10 @@ struct super_block {
 
 	/* Superblock event notifications */
 	u64			s_unique_id;
+
+#ifdef CONFIG_SB_NOTIFICATIONS
+	struct watch_list	*s_watchers;
+#endif
 } __randomize_layout;
 
 /* Helper functions so that in most cases filesystems will
@@ -3531,4 +3536,76 @@ static inline struct sock *io_uring_get_socket(struct file *file)
 }
 #endif
 
+extern void post_sb_notification(struct super_block *, struct superblock_notification *);
+
+/**
+ * notify_sb: Post simple superblock notification.
+ * @s: The superblock the notification is about.
+ * @subtype: The type of notification.
+ * @info: WATCH_INFO_FLAG_* flags to be set in the record.
+ */
+static inline void notify_sb(struct super_block *s,
+			     enum superblock_notification_type subtype,
+			     u32 info)
+{
+#ifdef CONFIG_SB_NOTIFICATIONS
+	if (unlikely(s->s_watchers)) {
+		struct superblock_notification n = {
+			.watch.type	= WATCH_TYPE_SB_NOTIFY,
+			.watch.subtype	= subtype,
+			.watch.info	= sizeof(n) | info,
+			.sb_id		= s->s_unique_id,
+		};
+
+		post_sb_notification(s, &n);
+	}
+			     
+#endif
+}
+
+/**
+ * notify_sb_error: Post superblock error notification.
+ * @s: The superblock the notification is about.
+ * @error: The error number to be recorded.
+ */
+static inline int notify_sb_error(struct super_block *s, int error)
+{
+#ifdef CONFIG_SB_NOTIFICATIONS
+	if (unlikely(s->s_watchers)) {
+		struct superblock_error_notification n = {
+			.s.watch.type	= WATCH_TYPE_SB_NOTIFY,
+			.s.watch.subtype = NOTIFY_SUPERBLOCK_ERROR,
+			.s.watch.info	= sizeof(n),
+			.s.sb_id	= s->s_unique_id,
+			.error_number	= error,
+			.error_cookie	= 0,
+		};
+
+		post_sb_notification(s, &n.s);
+	}
+#endif
+	return error;
+}
+
+/**
+ * notify_sb_EDQUOT: Post superblock quota overrun notification.
+ * @s: The superblock the notification is about.
+ */
+static inline int notify_sb_EQDUOT(struct super_block *s)
+{
+#ifdef CONFIG_SB_NOTIFICATIONS
+	if (unlikely(s->s_watchers)) {
+		struct superblock_notification n = {
+			.watch.type	= WATCH_TYPE_SB_NOTIFY,
+			.watch.subtype	= NOTIFY_SUPERBLOCK_EDQUOT,
+			.watch.info	= sizeof(n),
+			.sb_id		= s->s_unique_id,
+		};
+
+		post_sb_notification(s, &n);
+	}
+#endif
+	return -EDQUOT;
+}
+
 #endif /* _LINUX_FS_H */
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 7c2b66175f3c..204a6dbcc34a 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -1003,6 +1003,8 @@ asmlinkage long sys_fsinfo(int dfd, const char __user *path,
 			   void __user *buffer, size_t buf_size);
 asmlinkage long sys_mount_notify(int dfd, const char __user *path,
 				 unsigned int at_flags, int watch_fd, int watch_id);
+asmlinkage long sys_sb_notify(int dfd, const char __user *path,
+			      unsigned int at_flags, int watch_fd, int watch_id);
 
 /*
  * Architecture-specific system calls
diff --git a/include/uapi/linux/watch_queue.h b/include/uapi/linux/watch_queue.h
index 6cb923f3454e..1f09247e49f3 100644
--- a/include/uapi/linux/watch_queue.h
+++ b/include/uapi/linux/watch_queue.h
@@ -128,4 +128,30 @@ struct mount_notification {
 	__u32	changed_mount;		/* The mount that got changed */
 };
 
+/*
+ * Type of superblock notification.
+ */
+enum superblock_notification_type {
+	NOTIFY_SUPERBLOCK_READONLY	= 0, /* Filesystem toggled between R/O and R/W */
+	NOTIFY_SUPERBLOCK_ERROR		= 1, /* Error in filesystem or blockdev */
+	NOTIFY_SUPERBLOCK_EDQUOT	= 2, /* EDQUOT notification */
+	NOTIFY_SUPERBLOCK_NETWORK	= 3, /* Network status change */
+};
+
+/*
+ * Superblock notification record.
+ * - watch.type = WATCH_TYPE_MOUNT_NOTIFY
+ * - watch.subtype = enum superblock_notification_subtype
+ */
+struct superblock_notification {
+	struct watch_notification watch; /* WATCH_TYPE_SB_NOTIFY */
+	__u64	sb_id;			/* 64-bit superblock ID [fsinfo_ids::f_sb_id] */
+};
+
+struct superblock_error_notification {
+	struct superblock_notification s; /* subtype = notify_superblock_error */
+	__u32	error_number;
+	__u32	error_cookie;
+};
+
 #endif /* _UAPI_LINUX_WATCH_QUEUE_H */
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 97b025e7863c..565d1e3d1bed 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -108,6 +108,9 @@ COND_SYSCALL(quotactl);
 
 /* fs/read_write.c */
 
+/* fs/sb_notify.c */
+COND_SYSCALL(sb_notify);
+
 /* fs/sendfile.c */
 
 /* fs/select.c */


^ permalink raw reply	[flat|nested] 32+ messages in thread

* [PATCH 6/8] fsinfo: Export superblock notification counter [ver #2]
  2019-06-04 16:34 [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2] David Howells
                   ` (4 preceding siblings ...)
  2019-06-04 16:35 ` [PATCH 5/8] vfs: Add superblock notifications " David Howells
@ 2019-06-04 16:36 ` David Howells
  2019-06-04 16:36 ` [PATCH 7/8] block: Add block layer notifications " David Howells
                   ` (3 subsequent siblings)
  9 siblings, 0 replies; 32+ messages in thread
From: David Howells @ 2019-06-04 16:36 UTC (permalink / raw)
  To: viro
  Cc: dhowells, raven, linux-fsdevel, linux-api, linux-block, keyrings,
	linux-security-module, linux-kernel

Provide an fsinfo attribute to export the superblock notification counter
so that it can be polled in the case of a notification buffer overrun.
This is accessed with:

	struct fsinfo_params params = {
		.request = FSINFO_ATTR_SB_NOTIFICATIONS,
	};

and returns a structure that looks like:

	struct fsinfo_sb_notifications {
		__u64	watch_id;
		__u32	notify_counter;
		__u32	__reserved[1];
	};

Where watch_id is a number uniquely identifying the superblock in
notification records and notify_counter is incremented for each
superblock notification posted.

Signed-off-by: David Howells <dhowells@redhat.com>
---

 fs/fsinfo.c                      |   12 ++++++++++++
 fs/super.c                       |    1 +
 include/linux/fs.h               |    1 +
 include/uapi/linux/fsinfo.h      |   10 ++++++++++
 include/uapi/linux/watch_queue.h |    2 +-
 samples/vfs/test-fsinfo.c        |   13 +++++++++++++
 6 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/fs/fsinfo.c b/fs/fsinfo.c
index 3ec64d3cba08..1456e26d2f7c 100644
--- a/fs/fsinfo.c
+++ b/fs/fsinfo.c
@@ -284,6 +284,16 @@ static int fsinfo_generic_param_enum(struct file_system_type *f,
 	return sizeof(*p);
 }
 
+static int fsinfo_generic_sb_notifications(struct path *path,
+					   struct fsinfo_sb_notifications *p)
+{
+	struct super_block *sb = path->dentry->d_sb;
+
+	p->watch_id		= sb->s_unique_id;
+	p->notify_counter	= atomic_read(&sb->s_notify_counter);
+	return sizeof(*p);
+}
+
 static void fsinfo_insert_sb_flag_parameters(struct path *path,
 					     struct fsinfo_kparams *params)
 {
@@ -331,6 +341,7 @@ int generic_fsinfo(struct path *path, struct fsinfo_kparams *params)
 	case _genp(MOUNT_DEVNAME,	mount_devname);
 	case _genp(MOUNT_CHILDREN,	mount_children);
 	case _genp(MOUNT_SUBMOUNT,	mount_submount);
+	case _gen(SB_NOTIFICATIONS,	sb_notifications);
 	default:
 		return -EOPNOTSUPP;
 	}
@@ -606,6 +617,7 @@ static const struct fsinfo_attr_info fsinfo_buffer_info[FSINFO_ATTR__NR] = {
 	FSINFO_STRING_N		(SERVER_NAME,		server_name),
 	FSINFO_STRUCT_NM	(SERVER_ADDRESS,	server_address),
 	FSINFO_STRING		(CELL_NAME,		cell_name),
+	FSINFO_STRUCT		(SB_NOTIFICATIONS,	sb_notifications),
 };
 
 /**
diff --git a/fs/super.c b/fs/super.c
index ae44745e6e2c..832d1a1865c9 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1823,6 +1823,7 @@ EXPORT_SYMBOL(thaw_super);
  */
 void post_sb_notification(struct super_block *s, struct superblock_notification *n)
 {
+	atomic_inc(&s->s_notify_counter);
 	post_watch_notification(s->s_watchers, &n->watch, current_cred(),
 				s->s_unique_id);
 }
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 02ba4bfb9cc3..06e272a25ed7 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1536,6 +1536,7 @@ struct super_block {
 #ifdef CONFIG_SB_NOTIFICATIONS
 	struct watch_list	*s_watchers;
 #endif
+	atomic_t		s_notify_counter;
 } __randomize_layout;
 
 /* Helper functions so that in most cases filesystems will
diff --git a/include/uapi/linux/fsinfo.h b/include/uapi/linux/fsinfo.h
index 7247088332c2..b4c9446305bb 100644
--- a/include/uapi/linux/fsinfo.h
+++ b/include/uapi/linux/fsinfo.h
@@ -39,6 +39,7 @@ enum fsinfo_attribute {
 	FSINFO_ATTR_SERVER_NAME		= 21,	/* Name of the Nth server (string) */
 	FSINFO_ATTR_SERVER_ADDRESS	= 22,	/* Mth address of the Nth server */
 	FSINFO_ATTR_CELL_NAME		= 23,	/* Cell name (string) */
+	FSINFO_ATTR_SB_NOTIFICATIONS	= 24,	/* sb_notify() information */
 	FSINFO_ATTR__NR
 };
 
@@ -308,4 +309,13 @@ struct fsinfo_server_address {
 	struct __kernel_sockaddr_storage address;
 };
 
+/*
+ * Information struct for fsinfo(FSINFO_ATTR_SB_NOTIFICATIONS).
+ */
+struct fsinfo_sb_notifications {
+	__u64		watch_id;	/* Watch ID for superblock. */
+	__u32		notify_counter;	/* Number of notifications. */
+	__u32		__reserved[1];
+};
+
 #endif /* _UAPI_LINUX_FSINFO_H */
diff --git a/include/uapi/linux/watch_queue.h b/include/uapi/linux/watch_queue.h
index 1f09247e49f3..02c330462af8 100644
--- a/include/uapi/linux/watch_queue.h
+++ b/include/uapi/linux/watch_queue.h
@@ -145,7 +145,7 @@ enum superblock_notification_type {
  */
 struct superblock_notification {
 	struct watch_notification watch; /* WATCH_TYPE_SB_NOTIFY */
-	__u64	sb_id;			/* 64-bit superblock ID [fsinfo_ids::f_sb_id] */
+	__u64	sb_id;		/* 64-bit superblock ID [fsinfo_sb_notifications::watch_id] */
 };
 
 struct superblock_error_notification {
diff --git a/samples/vfs/test-fsinfo.c b/samples/vfs/test-fsinfo.c
index af29da74559e..0f8f9ded0925 100644
--- a/samples/vfs/test-fsinfo.c
+++ b/samples/vfs/test-fsinfo.c
@@ -90,6 +90,7 @@ static const struct fsinfo_attr_info fsinfo_buffer_info[FSINFO_ATTR__NR] = {
 	FSINFO_STRING_N		(SERVER_NAME,		server_name),
 	FSINFO_STRUCT_NM	(SERVER_ADDRESS,	server_address),
 	FSINFO_STRING		(CELL_NAME,		cell_name),
+	FSINFO_STRUCT		(SB_NOTIFICATIONS,	sb_notifications),
 };
 
 #define FSINFO_NAME(X,Y) [FSINFO_ATTR_##X] = #Y
@@ -118,6 +119,7 @@ static const char *fsinfo_attr_names[FSINFO_ATTR__NR] = {
 	FSINFO_NAME		(SERVER_NAME,		server_name),
 	FSINFO_NAME		(SERVER_ADDRESS,	server_address),
 	FSINFO_NAME		(CELL_NAME,		cell_name),
+	FSINFO_NAME		(SB_NOTIFICATIONS,	sb_notifications),
 };
 
 union reply {
@@ -133,6 +135,7 @@ union reply {
 	struct fsinfo_mount_info mount_info;
 	struct fsinfo_mount_child mount_children[1];
 	struct fsinfo_server_address srv_addr;
+	struct fsinfo_sb_notifications sb_notifications;
 };
 
 static void dump_hex(unsigned int *data, int from, int to)
@@ -377,6 +380,15 @@ static void dump_attr_MOUNT_CHILDREN(union reply *r, int size)
 		printf("\t[%u] %8x %8x\n", i++, f->mnt_id, f->notify_counter);
 }
 
+static void dump_attr_SB_NOTIFICATIONS(union reply *r, int size)
+{
+	struct fsinfo_sb_notifications *f = &r->sb_notifications;
+
+	printf("\n");
+	printf("\twatch_id: %llx\n", (unsigned long long)f->watch_id);
+	printf("\tnotifs  : %llx\n", (unsigned long long)f->notify_counter);
+}
+
 /*
  *
  */
@@ -395,6 +407,7 @@ static const dumper_t fsinfo_attr_dumper[FSINFO_ATTR__NR] = {
 	FSINFO_DUMPER(MOUNT_INFO),
 	FSINFO_DUMPER(MOUNT_CHILDREN),
 	FSINFO_DUMPER(SERVER_ADDRESS),
+	FSINFO_DUMPER(SB_NOTIFICATIONS),
 };
 
 static void dump_fsinfo(enum fsinfo_attribute attr,


^ permalink raw reply	[flat|nested] 32+ messages in thread

* [PATCH 7/8] block: Add block layer notifications [ver #2]
  2019-06-04 16:34 [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2] David Howells
                   ` (5 preceding siblings ...)
  2019-06-04 16:36 ` [PATCH 6/8] fsinfo: Export superblock notification counter " David Howells
@ 2019-06-04 16:36 ` David Howells
  2019-06-04 16:36 ` [PATCH 8/8] Add sample notification program " David Howells
                   ` (2 subsequent siblings)
  9 siblings, 0 replies; 32+ messages in thread
From: David Howells @ 2019-06-04 16:36 UTC (permalink / raw)
  To: viro
  Cc: dhowells, raven, linux-fsdevel, linux-api, linux-block, keyrings,
	linux-security-module, linux-kernel

Add a block layer notification mechanism whereby notifications about
block-layer events such as I/O errors, can be reported to a monitoring
process asynchronously.

