[PATCH 0/9] Keyrings, Block and USB notifications [ver #5]

[PATCH 0/9] Keyrings, Block and USB notifications [ver #5]

[David Howells]

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

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

 (2) General device events (single common queue) including:

     - Block layer events, such as device errors

     - USB subsystem events, such as device/bus attach/remove, device
       reset, device errors.

LSM hooks are included:

 (1) A set of hooks are provided that allow an LSM to rule on whether or
     not a watch may be set.  Each of these hooks takes a different
     "watched object" parameter, so they're not really shareable.  The LSM
     should use current's credentials.  [Wanted by SELinux & Smack]

 (2) A hook is provided to allow an LSM to rule on whether or not a
     particular message may be posted to a particular queue.  This is given
     the credentials from the event generator (which may be the system) and
     the watch setter.  [Wanted by Smack]


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 just a few, 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);
	watch_devices(fd, 0x02, 0);

     where in both 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.


The patches can be found here also:

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

Changes:

 ver #5:

 (*) Split the superblock watch and mount watch parts out into their own
     branch (notifications-mount) as they really need certain fsinfo()
     attributes.

 (*) Rearrange the watch notification UAPI header to push the length down
     to bits 0-5 and remove the lost-message bits.  The userspace's watch
     ID tag is moved to bits 8-15 and then the message type is allocated
     all of bits 16-31 for its own purposes.

     The lost-message bit is moved over to the header, rather than being
     placed in the next message to be generated and given its own word so
     it can be cleared with xchg(,0) for parisc.

 (*) The security_post_notification() hook is no longer called with the
     spinlock held and softirqs disabled - though the RCU readlock is still
     held.

 (*) Buffer pages are now accounted towards RLIMIT_MEMLOCK and CAP_IPC_LOCK
     will skip the overuse check.

 (*) The buffer is marked VM_DONTEXPAND.

 (*) Save the watch-setter's creds in struct watch and give that to the LSM
     hook for posting a message.

 ver #4:

 (*) Split the basic UAPI bits out into their own patch and then split the
     LSM hooks out into an intermediate patch.  Add LSM hooks for setting
     watches.

     Rename the *_notify() system calls to watch_*() for consistency.

 ver #3:

 (*) I've added a USB notification source and reformulated the block
     notification source so that there's now a common watch list, for which
     the system call is now device_notify().

     I've assigned a pair of unused ioctl numbers in the 'W' series to the
     ioctls added by this series.

     I've also added a description of the kernel API to the documentation.

 ver #2:

 (*) 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 (9):
      uapi: General notification ring definitions
      security: Add hooks to rule on setting a watch
      security: Add a hook for the point of notification insertion
      General notification queue with user mmap()'able ring buffer
      keys: Add a notification facility
      Add a general, global device notification watch list
      block: Add block layer notifications
      usb: Add USB subsystem notifications
      Add sample notification program


 Documentation/ioctl/ioctl-number.txt        |    1 
 Documentation/security/keys/core.rst        |   58 ++
 Documentation/watch_queue.rst               |  460 ++++++++++++++
 arch/alpha/kernel/syscalls/syscall.tbl      |    1 
 arch/arm/tools/syscall.tbl                  |    1 
 arch/ia64/kernel/syscalls/syscall.tbl       |    1 
 arch/m68k/kernel/syscalls/syscall.tbl       |    1 
 arch/microblaze/kernel/syscalls/syscall.tbl |    1 
 arch/mips/kernel/syscalls/syscall_n32.tbl   |    1 
 arch/mips/kernel/syscalls/syscall_n64.tbl   |    1 
 arch/mips/kernel/syscalls/syscall_o32.tbl   |    1 
 arch/parisc/kernel/syscalls/syscall.tbl     |    1 
 arch/powerpc/kernel/syscalls/syscall.tbl    |    1 
 arch/s390/kernel/syscalls/syscall.tbl       |    1 
 arch/sh/kernel/syscalls/syscall.tbl         |    1 
 arch/sparc/kernel/syscalls/syscall.tbl      |    1 
 arch/x86/entry/syscalls/syscall_32.tbl      |    1 
 arch/x86/entry/syscalls/syscall_64.tbl      |    1 
 arch/xtensa/kernel/syscalls/syscall.tbl     |    1 
 block/Kconfig                               |    9 
 block/blk-core.c                            |   29 +
 drivers/base/Kconfig                        |    9 
 drivers/base/Makefile                       |    1 
 drivers/base/watch.c                        |   90 +++
 drivers/misc/Kconfig                        |   13 
 drivers/misc/Makefile                       |    1 
 drivers/misc/watch_queue.c                  |  890 +++++++++++++++++++++++++++
 drivers/usb/core/Kconfig                    |   10 
 drivers/usb/core/devio.c                    |   56 ++
 drivers/usb/core/hub.c                      |    3 
 include/linux/blkdev.h                      |   15 
 include/linux/device.h                      |    7 
 include/linux/key.h                         |    4 
 include/linux/lsm_hooks.h                   |   32 +
 include/linux/security.h                    |   25 +
 include/linux/syscalls.h                    |    1 
 include/linux/usb.h                         |   19 +
 include/linux/watch_queue.h                 |   94 +++
 include/uapi/asm-generic/unistd.h           |    4 
 include/uapi/linux/keyctl.h                 |    1 
 include/uapi/linux/watch_queue.h            |  170 +++++
 kernel/sys_ni.c                             |    1 
 samples/Kconfig                             |    6 
 samples/Makefile                            |    1 
 samples/watch_queue/Makefile                |    8 
 samples/watch_queue/watch_test.c            |  233 +++++++
 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                      |   95 +++
 security/keys/keyring.c                     |   17 -
 security/keys/request_key.c                 |    4 
 security/security.c                         |   19 +
 55 files changed, 2461 insertions(+), 25 deletions(-)
 create mode 100644 Documentation/watch_queue.rst
 create mode 100644 drivers/base/watch.c
 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
 create mode 100644 samples/watch_queue/Makefile
 create mode 100644 samples/watch_queue/watch_test.c

[PATCH 1/9] uapi: General notification ring definitions [ver #5]

[David Howells]

Add UAPI definitions for the general notification ring, including the
following pieces:

 (1) struct watch_notification.

     This is the metadata header for each entry in the ring.  It includes a
     type and subtype that indicate the source of the message
     (eg. WATCH_TYPE_MOUNT_NOTIFY) and the kind of the message
     (eg. NOTIFY_MOUNT_NEW_MOUNT).

     The header also contains an information field that conveys the
     following information:

	- WATCH_INFO_LENGTH.  The size of the entry (entries are variable
          length).

	- WATCH_INFO_ID.  The watch ID specified when the watchpoint was
          set.

	- WATCH_INFO_TYPE_INFO.  (Sub)type-specific information.

	- WATCH_INFO_FLAG_*.  Flag bits overlain on the type-specific
          information.  For use by the type.

     All the information in the header can be used in filtering messages at
     the point of writing into the buffer.

 (2) struct watch_queue_buffer.

     This describes the layout of the ring.  Note that the first slots in
     the ring contain a special metadata entry that contains the ring
     pointers.  The producer in the kernel knows to skip this and it has a
     proper header (WATCH_TYPE_META, WATCH_META_SKIP_NOTIFICATION) that
     indicates the size so that the ring consumer can handle it the same as
     any other record and just skip it.

     Note that this means that ring entries can never be split over the end
     of the ring, so if an entry would need to be split, a skip record is
     inserted to wrap the ring first; this is also WATCH_TYPE_META,
     WATCH_META_SKIP_NOTIFICATION.

 (3) WATCH_INFO_NOTIFICATIONS_LOST.

     This is a flag that can be set in the metadata header by the kernel to
     indicate that at least one message was lost since it was last cleared
     by userspace.

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

 include/uapi/linux/watch_queue.h |   67 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 67 insertions(+)
 create mode 100644 include/uapi/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..70f575099968
--- /dev/null
+++ b/include/uapi/linux/watch_queue.h
@@ -0,0 +1,67 @@
+/* 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>
+
+enum watch_notification_type {
+	WATCH_TYPE_META		= 0,	/* Special record */
+	WATCH_TYPE___NR		= 1
+};
+
+enum watch_meta_notification_subtype {
+	WATCH_META_SKIP_NOTIFICATION	= 0,	/* Just skip this record */
+	WATCH_META_REMOVAL_NOTIFICATION	= 1,	/* Watched object was removed */
+};
+
+#define WATCH_LENGTH_GRANULARITY sizeof(__u64)
+
+/*
+ * Notification record header.  This is aligned to 64-bits so that subclasses
+ * can contain __u64 fields.
+ */
+struct watch_notification {
+	__u32			type:24;	/* enum watch_notification_type */
+	__u32			subtype:8;	/* Type-specific subtype (filterable) */
+	__u32			info;
+#define WATCH_INFO_LENGTH	0x0000003f	/* Length of record / sizeof(watch_notification) */
+#define WATCH_INFO_LENGTH__SHIFT 0
+#define WATCH_INFO_ID		0x0000ff00	/* ID of watchpoint, if type-appropriate */
+#define WATCH_INFO_ID__SHIFT	8
+#define WATCH_INFO_TYPE_INFO	0xffff0000	/* Type-specific info */
+#define WATCH_INFO_TYPE_INFO__SHIFT 16
+#define WATCH_INFO_FLAG_0	0x00010000	/* Type-specific info, flag bit 0 */
+#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
+} __attribute__((aligned(WATCH_LENGTH_GRANULARITY)));
+
+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 */
+			__u32		__reserved;
+		} meta;
+		struct watch_notification slots[0];
+	};
+};
+
+/*
+ * The Metadata pseudo-notification message uses a flag bits in the information
+ * field to convey the fact that messages have been lost.  We can only use a
+ * single bit in this manner per word as some arches that support SMP
+ * (eg. parisc) have no kernel<->user atomic bit ops.
+ */
+#define WATCH_INFO_NOTIFICATIONS_LOST WATCH_INFO_FLAG_0
+
+#endif /* _UAPI_LINUX_WATCH_QUEUE_H */

[PATCH 2/9] security: Add hooks to rule on setting a watch [ver #5]

[David Howells]

Add security hooks that will allow an LSM to rule on whether or not a watch
may be set.  More than one hook is required as the watches watch different
types of object.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Casey Schaufler <casey@schaufler-ca.com>
cc: Stephen Smalley <sds@tycho.nsa.gov>
cc: linux-security-module@vger.kernel.org
---

 include/linux/lsm_hooks.h |   22 ++++++++++++++++++++++
 include/linux/security.h  |   15 +++++++++++++++
 security/security.c       |   13 +++++++++++++
 3 files changed, 50 insertions(+)

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 47f58cfb6a19..f9d31f6445e4 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -1413,6 +1413,20 @@
  *	@ctx is a pointer in which to place the allocated security context.
  *	@ctxlen points to the place to put the length of @ctx.
  *
+ * Security hooks for the general notification queue:
+ *
+ * @watch_key:
+ *	Check to see if a process is allowed to watch for event notifications
+ *	from a key or keyring.
+ *	@watch: The watch object
+ *	@key: The key to watch.
+ *
+ * @watch_devices:
+ *	Check to see if a process is allowed to watch for event notifications
+ *	from devices (as a global set).
+ *	@watch: The watch object
+ *
+ *
  * Security hooks for using the eBPF maps and programs functionalities through
  * eBPF syscalls.
  *
@@ -1688,6 +1702,10 @@ 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 (*watch_key)(struct watch *watch, struct key *key);
+	int (*watch_devices)(struct watch *watch);
+#endif /* CONFIG_WATCH_QUEUE */
 
 #ifdef CONFIG_SECURITY_NETWORK
 	int (*unix_stream_connect)(struct sock *sock, struct sock *other,
@@ -1964,6 +1982,10 @@ 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 watch_key;
+	struct hlist_head watch_devices;
+#endif /* CONFIG_WATCH_QUEUE */
 #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 659071c2e57c..540863678355 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -57,6 +57,7 @@ struct mm_struct;
 struct fs_context;
 struct fs_parameter;
 enum fs_value_type;
+struct watch;
 
 /* Default (no) options for the capable function */
 #define CAP_OPT_NONE 0x0
@@ -392,6 +393,10 @@ 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_watch_key(struct watch *watch, struct key *key);
+int security_watch_devices(struct watch *watch);
+#endif /* CONFIG_WATCH_QUEUE */
 #else /* CONFIG_SECURITY */
 
 static inline int call_lsm_notifier(enum lsm_event event, void *data)
@@ -1204,6 +1209,16 @@ static inline int security_inode_getsecctx(struct inode *inode, void **ctx, u32
 {
 	return -EOPNOTSUPP;
 }
+#ifdef CONFIG_WATCH_QUEUE
+static inline int security_watch_key(struct watch *watch, struct key *key)
+{
+	return 0;
+}
+static inline int security_watch_devices(struct watch *watch)
+{
+	return 0;
+}
+#endif /* CONFIG_WATCH_QUEUE */
 #endif	/* CONFIG_SECURITY */
 
 #ifdef CONFIG_SECURITY_NETWORK
diff --git a/security/security.c b/security/security.c
index 613a5c00e602..2c9919226ad1 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1917,6 +1917,19 @@ int security_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen)
 }
 EXPORT_SYMBOL(security_inode_getsecctx);
 
+#ifdef CONFIG_WATCH_QUEUE
+int security_watch_key(struct watch *watch, struct key *key)
+{
+	return call_int_hook(watch_key, 0, watch, key);
+}
+
+int security_watch_devices(struct watch *watch)
+{
+	return call_int_hook(watch_devices, 0, watch);
+}
+
+#endif /* CONFIG_WATCH_QUEUE */
+
 #ifdef CONFIG_SECURITY_NETWORK
 
 int security_unix_stream_connect(struct sock *sock, struct sock *other, struct sock *newsk)

[PATCH 3/9] security: Add a hook for the point of notification insertion [ver #5]

[David Howells]

Add a security hook that allows an LSM to rule on whether a notification
message is allowed to be inserted into a particular watch queue.

The hook is given the following information:

 (1) The credentials of the triggerer (which may be init_cred for a system
     notification, eg. a hardware error).

 (2) The credentials of the whoever set the watch.

 (3) The notification message.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Casey Schaufler <casey@schaufler-ca.com>
cc: Stephen Smalley <sds@tycho.nsa.gov>
cc: linux-security-module@vger.kernel.org
---

 include/linux/lsm_hooks.h |   10 ++++++++++
 include/linux/security.h  |   10 ++++++++++
 security/security.c       |    6 ++++++
 3 files changed, 26 insertions(+)

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index f9d31f6445e4..fd4b2b14e7d0 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -1426,6 +1426,12 @@
  *	from devices (as a global set).
  *	@watch: The watch object
  *
+ * @post_notification:
+ *	Check to see if a watch notification can be posted to a particular
+ *	queue.
+ *	@w_cred: The credentials of the whoever set the watch.
+ *	@cred: The event-triggerer's credentials
+ *	@n: The notification being posted
  *
  * Security hooks for using the eBPF maps and programs functionalities through
  * eBPF syscalls.
@@ -1705,6 +1711,9 @@ union security_list_options {
 #ifdef CONFIG_WATCH_QUEUE
 	int (*watch_key)(struct watch *watch, struct key *key);
 	int (*watch_devices)(struct watch *watch);
+	int (*post_notification)(const struct cred *w_cred,
+				 const struct cred *cred,
+				 struct watch_notification *n);
 #endif /* CONFIG_WATCH_QUEUE */
 
 #ifdef CONFIG_SECURITY_NETWORK
@@ -1985,6 +1994,7 @@ struct security_hook_heads {
 #ifdef CONFIG_WATCH_QUEUE
 	struct hlist_head watch_key;
 	struct hlist_head watch_devices;
+	struct hlist_head post_notification;
 #endif /* CONFIG_WATCH_QUEUE */
 #ifdef CONFIG_SECURITY_NETWORK
 	struct hlist_head unix_stream_connect;
diff --git a/include/linux/security.h b/include/linux/security.h
index 540863678355..5c074bf18bea 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 watch;
+struct watch_notification;
 
 /* Default (no) options for the capable function */
 #define CAP_OPT_NONE 0x0
@@ -396,6 +397,9 @@ int security_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen);
 #ifdef CONFIG_WATCH_QUEUE
 int security_watch_key(struct watch *watch, struct key *key);
 int security_watch_devices(struct watch *watch);
+int security_post_notification(const struct cred *w_cred,
+			       const struct cred *cred,
+			       struct watch_notification *n);
 #endif /* CONFIG_WATCH_QUEUE */
 #else /* CONFIG_SECURITY */
 
@@ -1218,6 +1222,12 @@ static inline int security_watch_devices(struct watch *watch)
 {
 	return 0;
 }
+static inline int security_post_notification(const struct cred *w_cred,
+					     const struct cred *cred,
+					     struct watch_notification *n)
+{
+	return 0;
+}
 #endif /* CONFIG_WATCH_QUEUE */
 #endif	/* CONFIG_SECURITY */
 
diff --git a/security/security.c b/security/security.c
index 2c9919226ad1..459e87d55ac9 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1928,6 +1928,12 @@ int security_watch_devices(struct watch *watch)
 	return call_int_hook(watch_devices, 0, watch);
 }
 
+int security_post_notification(const struct cred *w_cred,
+			       const struct cred *cred,
+			       struct watch_notification *n)
+{
+	return call_int_hook(post_notification, 0, w_cred, cred, n);
+}
 #endif /* CONFIG_WATCH_QUEUE */
 
 #ifdef CONFIG_SECURITY_NETWORK

[PATCH 4/9] General notification queue with user mmap()'able ring buffer [ver #5]

[David Howells]

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/ioctl/ioctl-number.txt |    1 
 Documentation/watch_queue.rst        |  429 ++++++++++++++++
 drivers/misc/Kconfig                 |   13 
 drivers/misc/Makefile                |    1 
 drivers/misc/watch_queue.c           |  890 ++++++++++++++++++++++++++++++++++
 include/linux/watch_queue.h          |   94 ++++
 include/uapi/linux/watch_queue.h     |   21 +
 7 files changed, 1449 insertions(+)
 create mode 100644 Documentation/watch_queue.rst
 create mode 100644 drivers/misc/watch_queue.c
 create mode 100644 include/linux/watch_queue.h