Firstly, an event queue needs to be created:

	fd = open("/dev/event_queue", O_RDWR);
	ioctl(fd, IOC_WATCH_QUEUE_SET_SIZE, page_size << n);

then a notification can be set up to report block notifications via that
queue:

	struct watch_notification_filter filter = {
		.nr_filters = 1,
		.filters = {
			[0] = {
				.type = WATCH_TYPE_BLOCK_NOTIFY,
				.subtype_filter[0] = UINT_MAX;
			},
		},
	};
	ioctl(fd, IOC_WATCH_QUEUE_SET_FILTER, &filter);
	block_notify(fd, 12);

After that, records will be placed into the queue when, for example, errors
occur on a block device.  Records are of the following format:

	struct block_notification {
		struct watch_notification watch;
		__u64	dev;
		__u64	sector;
	} *n;

Where:

	n->watch.type will be WATCH_TYPE_BLOCK_NOTIFY

	n->watch.subtype will be the type of notification, such as
	NOTIFY_BLOCK_ERROR_CRITICAL_MEDIUM.

	n->watch.info & WATCH_INFO_LENGTH will indicate the length of the
	record.

	n->watch.info & WATCH_INFO_ID will be the second argument to
	block_notify(), shifted.

	n->dev will be the device numbers munged together.

	n->sector will indicate the affected sector (if appropriate for the
	event).

Note that it is permissible for event records to be of variable length -
or, at least, the length may be dependent on the subtype.

Signed-off-by: David Howells <dhowells@redhat.com>
---

 arch/x86/entry/syscalls/syscall_32.tbl |    1 
 arch/x86/entry/syscalls/syscall_64.tbl |    1 
 block/Kconfig                          |    9 +++
 block/Makefile                         |    1 
 block/blk-core.c                       |   29 +++++++++++
 block/blk-notify.c                     |   83 ++++++++++++++++++++++++++++++++
 include/linux/blkdev.h                 |   10 ++++
 include/linux/syscalls.h               |    1 
 include/uapi/linux/watch_queue.h       |   28 +++++++++++
 kernel/sys_ni.c                        |    1 
 10 files changed, 164 insertions(+)
 create mode 100644 block/blk-notify.c

diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index 429416ce60e1..22793f77c5f1 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -441,3 +441,4 @@
 434	i386	fsinfo			sys_fsinfo			__ia32_sys_fsinfo
 435	i386	mount_notify		sys_mount_notify		__ia32_sys_mount_notify
 436	i386	sb_notify		sys_sb_notify			__ia32_sys_sb_notify
+437	i386	block_notify		sys_block_notify		__ia32_sys_block_notify
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index 4ae146e472db..3f0b82272a9f 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -358,6 +358,7 @@
 434	common	fsinfo			__x64_sys_fsinfo
 435	common	mount_notify		__x64_sys_mount_notify
 436	common	sb_notify		__x64_sys_sb_notify
+437	common	block_notify		__x64_sys_block_notify
 
 #
 # x32-specific system call numbers start at 512 to avoid cache impact
diff --git a/block/Kconfig b/block/Kconfig
index 1b220101a9cb..3b0a0ddb83ef 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -163,6 +163,15 @@ config BLK_SED_OPAL
 	Enabling this option enables users to setup/unlock/lock
 	Locking ranges for SED devices using the Opal protocol.
 
+config BLK_NOTIFICATIONS
+	bool "Block layer event notifications"
+	select WATCH_QUEUE
+	help
+	  This option provides support for getting block layer event
+	  notifications.  This makes use of the /dev/watch_queue misc device to
+	  handle the notification buffer and provides the block_notify() system
+	  call to enable/disable watches.
+
 menu "Partition Types"
 
 source "block/partitions/Kconfig"
diff --git a/block/Makefile b/block/Makefile
index eee1b4ceecf9..2dca6273f8f3 100644
--- a/block/Makefile
+++ b/block/Makefile
@@ -35,3 +35,4 @@ obj-$(CONFIG_BLK_DEBUG_FS)	+= blk-mq-debugfs.o
 obj-$(CONFIG_BLK_DEBUG_FS_ZONED)+= blk-mq-debugfs-zoned.o
 obj-$(CONFIG_BLK_SED_OPAL)	+= sed-opal.o
 obj-$(CONFIG_BLK_PM)		+= blk-pm.o
+obj-$(CONFIG_BLK_NOTIFICATIONS)	+= blk-notify.o
diff --git a/block/blk-core.c b/block/blk-core.c
index 419d600e6637..edad86172d47 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -144,6 +144,22 @@ static const struct {
 	[BLK_STS_IOERR]		= { -EIO,	"I/O" },
 };
 
+#ifdef CONFIG_BLK_NOTIFICATIONS
+static const
+enum block_notification_type blk_notifications[ARRAY_SIZE(blk_errors)] = {
+	[BLK_STS_TIMEOUT]	= NOTIFY_BLOCK_ERROR_TIMEOUT,
+	[BLK_STS_NOSPC]		= NOTIFY_BLOCK_ERROR_NO_SPACE,
+	[BLK_STS_TRANSPORT]	= NOTIFY_BLOCK_ERROR_RECOVERABLE_TRANSPORT,
+	[BLK_STS_TARGET]	= NOTIFY_BLOCK_ERROR_CRITICAL_TARGET,
+	[BLK_STS_NEXUS]		= NOTIFY_BLOCK_ERROR_CRITICAL_NEXUS,
+	[BLK_STS_MEDIUM]	= NOTIFY_BLOCK_ERROR_CRITICAL_MEDIUM,
+	[BLK_STS_PROTECTION]	= NOTIFY_BLOCK_ERROR_PROTECTION,
+	[BLK_STS_RESOURCE]	= NOTIFY_BLOCK_ERROR_KERNEL_RESOURCE,
+	[BLK_STS_DEV_RESOURCE]	= NOTIFY_BLOCK_ERROR_DEVICE_RESOURCE,
+	[BLK_STS_IOERR]		= NOTIFY_BLOCK_ERROR_IO,
+};
+#endif
+
 blk_status_t errno_to_blk_status(int errno)
 {
 	int i;
@@ -179,6 +195,19 @@ static void print_req_error(struct request *req, blk_status_t status)
 				req->rq_disk ?  req->rq_disk->disk_name : "?",
 				(unsigned long long)blk_rq_pos(req),
 				req->cmd_flags);
+
+#ifdef CONFIG_BLK_NOTIFICATIONS
+	if (blk_notifications[idx]) {
+		struct block_notification n = {
+			.watch.type	= WATCH_TYPE_BLOCK_NOTIFY,
+			.watch.subtype	= blk_notifications[idx],
+			.watch.info	= sizeof(n),
+			.dev		= req->rq_disk ? disk_devt(req->rq_disk) : 0,
+			.sector		= blk_rq_pos(req),
+		};
+		post_block_notification(&n);
+	}
+#endif
 }
 
 static void req_bio_endio(struct request *rq, struct bio *bio,
diff --git a/block/blk-notify.c b/block/blk-notify.c
new file mode 100644
index 000000000000..b310aaf37e7c
--- /dev/null
+++ b/block/blk-notify.c
@@ -0,0 +1,83 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Block layer event notifications.
+ *
+ * Copyright (C) 2019 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/blkdev.h>
+#include <linux/watch_queue.h>
+#include <linux/syscalls.h>
+#include <linux/init_task.h>
+
+/*
+ * Global queue for watching for block layer events.
+ */
+static struct watch_list blk_watchers = {
+	.watchers	= HLIST_HEAD_INIT,
+	.lock		= __SPIN_LOCK_UNLOCKED(&blk_watchers.lock),
+};
+
+static DEFINE_SPINLOCK(blk_watchers_lock);
+
+/*
+ * Post superblock notifications.
+ *
+ * Note that there's only a global queue to which all events are posted.  Might
+ * want to provide per-dev queues also.
+ */
+void post_block_notification(struct block_notification *n)
+{
+	u64 id = 0; /* Might want to allow dev# here. */
+
+	post_watch_notification(&blk_watchers, &n->watch, &init_cred, id);
+}
+
+/**
+ * sys_block_notify - Watch for superblock events.
+ * @watch_fd: The watch queue to send notifications to.
+ * @watch_id: The watch ID to be placed in the notification (-1 to remove watch)
+ */
+SYSCALL_DEFINE2(block_notify, int, watch_fd, int, watch_id)
+{
+	struct watch_queue *wqueue;
+	struct watch_list *wlist = &blk_watchers;
+	struct watch *watch;
+	long ret = -ENOMEM;
+	u64 id = 0; /* Might want to allow dev# here. */
+
+	if (watch_id < -1 || watch_id > 0xff)
+		return -EINVAL;
+
+	wqueue = get_watch_queue(watch_fd);
+	if (IS_ERR(wqueue)) {
+		ret = PTR_ERR(wqueue);
+		goto err;
+	}
+
+	if (watch_id >= 0) {
+		watch = kzalloc(sizeof(*watch), GFP_KERNEL);
+		if (!watch)
+			goto err_wqueue;
+
+		init_watch(watch, wqueue);
+		watch->id	= id;
+		watch->info_id	= (u32)watch_id << WATCH_INFO_ID__SHIFT;
+
+		spin_lock(&blk_watchers_lock);
+		ret = add_watch_to_object(watch, wlist);
+		spin_unlock(&blk_watchers_lock);
+		if (ret < 0)
+			kfree(watch);
+	} else {
+		spin_lock(&blk_watchers_lock);
+		ret = remove_watch_from_object(wlist, wqueue, id, false);
+		spin_unlock(&blk_watchers_lock);
+	}
+
+err_wqueue:
+	put_watch_queue(wqueue);
+err:
+	return ret;
+}
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 1aafeb923e7b..c28f8647a76d 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -43,6 +43,7 @@ struct pr_ops;
 struct rq_qos;
 struct blk_queue_stats;
 struct blk_stat_callback;
+struct block_notification;
 
 #define BLKDEV_MIN_RQ	4
 #define BLKDEV_MAX_RQ	128	/* Default maximum */
@@ -1744,6 +1745,15 @@ static inline bool blk_req_can_dispatch_to_zone(struct request *rq)
 }
 #endif /* CONFIG_BLK_DEV_ZONED */
 
+#ifdef CONFIG_BLK_NOTIFICATIONS
+extern void post_block_notification(struct block_notification *n);
+#else
+static inline void post_block_notification(struct block_notification *n)
+{
+}
+#endif
+
+
 #else /* CONFIG_BLOCK */
 
 struct block_device;
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 204a6dbcc34a..77a9d84f1fbd 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -1005,6 +1005,7 @@ asmlinkage long sys_mount_notify(int dfd, const char __user *path,
 				 unsigned int at_flags, int watch_fd, int watch_id);
 asmlinkage long sys_sb_notify(int dfd, const char __user *path,
 			      unsigned int at_flags, int watch_fd, int watch_id);
+asmlinkage long sys_block_notify(int watch_fd, int watch_id);
 
 /*
  * Architecture-specific system calls
diff --git a/include/uapi/linux/watch_queue.h b/include/uapi/linux/watch_queue.h
index 02c330462af8..231eafa3df99 100644
--- a/include/uapi/linux/watch_queue.h
+++ b/include/uapi/linux/watch_queue.h
@@ -44,6 +44,7 @@ struct watch_notification {
 #define WATCH_INFO_FLAG_6	0x00400000
 #define WATCH_INFO_FLAG_7	0x00800000
 #define WATCH_INFO_ID		0xff000000	/* ID of watchpoint */
+#define WATCH_INFO_ID__SHIFT	24
 };
 
 #define WATCH_LENGTH_SHIFT	3
@@ -154,4 +155,31 @@ struct superblock_error_notification {
 	__u32	error_cookie;
 };
 
+/*
+ * Type of block layer notification.
+ */
+enum block_notification_type {
+	NOTIFY_BLOCK_ERROR_TIMEOUT		= 1, /* Timeout error */
+	NOTIFY_BLOCK_ERROR_NO_SPACE		= 2, /* Critical space allocation error */
+	NOTIFY_BLOCK_ERROR_RECOVERABLE_TRANSPORT = 3, /* Recoverable transport error */
+	NOTIFY_BLOCK_ERROR_CRITICAL_TARGET	= 4, /* Critical target error */
+	NOTIFY_BLOCK_ERROR_CRITICAL_NEXUS	= 5, /* Critical nexus error */
+	NOTIFY_BLOCK_ERROR_CRITICAL_MEDIUM	= 6, /* Critical medium error */
+	NOTIFY_BLOCK_ERROR_PROTECTION		= 7, /* Protection error */
+	NOTIFY_BLOCK_ERROR_KERNEL_RESOURCE	= 8, /* Kernel resource error */
+	NOTIFY_BLOCK_ERROR_DEVICE_RESOURCE	= 9, /* Device resource error */
+	NOTIFY_BLOCK_ERROR_IO			= 10, /* Other I/O error */
+};
+
+/*
+ * Block notification record.
+ * - watch.type = WATCH_TYPE_BLOCK_NOTIFY
+ * - watch.subtype = enum block_notification_type
+ */
+struct block_notification {
+	struct watch_notification watch; /* WATCH_TYPE_SB_NOTIFY */
+	__u64	dev;			/* Device number */
+	__u64	sector;			/* Affected sector */
+};
+
 #endif /* _UAPI_LINUX_WATCH_QUEUE_H */
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 565d1e3d1bed..6178455ac568 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -51,6 +51,7 @@ COND_SYSCALL_COMPAT(io_pgetevents);
 COND_SYSCALL(io_uring_setup);
 COND_SYSCALL(io_uring_enter);
 COND_SYSCALL(io_uring_register);
+COND_SYSCALL(block_notify);
 
 /* fs/xattr.c */
 


^ permalink raw reply	[flat|nested] 32+ messages in thread

* [PATCH 8/8] Add sample notification program [ver #2]
  2019-06-04 16:34 [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2] David Howells
                   ` (6 preceding siblings ...)
  2019-06-04 16:36 ` [PATCH 7/8] block: Add block layer notifications " David Howells
@ 2019-06-04 16:36 ` David Howells
  2019-06-04 17:43 ` [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications " Andy Lutomirski
  2019-06-04 20:39 ` David Howells
  9 siblings, 0 replies; 32+ messages in thread
From: David Howells @ 2019-06-04 16:36 UTC (permalink / raw)
  To: viro
  Cc: dhowells, raven, linux-fsdevel, linux-api, linux-block, keyrings,
	linux-security-module, linux-kernel

This needs to be linked with -lkeyutils.