diff --git a/Documentation/ioctl/ioctl-number.txt b/Documentation/ioctl/ioctl-number.txt
index c9558146ac58..e7b2e56fcfdd 100644
--- a/Documentation/ioctl/ioctl-number.txt
+++ b/Documentation/ioctl/ioctl-number.txt
@@ -194,6 +194,7 @@ Code  Seq#(hex)	Include File		Comments
 'W'	00-1F	linux/wanrouter.h	conflict!		(pre 3.9)
 'W'	00-3F	sound/asound.h		conflict!
 'W'	40-5F   drivers/pci/switch/switchtec.c
+'W'	60-61	linux/watch_queue.h
 'X'	all	fs/xfs/xfs_fs.h		conflict!
 		and fs/xfs/linux-2.6/xfs_ioctl32.h
 		and include/linux/falloc.h
diff --git a/Documentation/watch_queue.rst b/Documentation/watch_queue.rst
new file mode 100644
index 000000000000..6fb3aa3356d3
--- /dev/null
+++ b/Documentation/watch_queue.rst
@@ -0,0 +1,429 @@
+============================
+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
+
+  * General device 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;
+	} __attribute__((aligned(WATCH_LENGTH_GRANULARITY)));
+
+"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 watch was installed was removed or
+destroyed.
+
+"info" indicates a bunch of things, including:
+
+  * The length of the record in units of buffer slots (mask with
+    WATCH_INFO_LENGTH and shift by WATCH_INFO_LENGTH__SHIFT).  This indicates
+    the size of the record, which may be between 1 and 63 slots.  To turn this
+    into a number of bytes, multiply by WATCH_LENGTH_GRANULARITY.
+
+  * The watch ID (mask with WATCH_INFO_ID and shift by WATCH_INFO_ID__SHIFT).
+    This indicates that caller's ID of the watch, which may be between 0
+    and 255.  Multiple watches may share a queue, and this provides a means to
+    distinguish them.
+
+  * In the metadata header in slot 0, a flag (WATCH_INFO_NOTIFICATIONS_LOST)
+    that indicates that some notifications were lost for some reason, including
+    buffer overrun, insufficient memory and inconsistent tail index.
+
+  * A type-specific field (WATCH_INFO_TYPE_INFO).  This is 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 slots of size WATCH_LENGTH_GRANULARITY (8 bytes).  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 List (Notification Source) API
+====================================
+
+A "watch list" is a list of watchers that are subscribed to a source of
+notifications.  A list may be attached to an object (say a key or a superblock)
+or may be global (say for device events).  From a userspace perspective, a
+non-global watch list is typically referred to by reference to the object it
+belongs to (such as using KEYCTL_NOTIFY and giving it a key serial number to
+watch that specific key).
+
+To manage a watch list, the following functions are provided:
+
+  * ``void init_watch_list(struct watch_list *wlist,
+			   void (*release_watch)(struct watch *wlist));``
+
+    Initialise a watch list.  If ``release_watch`` is not NULL, then this
+    indicates a function that should be called when the watch_list object is
+    destroyed to discard any references the watch list holds on the watched
+    object.
+
+  * ``void remove_watch_list(struct watch_list *wlist);``
+
+    This removes all of the watches subscribed to a watch_list and frees them
+    and then destroys the watch_list object itself.
+
+
+Watch Queue (Notification Buffer) API
+=====================================
+
+A "watch queue" is the buffer allocated by or on behalf of the application that
+notification records will be written into.  The workings of this are hidden
+entirely inside of the watch_queue device driver, but it is necessary to gain a
+reference to it to place a watch.  These can be managed with:
+
+  * ``struct watch_queue *get_watch_queue(int fd);``
+
+    Since watch queues are indicated to the kernel by the fd of the character
+    device that implements the buffer, userspace must hand that fd through a
+    system call.  This can be used to look up an opaque pointer to the watch
+    queue from the system call.
+
+  * ``void put_watch_queue(struct watch_queue *wqueue);``
+
+    This discards the reference obtained from ``get_watch_queue()``.
+
+
+Watch Subscription API
+======================
+
+A "watch" is a subscription on a watch list, indicating the watch queue, and
+thus the buffer, into which notification records should be written.  The watch
+queue object may also carry filtering rules for that object, as set by
+userspace.  Some parts of the watch struct can be set by the driver::
+
+	struct watch {
+		union {
+			u32		info_id;	/* ID to be OR'd in to info field */
+			...
+		};
+		void			*private;	/* Private data for the watched object */
+		u64			id;		/* Internal identifier */
+		...
+	};
+
+The ``info_id`` value should be an 8-bit number obtained from userspace and
+shifted by WATCH_INFO_ID__SHIFT.  This is OR'd into the WATCH_INFO_ID field of
+struct watch_notification::info when and if the notification is written into
+the associated watch queue buffer.
+
+The ``private`` field is the driver's data associated with the watch_list and
+is cleaned up by the ``watch_list::release_watch()`` method.
+
+The ``id`` field is the source's ID.  Notifications that are posted with a
+different ID are ignored.
+
+The following functions are provided to manage watches:
+
+  * ``void init_watch(struct watch *watch, struct watch_queue *wqueue);``
+
+    Initialise a watch object, setting its pointer to the watch queue, using
+    appropriate barriering to avoid lockdep complaints.
+
+  * ``int add_watch_to_object(struct watch *watch, struct watch_list *wlist);``
+
+    Subscribe a watch to a watch list (notification source).  The
+    driver-settable fields in the watch struct must have been set before this
+    is called.
+
+  * ``int remove_watch_from_object(struct watch_list *wlist,
+				   struct watch_queue *wqueue,
+				   u64 id, false);``
+
+    Remove a watch from a watch list, where the watch must match the specified
+    watch queue (``wqueue``) and object identifier (``id``).  A notification
+    (``WATCH_META_REMOVAL_NOTIFICATION``) is sent to the watch queue to
+    indicate that the watch got removed.
+
+  * ``int remove_watch_from_object(struct watch_list *wlist, NULL, 0, true);``
+
+    Remove all the watches from a watch list.  It is expected that this will be
+    called preparatory to destruction and that the watch list will be
+    inaccessible to new watches by this point.  A notification
+    (``WATCH_META_REMOVAL_NOTIFICATION``) is sent to the watch queue of each
+    subscribed watch to indicate that the watch got removed.
+
+
+Notification Posting API
+========================
+
+To post a notification to watch list so that the subscribed watches can see it,
+the following function should be used::
+
+	void post_watch_notification(struct watch_list *wlist,
+				     struct watch_notification *n,
+				     const struct cred *cred,
+				     u64 id);
+
+The notification should be preformatted and a pointer to the header (``n``)
+should be passed in.  The notification may be larger than this and the size in
+units of buffer slots is noted in ``n->info & WATCH_INFO_LENGTH``.
+
+The ``cred`` struct indicates the credentials of the source (subject) and is
+passed to the LSMs, such as SELinux, to allow or suppress the recording of the
+note in each individual queue according to the credentials of that queue
+(object).
+
+The ``id`` is the ID of the source object (such as the serial number on a key).
+Only watches that have the same ID set in them will see this notification.
+
+
+Watch Sources
+=============
+
+Any particular buffer can be fed from multiple sources.  Sources include:
+
+  * 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.  Watches 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_KEY_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 could be used, for example, to ignore events that are not exactly on
+    the watched point in a mount tree.
+
+  * ``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.
+
+
+Waiting For Events
+==================
+
+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.
+
+
+Userspace Code 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 keyring change notifications and device event
+notifications::
+
+	keyctl(KEYCTL_WATCH_KEY, KEY_SPEC_SESSION_KEYRING, fd, 0x01);
+
+	watch_devices(fd, 0x2);
+
+The notifications can then be consumed by something like the following::
+
+	extern void saw_key_change(struct watch_notification *n);
+	extern void saw_block_event(struct watch_notification *n);
+	extern void saw_usb_event(struct watch_notification *n);
+
+	static int consumer(int fd, struct watch_queue_buffer *buf)
+	{
+		struct watch_notification *n;
+		struct pollfd p[1];
+		unsigned int len, 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];
+				len = (n->info & WATCH_INFO_LENGTH) >>
+					WATCH_INFO_LENGTH__SHIFT;
+				if (len == 0)
+					goto went_wrong;
+
+				switch (n->type) {
+				case WATCH_TYPE_KEY_NOTIFY:
+					saw_key_change(n);
+					break;
+				case WATCH_TYPE_BLOCK_NOTIFY:
+					saw_block_event(n);
+					break;
+				case WATCH_TYPE_USB_NOTIFY:
+					saw_usb_event(n);
+					break;
+				}
+
+				tail += len;
+				_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..e53f88783fe7 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 key/keyring change notifications and device
+	  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..d80d469f8cf8
--- /dev/null
+++ b/drivers/misc/watch_queue.c
@@ -0,0 +1,890 @@
+// SPDX-License-Identifier: GPL-2.0
+/* User-mappable watch queue
+ *
+ * Copyright (C) 2019 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * 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/sched/signal.h>
+#include <linux/watch_queue.h>
+
+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;
+	struct user_struct	*owner;		/* Owner of the queue for rlimit purposes */
+	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 */
+	u32			size;
+	struct watch_queue_buffer *buffer;	/* Pointer to first record */
+
+	/* The mappable pages.  The zeroth page holds the ring pointers. */
+	struct page		**pages;
+};
+
+/*
+ * Write 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).
+ */
+static bool write_one_notification(struct watch_queue *wqueue,
+				   struct watch_notification *n)
+{
+	struct watch_queue_buffer *buf = wqueue->buffer;
+	struct watch_notification *p;
+	unsigned int gran = WATCH_LENGTH_GRANULARITY;
+	unsigned int metalen = sizeof(buf->meta) / gran;
+	unsigned int size = wqueue->size, mask = size - 1;
+	unsigned int len;
+	unsigned int ring_tail, tail, head, used, gap, h;
+
+	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 lost_event; /* Inconsistent */
+	tail = ring_tail & mask;
+	if (tail > 0 && tail < metalen)
+		goto lost_event; /* Inconsistent */
+
+	len = (n->info & WATCH_INFO_LENGTH) >> WATCH_INFO_LENGTH__SHIFT;
+	h = head & mask;
+	if (h >= tail) {
+		/* Head is at or after tail in the buffer.  There may then be
+		 * two gaps: one to the end of buffer and one at the beginning
+		 * of the buffer between the metadata block and the tail
+		 * pointer.
+		 */
+		gap = size - h;
+		if (len > gap) {
+			/* Not enough space in the post-head gap; we need to
+			 * wrap.  When wrapping, we will have to skip the
+			 * metadata at the beginning of the buffer.
+			 */
+			if (len > tail - metalen)
+				goto lost_event; /* Overrun */
+
+			/* Fill the space at the end of the page */
+			p = &buf->slots[h];
+			p->type		= WATCH_TYPE_META;
+			p->subtype	= WATCH_META_SKIP_NOTIFICATION;
+			p->info		= gap << WATCH_INFO_LENGTH__SHIFT;
+			head += gap;
+			h = 0;
+			if (h >= tail)
+				goto lost_event; /* Overrun */
+		}
+	}
+
+	if (h == 0) {
+		/* Reset and skip the header metadata */
+		p = &buf->meta.watch;
+		p->type		= WATCH_TYPE_META;
+		p->subtype	= WATCH_META_SKIP_NOTIFICATION;
+		p->info		= metalen << WATCH_INFO_LENGTH__SHIFT;
+		head += metalen;
+		h = metalen;
+		if (h == tail)
+			goto lost_event; /* Overrun */
+	}
+
+	if (h < tail) {
+		/* Head is before tail in the buffer. */
+		gap = tail - h;
+		if (len > gap)
+			goto lost_event; /* Overrun */
+	}
+
+	n->info |= wqueue->flag_next;
+	wqueue->flag_next = 0;
+	p = &buf->slots[h];
+	memcpy(p, n, len * gran);
+	head += len;
+
+	smp_store_release(&buf->meta.head, head);
+	if (used == 0)
+		wake_up(&wqueue->waiters);
+	return true;
+
+lost_event:
+	WRITE_ONCE(buf->meta.watch.info,
+		   buf->meta.watch.info | WATCH_INFO_NOTIFICATIONS_LOST);
+	return false;
+}
+
+/*
+ * Post a notification to a watch queue.
+ */
+static bool post_one_notification(struct watch_queue *wqueue,
+				  struct watch_notification *n)
+{
+	bool done = false;
+
+	if (!wqueue->buffer)
+		return false;
+
+	spin_lock_bh(&wqueue->lock); /* Protect head pointer */
+
+	if (!wqueue->defunct)
+		done = write_one_notification(wqueue, n);
+	spin_unlock_bh(&wqueue->lock);
+	return done;
+}
+
+/*
+ * 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.
+ *
+ * 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;
+
+	if (((n->info & WATCH_INFO_LENGTH) >> WATCH_INFO_LENGTH__SHIFT) == 0) {
+		WARN_ON(1);
+		return;
+	}
+
+	rcu_read_lock();
+
+	hlist_for_each_entry_rcu(watch, &wlist->watchers, list_node) {
+		if (watch->id != id)
+			continue;
+		n->info &= ~WATCH_INFO_ID;
+		n->info |= watch->info_id;
+
+		wqueue = rcu_dereference(watch->queue);
+		wf = rcu_dereference(wqueue->filter);
+		if (wf && !filter_watch_notification(wf, n))
+			continue;
+
+		if (security_post_notification(watch->cred, cred, n) < 0)
+			continue;
+
+		post_one_notification(wqueue, n);
+	}
+
+	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;
+
+	if (!buf)
+		return EPOLLERR;
+
+	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 int watch_queue_account_mem(struct watch_queue *wqueue,
+				   unsigned long nr_pages)
+{
+	struct user_struct *user = wqueue->owner;
+	unsigned long page_limit, cur_pages, new_pages;
+
+	/* Don't allow more pages than we can safely lock */
+	page_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
+	cur_pages = atomic_long_read(&user->locked_vm);
+
+	do {
+		new_pages = cur_pages + nr_pages;
+		if (new_pages > page_limit && !capable(CAP_IPC_LOCK))
+			return -ENOMEM;
+	} while (atomic_long_try_cmpxchg_relaxed(&user->locked_vm, &cur_pages,
+						 new_pages));
+
+	wqueue->nr_pages = nr_pages;
+	return 0;
+}
+
+static void watch_queue_unaccount_mem(struct watch_queue *wqueue)
+{
+	struct user_struct *user = wqueue->owner;
+
+	if (wqueue->nr_pages) {
+		atomic_long_sub(wqueue->nr_pages, &user->locked_vm);
+		wqueue->nr_pages = 0;
+	}
+}
+
+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;
+	unsigned int gran = WATCH_LENGTH_GRANULARITY;
+	unsigned int metalen = sizeof(buf->meta) / gran;
+	int i;
+
+	BUILD_BUG_ON(gran != sizeof(__u64));
+
+	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;
+
+	if (watch_queue_account_mem(wqueue, nr_pages) < 0)
+		goto err;
+
+	wqueue->pages = kcalloc(nr_pages, sizeof(struct page *), GFP_KERNEL);
+	if (!wqueue->pages)
+		goto err_unaccount;
+
+	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->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.
+	 */
+	buf->meta.watch.info	= metalen << WATCH_INFO_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		= metalen;
+	buf->meta.tail		= metalen;
+	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_unaccount:
+	watch_queue_unaccount_mem(wqueue);
+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->owner = get_uid(file->f_cred->user);
+
+	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);
+	struct watch_filter *wfilter;
+
+	wfilter = rcu_access_pointer(wqueue->filter);
+	if (wfilter)
+		kfree_rcu(wfilter, rcu);
+	free_uid(wqueue->owner);
+	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));
+	put_cred(watch->cred);
+}
+
+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) {
+		struct watch_queue *wq = rcu_access_pointer(w->queue);
+		if (wqueue == wq && watch->id == w->id)
+			return -EBUSY;
+	}
+
+	rcu_assign_pointer(watch->watch_list, wlist);
+	watch->cred = get_current_cred();
+
+	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);
+
+		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_queue *wqueue = file->private_data;
+	int i;
+
+	watch_queue_clear(wqueue);
+
+	if (wqueue->buffer)
+		vunmap(wqueue->buffer);
+
+	for (i = 0; i < wqueue->nr_pages; i++) {
+		ClearPageUptodate(wqueue->pages[i]);
+		wqueue->pages[i]->mapping = NULL;
+		__free_page(wqueue->pages[i]);
+	}
+
+	kfree(wqueue->pages);
+	watch_queue_unaccount_mem(wqueue);
+	put_watch_queue(wqueue);
+	return 0;
+}
+
+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,
+	.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/watch_queue.h b/include/linux/watch_queue.h
new file mode 100644
index 000000000000..aa9b251a469c
--- /dev/null
+++ b/include/linux/watch_queue.h
@@ -0,0 +1,94 @@
+// SPDX-License-Identifier: GPL-2.0
+/* User-mappable watch queue
+ *
+ * Copyright (C) 2019 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * 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>
+#include <linux/rcupdate.h>
+
+#ifdef CONFIG_WATCH_QUEUE
+
+struct watch_queue;
+struct cred;
+
+/*
+ * 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 */
+	const struct cred	*cred;		/* Creds of the owner of the watch */
+	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 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,
+				   void (*release_watch)(struct watch *))
+{
+	INIT_HLIST_HEAD(&wlist->watchers);
+	spin_lock_init(&wlist->lock);
+	wlist->release_watch = release_watch;
+}
+
+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);
+	}
+}
+
+/**
+ * watch_sizeof - Calculate the information part of the size of a watch record,
+ * given the structure size.
+ */
+#define watch_sizeof(STRUCT) \
+	((sizeof(STRUCT) / WATCH_LENGTH_GRANULARITY) << WATCH_INFO_LENGTH__SHIFT)
+
+#endif
+
+#endif /* _LINUX_WATCH_QUEUE_H */
diff --git a/include/uapi/linux/watch_queue.h b/include/uapi/linux/watch_queue.h
index 70f575099968..eabd7601ba0a 100644
--- a/include/uapi/linux/watch_queue.h
+++ b/include/uapi/linux/watch_queue.h
@@ -3,6 +3,10 @@
 #define _UAPI_LINUX_WATCH_QUEUE_H
 
 #include <linux/types.h>
+#include <linux/ioctl.h>
+
+#define IOC_WATCH_QUEUE_SET_SIZE	_IO('W', 0x60)	/* Set the size in pages */
+#define IOC_WATCH_QUEUE_SET_FILTER	_IO('W', 0x61)	/* Set the filter */
 
 enum watch_notification_type {
 	WATCH_TYPE_META		= 0,	/* Special record */
@@ -64,4 +68,21 @@ struct watch_queue_buffer {
  */
 #define WATCH_INFO_NOTIFICATIONS_LOST WATCH_INFO_FLAG_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 */

[PATCH 5/9] keys: Add a notification facility [ver #5]

[David Howells]

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     |   28 ++++++++++
 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               |   95 +++++++++++++++++++++++++++++++++-
 security/keys/keyring.c              |   17 ++++--
 security/keys/request_key.c          |    4 +
 12 files changed, 266 insertions(+), 25 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 eabd7601ba0a..bcffd599c07b 100644
--- a/include/uapi/linux/watch_queue.h
+++ b/include/uapi/linux/watch_queue.h
@@ -10,7 +10,8 @@
 
 enum watch_notification_type {
 	WATCH_TYPE_META		= 0,	/* Special record */
-	WATCH_TYPE___NR		= 1
+	WATCH_TYPE_KEY_NOTIFY	= 1,	/* Key change event notification */
+	WATCH_TYPE___NR		= 2
 };
 
 enum watch_meta_notification_subtype {
@@ -85,4 +86,29 @@ struct watch_notification_filter {
 };
 
 
+/*
+ * 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..caf8707da1f0 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	= watch_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..f3b71efd76c5 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 +1635,90 @@ 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;
+
+	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) {
+		ret = -ENOMEM;
+		if (!key->watchers) {
+			wlist = kzalloc(sizeof(*wlist), GFP_KERNEL);
+			if (!wlist)
+				goto err_wqueue;
+			init_watch_list(wlist, NULL);
+		}
+
+		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;
+
+		ret = security_watch_key(watch, key);
+		if (ret < 0)
+			goto err_watch;
+
+		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)
+			watch = NULL;
+	} 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_watch:
+	kfree(watch);
+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 +1859,9 @@ 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;

[PATCH 6/9] Add a general, global device notification watch list [ver #5]

[David Howells]

Create a general, global watch list that can be used for the posting of
device notification events, for such things as device attachment,
detachment and errors on sources such as block devices and USB devices.
This can be enabled with:

	CONFIG_DEVICE_NOTIFICATIONS

To add a watch on this list, an event queue must be created and configured:

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

and then a watch can be placed upon it using a system call:

        watch_devices(fd, 12, 0);

Unless the application wants to receive all events, it should employ
appropriate filters.

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

 Documentation/watch_queue.rst               |   22 ++++++-
 arch/alpha/kernel/syscalls/syscall.tbl      |    1 
 arch/arm/tools/syscall.tbl                  |    1 
 arch/ia64/kernel/syscalls/syscall.tbl       |    1 
 arch/m68k/kernel/syscalls/syscall.tbl       |    1 
 arch/microblaze/kernel/syscalls/syscall.tbl |    1 
 arch/mips/kernel/syscalls/syscall_n32.tbl   |    1 
 arch/mips/kernel/syscalls/syscall_n64.tbl   |    1 
 arch/mips/kernel/syscalls/syscall_o32.tbl   |    1 
 arch/parisc/kernel/syscalls/syscall.tbl     |    1 
 arch/powerpc/kernel/syscalls/syscall.tbl    |    1 
 arch/s390/kernel/syscalls/syscall.tbl       |    1 
 arch/sh/kernel/syscalls/syscall.tbl         |    1 
 arch/sparc/kernel/syscalls/syscall.tbl      |    1 
 arch/x86/entry/syscalls/syscall_32.tbl      |    1 
 arch/x86/entry/syscalls/syscall_64.tbl      |    1 
 arch/xtensa/kernel/syscalls/syscall.tbl     |    1 
 drivers/base/Kconfig                        |    9 +++
 drivers/base/Makefile                       |    1 
 drivers/base/watch.c                        |   90 +++++++++++++++++++++++++++
 include/linux/device.h                      |    7 ++
 include/linux/syscalls.h                    |    1 
 include/uapi/asm-generic/unistd.h           |    4 +
 kernel/sys_ni.c                             |    1 
 24 files changed, 149 insertions(+), 2 deletions(-)
 create mode 100644 drivers/base/watch.c

diff --git a/Documentation/watch_queue.rst b/Documentation/watch_queue.rst
index 6fb3aa3356d3..393905b904c8 100644
--- a/Documentation/watch_queue.rst
+++ b/Documentation/watch_queue.rst
@@ -276,6 +276,25 @@ The ``id`` is the ID of the source object (such as the serial number on a key).
 Only watches that have the same ID set in them will see this notification.
 
 
+Global Device Watch List
+========================
+
+There is a global watch list that hardware generated events, such as device
+connection, disconnection, failure and error can be posted upon.  It must be
+enabled using::
+
+	CONFIG_DEVICE_NOTIFICATIONS
+
+Watchpoints are set in userspace using the device_notify(2) system call.
+Within the kernel events are posted upon it using::
+
+	void post_device_notification(struct watch_notification *n, u64 id);
+
+where ``n`` is the formatted notification record to post.  ``id`` is an
+identifier that can be used to direct to specific watches, but it should be 0
+for general use on this queue.
+
+
 Watch Sources
 =============
 
@@ -291,7 +310,8 @@ Any particular buffer can be fed from multiple sources.  Sources include:
   * WATCH_TYPE_BLOCK_NOTIFY
 
     Notifications of this type indicate block layer events, such as I/O errors
-    or temporary link loss.  Watches of this type are set on a global queue.
+    or temporary link loss.  Watches of this type are set on the global device
+    watch list.
 