It is run like:

	./watch_test

and watches "/" for mount changes and the current session keyring for key
changes:

	# keyctl add user a a @s
	1035096409
	# keyctl unlink 1035096409 @s
	# mount -t tmpfs none /mnt/nfsv3tcp/
	# umount /mnt/nfsv3tcp

producing:

	# ./watch_test
	ptrs h=4 t=2 m=20003
	NOTIFY[00000004-00000002] ty=0003 sy=0002 i=01000010
	KEY 2ffc2e5d change=2[linked] aux=1035096409
	ptrs h=6 t=4 m=20003
	NOTIFY[00000006-00000004] ty=0003 sy=0003 i=01000010
	KEY 2ffc2e5d change=3[unlinked] aux=1035096409
	ptrs h=8 t=6 m=20003
	NOTIFY[00000008-00000006] ty=0001 sy=0000 i=02000010
	MOUNT 00000013 change=0[new_mount] aux=168
	ptrs h=a t=8 m=20003
	NOTIFY[0000000a-00000008] ty=0001 sy=0001 i=02000010
	MOUNT 00000013 change=1[unmount] aux=168

Other events may be produced, such as with a failing disk:

	ptrs h=5 t=2 m=6000004
	NOTIFY[00000005-00000002] ty=0004 sy=0006 i=04000018
	BLOCK 00800050 e=6[critical medium] s=5be8

This corresponds to:

	print_req_error: critical medium error, dev sdf, sector 23528 flags 0

in dmesg.

Signed-off-by: David Howells <dhowells@redhat.com>
---

 samples/Kconfig                  |    6 +
 samples/Makefile                 |    1 
 samples/watch_queue/Makefile     |    9 +
 samples/watch_queue/watch_test.c |  284 ++++++++++++++++++++++++++++++++++++++
 4 files changed, 300 insertions(+)
 create mode 100644 samples/watch_queue/Makefile
 create mode 100644 samples/watch_queue/watch_test.c

diff --git a/samples/Kconfig b/samples/Kconfig
index 0561a94f6fdb..a2b7a7babee5 100644
--- a/samples/Kconfig
+++ b/samples/Kconfig
@@ -160,4 +160,10 @@ config SAMPLE_VFS
 	  as mount API and statx().  Note that this is restricted to the x86
 	  arch whilst it accesses system calls that aren't yet in all arches.
 
+config SAMPLE_WATCH_QUEUE
+	bool "Build example /dev/watch_queue notification consumer"
+	help
+	  Build example userspace program to use the new mount_notify(),
+	  sb_notify() syscalls and the KEYCTL_WATCH_KEY keyctl() function.
+
 endif # SAMPLES
diff --git a/samples/Makefile b/samples/Makefile
index debf8925f06f..ed3b8bab6e9b 100644
--- a/samples/Makefile
+++ b/samples/Makefile
@@ -20,3 +20,4 @@ obj-$(CONFIG_SAMPLE_TRACE_PRINTK)	+= trace_printk/
 obj-$(CONFIG_VIDEO_PCI_SKELETON)	+= v4l/
 obj-y					+= vfio-mdev/
 subdir-$(CONFIG_SAMPLE_VFS)		+= vfs
+subdir-$(CONFIG_SAMPLE_WATCH_QUEUE)	+= watch_queue
diff --git a/samples/watch_queue/Makefile b/samples/watch_queue/Makefile
new file mode 100644
index 000000000000..42b694430d0f
--- /dev/null
+++ b/samples/watch_queue/Makefile
@@ -0,0 +1,9 @@
+# List of programs to build
+hostprogs-y := watch_test
+
+# Tell kbuild to always build the programs
+always := $(hostprogs-y)
+
+HOSTCFLAGS_watch_test.o += -I$(objtree)/usr/include
+
+HOSTLOADLIBES_watch_test += -lkeyutils
diff --git a/samples/watch_queue/watch_test.c b/samples/watch_queue/watch_test.c
new file mode 100644
index 000000000000..0bbab492e237
--- /dev/null
+++ b/samples/watch_queue/watch_test.c
@@ -0,0 +1,284 @@
+/* Use /dev/watch_queue to watch for keyring and mount topology changes.
+ *
+ * Copyright (C) 2018 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#include <stdbool.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <signal.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <dirent.h>
+#include <errno.h>
+#include <sys/wait.h>
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+#include <poll.h>
+#include <limits.h>
+#include <linux/watch_queue.h>
+#include <linux/unistd.h>
+#include <linux/keyctl.h>
+
+#ifndef __NR_mount_notify
+#define __NR_mount_notify -1
+#endif
+#ifndef __NR_sb_notify
+#define __NR_sb_notify -1
+#endif
+#ifndef __NR_block_notify
+#define __NR_block_notify -1
+#endif
+#ifndef KEYCTL_WATCH_KEY
+#define KEYCTL_WATCH_KEY -1
+#endif
+
+#define BUF_SIZE 4
+
+static const char *key_subtypes[256] = {
+	[NOTIFY_KEY_INSTANTIATED]	= "instantiated",
+	[NOTIFY_KEY_UPDATED]		= "updated",
+	[NOTIFY_KEY_LINKED]		= "linked",
+	[NOTIFY_KEY_UNLINKED]		= "unlinked",
+	[NOTIFY_KEY_CLEARED]		= "cleared",
+	[NOTIFY_KEY_REVOKED]		= "revoked",
+	[NOTIFY_KEY_INVALIDATED]	= "invalidated",
+	[NOTIFY_KEY_SETATTR]		= "setattr",
+};
+
+static void saw_key_change(struct watch_notification *n)
+{
+	struct key_notification *k = (struct key_notification *)n;
+	unsigned int len = n->info & WATCH_INFO_LENGTH;
+
+	if (len != sizeof(struct key_notification))
+		return;
+
+	printf("KEY %08x change=%u[%s] aux=%u\n",
+	       k->key_id, n->subtype, key_subtypes[n->subtype], k->aux);
+}
+
+static const char *mount_subtypes[256] = {
+	[NOTIFY_MOUNT_NEW_MOUNT]	= "new_mount",
+	[NOTIFY_MOUNT_UNMOUNT]		= "unmount",
+	[NOTIFY_MOUNT_EXPIRY]		= "expiry",
+	[NOTIFY_MOUNT_READONLY]		= "readonly",
+	[NOTIFY_MOUNT_SETATTR]		= "setattr",
+	[NOTIFY_MOUNT_MOVE_FROM]	= "move_from",
+	[NOTIFY_MOUNT_MOVE_TO]		= "move_to",
+};
+
+static long keyctl_watch_key(int key, int watch_fd, int watch_id)
+{
+	return syscall(__NR_keyctl, KEYCTL_WATCH_KEY, key, watch_fd, watch_id);
+}
+
+static void saw_mount_change(struct watch_notification *n)
+{
+	struct mount_notification *m = (struct mount_notification *)n;
+	unsigned int len = n->info & WATCH_INFO_LENGTH;
+
+	if (len != sizeof(struct mount_notification))
+		return;
+
+	printf("MOUNT %08x change=%u[%s] aux=%u\n",
+	       m->triggered_on, n->subtype, mount_subtypes[n->subtype], m->changed_mount);
+}
+
+static const char *super_subtypes[256] = {
+	[NOTIFY_SUPERBLOCK_READONLY]	= "readonly",
+	[NOTIFY_SUPERBLOCK_ERROR]	= "error",
+	[NOTIFY_SUPERBLOCK_EDQUOT]	= "edquot",
+	[NOTIFY_SUPERBLOCK_NETWORK]	= "network",
+};
+
+static void saw_super_change(struct watch_notification *n)
+{
+	struct superblock_notification *s = (struct superblock_notification *)n;
+	unsigned int len = n->info & WATCH_INFO_LENGTH;
+
+	if (len < sizeof(struct superblock_notification))
+		return;
+
+	printf("SUPER %08llx change=%u[%s]\n",
+	       s->sb_id, n->subtype, super_subtypes[n->subtype]);
+}
+
+static const char *block_subtypes[256] = {
+	[NOTIFY_BLOCK_ERROR_TIMEOUT]			= "timeout",
+	[NOTIFY_BLOCK_ERROR_NO_SPACE]			= "critical space allocation",
+	[NOTIFY_BLOCK_ERROR_RECOVERABLE_TRANSPORT]	= "recoverable transport",
+	[NOTIFY_BLOCK_ERROR_CRITICAL_TARGET]		= "critical target",
+	[NOTIFY_BLOCK_ERROR_CRITICAL_NEXUS]		= "critical nexus",
+	[NOTIFY_BLOCK_ERROR_CRITICAL_MEDIUM]		= "critical medium",
+	[NOTIFY_BLOCK_ERROR_PROTECTION]			= "protection",
+	[NOTIFY_BLOCK_ERROR_KERNEL_RESOURCE]		= "kernel resource",
+	[NOTIFY_BLOCK_ERROR_DEVICE_RESOURCE]		= "device resource",
+	[NOTIFY_BLOCK_ERROR_IO]				= "I/O",
+};
+
+static void saw_block_change(struct watch_notification *n)
+{
+	struct block_notification *b = (struct block_notification *)n;
+	unsigned int len = n->info & WATCH_INFO_LENGTH;
+
+	if (len < sizeof(struct block_notification))
+		return;
+
+	printf("BLOCK %08llx e=%u[%s] s=%llx\n",
+	       (unsigned long long)b->dev,
+	       n->subtype, block_subtypes[n->subtype],
+	       (unsigned long long)b->sector);
+}
+
+/*
+ * Consume and display events.
+ */
+static int consumer(int fd, struct watch_queue_buffer *buf)
+{
+	struct watch_notification *n;
+	struct pollfd p[1];
+	unsigned int head, tail, mask = buf->meta.mask;
+
+	for (;;) {
+		p[0].fd = fd;
+		p[0].events = POLLIN | POLLERR;
+		p[0].revents = 0;
+
+		if (poll(p, 1, -1) == -1) {
+			perror("poll");
+			break;
+		}
+
+		printf("ptrs h=%x t=%x m=%x\n",
+		       buf->meta.head, buf->meta.tail, buf->meta.mask);
+
+		while (head = buf->meta.head,
+		       tail = buf->meta.tail,
+		       tail != head
+		       ) {
+			asm ("lfence" : : : "memory" );
+			n = &buf->slots[tail & mask];
+			printf("NOTIFY[%08x-%08x] ty=%04x sy=%04x i=%08x\n",
+			       head, tail, n->type, n->subtype, n->info);
+			if ((n->info & WATCH_INFO_LENGTH) == 0)
+				goto out;
+
+			switch (n->type) {
+			case WATCH_TYPE_META:
+				if (n->subtype == WATCH_META_REMOVAL_NOTIFICATION)
+					printf("REMOVAL of watchpoint %08x\n",
+					       n->info & WATCH_INFO_ID);
+				break;
+			case WATCH_TYPE_MOUNT_NOTIFY:
+				saw_mount_change(n);
+				break;
+			case WATCH_TYPE_SB_NOTIFY:
+				saw_super_change(n);
+				break;
+			case WATCH_TYPE_KEY_NOTIFY:
+				saw_key_change(n);
+				break;
+			case WATCH_TYPE_BLOCK_NOTIFY:
+				saw_block_change(n);
+				break;
+			}
+
+			tail += (n->info & WATCH_INFO_LENGTH) >> WATCH_LENGTH_SHIFT;
+			asm("mfence" ::: "memory");
+			buf->meta.tail = tail;
+		}
+	}
+
+out:
+	return 0;
+}
+
+static struct watch_notification_filter filter = {
+	.nr_filters	= 4,
+	.__reserved	= 0,
+	.filters = {
+		[0] = {
+			.type			= WATCH_TYPE_MOUNT_NOTIFY,
+			// Reject move-from notifications
+			.subtype_filter[0]	= UINT_MAX & ~(1 << NOTIFY_MOUNT_MOVE_FROM),
+		},
+		[1]	= {
+			.type			= WATCH_TYPE_SB_NOTIFY,
+			// Only accept notification of changes to R/O state
+			.subtype_filter[0]	= (1 << NOTIFY_SUPERBLOCK_READONLY),
+			// Only accept notifications of change-to-R/O
+			.info_mask		= WATCH_INFO_FLAG_0,
+			.info_filter		= WATCH_INFO_FLAG_0,
+		},
+		[2]	= {
+			.type			= WATCH_TYPE_KEY_NOTIFY,
+			.subtype_filter[0]	= UINT_MAX,
+		},
+		[3]	= {
+			.type			= WATCH_TYPE_BLOCK_NOTIFY,
+			.subtype_filter[0]	= UINT_MAX,
+		},
+	},
+};
+
+int main(int argc, char **argv)
+{
+	struct watch_queue_buffer *buf;
+	size_t page_size;
+	int fd;
+
+	fd = open("/dev/watch_queue", O_RDWR);
+	if (fd == -1) {
+		perror("/dev/watch_queue");
+		exit(1);
+	}
+
+	if (ioctl(fd, IOC_WATCH_QUEUE_SET_SIZE, BUF_SIZE) == -1) {
+		perror("/dev/watch_queue(size)");
+		exit(1);
+	}
+
+	if (ioctl(fd, IOC_WATCH_QUEUE_SET_FILTER, &filter) == -1) {
+		perror("/dev/watch_queue(filter)");
+		exit(1);
+	}
+
+	page_size = sysconf(_SC_PAGESIZE);
+	buf = mmap(NULL, BUF_SIZE * page_size, PROT_READ | PROT_WRITE,
+		   MAP_SHARED, fd, 0);
+	if (buf == MAP_FAILED) {
+		perror("mmap");
+		exit(1);
+	}
+
+	if (keyctl_watch_key(KEY_SPEC_SESSION_KEYRING, fd, 0x01) == -1) {
+		perror("keyctl");
+		exit(1);
+	}
+
+	if (syscall(__NR_mount_notify, AT_FDCWD, "/", 0, fd, 0x02) == -1) {
+		perror("mount_notify");
+		exit(1);
+	}
+
+	if (syscall(__NR_sb_notify, AT_FDCWD, "/mnt", 0, fd, 0x03) == -1) {
+		perror("sb_notify");
+		exit(1);
+	}
+
+	if (syscall(__NR_block_notify, fd, 0x04) == -1) {
+		perror("block_notify");
+		exit(1);
+	}
+
+	return consumer(fd, buf);
+}


^ permalink raw reply	[flat|nested] 32+ messages in thread

* Re: [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2]
  2019-06-04 16:34 [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2] David Howells
                   ` (7 preceding siblings ...)
  2019-06-04 16:36 ` [PATCH 8/8] Add sample notification program " David Howells
@ 2019-06-04 17:43 ` Andy Lutomirski
  2019-06-04 20:31   ` Casey Schaufler
  2019-06-05  8:41   ` David Howells
  2019-06-04 20:39 ` David Howells
  9 siblings, 2 replies; 32+ messages in thread
From: Andy Lutomirski @ 2019-06-04 17:43 UTC (permalink / raw)
  To: David Howells
  Cc: Al Viro, Casey Schaufler, raven, Linux FS Devel, Linux API,
	linux-block, keyrings, LSM List, LKML

On Tue, Jun 4, 2019 at 9:35 AM David Howells <dhowells@redhat.com> wrote:
>
>
> Hi Al,
>
> Here's a set of patches to add a general variable-length notification queue
> concept and to add sources of events for:

I asked before and didn't see a response, so I'll ask again.  Why are
you paying any attention at all to the creds that generate an event?
It seems like the resulting security model will be vary hard to
understand and probably buggy.  Can't you define a sensible model in
which only the listener creds matter?