 
 Event Filtering
diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl
index 9e7704e44f6d..a3963f0434dc 100644
--- a/arch/alpha/kernel/syscalls/syscall.tbl
+++ b/arch/alpha/kernel/syscalls/syscall.tbl
@@ -473,3 +473,4 @@
 541	common	fsconfig			sys_fsconfig
 542	common	fsmount				sys_fsmount
 543	common	fspick				sys_fspick
+544	common	watch_devices			sys_watch_devices
diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl
index aaf479a9e92d..af255f13c99b 100644
--- a/arch/arm/tools/syscall.tbl
+++ b/arch/arm/tools/syscall.tbl
@@ -447,3 +447,4 @@
 431	common	fsconfig			sys_fsconfig
 432	common	fsmount				sys_fsmount
 433	common	fspick				sys_fspick
+434	common	watch_devices			sys_watch_devices
diff --git a/arch/ia64/kernel/syscalls/syscall.tbl b/arch/ia64/kernel/syscalls/syscall.tbl
index e01df3f2f80d..7bb8ae23df85 100644
--- a/arch/ia64/kernel/syscalls/syscall.tbl
+++ b/arch/ia64/kernel/syscalls/syscall.tbl
@@ -354,3 +354,4 @@
 431	common	fsconfig			sys_fsconfig
 432	common	fsmount				sys_fsmount
 433	common	fspick				sys_fspick
+434	common	watch_devices			sys_watch_devices
diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl
index 7e3d0734b2f3..631d760a3f9a 100644
--- a/arch/m68k/kernel/syscalls/syscall.tbl
+++ b/arch/m68k/kernel/syscalls/syscall.tbl
@@ -433,3 +433,4 @@
 431	common	fsconfig			sys_fsconfig
 432	common	fsmount				sys_fsmount
 433	common	fspick				sys_fspick
+434	common	watch_devices			sys_watch_devices
diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl
index 26339e417695..43442dab1720 100644
--- a/arch/microblaze/kernel/syscalls/syscall.tbl
+++ b/arch/microblaze/kernel/syscalls/syscall.tbl
@@ -439,3 +439,4 @@
 431	common	fsconfig			sys_fsconfig
 432	common	fsmount				sys_fsmount
 433	common	fspick				sys_fspick
+434	common	watch_devices			sys_watch_devices
diff --git a/arch/mips/kernel/syscalls/syscall_n32.tbl b/arch/mips/kernel/syscalls/syscall_n32.tbl
index 0e2dd68ade57..d3b79b12a781 100644
--- a/arch/mips/kernel/syscalls/syscall_n32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n32.tbl
@@ -372,3 +372,4 @@
 431	n32	fsconfig			sys_fsconfig
 432	n32	fsmount				sys_fsmount
 433	n32	fspick				sys_fspick
+434	n32	watch_devices			sys_watch_devices
diff --git a/arch/mips/kernel/syscalls/syscall_n64.tbl b/arch/mips/kernel/syscalls/syscall_n64.tbl
index 5eebfa0d155c..fd4886825ae9 100644
--- a/arch/mips/kernel/syscalls/syscall_n64.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n64.tbl
@@ -348,3 +348,4 @@
 431	n64	fsconfig			sys_fsconfig
 432	n64	fsmount				sys_fsmount
 433	n64	fspick				sys_fspick
+434	n64	watch_devices			sys_watch_devices
diff --git a/arch/mips/kernel/syscalls/syscall_o32.tbl b/arch/mips/kernel/syscalls/syscall_o32.tbl
index 3cc1374e02d0..9c47ba4a225c 100644
--- a/arch/mips/kernel/syscalls/syscall_o32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_o32.tbl
@@ -421,3 +421,4 @@
 431	o32	fsconfig			sys_fsconfig
 432	o32	fsmount				sys_fsmount
 433	o32	fspick				sys_fspick
+434	o32	watch_devices			sys_watch_devices
diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl
index c9e377d59232..3bf52203d272 100644
--- a/arch/parisc/kernel/syscalls/syscall.tbl
+++ b/arch/parisc/kernel/syscalls/syscall.tbl
@@ -430,3 +430,4 @@
 431	common	fsconfig			sys_fsconfig
 432	common	fsmount				sys_fsmount
 433	common	fspick				sys_fspick
+434	common	watch_devices			sys_watch_devices
diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl
index 103655d84b4b..2d2fc51a151f 100644
--- a/arch/powerpc/kernel/syscalls/syscall.tbl
+++ b/arch/powerpc/kernel/syscalls/syscall.tbl
@@ -515,3 +515,4 @@
 431	common	fsconfig			sys_fsconfig
 432	common	fsmount				sys_fsmount
 433	common	fspick				sys_fspick
+434	common	watch_devices			sys_watch_devices
diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl
index e822b2964a83..a7f13f3ff40c 100644
--- a/arch/s390/kernel/syscalls/syscall.tbl
+++ b/arch/s390/kernel/syscalls/syscall.tbl
@@ -436,3 +436,4 @@
 431  common	fsconfig		sys_fsconfig			sys_fsconfig
 432  common	fsmount			sys_fsmount			sys_fsmount
 433  common	fspick			sys_fspick			sys_fspick
+434	common	watch_devices		sys_watch_devices		sys_watch_devices
diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl
index 016a727d4357..54dd7f912148 100644
--- a/arch/sh/kernel/syscalls/syscall.tbl
+++ b/arch/sh/kernel/syscalls/syscall.tbl
@@ -436,3 +436,4 @@
 431	common	fsconfig			sys_fsconfig
 432	common	fsmount				sys_fsmount
 433	common	fspick				sys_fspick
+434	common	watch_devices			sys_watch_devices
diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl
index e047480b1605..519c96cc6fec 100644
--- a/arch/sparc/kernel/syscalls/syscall.tbl
+++ b/arch/sparc/kernel/syscalls/syscall.tbl
@@ -479,3 +479,4 @@
 431	common	fsconfig			sys_fsconfig
 432	common	fsmount				sys_fsmount
 433	common	fspick				sys_fspick
+434	common	watch_devices			sys_watch_devices
diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index ad968b7bac72..75f92c016e3e 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -438,3 +438,4 @@
 431	i386	fsconfig		sys_fsconfig			__ia32_sys_fsconfig
 432	i386	fsmount			sys_fsmount			__ia32_sys_fsmount
 433	i386	fspick			sys_fspick			__ia32_sys_fspick
+434	i386	watch_devices		sys_watch_devices		__ia32_sys_watch_devices
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index b4e6f9e6204a..76975ce78206 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -355,6 +355,7 @@
 431	common	fsconfig		__x64_sys_fsconfig
 432	common	fsmount			__x64_sys_fsmount
 433	common	fspick			__x64_sys_fspick
+434	common	watch_devices		__x64_sys_watch_devices
 
 #
 # x32-specific system call numbers start at 512 to avoid cache impact
diff --git a/arch/xtensa/kernel/syscalls/syscall.tbl b/arch/xtensa/kernel/syscalls/syscall.tbl
index 5fa0ee1c8e00..fe726bbeb6e4 100644
--- a/arch/xtensa/kernel/syscalls/syscall.tbl
+++ b/arch/xtensa/kernel/syscalls/syscall.tbl
@@ -404,3 +404,4 @@
 431	common	fsconfig			sys_fsconfig
 432	common	fsmount				sys_fsmount
 433	common	fspick				sys_fspick
+434	common	watch_devices			sys_watch_devices
diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
index dc404492381d..63db34efb23b 100644
--- a/drivers/base/Kconfig
+++ b/drivers/base/Kconfig
@@ -1,6 +1,15 @@
 # SPDX-License-Identifier: GPL-2.0
 menu "Generic Driver Options"
 
+config DEVICE_NOTIFICATIONS
+	bool "Provide device event notifications"
+	select WATCH_QUEUE
+	help
+	  This option provides support for getting hardware event notifications
+	  on devices, buses and interfaces.  This makes use of the
+	  /dev/watch_queue misc device to handle the notification buffer.
+	  device_notify(2) is used to set/remove watches.
+
 config UEVENT_HELPER
 	bool "Support for uevent helper"
 	help
diff --git a/drivers/base/Makefile b/drivers/base/Makefile
index 157452080f3d..4db2e8f1a1f4 100644
--- a/drivers/base/Makefile
+++ b/drivers/base/Makefile
@@ -7,6 +7,7 @@ obj-y			:= component.o core.o bus.o dd.o syscore.o \
 			   attribute_container.o transport_class.o \
 			   topology.o container.o property.o cacheinfo.o \
 			   devcon.o swnode.o
+obj-$(CONFIG_DEVICE_NOTIFICATIONS) += watch.o
 obj-$(CONFIG_DEVTMPFS)	+= devtmpfs.o
 obj-y			+= power/
 obj-$(CONFIG_ISA_BUS_API)	+= isa.o
diff --git a/drivers/base/watch.c b/drivers/base/watch.c
new file mode 100644
index 000000000000..00336607dc73
--- /dev/null
+++ b/drivers/base/watch.c
@@ -0,0 +1,90 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Event notifications.
+ *
+ * Copyright (C) 2019 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/watch_queue.h>
+#include <linux/syscalls.h>
+#include <linux/init_task.h>
+#include <linux/security.h>
+
+/*
+ * Global queue for watching for device layer events.
+ */
+static struct watch_list device_watchers = {
+	.watchers	= HLIST_HEAD_INIT,
+	.lock		= __SPIN_LOCK_UNLOCKED(&device_watchers.lock),
+};
+
+static DEFINE_SPINLOCK(device_watchers_lock);
+
+/**
+ * post_device_notification - Post notification of a device event
+ * @n - The notification to post
+ * @id - The device ID
+ *
+ * Note that there's only a global queue to which all events are posted.  Might
+ * want to provide per-dev queues also.
+ */
+void post_device_notification(struct watch_notification *n, u64 id)
+{
+	post_watch_notification(&device_watchers, n, &init_cred, id);
+}
+
+/**
+ * sys_watch_devices - Watch for device 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)
+ * @flags: Flags (reserved for future)
+ */
+SYSCALL_DEFINE3(watch_devices, int, watch_fd, int, watch_id, unsigned int, flags)
+{
+	struct watch_queue *wqueue;
+	struct watch_list *wlist = &device_watchers;
+	struct watch *watch;
+	long ret = -ENOMEM;
+	u64 id = 0; /* Might want to allow dev# here. */
+
+	if (watch_id < -1 || watch_id > 0xff || flags)
+		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;
+
+		ret = security_watch_devices(watch);
+		if (ret < 0)
+			goto err_watch;
+
+		spin_lock(&device_watchers_lock);
+		ret = add_watch_to_object(watch, wlist);
+		spin_unlock(&device_watchers_lock);
+		if (ret == 0)
+			watch = NULL;
+	} else {
+		spin_lock(&device_watchers_lock);
+		ret = remove_watch_from_object(wlist, wqueue, id, false);
+		spin_unlock(&device_watchers_lock);
+	}
+
+err_watch:
+	kfree(watch);
+err_wqueue:
+	put_watch_queue(wqueue);
+err:
+	return ret;
+}
diff --git a/include/linux/device.h b/include/linux/device.h
index e85264fb6616..c947c078b1be 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -26,6 +26,7 @@
 #include <linux/uidgid.h>
 #include <linux/gfp.h>
 #include <linux/overflow.h>
+#include <linux/watch_queue.h>
 #include <asm/device.h>
 
 struct device;
@@ -1396,6 +1397,12 @@ struct device_link *device_link_add(struct device *consumer,
 void device_link_del(struct device_link *link);
 void device_link_remove(void *consumer, struct device *supplier);
 
+#ifdef CONFIG_DEVICE_NOTIFICATIONS
+extern void post_device_notification(struct watch_notification *n, u64 id);
+#else
+static inline void post_device_notification(struct watch_notification *n, u64 id) {}
+#endif
+
 #ifndef dev_fmt
 #define dev_fmt(fmt) fmt
 #endif
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index e2870fe1be5b..abb5c8c3cd4b 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -997,6 +997,7 @@ asmlinkage long sys_fspick(int dfd, const char __user *path, unsigned int flags)
 asmlinkage long sys_pidfd_send_signal(int pidfd, int sig,
 				       siginfo_t __user *info,
 				       unsigned int flags);
+asmlinkage long sys_watch_devices(int watch_fd, int watch_id, unsigned int flags);
 
 /*
  * Architecture-specific system calls
diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
index a87904daf103..7477925e96ea 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -844,9 +844,11 @@ __SYSCALL(__NR_fsconfig, sys_fsconfig)
 __SYSCALL(__NR_fsmount, sys_fsmount)
 #define __NR_fspick 433
 __SYSCALL(__NR_fspick, sys_fspick)
+#define __NR_watch_devices 434
+__SYSCALL(__NR_watch_devices, sys_watch_devices)
 
 #undef __NR_syscalls
-#define __NR_syscalls 434
+#define __NR_syscalls 435
 
 /*
  * 32 bit systems traditionally used different
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 4d9ae5ea6caf..b2fe8b2c1107 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(watch_devices);
 
 /* fs/xattr.c */
 

[PATCH 7/9] block: Add block layer notifications [ver #5]

[David Howells]

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);
	watch_devices(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
	watch_devices(), 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>
---

 Documentation/watch_queue.rst    |    4 +++-
 block/Kconfig                    |    9 +++++++++
 block/blk-core.c                 |   29 +++++++++++++++++++++++++++++
 include/linux/blkdev.h           |   15 +++++++++++++++
 include/uapi/linux/watch_queue.h |   30 +++++++++++++++++++++++++++++-
 5 files changed, 85 insertions(+), 2 deletions(-)

diff --git a/Documentation/watch_queue.rst b/Documentation/watch_queue.rst
index 393905b904c8..5cc9c6924727 100644
--- a/Documentation/watch_queue.rst
+++ b/Documentation/watch_queue.rst
@@ -7,7 +7,9 @@ receive notifications from the kernel.  This can be used in conjunction with::
 
   * Key/keyring notifications
 
-  * General device event notifications
+  * General device event notifications, including::
+
+    * Block layer event notifications
 
 
 The notifications buffers can be enabled by:
diff --git a/block/Kconfig b/block/Kconfig
index 1b220101a9cb..4ff4a56ba9f9 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 DEVICE_NOTIFICATIONS
+	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 device_notify() system
+	  call to enable/disable watches.
+
 menu "Partition Types"
 
 source "block/partitions/Kconfig"
diff --git a/block/blk-core.c b/block/blk-core.c
index 419d600e6637..6b81a2b1af4b 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	= watch_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/include/linux/blkdev.h b/include/linux/blkdev.h
index 1aafeb923e7b..8b8e235f47c9 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 +1745,20 @@ static inline bool blk_req_can_dispatch_to_zone(struct request *rq)
 }
 #endif /* CONFIG_BLK_DEV_ZONED */
 
+#ifdef CONFIG_BLK_NOTIFICATIONS
+static inline void post_block_notification(struct block_notification *n)
+{
+	u64 id = 0; /* Might want to allow dev# here. */
+
+	post_device_notification(&n->watch, id);
+}
+#else
+static inline void post_block_notification(struct block_notification *n)
+{
+}
+#endif
+
+
 #else /* CONFIG_BLOCK */
 
 struct block_device;
diff --git a/include/uapi/linux/watch_queue.h b/include/uapi/linux/watch_queue.h
index bcffd599c07b..776666c3bde9 100644
--- a/include/uapi/linux/watch_queue.h
+++ b/include/uapi/linux/watch_queue.h
@@ -11,7 +11,8 @@
 enum watch_notification_type {
 	WATCH_TYPE_META		= 0,	/* Special record */
 	WATCH_TYPE_KEY_NOTIFY	= 1,	/* Key change event notification */
-	WATCH_TYPE___NR		= 2
+	WATCH_TYPE_BLOCK_NOTIFY	= 2,	/* Block layer event notification */
+	WATCH_TYPE___NR		= 3
 };
 
 enum watch_meta_notification_subtype {
@@ -111,4 +112,31 @@ struct key_notification {
 	__u32	aux;		/* Per-type auxiliary data */
 };
 
+/*
+ * 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 layer notification record.
+ * - watch.type = WATCH_TYPE_BLOCK_NOTIFY
+ * - watch.subtype = enum block_notification_type
+ */
+struct block_notification {
+	struct watch_notification watch; /* WATCH_TYPE_BLOCK_NOTIFY */
+	__u64	dev;			/* Device number */
+	__u64	sector;			/* Affected sector */
+};
+
 #endif /* _UAPI_LINUX_WATCH_QUEUE_H */

[PATCH 8/9] usb: Add USB subsystem notifications [ver #5]

[David Howells]

Add a USB subsystem notification mechanism whereby notifications about
hardware events such as device connection, disconnection, reset and 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 USB notifications via that
queue:

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

After that, records will be placed into the queue when events occur on a
USB device or bus.  Records are of the following format:

	struct usb_notification {
		struct watch_notification watch;
		__u32	error;
		__u32	reserved;
		__u8	name_len;
		__u8	name[0];
	} *n;

Where:

	n->watch.type will be WATCH_TYPE_USB_NOTIFY

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

	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
	device_notify(), shifted.

	n->error and n->reserved are intended to convey information such as
	error codes, but are currently not used

	n->name_len and n->name convey the USB device name as an
	unterminated string.  This may be truncated - it is currently
	limited to a maximum 63 chars.

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>
cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
cc: linux-usb@vger.kernel.org
---

 Documentation/watch_queue.rst    |    9 ++++++
 drivers/usb/core/Kconfig         |   10 +++++++
 drivers/usb/core/devio.c         |   56 ++++++++++++++++++++++++++++++++++++++
 drivers/usb/core/hub.c           |    3 ++
 include/linux/usb.h              |   19 +++++++++++++
 include/uapi/linux/watch_queue.h |   30 ++++++++++++++++++++
 6 files changed, 126 insertions(+), 1 deletion(-)

diff --git a/Documentation/watch_queue.rst b/Documentation/watch_queue.rst
index 5cc9c6924727..4087a8e670a8 100644
--- a/Documentation/watch_queue.rst
+++ b/Documentation/watch_queue.rst
@@ -11,6 +11,8 @@ receive notifications from the kernel.  This can be used in conjunction with::
 
     * Block layer event notifications
 
+    * USB subsystem event notifications
+
 
 The notifications buffers can be enabled by:
 
@@ -315,6 +317,13 @@ Any particular buffer can be fed from multiple sources.  Sources include:
     or temporary link loss.  Watches of this type are set on the global device
     watch list.
 
+  * WATCH_TYPE_USB_NOTIFY
+
+    Notifications of this type indicate USB subsystem events, such as
+    attachment, removal, reset and I/O errors.  Separate events are generated
+    for buses and devices.  Watchpoints of this type are set on the global
+    device watch list.
+
 
 Event Filtering
 ===============
diff --git a/drivers/usb/core/Kconfig b/drivers/usb/core/Kconfig
index bdb6bd0b63a6..4be88368ab6b 100644
--- a/drivers/usb/core/Kconfig
+++ b/drivers/usb/core/Kconfig
@@ -103,3 +103,13 @@ config USB_AUTOSUSPEND_DELAY
 	  The default value Linux has always had is 2 seconds.  Change
 	  this value if you want a different delay and cannot modify
 	  the command line or module parameter.
+
+config USB_NOTIFICATIONS
+	bool "Provide USB hardware event notifications"
+	depends on USB
+	select DEVICE_NOTIFICATIONS
+	help
+	  This option provides support for getting hardware event notifications
+	  on USB devices and interfaces.  This makes use of the
+	  /dev/watch_queue misc device to handle the notification buffer.
+	  device_notify(2) is used to set/remove watches.
diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
index fa783531ee88..2727c10f55f6 100644
--- a/drivers/usb/core/devio.c
+++ b/drivers/usb/core/devio.c
@@ -41,6 +41,7 @@
 #include <linux/dma-mapping.h>
 #include <asm/byteorder.h>
 #include <linux/moduleparam.h>
+#include <linux/watch_queue.h>
 
 #include "usb.h"
 
@@ -2633,13 +2634,68 @@ static void usbdev_remove(struct usb_device *udev)
 	}
 }
 
+#ifdef CONFIG_USB_NOTIFICATIONS
+static noinline void post_usb_notification(const char *devname,
+					   enum usb_notification_type subtype,
+					   u32 error)
+{
+	unsigned int gran = WATCH_LENGTH_GRANULARITY;
+	unsigned int name_len, n_len;
+	u64 id = 0; /* Might want to put a dev# here. */
+
+	struct {
+		struct usb_notification n;
+		char more_name[USB_NOTIFICATION_MAX_NAME_LEN -
+			       (sizeof(struct usb_notification) -
+				offsetof(struct usb_notification, name))];
+	} n;
+
+	name_len = strlen(devname);
+	name_len = min_t(size_t, name_len, USB_NOTIFICATION_MAX_NAME_LEN);
+	n_len = round_up(offsetof(struct usb_notification, name) + name_len,
+			 gran) / gran;
+
+	memset(&n, 0, sizeof(n));
+	memcpy(n.n.name, devname, n_len);
+
+	n.n.watch.type		= WATCH_TYPE_USB_NOTIFY;
+	n.n.watch.subtype	= subtype;
+	n.n.watch.info		= n_len;
+	n.n.error		= error;
+	n.n.name_len		= name_len;
+
+	post_device_notification(&n.n.watch, id);
+}
+
+void post_usb_device_notification(const struct usb_device *udev,
+				  enum usb_notification_type subtype, u32 error)
+{
+	post_usb_notification(dev_name(&udev->dev), subtype, error);
+}
+
+void post_usb_bus_notification(const struct usb_bus *ubus,
+			       enum usb_notification_type subtype, u32 error)
+{
+	post_usb_notification(ubus->bus_name, subtype, error);
+}
+#endif
+
 static int usbdev_notify(struct notifier_block *self,
 			       unsigned long action, void *dev)
 {
 	switch (action) {
 	case USB_DEVICE_ADD:
+		post_usb_device_notification(dev, NOTIFY_USB_DEVICE_ADD, 0);
 		break;
 	case USB_DEVICE_REMOVE:
+		post_usb_device_notification(dev, NOTIFY_USB_DEVICE_REMOVE, 0);
+		usbdev_remove(dev);
+		break;
+	case USB_BUS_ADD:
+		post_usb_bus_notification(dev, NOTIFY_USB_BUS_ADD, 0);
+		break;
+	case USB_BUS_REMOVE:
+		post_usb_bus_notification(dev, NOTIFY_USB_BUS_REMOVE, 0);
 		usbdev_remove(dev);
 		break;
 	}
diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 2f94568ba385..722013d8142c 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -4596,6 +4596,9 @@ hub_port_init(struct usb_hub *hub, struct usb_device *udev, int port1,
 				(udev->config) ? "reset" : "new", speed,
 				devnum, driver_name);
 