> LSM support is included:
>
>  (1) The creds of the process that did the fput() that reduced the refcount
>      to zero are cached in the file struct.
>
>  (2) __fput() overrides the current creds with the creds from (1) whilst
>      doing the cleanup, thereby making sure that the creds seen by the
>      destruction notification generated by mntput() appears to come from
>      the last fputter.

That looks like duct tape that is, at best, likely to be very buggy.

>
>  (3) security_post_notification() is called for each queue that we might
>      want to post a notification into, thereby allowing the LSM to prevent
>      covert communications.

This seems like the wrong approach.  If an LSM wants to prevent covert
communication from, say, mount actions, then it shouldn't allow the
watch to be set up in the first place.

^ permalink raw reply	[flat|nested] 32+ messages in thread

* Re: [PATCH 1/8] security: Override creds in __fput() with last fputter's creds [ver #2]
  2019-06-04 16:35 ` [PATCH 1/8] security: Override creds in __fput() with last fputter's creds " David Howells
@ 2019-06-04 18:15   ` Andy Lutomirski
  0 siblings, 0 replies; 32+ messages in thread
From: Andy Lutomirski @ 2019-06-04 18:15 UTC (permalink / raw)
  To: David Howells, Jann Horn
  Cc: Al Viro, Casey Schaufler, raven, Linux FS Devel, Linux API,
	linux-block, keyrings, LSM List, LKML

On Tue, Jun 4, 2019 at 9:35 AM David Howells <dhowells@redhat.com> wrote:
>
> So that the LSM can see the credentials of the last process to do an fput()
> on a file object when the file object is being dismantled, do the following
> steps:
>
>  (1) Cache the current credentials in file->f_fput_cred at the point the
>      file object's reference count reaches zero.

I don't think it's valid to capture credentials in close().  This
sounds very easy to spoof, especially when you consider that you can
stick an fd in unix socket and aim it at a service that's just going
to ignore it and close it.

IOW I think this is at least as invalid as looking at current_cred()
in write(), which is a classic bug that gets repeated regularly.

--Andy

^ permalink raw reply	[flat|nested] 32+ messages in thread

* Re: [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2]
  2019-06-04 17:43 ` [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications " Andy Lutomirski
@ 2019-06-04 20:31   ` Casey Schaufler
  2019-06-04 21:05     ` Andy Lutomirski
  2019-06-05  8:41   ` David Howells
  1 sibling, 1 reply; 32+ messages in thread
From: Casey Schaufler @ 2019-06-04 20:31 UTC (permalink / raw)
  To: Andy Lutomirski, David Howells
  Cc: Al Viro, raven, Linux FS Devel, Linux API, linux-block, keyrings,
	LSM List, LKML, casey

n 6/4/2019 10:43 AM, Andy Lutomirski wrote:
> On Tue, Jun 4, 2019 at 9:35 AM David Howells <dhowells@redhat.com> wrote:
>>
>> Hi Al,
>>
>> Here's a set of patches to add a general variable-length notification queue
>> concept and to add sources of events for:
> I asked before and didn't see a response, so I'll ask again.  Why are
> you paying any attention at all to the creds that generate an event?
> It seems like the resulting security model will be vary hard to
> understand and probably buggy.  Can't you define a sensible model in
> which only the listener creds matter?

We've spent the last 18 months reeling from the implications
of what can happen when one process has the ability to snoop
on another. Introducing yet another mechanism that is trivial
to exploit is a very bad idea.

I will try to explain the problem once again. If process A
sends a signal (writes information) to process B the kernel
checks that either process A has the same UID as process B
or that process A has privilege to override that policy.
Process B is passive in this access control decision, while
process A is active. In the event delivery case, process A
does something (e.g. modifies a keyring) that generates an
event, which is then sent to process B's event buffer. Again,
A is active and B is passive. Process A must have write access
(defined by some policy) to process B's event buffer. To
implement such a policy requires A's credential, and some
information about the object (passive entity) to which the
event is being delivered. You can't just use the credential
from Process B because it is not the active entity, it is the
passive entity.


>
>> LSM support is included:
>>
>>  (1) The creds of the process that did the fput() that reduced the refcount
>>      to zero are cached in the file struct.
>>
>>  (2) __fput() overrides the current creds with the creds from (1) whilst
>>      doing the cleanup, thereby making sure that the creds seen by the
>>      destruction notification generated by mntput() appears to come from
>>      the last fputter.
> That looks like duct tape that is, at best, likely to be very buggy.
>
>>  (3) security_post_notification() is called for each queue that we might
>>      want to post a notification into, thereby allowing the LSM to prevent
>>      covert communications.
> This seems like the wrong approach.  If an LSM wants to prevent covert
> communication from, say, mount actions, then it shouldn't allow the
> watch to be set up in the first place.


^ permalink raw reply	[flat|nested] 32+ messages in thread

* Re: [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2]
  2019-06-04 16:34 [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2] David Howells
                   ` (8 preceding siblings ...)
  2019-06-04 17:43 ` [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications " Andy Lutomirski
@ 2019-06-04 20:39 ` David Howells
  2019-06-04 20:57   ` Andy Lutomirski
  2019-06-04 21:11   ` Casey Schaufler
  9 siblings, 2 replies; 32+ messages in thread
From: David Howells @ 2019-06-04 20:39 UTC (permalink / raw)
  To: Andy Lutomirski
  Cc: dhowells, Al Viro, Casey Schaufler, raven, Linux FS Devel,
	Linux API, linux-block, keyrings, LSM List, LKML

Andy Lutomirski <luto@kernel.org> wrote:

> > Here's a set of patches to add a general variable-length notification queue
> > concept and to add sources of events for:
> 
> I asked before and didn't see a response, so I'll ask again.  Why are you
> paying any attention at all to the creds that generate an event?

Casey responded to you.  It's one of his requirements.

I'm not sure of the need, and I particularly don't like trying to make
indirect destruction events (mount destruction keyed on fput, for instance)
carry the creds of the triggerer.  Indeed, the trigger can come from all sorts
of places - including af_unix queue destruction, someone poking around in
procfs, a variety of processes fputting simultaneously.  Only one of them can
win, and the LSM needs to handle *all* the possibilities.

However, the LSMs (or at least SELinux) ignore f_cred and use current_cred()
when checking permissions.  See selinux_revalidate_file_permission() for
example - it uses current_cred() not file->f_cred to re-evaluate the perms,
and the fd might be shared between a number of processes with different creds.

> This seems like the wrong approach.  If an LSM wants to prevent covert
> communication from, say, mount actions, then it shouldn't allow the
> watch to be set up in the first place.

Yeah, I can agree to that.  Casey?

David

^ permalink raw reply	[flat|nested] 32+ messages in thread

* Re: [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2]
  2019-06-04 20:39 ` David Howells
@ 2019-06-04 20:57   ` Andy Lutomirski
       [not found]     ` <CAB9W1A0AgMYOwGx9c-TmAt=1O6Bjsr2P3Nhd=2+QV39dgw0CrA@mail.gmail.com>
  2019-06-04 21:11   ` Casey Schaufler
  1 sibling, 1 reply; 32+ messages in thread
From: Andy Lutomirski @ 2019-06-04 20:57 UTC (permalink / raw)
  To: David Howells
  Cc: Andy Lutomirski, Al Viro, Casey Schaufler, raven, Linux FS Devel,
	Linux API, linux-block, keyrings, LSM List, LKML

On Tue, Jun 4, 2019 at 1:39 PM David Howells <dhowells@redhat.com> wrote:
>
> Andy Lutomirski <luto@kernel.org> wrote:
>
> > > Here's a set of patches to add a general variable-length notification queue
> > > concept and to add sources of events for:
> >
> > I asked before and didn't see a response, so I'll ask again.  Why are you
> > paying any attention at all to the creds that generate an event?
>
> Casey responded to you.  It's one of his requirements.
>

It being a "requirement" doesn't make it okay.

> However, the LSMs (or at least SELinux) ignore f_cred and use current_cred()
> when checking permissions.  See selinux_revalidate_file_permission() for
> example - it uses current_cred() not file->f_cred to re-evaluate the perms,
> and the fd might be shared between a number of processes with different creds.

That's a bug.  It's arguably a rather severe bug.  If I ever get
around to writing the patch I keep thinking of that will warn if we
use creds from invalid contexts, it will warn.

Let's please not repeat this.

^ permalink raw reply	[flat|nested] 32+ messages in thread

* Re: [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2]
  2019-06-04 20:31   ` Casey Schaufler
@ 2019-06-04 21:05     ` Andy Lutomirski
  2019-06-04 22:03       ` Casey Schaufler
  0 siblings, 1 reply; 32+ messages in thread
From: Andy Lutomirski @ 2019-06-04 21:05 UTC (permalink / raw)
  To: Casey Schaufler
  Cc: Andy Lutomirski, David Howells, Al Viro, raven, Linux FS Devel,
	Linux API, linux-block, keyrings, LSM List, LKML

On Tue, Jun 4, 2019 at 1:31 PM Casey Schaufler <casey@schaufler-ca.com> wrote:
>
> n 6/4/2019 10:43 AM, Andy Lutomirski wrote:
> > On Tue, Jun 4, 2019 at 9:35 AM David Howells <dhowells@redhat.com> wrote:
> >>
> >> Hi Al,
> >>
> >> Here's a set of patches to add a general variable-length notification queue
> >> concept and to add sources of events for:
> > I asked before and didn't see a response, so I'll ask again.  Why are
> > you paying any attention at all to the creds that generate an event?
> > It seems like the resulting security model will be vary hard to
> > understand and probably buggy.  Can't you define a sensible model in
> > which only the listener creds matter?
>
> We've spent the last 18 months reeling from the implications
> of what can happen when one process has the ability to snoop
> on another. Introducing yet another mechanism that is trivial
> to exploit is a very bad idea.

If you're talking about Spectre, etc, this is IMO entirely irrelevant.
Among other things, setting these watches can and should require some
degree of privilege.

>
> I will try to explain the problem once again. If process A
> sends a signal (writes information) to process B the kernel
> checks that either process A has the same UID as process B
> or that process A has privilege to override that policy.
> Process B is passive in this access control decision, while
> process A is active.

Are you stating what you see to be a requirement?

> Process A must have write access
> (defined by some policy) to process B's event buffer.

No, stop right here.  Process B is monitoring some aspect of the
system.  Process A is doing something.  Process B should need
permission to monitor whatever it's monitoring, and process A should
have permission to do whatever it's doing.  I don't think it makes
sense to try to ascribe an identity to the actor doing some action to
decide to omit it from the watch -- this has all kinds of correctness
issues.

If you're writing a policy and you don't like letting process B spy on
processes doing various things, then disallow that type of spying.

> To
> implement such a policy requires A's credential,

You may not design a new mechanism that looks at the credential in a
context where looking at a credential is invalid unless you have some
very strong justification for why all of the known reasons that it's a
bad idea don't apply to what you're doing.

So, without a much stronger justification, NAK.

^ permalink raw reply	[flat|nested] 32+ messages in thread

* Re: [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2]
  2019-06-04 20:39 ` David Howells
  2019-06-04 20:57   ` Andy Lutomirski
@ 2019-06-04 21:11   ` Casey Schaufler
  1 sibling, 0 replies; 32+ messages in thread
From: Casey Schaufler @ 2019-06-04 21:11 UTC (permalink / raw)
  To: David Howells, Andy Lutomirski
  Cc: Al Viro, raven, Linux FS Devel, Linux API, linux-block, keyrings,
	LSM List, LKML, casey

On 6/4/2019 1:39 PM, David Howells wrote:
> Andy Lutomirski <luto@kernel.org> wrote:
>
>>> Here's a set of patches to add a general variable-length notification queue
>>> concept and to add sources of events for:
>> I asked before and didn't see a response, so I'll ask again.  Why are you
>> paying any attention at all to the creds that generate an event?
> Casey responded to you.  It's one of his requirements.

Process A takes an action. As a result of that action,
an event is written to Process B's event buffer. This isn't
a covert channel, it's a direct access, just like sending
a signal. Process A is the subject and the event buffer,
which is part of Process B, is the object.


> I'm not sure of the need, and I particularly don't like trying to make
> indirect destruction events (mount destruction keyed on fput, for instance)
> carry the creds of the triggerer.  Indeed, the trigger can come from all sorts
> of places - including af_unix queue destruction, someone poking around in
> procfs, a variety of processes fputting simultaneously.  Only one of them can
> win, and the LSM needs to handle *all* the possibilities.

Yes, it's a hairy problem. It was a significant factor in the
demise of kdbus.

> However, the LSMs (or at least SELinux) ignore f_cred and use current_cred()
> when checking permissions.  See selinux_revalidate_file_permission() for
> example - it uses current_cred() not file->f_cred to re-evaluate the perms,
> and the fd might be shared between a number of processes with different creds.
>
>> This seems like the wrong approach.  If an LSM wants to prevent covert
>> communication from, say, mount actions, then it shouldn't allow the
>> watch to be set up in the first place.
> Yeah, I can agree to that.  Casey?

Back to your earlier point, you don't know where the
event is coming from when you create the event watch.
If you enforce a watch time, what are you going to check?
Isn't this going to be considered too restrictive?



^ permalink raw reply	[flat|nested] 32+ messages in thread

* Re: [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2]
  2019-06-04 21:05     ` Andy Lutomirski
@ 2019-06-04 22:03       ` Casey Schaufler
  0 siblings, 0 replies; 32+ messages in thread
From: Casey Schaufler @ 2019-06-04 22:03 UTC (permalink / raw)
  To: Andy Lutomirski
  Cc: David Howells, Al Viro, raven, Linux FS Devel, Linux API,
	linux-block, keyrings, LSM List, LKML, casey

On 6/4/2019 2:05 PM, Andy Lutomirski wrote:
> On Tue, Jun 4, 2019 at 1:31 PM Casey Schaufler <casey@schaufler-ca.com> wrote:
>> n 6/4/2019 10:43 AM, Andy Lutomirski wrote:
>>> On Tue, Jun 4, 2019 at 9:35 AM David Howells <dhowells@redhat.com> wrote:
>>>> Hi Al,
>>>>
>>>> Here's a set of patches to add a general variable-length notification queue
>>>> concept and to add sources of events for:
>>> I asked before and didn't see a response, so I'll ask again.  Why are
>>> you paying any attention at all to the creds that generate an event?
>>> It seems like the resulting security model will be vary hard to
>>> understand and probably buggy.  Can't you define a sensible model in
>>> which only the listener creds matter?
>> We've spent the last 18 months reeling from the implications
>> of what can happen when one process has the ability to snoop
>> on another. Introducing yet another mechanism that is trivial
>> to exploit is a very bad idea.
> If you're talking about Spectre, etc, this is IMO entirely irrelevant.

We're seeing significant interest in using obscure mechanisms
in system exploits. Mechanisms will be exploited.

> Among other things, setting these watches can and should require some
> degree of privilege.

Requiring privilege would address the concerns for most
situations, although I don't see that it would help for
SELinux. SELinux does not generally put much credence in
what others consider "privilege".

Extreme care would probably be required for namespaces, too.

>
>> I will try to explain the problem once again. If process A
>> sends a signal (writes information) to process B the kernel
>> checks that either process A has the same UID as process B
>> or that process A has privilege to override that policy.
>> Process B is passive in this access control decision, while
>> process A is active.
> Are you stating what you see to be a requirement?

Basic subject/object access control is the core of
the Linux security model. Yes, there are exceptions,
but mostly they're historical in origin.


>> Process A must have write access
>> (defined by some policy) to process B's event buffer.
> No, stop right here.

Listening ...

>   Process B is monitoring some aspect of the
> system.

Process B is not "monitoring". At some point in the past it
has registered a request for information should an event occur.
It is currently passive.

> Process A is doing something.

Yes. It is active.'

> Process B should need
> permission to monitor whatever it's monitoring,

OK, I'm good with that. But the only time you
can tell that is when the event is registered,
and at that time you can't tell who might be causing
the event. (Or can you?)

> and process A should
> have permission to do whatever it's doing.

So there needs to be some connection between what B
can request events for and what events A can cause.
Then you can deny B's requests because of A.

>   I don't think it makes
> sense to try to ascribe an identity to the actor doing some action to
> decide to omit it from the watch -- this has all kinds of correctness
> issues.

It works for signals and UDP, but in general I get the concern.

> If you're writing a policy and you don't like letting process B spy on
> processes doing various things, then disallow that type of spying.

That gets you into a situation where you can't do the legitimate
monitoring you want to do just because there's the off chance you
might see something you shouldn't. "I hate security! It's confusing,
and always gets in the way!"

>> To
>> implement such a policy requires A's credential,
> You may not design a new mechanism that looks at the credential in a
> context where looking at a credential is invalid unless you have some
> very strong justification for why all of the known reasons that it's a
> bad idea don't apply to what you're doing.

Point. But you also don't get to ignore basic security policy
just because someone's spiffy lazy memory free cache hashing
tree (or similar mechanism) throws away references to important
information while it's still needed.

> So, without a much stronger justification, NAK.

I try to be reasonable. Really. All I want is something
with a security model that can be explained coherently 
within the context of the basic Linux security model.
There are enough variations as it is.



^ permalink raw reply	[flat|nested] 32+ messages in thread

* Re: [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2]
       [not found]     ` <CAB9W1A0AgMYOwGx9c-TmAt=1O6Bjsr2P3Nhd=2+QV39dgw0CrA@mail.gmail.com>
@ 2019-06-05  4:19       ` Andy Lutomirski
  2019-06-05 13:47         ` Stephen Smalley
  0 siblings, 1 reply; 32+ messages in thread
From: Andy Lutomirski @ 2019-06-05  4:19 UTC (permalink / raw)
  To: Stephen Smalley
  Cc: Andy Lutomirski, David Howells, Al Viro, Casey Schaufler, raven,
	Linux FS Devel, Linux API, linux-block, keyrings, LSM List, LKML

On Tue, Jun 4, 2019 at 6:18 PM Stephen Smalley
<stephen.smalley@gmail.com> wrote:
>
> On Tue, Jun 4, 2019 at 4:58 PM Andy Lutomirski <luto@kernel.org> wrote:
>>
>> On Tue, Jun 4, 2019 at 1:39 PM David Howells <dhowells@redhat.com> wrote:
>> >
>> > Andy Lutomirski <luto@kernel.org> wrote:
>> >
>> > > > Here's a set of patches to add a general variable-length notification queue
>> > > > concept and to add sources of events for:
>> > >
>> > > I asked before and didn't see a response, so I'll ask again.  Why are you
>> > > paying any attention at all to the creds that generate an event?
>> >
>> > Casey responded to you.  It's one of his requirements.
>> >
>>
>> It being a "requirement" doesn't make it okay.
>>
>> > However, the LSMs (or at least SELinux) ignore f_cred and use current_cred()
>> > when checking permissions.  See selinux_revalidate_file_permission() for
>> > example - it uses current_cred() not file->f_cred to re-evaluate the perms,
>> > and the fd might be shared between a number of processes with different creds.
>>
>> That's a bug.  It's arguably a rather severe bug.  If I ever get
>> around to writing the patch I keep thinking of that will warn if we
>> use creds from invalid contexts, it will warn.
>
>
> No, not a bug.  Working as designed. Initial validation on open, but revalidation upon read/write if something has changed since open (process SID differs from opener, inode SID has changed, policy has changed). Current subject SID should be used for the revalidation. It's a MAC vs DAC difference.
>

Can you explain how the design is valid, then?  Consider nasty cases like this:

$ sudo -u lotsofgarbage 2>/dev/whatever

It is certainly the case that drivers, fs code, and other core code
MUST NOT look at current_cred() in the context of syscalls like
open().  Jann, I, and others have found quite a few rootable bugs of
this sort.  What makes MAC special here?

I would believe there are cases where auditing write() callers makes
some sense, but anyone reading those logs needs to understand that the
creds are dubious at best.

^ permalink raw reply	[flat|nested] 32+ messages in thread

* Re: [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2]
  2019-06-04 17:43 ` [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications " Andy Lutomirski
  2019-06-04 20:31   ` Casey Schaufler
@ 2019-06-05  8:41   ` David Howells
  2019-06-05 14:50     ` Casey Schaufler
                       ` (2 more replies)
  1 sibling, 3 replies; 32+ messages in thread
From: David Howells @ 2019-06-05  8:41 UTC (permalink / raw)
  To: Casey Schaufler
  Cc: dhowells, Andy Lutomirski, Al Viro, raven, Linux FS Devel,
	Linux API, linux-block, keyrings, LSM List, LKML

Casey Schaufler <casey@schaufler-ca.com> wrote:

> I will try to explain the problem once again. If process A
> sends a signal (writes information) to process B the kernel
> checks that either process A has the same UID as process B
> or that process A has privilege to override that policy.
> Process B is passive in this access control decision, while
> process A is active. In the event delivery case, process A
> does something (e.g. modifies a keyring) that generates an
> event, which is then sent to process B's event buffer.

I think this might be the core sticking point here.  It looks like two
different situations:

 (1) A explicitly sends event to B (eg. signalling, sendmsg, etc.)

 (2) A implicitly and unknowingly sends event to B as a side effect of some
     other action (eg. B has a watch for the event A did).

The LSM treats them as the same: that is B must have MAC authorisation to send
a message to A.

But there are problems with not sending the event:

 (1) B's internal state is then corrupt (or, at least, unknowingly invalid).

 (2) B can potentially figure out that the event happened by other means.


I've implemented four event sources so far:

 (1) Keys/keyrings.  You can only get events on a key you have View permission
     on and the other process has to have write access to it, so I think this
     is good enough.

 (2) Block layer.  Currently this will only get you hardware error events,
     which is probably safe.  I'm not sure you can manipulate those without
     permission to directly access the device files.

 (3) Superblock.  This is trickier since it can see events that can be
     manufactured (R/W <-> R/O remounting, EDQUOT) as well as events that
     can't without hardware control (EIO, network link loss, RF kill).

 (4) Mount topology.  This is the trickiest since it allows you to see events
     beyond the point at which you placed your watch (in essence, you place a
     subtree watch).

     The question is what permission checking should I do?  Ideally, I'd
     emulate a pathwalk between the watchpoint and the eventing object to see
     if the owner of the watchpoint could reach it.

     I'd need to do a reverse walk, calling inode_permission(MAY_NOT_BLOCK)
     for each directory between the eventing object and the watchpoint to see
     if one rejects it - but some filesystems have a permission check that
     can't be called in this state.

     It would also be necessary to do this separately for each watchpoint in
     the parental chain.

     Further, each permissions check would generate an audit event and could
     generate FAN_ACCESS and/or FAN_ACCESS_PERM fanotify events - which could
     be a problem if fanotify is also trying to post those events to the same
     watch queue.

David

^ permalink raw reply	[flat|nested] 32+ messages in thread

* Re: [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2]
  2019-06-05  4:19       ` Andy Lutomirski
@ 2019-06-05 13:47         ` Stephen Smalley
  0 siblings, 0 replies; 32+ messages in thread
From: Stephen Smalley @ 2019-06-05 13:47 UTC (permalink / raw)
  To: Andy Lutomirski, Stephen Smalley
  Cc: David Howells, Al Viro, Casey Schaufler, raven, Linux FS Devel,
	Linux API, linux-block, keyrings, LSM List, LKML, Paul Moore

On 6/5/19 12:19 AM, Andy Lutomirski wrote:
> On Tue, Jun 4, 2019 at 6:18 PM Stephen Smalley
> <stephen.smalley@gmail.com> wrote:
>>
>> On Tue, Jun 4, 2019 at 4:58 PM Andy Lutomirski <luto@kernel.org> wrote:
>>>
>>> On Tue, Jun 4, 2019 at 1:39 PM David Howells <dhowells@redhat.com> wrote:
>>>>
>>>> Andy Lutomirski <luto@kernel.org> wrote:
>>>>
>>>>>> Here's a set of patches to add a general variable-length notification queue
>>>>>> concept and to add sources of events for:
>>>>>
>>>>> I asked before and didn't see a response, so I'll ask again.  Why are you
>>>>> paying any attention at all to the creds that generate an event?
>>>>
>>>> Casey responded to you.  It's one of his requirements.
>>>>
>>>
>>> It being a "requirement" doesn't make it okay.
>>>
>>>> However, the LSMs (or at least SELinux) ignore f_cred and use current_cred()
>>>> when checking permissions.  See selinux_revalidate_file_permission() for
>>>> example - it uses current_cred() not file->f_cred to re-evaluate the perms,
>>>> and the fd might be shared between a number of processes with different creds.
>>>
>>> That's a bug.  It's arguably a rather severe bug.  If I ever get
>>> around to writing the patch I keep thinking of that will warn if we
>>> use creds from invalid contexts, it will warn.
>>
>>
>> No, not a bug.  Working as designed. Initial validation on open, but revalidation upon read/write if something has changed since open (process SID differs from opener, inode SID has changed, policy has changed). Current subject SID should be used for the revalidation. It's a MAC vs DAC difference.
>>
> 
> Can you explain how the design is valid, then?  Consider nasty cases like this:
> 
> $ sudo -u lotsofgarbage 2>/dev/whatever

(sorry for the previous html email; gmail or my inability to properly 
use it strikes again!)

Here we have four (or more) opportunities to say no:
1) Upon selinux_inode_permission(), when checking write access to 
/dev/whatever in the context of the shell process,
2) Upon selinux_file_open(), when checking and caching the open and 
write access for shell to /dev/whatever in the file security struct,
3) Upon selinux_bprm_committing_creds() -> flush_unauthorized_files(), 
when revalidating write access to /dev/whatever in the context of sudo,
4) Upon selinux_file_permission() -> 
selinux_revalidate_file_permission(), when revalidating write access to 
/dev/whatever in the context of sudo.

If any of those fail, then access is denied, so unless both the shell 
and sudo are authorized to write to /dev/whatever, it is a no-go.  NB 
Only the shell context requires open permission here; the sudo context 
only needs write.

> It is certainly the case that drivers, fs code, and other core code
> MUST NOT look at current_cred() in the context of syscalls like
> open().  Jann, I, and others have found quite a few rootable bugs of
> this sort.  What makes MAC special here?

Do you mean syscalls like write(), not open()?  I think your concern is 
that they apply some check only during write() and not open() and 
therefore are susceptible to confused deputy scenario above.  In 
contrast we are validating access at open, transfer/inherit, and use. If 
we use file->f_cred instead of current_cred() in 
selinux_revalidate_file_permission() and the current process SID differs 
from that of the opener, we'll never apply a check for the actual 
security context performing the write(), so information can flow in 
violation of the MAC policy.

> I would believe there are cases where auditing write() callers makes
> some sense, but anyone reading those logs needs to understand that the
> creds are dubious at best.

^ permalink raw reply	[flat|nested] 32+ messages in thread

* Re: [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2]
  2019-06-05  8:41   ` David Howells
@ 2019-06-05 14:50     ` Casey Schaufler
  2019-06-05 16:04       ` Andy Lutomirski
  2019-06-05 16:56     ` Rational model for UID based controls David Howells
  2019-06-05 17:21     ` [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2] David Howells
  2 siblings, 1 reply; 32+ messages in thread
From: Casey Schaufler @ 2019-06-05 14:50 UTC (permalink / raw)
  To: David Howells
  Cc: Andy Lutomirski, Al Viro, raven, Linux FS Devel, Linux API,
	linux-block, keyrings, LSM List, LKML, casey

[-- Attachment #1.1: Type: text/plain, Size: 4255 bytes --]

On 6/5/2019 1:41 AM, David Howells wrote:
> Casey Schaufler <casey@schaufler-ca.com> wrote:
>
>> I will try to explain the problem once again. If process A
>> sends a signal (writes information) to process B the kernel
>> checks that either process A has the same UID as process B
>> or that process A has privilege to override that policy.
>> Process B is passive in this access control decision, while
>> process A is active. In the event delivery case, process A
>> does something (e.g. modifies a keyring) that generates an
>> event, which is then sent to process B's event buffer.
> I think this might be the core sticking point here.  It looks like two
> different situations:
>
>  (1) A explicitly sends event to B (eg. signalling, sendmsg, etc.)
>
>  (2) A implicitly and unknowingly sends event to B as a side effect of some
>      other action (eg. B has a watch for the event A did).
>
> The LSM treats them as the same: that is B must have MAC authorisation to send
> a message to A.

YES!

Threat is about what you can do, not what you intend to do.

And it would be really great if you put some thought into what
a rational model would be for UID based controls, too.