+	if (udev->config)
+		post_usb_device_notification(udev, NOTIFY_USB_DEVICE_RESET, 0);
+
 	/* Set up TT records, if needed  */
 	if (hdev->tt) {
 		udev->tt = hdev->tt;
diff --git a/include/linux/usb.h b/include/linux/usb.h
index ae82d9d1112b..12687b55811d 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -2008,6 +2008,25 @@ extern void usb_led_activity(enum usb_led_event ev);
 static inline void usb_led_activity(enum usb_led_event ev) {}
 #endif
 
+/*
+ * Notification functions.
+ */
+#ifdef CONFIG_USB_NOTIFICATIONS
+extern void post_usb_device_notification(const struct usb_device *udev,
+					 enum usb_notification_type subtype,
+					 u32 error);
+extern void post_usb_bus_notification(const struct usb_bus *ubus,
+				      enum usb_notification_type subtype,
+				      u32 error);
+#else
+static inline void post_usb_device_notification(const struct usb_device *udev,
+						enum usb_notification_type subtype,
+						u32 error) {}
+static inline void post_usb_bus_notification(const struct usb_bus *ubus,
+					     enum usb_notification_type subtype,
+					     u32 error) {}
+#endif
+
 #endif  /* __KERNEL__ */
 
 #endif
diff --git a/include/uapi/linux/watch_queue.h b/include/uapi/linux/watch_queue.h
index 776666c3bde9..7e695ac43104 100644
--- a/include/uapi/linux/watch_queue.h
+++ b/include/uapi/linux/watch_queue.h
@@ -12,7 +12,8 @@ enum watch_notification_type {
 	WATCH_TYPE_META		= 0,	/* Special record */
 	WATCH_TYPE_KEY_NOTIFY	= 1,	/* Key change event notification */
 	WATCH_TYPE_BLOCK_NOTIFY	= 2,	/* Block layer event notification */
-	WATCH_TYPE___NR		= 3
+	WATCH_TYPE_USB_NOTIFY	= 3,	/* USB subsystem event notification */
+	WATCH_TYPE___NR		= 4
 };
 
 enum watch_meta_notification_subtype {
@@ -139,4 +140,31 @@ struct block_notification {
 	__u64	sector;			/* Affected sector */
 };
 
+/*
+ * Type of USB layer notification.
+ */
+enum usb_notification_type {
+	NOTIFY_USB_DEVICE_ADD		= 0, /* USB device added */
+	NOTIFY_USB_DEVICE_REMOVE	= 1, /* USB device removed */
+	NOTIFY_USB_BUS_ADD		= 2, /* USB bus added */
+	NOTIFY_USB_BUS_REMOVE		= 3, /* USB bus removed */
+	NOTIFY_USB_DEVICE_RESET		= 4, /* USB device reset */
+	NOTIFY_USB_DEVICE_ERROR		= 5, /* USB device error */
+};
+
+/*
+ * USB subsystem notification record.
+ * - watch.type = WATCH_TYPE_USB_NOTIFY
+ * - watch.subtype = enum usb_notification_type
+ */
+struct usb_notification {
+	struct watch_notification watch; /* WATCH_TYPE_USB_NOTIFY */
+	__u32	error;
+	__u32	reserved;
+	__u8	name_len;		/* Length of device name */
+	__u8	name[0];		/* Device name (padded to __u64, truncated at 63 chars) */
+};
+
+#define USB_NOTIFICATION_MAX_NAME_LEN 63
+
 #endif /* _UAPI_LINUX_WATCH_QUEUE_H */

[PATCH 9/9] Add sample notification program [ver #5]

[David Howells]

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

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

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     |    8 +
 samples/watch_queue/watch_test.c |  233 ++++++++++++++++++++++++++++++++++++++
 4 files changed, 248 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..6ee61e3ca8d2
--- /dev/null
+++ b/samples/watch_queue/Makefile
@@ -0,0 +1,8 @@
+# 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
+HOSTLDLIBS_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..f792c13614f4
--- /dev/null
+++ b/samples/watch_queue/watch_test.c
@@ -0,0 +1,233 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Use /dev/watch_queue to watch for notifications.
+ *
+ * Copyright (C) 2019 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#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 KEYCTL_WATCH_KEY
+#define KEYCTL_WATCH_KEY -1
+#endif
+#ifndef __NR_watch_devices
+#define __NR_watch_devices -1
+#endif
+
+#define BUF_SIZE 4
+
+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 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) >> WATCH_INFO_LENGTH__SHIFT;
+
+	if (len != sizeof(struct key_notification) / WATCH_LENGTH_GRANULARITY)
+		return;
+
+	printf("KEY %08x change=%u[%s] aux=%u\n",
+	       k->key_id, n->subtype, key_subtypes[n->subtype], k->aux);
+}
+
+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) >> WATCH_INFO_LENGTH__SHIFT;
+
+	if (len < sizeof(struct block_notification) / WATCH_LENGTH_GRANULARITY)
+		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);
+}
+
+static const char *usb_subtypes[256] = {
+	[NOTIFY_USB_DEVICE_ADD]		= "dev-add",
+	[NOTIFY_USB_DEVICE_REMOVE]	= "dev-remove",
+	[NOTIFY_USB_BUS_ADD]		= "bus-add",
+	[NOTIFY_USB_BUS_REMOVE]		= "bus-remove",
+	[NOTIFY_USB_DEVICE_RESET]	= "dev-reset",
+	[NOTIFY_USB_DEVICE_ERROR]	= "dev-error",
+};
+
+static void saw_usb_event(struct watch_notification *n)
+{
+	struct usb_notification *u = (struct usb_notification *)n;
+	unsigned int len = (n->info & WATCH_INFO_LENGTH) >> WATCH_INFO_LENGTH__SHIFT;
+
+	if (len < sizeof(struct usb_notification) / WATCH_LENGTH_GRANULARITY)
+		return;
+
+	printf("USB %*.*s %s e=%x r=%x\n",
+	       u->name_len, u->name_len, u->name,
+	       usb_subtypes[n->subtype],
+	       u->error, u->reserved);
+}
+
+/*
+ * 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 = __atomic_load_n(&buf->meta.head, __ATOMIC_ACQUIRE),
+		       tail = buf->meta.tail,
+		       tail != head
+		       ) {
+			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) >>
+					       WATCH_INFO_ID__SHIFT);
+				break;
+			case WATCH_TYPE_KEY_NOTIFY:
+				saw_key_change(n);
+				break;
+			case WATCH_TYPE_BLOCK_NOTIFY:
+				saw_block_change(n);
+				break;
+			case WATCH_TYPE_USB_NOTIFY:
+				saw_usb_event(n);
+				break;
+			}
+
+			tail += (n->info & WATCH_INFO_LENGTH) >> WATCH_INFO_LENGTH__SHIFT;
+			__atomic_store_n(&buf->meta.tail, tail, __ATOMIC_RELEASE);
+		}
+	}
+
+out:
+	return 0;
+}
+
+static struct watch_notification_filter filter = {
+	.nr_filters	= 5,
+	.__reserved	= 0,
+	.filters = {
+		[0]	= {
+			.type			= WATCH_TYPE_KEY_NOTIFY,
+			.subtype_filter[0]	= UINT_MAX,
+		},
+		[1]	= {
+			.type			= WATCH_TYPE_BLOCK_NOTIFY,
+			.subtype_filter[0]	= UINT_MAX,
+		},
+		[2]	= {
+			.type			= WATCH_TYPE_USB_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_watch_devices, fd, 0x04, 0) == -1) {
+		perror("watch_devices");
+		exit(1);
+	}
+
+	return consumer(fd, buf);
+}

Re: [PATCH 8/9] usb: Add USB subsystem notifications [ver #5]

[Greg Kroah-Hartman]

On Fri, Jun 28, 2019 at 04:49:49PM +0100, David Howells wrote:
> Add a USB subsystem notification mechanism whereby notifications about
> hardware events such as device connection, disconnection, reset and 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 USB notifications via that
> queue:
> 
> 	struct watch_notification_filter filter = {
> 		.nr_filters = 1,
> 		.filters = {
> 			[0] = {
> 				.type = WATCH_TYPE_USB_NOTIFY,
> 				.subtype_filter[0] = UINT_MAX;
> 			},
> 		},
> 	};
> 	ioctl(fd, IOC_WATCH_QUEUE_SET_FILTER, &filter);
> 	notify_devices(fd, 12);
> 
> After that, records will be placed into the queue when events occur on a
> USB device or bus.  Records are of the following format:
> 
> 	struct usb_notification {
> 		struct watch_notification watch;
> 		__u32	error;
> 		__u32	reserved;
> 		__u8	name_len;
> 		__u8	name[0];
> 	} *n;
> 
> Where:
> 
> 	n->watch.type will be WATCH_TYPE_USB_NOTIFY
> 
> 	n->watch.subtype will be the type of notification, such as
> 	NOTIFY_USB_DEVICE_ADD.
> 
> 	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
> 	device_notify(), shifted.
> 
> 	n->error and n->reserved are intended to convey information such as
> 	error codes, but are currently not used
> 
> 	n->name_len and n->name convey the USB device name as an
> 	unterminated string.  This may be truncated - it is currently
> 	limited to a maximum 63 chars.
> 
> 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>
> cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> cc: linux-usb@vger.kernel.org

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Re: [PATCH 1/9] uapi: General notification ring definitions [ver #5]

[Greg Kroah-Hartman]

On Fri, Jun 28, 2019 at 04:48:34PM +0100, David Howells wrote:
> Add UAPI definitions for the general notification ring, including the
> following pieces:
> 
>  (1) struct watch_notification.
> 
>      This is the metadata header for each entry in the ring.  It includes a
>      type and subtype that indicate the source of the message
>      (eg. WATCH_TYPE_MOUNT_NOTIFY) and the kind of the message
>      (eg. NOTIFY_MOUNT_NEW_MOUNT).
> 
>      The header also contains an information field that conveys the
>      following information:
> 
> 	- WATCH_INFO_LENGTH.  The size of the entry (entries are variable
>           length).
> 
> 	- WATCH_INFO_ID.  The watch ID specified when the watchpoint was
>           set.
> 
> 	- WATCH_INFO_TYPE_INFO.  (Sub)type-specific information.
> 
> 	- WATCH_INFO_FLAG_*.  Flag bits overlain on the type-specific
>           information.  For use by the type.
> 
>      All the information in the header can be used in filtering messages at
>      the point of writing into the buffer.
> 
>  (2) struct watch_queue_buffer.
> 
>      This describes the layout of the ring.  Note that the first slots in
>      the ring contain a special metadata entry that contains the ring
>      pointers.  The producer in the kernel knows to skip this and it has a
>      proper header (WATCH_TYPE_META, WATCH_META_SKIP_NOTIFICATION) that
>      indicates the size so that the ring consumer can handle it the same as
>      any other record and just skip it.
> 
>      Note that this means that ring entries can never be split over the end
>      of the ring, so if an entry would need to be split, a skip record is
>      inserted to wrap the ring first; this is also WATCH_TYPE_META,
>      WATCH_META_SKIP_NOTIFICATION.
> 
>  (3) WATCH_INFO_NOTIFICATIONS_LOST.
> 
>      This is a flag that can be set in the metadata header by the kernel to
>      indicate that at least one message was lost since it was last cleared
>      by userspace.
> 
> Signed-off-by: David Howells <dhowells@redhat.com>

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Re: [PATCH 4/9] General notification queue with user mmap()'able ring buffer [ver #5]

[Greg Kroah-Hartman]

On Fri, Jun 28, 2019 at 04:49:10PM +0100, David Howells wrote:
> 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>

I don't know if I mentioned this before, but your naming seems a bit
"backwards" from other subsystems. Should "watch_queue" always be the
prefix, instead of a mix of prefix/suffix usage?