> But there are problems with not sending the event:
>
>  (1) B's internal state is then corrupt (or, at least, unknowingly invalid).

Then B is a badly written program.

>  (2) B can potentially figure out that the event happened by other means.

Then why does it need the event mechanism in the first place?

> I've implemented four event sources so far:
>
>  (1) Keys/keyrings.  You can only get events on a key you have View permission
>      on and the other process has to have write access to it, so I think this
>      is good enough.

Sounds fine.

>  (2) Block layer.  Currently this will only get you hardware error events,
>      which is probably safe.  I'm not sure you can manipulate those without
>      permission to directly access the device files.

There's an argument to be made that this should require CAP_SYS_ADMIN,
or that an LSM like SELinux might include hardware error events in
policy, but generally I agree that system generated events like this
are both harmless and pointless for the general public to watch.

>  (3) Superblock.  This is trickier since it can see events that can be
>      manufactured (R/W <-> R/O remounting, EDQUOT) as well as events that
>      can't without hardware control (EIO, network link loss, RF kill).

The events generated by processes (the 1st set) need controls
like keys. The events generated by the system (the 2nd set) may
need controls like the block layer.


>  (4) Mount topology.  This is the trickiest since it allows you to see events
>      beyond the point at which you placed your watch (in essence, you place a
>      subtree watch).

Like keys.

>      The question is what permission checking should I do?  Ideally, I'd
>      emulate a pathwalk between the watchpoint and the eventing object to see
>      if the owner of the watchpoint could reach it.

That will depend, as I've been saying, on what causes
the event to be generated. If it's from a process, the
question is "can the active process, the one that generated
the event, write to the passive, watching process?"
If it's the system on a hardware event, you may want the watcher
to have CAP_SYS_ADMIN.

>      I'd need to do a reverse walk, calling inode_permission(MAY_NOT_BLOCK)
>      for each directory between the eventing object and the watchpoint to see
>      if one rejects it - but some filesystems have a permission check that
>      can't be called in this state.

This is for setting the watch, right?

>      It would also be necessary to do this separately for each watchpoint in
>      the parental chain.
>
>      Further, each permissions check would generate an audit event and could
>      generate FAN_ACCESS and/or FAN_ACCESS_PERM fanotify events - which could
>      be a problem if fanotify is also trying to post those events to the same
>      watch queue.

If you required that the watching process open(dir) what
you want to watch you'd get this for free. Or did I miss
something obvious?

> David


[-- Attachment #2: OpenPGP digital signature --]
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^ permalink raw reply	[flat|nested] 32+ messages in thread

* Re: [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2]
  2019-06-05 14:50     ` Casey Schaufler
@ 2019-06-05 16:04       ` Andy Lutomirski
  2019-06-05 17:01         ` Casey Schaufler
  0 siblings, 1 reply; 32+ messages in thread
From: Andy Lutomirski @ 2019-06-05 16:04 UTC (permalink / raw)
  To: Casey Schaufler
  Cc: David Howells, Andy Lutomirski, Al Viro, raven, Linux FS Devel,
	Linux API, linux-block, keyrings, LSM List, LKML

On Wed, Jun 5, 2019 at 7:51 AM Casey Schaufler <casey@schaufler-ca.com> wrote:
>
> On 6/5/2019 1:41 AM, David Howells wrote:
> > Casey Schaufler <casey@schaufler-ca.com> wrote:
> >
> >> I will try to explain the problem once again. If process A
> >> sends a signal (writes information) to process B the kernel
> >> checks that either process A has the same UID as process B
> >> or that process A has privilege to override that policy.
> >> Process B is passive in this access control decision, while
> >> process A is active. In the event delivery case, process A
> >> does something (e.g. modifies a keyring) that generates an
> >> event, which is then sent to process B's event buffer.
> > I think this might be the core sticking point here.  It looks like two
> > different situations:
> >
> >  (1) A explicitly sends event to B (eg. signalling, sendmsg, etc.)
> >
> >  (2) A implicitly and unknowingly sends event to B as a side effect of some
> >      other action (eg. B has a watch for the event A did).
> >
> > The LSM treats them as the same: that is B must have MAC authorisation to send
> > a message to A.
>
> YES!
>
> Threat is about what you can do, not what you intend to do.
>
> And it would be really great if you put some thought into what
> a rational model would be for UID based controls, too.
>
> > But there are problems with not sending the event:
> >
> >  (1) B's internal state is then corrupt (or, at least, unknowingly invalid).
>
> Then B is a badly written program.

Either I'm misunderstanding you or I strongly disagree.  If B has
authority to detect a certain action, and A has authority to perform
that action, then refusing to notify B because B is somehow missing
some special authorization to be notified by A is nuts.  This is just
introducing incorrectness into the design in support of a
not-actually-helpful security idea.

If I can read /proc/self/mounts, I can detect changes to my mount
namespace.  Giving me a faster and nicer way to do this is fine, AS
LONG AS IT ACTUALLY WORKS.  "Works" means it needs to detect all
changes.

^ permalink raw reply	[flat|nested] 32+ messages in thread

* Rational model for UID based controls
  2019-06-05  8:41   ` David Howells
  2019-06-05 14:50     ` Casey Schaufler
@ 2019-06-05 16:56     ` David Howells
  2019-06-05 17:40       ` Casey Schaufler
  2019-06-05 21:06       ` David Howells
  2019-06-05 17:21     ` [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2] David Howells
  2 siblings, 2 replies; 32+ messages in thread
From: David Howells @ 2019-06-05 16:56 UTC (permalink / raw)
  To: Casey Schaufler
  Cc: dhowells, Andy Lutomirski, Al Viro, raven, Linux FS Devel,
	Linux API, linux-block, keyrings, LSM List, LKML

Casey Schaufler <casey@schaufler-ca.com> wrote:

> YES!

I'm trying to decide if that's fervour or irritation at this point ;-)

> And it would be really great if you put some thought into what
> a rational model would be for UID based controls, too.

I have put some thought into it, but I don't see a single rational model.  It
depends very much on the situation.

In any case, that's what I was referring to when I said I might need to call
inode_permission().  But UIDs don't exist for all filesystems, for example,
and there are no UIDs on superblocks, mount objects or hardware events.

Now, I could see that you ignore UIDs on things like keys and
hardware-triggered events, but how does this interact with things like mount
watches that see directories that have UIDs?

Are you advocating making it such that process B can only see events triggered
by process A if they have the same UID, for example?

David

^ permalink raw reply	[flat|nested] 32+ messages in thread

* Re: [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2]
  2019-06-05 16:04       ` Andy Lutomirski
@ 2019-06-05 17:01         ` Casey Schaufler
  2019-06-05 17:47           ` Andy Lutomirski
  0 siblings, 1 reply; 32+ messages in thread
From: Casey Schaufler @ 2019-06-05 17:01 UTC (permalink / raw)
  To: Andy Lutomirski
  Cc: David Howells, Al Viro, raven, Linux FS Devel, Linux API,
	linux-block, keyrings, LSM List, LKML, casey

On 6/5/2019 9:04 AM, Andy Lutomirski wrote:
> On Wed, Jun 5, 2019 at 7:51 AM Casey Schaufler <casey@schaufler-ca.com> wrote:
>> On 6/5/2019 1:41 AM, David Howells wrote:
>>> Casey Schaufler <casey@schaufler-ca.com> wrote:
>>>
>>>> I will try to explain the problem once again. If process A
>>>> sends a signal (writes information) to process B the kernel
>>>> checks that either process A has the same UID as process B
>>>> or that process A has privilege to override that policy.
>>>> Process B is passive in this access control decision, while
>>>> process A is active. In the event delivery case, process A
>>>> does something (e.g. modifies a keyring) that generates an
>>>> event, which is then sent to process B's event buffer.
>>> I think this might be the core sticking point here.  It looks like two
>>> different situations:
>>>
>>>  (1) A explicitly sends event to B (eg. signalling, sendmsg, etc.)
>>>
>>>  (2) A implicitly and unknowingly sends event to B as a side effect of some
>>>      other action (eg. B has a watch for the event A did).
>>>
>>> The LSM treats them as the same: that is B must have MAC authorisation to send
>>> a message to A.
>> YES!
>>
>> Threat is about what you can do, not what you intend to do.
>>
>> And it would be really great if you put some thought into what
>> a rational model would be for UID based controls, too.
>>
>>> But there are problems with not sending the event:
>>>
>>>  (1) B's internal state is then corrupt (or, at least, unknowingly invalid).
>> Then B is a badly written program.
> Either I'm misunderstanding you or I strongly disagree.

A program needs to be aware of the conditions under
which it gets event, *including the possibility that
it may not get an event that it's not allowed*. Do you
regularly write programs that go into corrupt states
if an open() fails? Or where read() returns less than
the amount of data you ask for?

>   If B has
> authority to detect a certain action, and A has authority to perform
> that action, then refusing to notify B because B is somehow missing
> some special authorization to be notified by A is nuts.

You are hand-waving the notion of authority. You are assuming
that if A can read X and B can read X that A can write B.

>   This is just
> introducing incorrectness into the design in support of a
> not-actually-helpful security idea.

Where is the incorrectness? Are you seriously saying that
you expect all events to be generated exactly as you think
they should? Have you ever even used systemd? 

> If I can read /proc/self/mounts, I can detect changes to my mount
> namespace.

Then read /proc/self/mounts!
Can't you poll on an fd open on /proc/self/mounts?

>   Giving me a faster and nicer way to do this is fine, AS
> LONG AS IT ACTUALLY WORKS.  "Works" means it needs to detect all
> changes.

So long as "WORKS" includes maintaining the system security
policy, I agree. No, I don't. We already have too many bizarre
and unnatural mechanisms to address whimsical special cases.
If speed is such an issue you could look at making /proc better.



^ permalink raw reply	[flat|nested] 32+ messages in thread

* Re: [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2]
  2019-06-05  8:41   ` David Howells
  2019-06-05 14:50     ` Casey Schaufler
  2019-06-05 16:56     ` Rational model for UID based controls David Howells
@ 2019-06-05 17:21     ` David Howells
  2 siblings, 0 replies; 32+ messages in thread
From: David Howells @ 2019-06-05 17:21 UTC (permalink / raw)
  To: Casey Schaufler
  Cc: dhowells, Andy Lutomirski, Al Viro, raven, Linux FS Devel,
	Linux API, linux-block, keyrings, LSM List, LKML

Casey Schaufler <casey@schaufler-ca.com> wrote:

> > But there are problems with not sending the event:
> >
> >  (1) B's internal state is then corrupt (or, at least, unknowingly invalid).
> 
> Then B is a badly written program.

No.  It may have the expectation that it will get events but then it is denied
those events and doesn't even know they've happened.

> >  (2) B can potentially figure out that the event happened by other means.
> 
> Then why does it need the event mechanism in the first place?

Why does a CPU have interrupt lines?  It can always continuously poll the
hardware.  Why do poll() and select() exist?

> > I've implemented four event sources so far:
> >
> >  (1) Keys/keyrings.  You can only get events on a key you have View permission
> >      on and the other process has to have write access to it, so I think this
> >      is good enough.
> 
> Sounds fine.
> 
> >  (2) Block layer.  Currently this will only get you hardware error events,
> >      which is probably safe.  I'm not sure you can manipulate those without
> >      permission to directly access the device files.
> 
> There's an argument to be made that this should require CAP_SYS_ADMIN,
> or that an LSM like SELinux might include hardware error events in
> policy, but generally I agree that system generated events like this
> are both harmless and pointless for the general public to watch.

CAP_SYS_ADMIN is probably too broad a hammer - this is something you might
want to let a file manager or desktop environment use.  I wonder if we could
add a CAP_SYS_NOTIFY - or is it too late for adding new caps?

> >  (3) Superblock.  This is trickier since it can see events that can be
> >      manufactured (R/W <-> R/O remounting, EDQUOT) as well as events that
> >      can't without hardware control (EIO, network link loss, RF kill).
> 
> The events generated by processes (the 1st set) need controls
> like keys. The events generated by the system (the 2nd set) may
> need controls like the block layer.
>
>
> > (4)  Mount topology.  This is the trickiest since it allows you to see
> >      events beyond the point at which you placed your watch (in essence,
> >      you place a subtree watch).
> 
> Like keys.
> 
> >      The question is what permission checking should I do?  Ideally, I'd
> >      emulate a pathwalk between the watchpoint and the eventing object to
> >      see if the owner of the watchpoint could reach it.
> 
> That will depend, as I've been saying, on what causes
> the event to be generated. If it's from a process, the
> question is "can the active process, the one that generated
> the event, write to the passive, watching process?"
> If it's the system on a hardware event, you may want the watcher
> to have CAP_SYS_ADMIN.
> 
> >      I'd need to do a reverse walk, calling
> >      inode_permission(MAY_NOT_BLOCK) for each directory between the
> >      eventing object and the watchpoint to see if one rejects it - but
> >      some filesystems have a permission check that can't be called in this
> >      state.
> 
> This is for setting the watch, right?

No.  Setting the watch requires execute permission on the directory on which
you're setting the watch, but there's no way to know what permissions will be
required for an event at that point.

I'm talking about when an event is generated (hence "eventing object").
Imagine you have a subpath:

	dirA/dirB/dirC/dirD/dirE

where dir* are directories.  If you place a watch on dirA and then an event
occurs on dirB (such as someone mounting on it), I do a walk back up the
parental tree, in the order:

	dirE, dirD, dirC, dirB, dirA

If I need to check permissions on all the directories, I would find the
watchpoint on dirA, then I would have to repeat the walk to find out whether
the owner of the watchpoint can access all of those directories (perhaps
skipping dirA since I had permission to place a watchpoint thereon).

Note that this is subject to going awry if there's a race versus rename().

> >      It would also be necessary to do this separately for each watchpoint in
> >      the parental chain.
> >
> >      Further, each permissions check would generate an audit event and
> >      could generate FAN_ACCESS and/or FAN_ACCESS_PERM fanotify events -
> >      which could be a problem if fanotify is also trying to post those
> >      events to the same watch queue.
> 
> If you required that the watching process open(dir) what
> you want to watch you'd get this for free. Or did I miss
> something obvious?

A subtree watch, such as the mount topology watch, watches not only the
directory and mount object you pointed directly at, but the subtree rooted
thereon.

Take the sample program in the last patch.  It places a watch on "/" with no
filter against WATCH_INFO_RECURSIVE, so it sees all mount topology events that
happen under the VFS path subtree rooted at "/" - whether or not it can
actually pathwalk to those mounts.

David

^ permalink raw reply	[flat|nested] 32+ messages in thread

* Re: Rational model for UID based controls
  2019-06-05 16:56     ` Rational model for UID based controls David Howells
@ 2019-06-05 17:40       ` Casey Schaufler
  2019-06-05 21:06       ` David Howells
  1 sibling, 0 replies; 32+ messages in thread
From: Casey Schaufler @ 2019-06-05 17:40 UTC (permalink / raw)
  To: David Howells
  Cc: Andy Lutomirski, Al Viro, raven, Linux FS Devel, Linux API,
	linux-block, keyrings, LSM List, LKML, casey

On 6/5/2019 9:56 AM, David Howells wrote:
> Casey Schaufler <casey@schaufler-ca.com> wrote:
>
>> YES!
> I'm trying to decide if that's fervour or irritation at this point ;-)

I think I finally got the point that the underlying mechanism,
direct or indirect, isn't the issue. It's the end result that
matters. That makes me happier.

>> And it would be really great if you put some thought into what
>> a rational model would be for UID based controls, too.
> I have put some thought into it, but I don't see a single rational model.  It
> depends very much on the situation.

Right. You're mixing the kind of things that can generate events,
and that makes having a single policy difficult.

> In any case, that's what I was referring to when I said I might need to call
> inode_permission().  But UIDs don't exist for all filesystems, for example,
> and there are no UIDs on superblocks, mount objects or hardware events.

If you open() or stat() a file on those filesystems the UID
used in the access control comes from somewhere. Setting a watch
on things with UIDs should use the access mode on the file,
just like any other filesystem operation.

Things like superblocks are sticker because we don't generally
think of them as objects. If you can do statfs(), you should be
able to set a watch on the filesystem metadata.

How would you specify a watch for a hardware event? If you say
you have to open /dev/mumble to sent a watch for mumbles, you're
good there, too.

> Now, I could see that you ignore UIDs on things like keys and
> hardware-triggered events, but how does this interact with things like mount
> watches that see directories that have UIDs?
>
> Are you advocating making it such that process B can only see events triggered
> by process A if they have the same UID, for example?

It's always seemed arbitrary to me that you can't open
your process up to get signals from other users. What about
putting mode bits on your ring buffer? By default you could
only accept your own events, but you could do a rb_chmod(0222)
and let all events through. Subject to LSM addition restrictions,
of course. That would require the cred of the process that
triggered the event or a system cred for "hardware" events.
If you don't like mode bits you could use an ACL for fine
granularity or a single "let'em all in" bit for coarse.

I'm not against access, I'm against uncontrolled access
in conflict with basic system policy.

> David


^ permalink raw reply	[flat|nested] 32+ messages in thread

* Re: [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2]
  2019-06-05 17:01         ` Casey Schaufler
@ 2019-06-05 17:47           ` Andy Lutomirski
  2019-06-05 18:12             ` Casey Schaufler
  2019-06-05 18:25             ` Stephen Smalley
  0 siblings, 2 replies; 32+ messages in thread
From: Andy Lutomirski @ 2019-06-05 17:47 UTC (permalink / raw)
  To: Casey Schaufler
  Cc: Andy Lutomirski, David Howells, Al Viro, raven, Linux FS Devel,
	Linux API, linux-block, keyrings, LSM List, LKML


> On Jun 5, 2019, at 10:01 AM, Casey Schaufler <casey@schaufler-ca.com> wrote:
> 
>> On 6/5/2019 9:04 AM, Andy Lutomirski wrote:
>>> On Wed, Jun 5, 2019 at 7:51 AM Casey Schaufler <casey@schaufler-ca.com> wrote:
>>>> On 6/5/2019 1:41 AM, David Howells wrote:
>>>> Casey Schaufler <casey@schaufler-ca.com> wrote:
>>>> 
>>>>> I will try to explain the problem once again. If process A
>>>>> sends a signal (writes information) to process B the kernel
>>>>> checks that either process A has the same UID as process B
>>>>> or that process A has privilege to override that policy.
>>>>> Process B is passive in this access control decision, while
>>>>> process A is active. In the event delivery case, process A
>>>>> does something (e.g. modifies a keyring) that generates an
>>>>> event, which is then sent to process B's event buffer.
>>>> I think this might be the core sticking point here.  It looks like two
>>>> different situations:
>>>> 
>>>> (1) A explicitly sends event to B (eg. signalling, sendmsg, etc.)
>>>> 
>>>> (2) A implicitly and unknowingly sends event to B as a side effect of some
>>>>     other action (eg. B has a watch for the event A did).
>>>> 
>>>> The LSM treats them as the same: that is B must have MAC authorisation to send
>>>> a message to A.
>>> YES!
>>> 
>>> Threat is about what you can do, not what you intend to do.
>>> 
>>> And it would be really great if you put some thought into what
>>> a rational model would be for UID based controls, too.
>>> 
>>>> But there are problems with not sending the event:
>>>> 
>>>> (1) B's internal state is then corrupt (or, at least, unknowingly invalid).
>>> Then B is a badly written program.
>> Either I'm misunderstanding you or I strongly disagree.
> 
> A program needs to be aware of the conditions under
> which it gets event, *including the possibility that
> it may not get an event that it's not allowed*. Do you
> regularly write programs that go into corrupt states
> if an open() fails? Or where read() returns less than
> the amount of data you ask for?

I do not regularly write programs that handle read() omitting data in the middle of a TCP stream.  I also don’t write programs that wait for processes to die and need to handle the case where a child is dead, waitid() can see it, but SIGCHLD wasn’t sent because “security”.

> 
>>  If B has
>> authority to detect a certain action, and A has authority to perform
>> that action, then refusing to notify B because B is somehow missing
>> some special authorization to be notified by A is nuts.
> 
> You are hand-waving the notion of authority. You are assuming
> that if A can read X and B can read X that A can write B.

No, read it again please. I’m assuming that if A can *write* X and B can read X then A can send information to B.


^ permalink raw reply	[flat|nested] 32+ messages in thread

* Re: [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2]
  2019-06-05 17:47           ` Andy Lutomirski
@ 2019-06-05 18:12             ` Casey Schaufler
  2019-06-05 18:25             ` Stephen Smalley
  1 sibling, 0 replies; 32+ messages in thread
From: Casey Schaufler @ 2019-06-05 18:12 UTC (permalink / raw)
  To: Andy Lutomirski
  Cc: Andy Lutomirski, David Howells, Al Viro, raven, Linux FS Devel,
	Linux API, linux-block, keyrings, LSM List, LKML, casey

On 6/5/2019 10:47 AM, Andy Lutomirski wrote:
>> On Jun 5, 2019, at 10:01 AM, Casey Schaufler <casey@schaufler-ca.com> wrote:
>>
>>> On 6/5/2019 9:04 AM, Andy Lutomirski wrote:
>>>> On Wed, Jun 5, 2019 at 7:51 AM Casey Schaufler <casey@schaufler-ca.com> wrote:
>>>>> On 6/5/2019 1:41 AM, David Howells wrote:
>>>>> Casey Schaufler <casey@schaufler-ca.com> wrote:
>>>>>
>>>>>> I will try to explain the problem once again. If process A
>>>>>> sends a signal (writes information) to process B the kernel
>>>>>> checks that either process A has the same UID as process B
>>>>>> or that process A has privilege to override that policy.
>>>>>> Process B is passive in this access control decision, while
>>>>>> process A is active. In the event delivery case, process A
>>>>>> does something (e.g. modifies a keyring) that generates an
>>>>>> event, which is then sent to process B's event buffer.
>>>>> I think this might be the core sticking point here.  It looks like two
>>>>> different situations:
>>>>>
>>>>> (1) A explicitly sends event to B (eg. signalling, sendmsg, etc.)
>>>>>
>>>>> (2) A implicitly and unknowingly sends event to B as a side effect of some
>>>>>     other action (eg. B has a watch for the event A did).
>>>>>
>>>>> The LSM treats them as the same: that is B must have MAC authorisation to send
>>>>> a message to A.
>>>> YES!
>>>>
>>>> Threat is about what you can do, not what you intend to do.
>>>>
>>>> And it would be really great if you put some thought into what
>>>> a rational model would be for UID based controls, too.
>>>>
>>>>> But there are problems with not sending the event:
>>>>>
>>>>> (1) B's internal state is then corrupt (or, at least, unknowingly invalid).
>>>> Then B is a badly written program.
>>> Either I'm misunderstanding you or I strongly disagree.
>> A program needs to be aware of the conditions under
>> which it gets event, *including the possibility that
>> it may not get an event that it's not allowed*. Do you
>> regularly write programs that go into corrupt states
>> if an open() fails? Or where read() returns less than
>> the amount of data you ask for?
> I do not regularly write programs that handle read() omitting data in the middle of a TCP stream.  I also don’t write programs that wait for processes to die and need to handle the case where a child is dead, waitid() can see it, but SIGCHLD wasn’t sent because “security”.
>
>>>  If B has
>>> authority to detect a certain action, and A has authority to perform
>>> that action, then refusing to notify B because B is somehow missing
>>> some special authorization to be notified by A is nuts.
>> You are hand-waving the notion of authority. You are assuming
>> that if A can read X and B can read X that A can write B.
> No, read it again please. I’m assuming that if A can *write* X and B can read X then A can send information to B.

That is *not* a valid assumption:

	A can write to /dev/null.
	B can read from /dev/null.
	Does not imply B can read what A wrote.
	Does not imply A can send a signal to B.

	A can send a UDP datagram to port 3343
	B can is bound to port 3343
	Does not imply the packet will be delivered


 



^ permalink raw reply	[flat|nested] 32+ messages in thread

* Re: [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2]
  2019-06-05 17:47           ` Andy Lutomirski
  2019-06-05 18:12             ` Casey Schaufler
@ 2019-06-05 18:25             ` Stephen Smalley
  2019-06-05 19:28               ` Greg KH
  1 sibling, 1 reply; 32+ messages in thread
From: Stephen Smalley @ 2019-06-05 18:25 UTC (permalink / raw)
  To: Andy Lutomirski, Casey Schaufler
  Cc: Andy Lutomirski, David Howells, Al Viro, raven, Linux FS Devel,
	Linux API, linux-block, keyrings, LSM List, LKML

On 6/5/19 1:47 PM, Andy Lutomirski wrote:
> 
>> On Jun 5, 2019, at 10:01 AM, Casey Schaufler <casey@schaufler-ca.com> wrote:
>>
>>> On 6/5/2019 9:04 AM, Andy Lutomirski wrote:
>>>> On Wed, Jun 5, 2019 at 7:51 AM Casey Schaufler <casey@schaufler-ca.com> wrote:
>>>>> On 6/5/2019 1:41 AM, David Howells wrote:
>>>>> Casey Schaufler <casey@schaufler-ca.com> wrote:
>>>>>
>>>>>> I will try to explain the problem once again. If process A
>>>>>> sends a signal (writes information) to process B the kernel
>>>>>> checks that either process A has the same UID as process B
>>>>>> or that process A has privilege to override that policy.
>>>>>> Process B is passive in this access control decision, while
>>>>>> process A is active. In the event delivery case, process A
>>>>>> does something (e.g. modifies a keyring) that generates an
>>>>>> event, which is then sent to process B's event buffer.
>>>>> I think this might be the core sticking point here.  It looks like two
>>>>> different situations:
>>>>>
>>>>> (1) A explicitly sends event to B (eg. signalling, sendmsg, etc.)
>>>>>
>>>>> (2) A implicitly and unknowingly sends event to B as a side effect of some
>>>>>      other action (eg. B has a watch for the event A did).
>>>>>
>>>>> The LSM treats them as the same: that is B must have MAC authorisation to send
>>>>> a message to A.
>>>> YES!
>>>>
>>>> Threat is about what you can do, not what you intend to do.
>>>>
>>>> And it would be really great if you put some thought into what
>>>> a rational model would be for UID based controls, too.
>>>>
>>>>> But there are problems with not sending the event:
>>>>>
>>>>> (1) B's internal state is then corrupt (or, at least, unknowingly invalid).
>>>> Then B is a badly written program.
>>> Either I'm misunderstanding you or I strongly disagree.
>>
>> A program needs to be aware of the conditions under
>> which it gets event, *including the possibility that
>> it may not get an event that it's not allowed*. Do you
>> regularly write programs that go into corrupt states
>> if an open() fails? Or where read() returns less than
>> the amount of data you ask for?
> 
> I do not regularly write programs that handle read() omitting data in the middle of a TCP stream.  I also don’t write programs that wait for processes to die and need to handle the case where a child is dead, waitid() can see it, but SIGCHLD wasn’t sent because “security”.
> 
>>
>>>   If B has
>>> authority to detect a certain action, and A has authority to perform
>>> that action, then refusing to notify B because B is somehow missing
>>> some special authorization to be notified by A is nuts.
>>
>> You are hand-waving the notion of authority. You are assuming
>> that if A can read X and B can read X that A can write B.
> 
> No, read it again please. I’m assuming that if A can *write* X and B can read X then A can send information to B.

I guess the questions here are:

1) How do we handle recursive notification support, since we can't check 
that B can read everything below a given directory easily?  Perhaps we 
can argue that if I have watch permission to / then that implies 
visibility to everything below it but that is rather broad.

2) Is there always a corresponding labeled object in view for each of 
these notifications to which we can check access when the watch is set?

3) Are notifications only generated for write events or can they be 
generated by processes that only have read access to the object?



^ permalink raw reply	[flat|nested] 32+ messages in thread

* Re: [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2]
  2019-06-05 18:25             ` Stephen Smalley
@ 2019-06-05 19:28               ` Greg KH
  2019-06-05 21:01                 ` Stephen Smalley
  0 siblings, 1 reply; 32+ messages in thread
From: Greg KH @ 2019-06-05 19:28 UTC (permalink / raw)
  To: Stephen Smalley
  Cc: Andy Lutomirski, Casey Schaufler, Andy Lutomirski, David Howells,
	Al Viro, raven, Linux FS Devel, Linux API, linux-block, keyrings,
	LSM List, LKML

On Wed, Jun 05, 2019 at 02:25:33PM -0400, Stephen Smalley wrote:
> On 6/5/19 1:47 PM, Andy Lutomirski wrote:
> > 
> > > On Jun 5, 2019, at 10:01 AM, Casey Schaufler <casey@schaufler-ca.com> wrote:
> > > 
> > > > On 6/5/2019 9:04 AM, Andy Lutomirski wrote:
> > > > > On Wed, Jun 5, 2019 at 7:51 AM Casey Schaufler <casey@schaufler-ca.com> wrote:
> > > > > > On 6/5/2019 1:41 AM, David Howells wrote:
> > > > > > Casey Schaufler <casey@schaufler-ca.com> wrote:
> > > > > > 
> > > > > > > I will try to explain the problem once again. If process A
> > > > > > > sends a signal (writes information) to process B the kernel
> > > > > > > checks that either process A has the same UID as process B
> > > > > > > or that process A has privilege to override that policy.
> > > > > > > Process B is passive in this access control decision, while
> > > > > > > process A is active. In the event delivery case, process A
> > > > > > > does something (e.g. modifies a keyring) that generates an
> > > > > > > event, which is then sent to process B's event buffer.
> > > > > > I think this might be the core sticking point here.  It looks like two
> > > > > > different situations:
> > > > > > 
> > > > > > (1) A explicitly sends event to B (eg. signalling, sendmsg, etc.)
> > > > > > 
> > > > > > (2) A implicitly and unknowingly sends event to B as a side effect of some
> > > > > >      other action (eg. B has a watch for the event A did).
> > > > > > 
> > > > > > The LSM treats them as the same: that is B must have MAC authorisation to send
> > > > > > a message to A.
> > > > > YES!
> > > > > 
> > > > > Threat is about what you can do, not what you intend to do.
> > > > > 
> > > > > And it would be really great if you put some thought into what
> > > > > a rational model would be for UID based controls, too.
> > > > > 
> > > > > > But there are problems with not sending the event:
> > > > > > 
> > > > > > (1) B's internal state is then corrupt (or, at least, unknowingly invalid).
> > > > > Then B is a badly written program.
> > > > Either I'm misunderstanding you or I strongly disagree.
> > > 
> > > A program needs to be aware of the conditions under
> > > which it gets event, *including the possibility that
> > > it may not get an event that it's not allowed*. Do you
> > > regularly write programs that go into corrupt states
> > > if an open() fails? Or where read() returns less than
> > > the amount of data you ask for?
> > 
> > I do not regularly write programs that handle read() omitting data in the middle of a TCP stream.  I also don’t write programs that wait for processes to die and need to handle the case where a child is dead, waitid() can see it, but SIGCHLD wasn’t sent because “security”.
> > 
> > > 
> > > >   If B has
> > > > authority to detect a certain action, and A has authority to perform
> > > > that action, then refusing to notify B because B is somehow missing
> > > > some special authorization to be notified by A is nuts.
> > > 
> > > You are hand-waving the notion of authority. You are assuming
> > > that if A can read X and B can read X that A can write B.
> > 
> > No, read it again please. I’m assuming that if A can *write* X and B can read X then A can send information to B.
> 
> I guess the questions here are:
> 
> 1) How do we handle recursive notification support, since we can't check
> that B can read everything below a given directory easily?  Perhaps we can
> argue that if I have watch permission to / then that implies visibility to
> everything below it but that is rather broad.

How do you handle fanotify today which I think can do this?

thanks,

greg k-h

^ permalink raw reply	[flat|nested] 32+ messages in thread

* Re: [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2]
  2019-06-05 19:28               ` Greg KH
@ 2019-06-05 21:01                 ` Stephen Smalley
  0 siblings, 0 replies; 32+ messages in thread
From: Stephen Smalley @ 2019-06-05 21:01 UTC (permalink / raw)
  To: Greg KH
  Cc: Andy Lutomirski, Casey Schaufler, Andy Lutomirski, David Howells,
	Al Viro, raven, Linux FS Devel, Linux API, linux-block, keyrings,
	LSM List, LKML, Paul Moore

On 6/5/19 3:28 PM, Greg KH wrote:
> On Wed, Jun 05, 2019 at 02:25:33PM -0400, Stephen Smalley wrote:
>> On 6/5/19 1:47 PM, Andy Lutomirski wrote:
>>>
>>>> On Jun 5, 2019, at 10:01 AM, Casey Schaufler <casey@schaufler-ca.com> wrote:
>>>>
>>>>> On 6/5/2019 9:04 AM, Andy Lutomirski wrote:
>>>>>> On Wed, Jun 5, 2019 at 7:51 AM Casey Schaufler <casey@schaufler-ca.com> wrote:
>>>>>>> On 6/5/2019 1:41 AM, David Howells wrote:
>>>>>>> Casey Schaufler <casey@schaufler-ca.com> wrote:
>>>>>>>
>>>>>>>> I will try to explain the problem once again. If process A
>>>>>>>> sends a signal (writes information) to process B the kernel
>>>>>>>> checks that either process A has the same UID as process B
>>>>>>>> or that process A has privilege to override that policy.
>>>>>>>> Process B is passive in this access control decision, while
>>>>>>>> process A is active. In the event delivery case, process A
>>>>>>>> does something (e.g. modifies a keyring) that generates an
>>>>>>>> event, which is then sent to process B's event buffer.
>>>>>>> I think this might be the core sticking point here.  It looks like two
>>>>>>> different situations:
>>>>>>>
>>>>>>> (1) A explicitly sends event to B (eg. signalling, sendmsg, etc.)
>>>>>>>
>>>>>>> (2) A implicitly and unknowingly sends event to B as a side effect of some
>>>>>>>       other action (eg. B has a watch for the event A did).
>>>>>>>
>>>>>>> The LSM treats them as the same: that is B must have MAC authorisation to send
>>>>>>> a message to A.
>>>>>> YES!
>>>>>>
>>>>>> Threat is about what you can do, not what you intend to do.
>>>>>>
>>>>>> And it would be really great if you put some thought into what
>>>>>> a rational model would be for UID based controls, too.
>>>>>>
>>>>>>> But there are problems with not sending the event:
>>>>>>>
>>>>>>> (1) B's internal state is then corrupt (or, at least, unknowingly invalid).
>>>>>> Then B is a badly written program.
>>>>> Either I'm misunderstanding you or I strongly disagree.
>>>>
>>>> A program needs to be aware of the conditions under
>>>> which it gets event, *including the possibility that
>>>> it may not get an event that it's not allowed*. Do you
>>>> regularly write programs that go into corrupt states
>>>> if an open() fails? Or where read() returns less than
>>>> the amount of data you ask for?
>>>
>>> I do not regularly write programs that handle read() omitting data in the middle of a TCP stream.  I also don’t write programs that wait for processes to die and need to handle the case where a child is dead, waitid() can see it, but SIGCHLD wasn’t sent because “security”.
>>>
>>>>
>>>>>    If B has
>>>>> authority to detect a certain action, and A has authority to perform
>>>>> that action, then refusing to notify B because B is somehow missing
>>>>> some special authorization to be notified by A is nuts.
>>>>
>>>> You are hand-waving the notion of authority. You are assuming
>>>> that if A can read X and B can read X that A can write B.
>>>
>>> No, read it again please. I’m assuming that if A can *write* X and B can read X then A can send information to B.
>>
>> I guess the questions here are:
>>
>> 1) How do we handle recursive notification support, since we can't check
>> that B can read everything below a given directory easily?  Perhaps we can
>> argue that if I have watch permission to / then that implies visibility to
>> everything below it but that is rather broad.
> 
> How do you handle fanotify today which I think can do this?

Doesn't appear to have been given much thought; looks like 
fanotify_init() checks capable(CAP_SYS_ADMIN) and fanotify_mark() checks 
inode_permission(MAY_READ) on the mount/directory/file.  File 
descriptors for monitored files returned upon events at least get vetted 
through security_file_open() so that can prevent the monitoring process 
from receiving arbitrary descriptors. Would be preferable if 
fanotify_mark() did some kind of security_path_watch() or similar check, 
and distinguished mounts versus directories since monitoring of 
directories is not recursive.

^ permalink raw reply	[flat|nested] 32+ messages in thread

* Re: Rational model for UID based controls
  2019-06-05 16:56     ` Rational model for UID based controls David Howells
  2019-06-05 17:40       ` Casey Schaufler
@ 2019-06-05 21:06       ` David Howells
  1 sibling, 0 replies; 32+ messages in thread
From: David Howells @ 2019-06-05 21:06 UTC (permalink / raw)
  To: Casey Schaufler, Stephen Smalley
  Cc: dhowells, Andy Lutomirski, Al Viro, raven, Linux FS Devel,
	Linux API, linux-block, keyrings, LSM List, LKML

Casey Schaufler <casey@schaufler-ca.com> wrote:

> Right. You're mixing the kind of things that can generate events,
> and that makes having a single policy difficult.

Whilst that's true, the notifications are clearly marked as to type, so it
should be possible to select different policies for different notification
types.

Question for you: what does the LSM *actually* need?  There are a bunch of
things available, some of which may be the same thing:

 (1) The creds of the process that created a watch_queue (ie. opened
     /dev/watch_queue).

 (2) The creds of the process that set a watch (ie. called sb_notify,
     KEYCTL_NOTIFY, ...);

 (3) The creds of the process that tripped the event (which might be the
     system).

 (4) The security attributes of the object on which the watch was set (uid,
     gid, mode, labels).

 (5) The security attributes of the object on which the event was tripped.

 (6) The security attributes of all the objects between the object in (5) and
     the object in (4), assuming we work from (5) towards (4) if the two
     aren't coincident (WATCH_INFO_RECURSIVE).

At the moment, when post_one_notification() wants to write a notification into
a queue, it calls security_post_notification() to ask if it should be allowed
to do so.  This is passed (1) and (3) above plus the notification record.

The only problem I really have is that for a destruction message you want to
get the creds of who did the last put on an object and caused it to be
destroyed - I think everything else probably gets the right creds, even if
they aren't even in the same namespaces (mount propagation, yuck).

However, that one is a biggie because close()/exit() must propagate it to
deferred-fput, which must propagate it to af_unix-cleanup, and thence back to
deferred-fput and thence to implicit unmount (dissolve_on_fput()[*]).

[*] Though it should be noted that if this happens, the subtree cannot be
    attached to the root of a namespace.

> > In any case, that's what I was referring to when I said I might need to call
> > inode_permission().  But UIDs don't exist for all filesystems, for example,
> > and there are no UIDs on superblocks, mount objects or hardware events.
> 
> If you open() or stat() a file on those filesystems the UID
> used in the access control comes from somewhere. Setting a watch
> on things with UIDs should use the access mode on the file,
> just like any other filesystem operation.

Another question for you: Do I need to let the LSM pass judgement on a watch
that a process is trying to set?  I think I probably do.  This would require
separate hooks for different object types:

	int security_watch_key(struct watch *watch, struct key *key);
	int security_watch_sb(struct watch *watch, struct path *path);
	int security_watch_mount(struct watch *watch, struct path *path);
	int security_watch_devices(struct watch *watch);

so that the LSM can see the object the watch is being placed on (the last has
a global queue, so there is no object).  

Further, do I need to put a "void *security" pointer in struct watch and
indicate to the LSM the object bring watched?  The watch could then be passed
to security_post_notification() instead of the watch queue creds (which I
could then dispense with).

	security_post_notification(const struct watch *watch,
				   const struct cred *trigger_cred,
				   struct watch_notification *n);


Also, should I let the LSM audit/edit the filter set by
IOC_WATCH_QUEUE_SET_FILTER?  Userspace can't retrieve the filter, so the LSM
could edit it to exclude certain things.  That might be a bit too complicated,
though.

> Things like superblocks are sticker because we don't generally
> think of them as objects. If you can do statfs(), you should be
> able to set a watch on the filesystem metadata.
> 
> How would you specify a watch for a hardware event? If you say
> you have to open /dev/mumble to sent a watch for mumbles, you're
> good there, too.

That's not how that works at the moment.  There's a global watch list for
device events.  I've repurposed it to carry any device's events - so it will
carry blockdev events (I/O errors only at the moment) and usb events
(add/remove device, add/remove bus, reset device at the moment).

> > Now, I could see that you ignore UIDs on things like keys and
> > hardware-triggered events, but how does this interact with things like mount
> > watches that see directories that have UIDs?
> >
> > Are you advocating making it such that process B can only see events
> > triggered by process A if they have the same UID, for example?
> 
> It's always seemed arbitrary to me that you can't open your process up to
> get signals from other users. What about putting mode bits on your ring
> buffer? By default you could only accept your own events, but you could do a
> rb_chmod(0222) and let all events through.

Ummm...  This mechanism is pretty much about events generated by others.
Depend on what you mean by 'you' and 'your own events', it might be considered
that you would know what events you were directly causing and wouldn't need a
notification system for it.

> Subject to LSM addition restrictions, of course. That would require the cred
> of the process that triggered the event or a system cred for "hardware"
> events.  If you don't like mode bits you could use an ACL for fine
> granularity or a single "let'em all in" bit for coarse.

I'm not entirely sure how an ACL would help.  If someone creates a watch
queue, sets an ACL with only a "let everything in" ACE, we're back to the
situation we're in now.

As I understand it, the issue you have is stopping them getting events that
they're willing to accept that you think they shouldn't be allowed.

> I'm not against access, I'm against uncontrolled access in conflict with
> basic system policy.

David

^ permalink raw reply	[flat|nested] 32+ messages in thread

end of thread, back to index

Thread overview: 32+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-06-04 16:34 [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2] David Howells
2019-06-04 16:35 ` [PATCH 1/8] security: Override creds in __fput() with last fputter's creds " David Howells
2019-06-04 18:15   ` Andy Lutomirski
2019-06-04 16:35 ` [PATCH 2/8] General notification queue with user mmap()'able ring buffer " David Howells
2019-06-04 16:35 ` [PATCH 3/8] keys: Add a notification facility " David Howells
2019-06-04 16:35 ` [PATCH 4/8] vfs: Add a mount-notification " David Howells
2019-06-04 16:35 ` [PATCH 5/8] vfs: Add superblock notifications " David Howells
2019-06-04 16:36 ` [PATCH 6/8] fsinfo: Export superblock notification counter " David Howells
2019-06-04 16:36 ` [PATCH 7/8] block: Add block layer notifications " David Howells
2019-06-04 16:36 ` [PATCH 8/8] Add sample notification program " David Howells
2019-06-04 17:43 ` [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications " Andy Lutomirski
2019-06-04 20:31   ` Casey Schaufler
2019-06-04 21:05     ` Andy Lutomirski
2019-06-04 22:03       ` Casey Schaufler
2019-06-05  8:41   ` David Howells
2019-06-05 14:50     ` Casey Schaufler
2019-06-05 16:04       ` Andy Lutomirski
2019-06-05 17:01         ` Casey Schaufler
2019-06-05 17:47           ` Andy Lutomirski
2019-06-05 18:12             ` Casey Schaufler
2019-06-05 18:25             ` Stephen Smalley
2019-06-05 19:28               ` Greg KH
2019-06-05 21:01                 ` Stephen Smalley
2019-06-05 16:56     ` Rational model for UID based controls David Howells
2019-06-05 17:40       ` Casey Schaufler
2019-06-05 21:06       ` David Howells
2019-06-05 17:21     ` [RFC][PATCH 0/8] Mount, FS, Block and Keyrings notifications [ver #2] David Howells
2019-06-04 20:39 ` David Howells
2019-06-04 20:57   ` Andy Lutomirski
     [not found]     ` <CAB9W1A0AgMYOwGx9c-TmAt=1O6Bjsr2P3Nhd=2+QV39dgw0CrA@mail.gmail.com>
2019-06-05  4:19       ` Andy Lutomirski
2019-06-05 13:47         ` Stephen Smalley
2019-06-04 21:11   ` Casey Schaufler

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