Anyway, your call, it's your code :)

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Re: [PATCH 6/9] Add a general, global device notification watch list [ver #5]

[Greg Kroah-Hartman]

On Fri, Jun 28, 2019 at 04:49:30PM +0100, David Howells wrote:
> Create a general, global watch list that can be used for the posting of
> device notification events, for such things as device attachment,
> detachment and errors on sources such as block devices and USB devices.
> This can be enabled with:
> 
> 	CONFIG_DEVICE_NOTIFICATIONS
> 
> To add a watch on this list, an event queue must be created and configured:
> 
>         fd = open("/dev/event_queue", O_RDWR);
>         ioctl(fd, IOC_WATCH_QUEUE_SET_SIZE, page_size << n);
> 
> and then a watch can be placed upon it using a system call:
> 
>         watch_devices(fd, 12, 0);
> 
> Unless the application wants to receive all events, it should employ
> appropriate filters.

What "filter"?  Who is going to use this and why a new system call for
this?  You can do this today with udev/netlink/hotplug/whatever so why
create yet-another-way?

I don't think this is a good idea unless we really nail down the api and
who is going to be using it.

thanks,

greg k-h

Re: [PATCH 6/9] Add a general, global device notification watch list [ver #5]

[Greg Kroah-Hartman]

On Fri, Jun 28, 2019 at 04:49:30PM +0100, David Howells wrote:
> Create a general, global watch list that can be used for the posting of
> device notification events, for such things as device attachment,
> detachment and errors on sources such as block devices and USB devices.
> This can be enabled with:
> 
> 	CONFIG_DEVICE_NOTIFICATIONS
> 
> To add a watch on this list, an event queue must be created and configured:
> 
>         fd = open("/dev/event_queue", O_RDWR);
>         ioctl(fd, IOC_WATCH_QUEUE_SET_SIZE, page_size << n);
> 
> and then a watch can be placed upon it using a system call:
> 
>         watch_devices(fd, 12, 0);
> 
> Unless the application wants to receive all events, it should employ
> appropriate filters.

Ok, as discussed off-list, this is needed by the other patches
afterward, i.e. the USB and block ones, which makes more sense.

Some tiny nits:

> diff --git a/drivers/base/watch.c b/drivers/base/watch.c
> new file mode 100644
> index 000000000000..00336607dc73
> --- /dev/null
> +++ b/drivers/base/watch.c
> @@ -0,0 +1,90 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Event notifications.
> + *
> + * Copyright (C) 2019 Red Hat, Inc. All Rights Reserved.
> + * Written by David Howells (dhowells@redhat.com)
> + */
> +
> +#include <linux/watch_queue.h>
> +#include <linux/syscalls.h>
> +#include <linux/init_task.h>
> +#include <linux/security.h>

You forgot to include device.h which has the prototype for your global
function :)

> +
> +/*
> + * Global queue for watching for device layer events.
> + */
> +static struct watch_list device_watchers = {
> +	.watchers	= HLIST_HEAD_INIT,
> +	.lock		= __SPIN_LOCK_UNLOCKED(&device_watchers.lock),
> +};
> +
> +static DEFINE_SPINLOCK(device_watchers_lock);
> +
> +/**
> + * post_device_notification - Post notification of a device event
> + * @n - The notification to post
> + * @id - The device ID
> + *
> + * Note that there's only a global queue to which all events are posted.  Might
> + * want to provide per-dev queues also.
> + */
> +void post_device_notification(struct watch_notification *n, u64 id)
> +{
> +	post_watch_notification(&device_watchers, n, &init_cred, id);
> +}

Don't you need to export this symbol?

> +
> +/**
> + * sys_watch_devices - Watch for device 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)
> + * @flags: Flags (reserved for future)
> + */
> +SYSCALL_DEFINE3(watch_devices, int, watch_fd, int, watch_id, unsigned int, flags)

Finally, the driver core gets a syscall!  :)

Don't we need a manpage and a kselftest for it?

> +{
> +	struct watch_queue *wqueue;
> +	struct watch_list *wlist = &device_watchers;

No real need for wlist, right?  You just set it to this value and then
it never changes?

> +	struct watch *watch;
> +	long ret = -ENOMEM;
> +	u64 id = 0; /* Might want to allow dev# here. */

I don't understand the comment here, what does "dev#" refer to?

> +
> +	if (watch_id < -1 || watch_id > 0xff || flags)
> +		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;
> +
> +		ret = security_watch_devices(watch);
> +		if (ret < 0)
> +			goto err_watch;
> +
> +		spin_lock(&device_watchers_lock);
> +		ret = add_watch_to_object(watch, wlist);
> +		spin_unlock(&device_watchers_lock);
> +		if (ret == 0)
> +			watch = NULL;
> +	} else {
> +		spin_lock(&device_watchers_lock);
> +		ret = remove_watch_from_object(wlist, wqueue, id, false);
> +		spin_unlock(&device_watchers_lock);
> +	}
> +
> +err_watch:
> +	kfree(watch);
> +err_wqueue:
> +	put_watch_queue(wqueue);
> +err:
> +	return ret;
> +}
> diff --git a/include/linux/device.h b/include/linux/device.h
> index e85264fb6616..c947c078b1be 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -26,6 +26,7 @@
>  #include <linux/uidgid.h>
>  #include <linux/gfp.h>
>  #include <linux/overflow.h>
> +#include <linux/watch_queue.h>

No need for this, just do:

struct watch_notification;

so that things build.

thanks,

greg k-h

Re: [PATCH 6/9] Add a general, global device notification watch list [ver #5]

[David Howells]

Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:

> Don't we need a manpage and a kselftest for it?

I've got part of a manpage, but it needs more work.

How do you do a kselftest for this when it does nothing unless hardware events
happen?

> > +	u64 id = 0; /* Might want to allow dev# here. */
> 
> I don't understand the comment here, what does "dev#" refer to?

This is really for mount subtree watches, so I'm removing it for now.

The reason it's there is because a mount object may have multiple watches, but
each watch is set on a dentry within that mount, and it doesn't have to be the
same dentry each time.  The queue is shared between all the dentries, and the
ID is used (a) to label them so that they can be manually removed, (b) to
match them to each dentry when the notification is being propagated rootwards
along the tree and (c) to avoid adding another field to struct dentry.

David

Re: [PATCH 6/9] Add a general, global device notification watch list [ver #5]

[Greg Kroah-Hartman]

On Thu, Jul 04, 2019 at 05:04:20PM +0100, David Howells wrote:
> Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:
> 
> > Don't we need a manpage and a kselftest for it?
> 
> I've got part of a manpage, but it needs more work.
> 
> How do you do a kselftest for this when it does nothing unless hardware events
> happen?

Hm, good point, but there should be some way to test this to verify it
works.  Maybe for the other types of events?

thanks,

greg k-h

Re: [PATCH 6/9] Add a general, global device notification watch list [ver #5]

[David Howells]

Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:

> Hm, good point, but there should be some way to test this to verify it
> works.  Maybe for the other types of events?

Keyrings is the simplest.  keyutils's testsuite will handle that.  I'm trying
to work out if I can simply make every macro in there that does a modification
perform a watch automatically to make sure the appropriate events happen.

David

Re: [PATCH 6/9] Add a general, global device notification watch list [ver #5]

[Greg Kroah-Hartman]

On Fri, Jul 05, 2019 at 09:04:17AM +0100, David Howells wrote:
> Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:
> 
> > Hm, good point, but there should be some way to test this to verify it
> > works.  Maybe for the other types of events?
> 
> Keyrings is the simplest.  keyutils's testsuite will handle that.  I'm trying
> to work out if I can simply make every macro in there that does a modification
> perform a watch automatically to make sure the appropriate events happen.

That should be good enough to test the basic functionality.  After this
gets merged I'll see if I can come up with a way to test the USB
stuff...

thanks,

greg k-h

Re: [PATCH 6/9] Add a general, global device notification watch list [ver #5]

[Alan Stern]

On Fri, 5 Jul 2019, Greg Kroah-Hartman wrote:

> On Fri, Jul 05, 2019 at 09:04:17AM +0100, David Howells wrote:
> > Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:
> > 
> > > Hm, good point, but there should be some way to test this to verify it
> > > works.  Maybe for the other types of events?
> > 
> > Keyrings is the simplest.  keyutils's testsuite will handle that.  I'm trying
> > to work out if I can simply make every macro in there that does a modification
> > perform a watch automatically to make sure the appropriate events happen.
> 
> That should be good enough to test the basic functionality.  After this
> gets merged I'll see if I can come up with a way to test the USB
> stuff...

You can create USB connect and disconnect events programmatically by
using dummy-hcd with gadget-zero.  Turning off the port's POWER feature
will cause a disconnect, and turning it back on will cause a connect.

Alan Stern

Re: [PATCH 2/9] security: Add hooks to rule on setting a watch [ver #5]

[Stephen Smalley]

On 6/28/19 11:48 AM, David Howells wrote:
> Add security hooks that will allow an LSM to rule on whether or not a watch
> may be set.  More than one hook is required as the watches watch different
> types of object.
> 
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: Casey Schaufler <casey@schaufler-ca.com>
> cc: Stephen Smalley <sds@tycho.nsa.gov>
> cc: linux-security-module@vger.kernel.org
> ---
> 
>   include/linux/lsm_hooks.h |   22 ++++++++++++++++++++++
>   include/linux/security.h  |   15 +++++++++++++++
>   security/security.c       |   13 +++++++++++++
>   3 files changed, 50 insertions(+)
> 
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index 47f58cfb6a19..f9d31f6445e4 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -1413,6 +1413,20 @@
>    *	@ctx is a pointer in which to place the allocated security context.
>    *	@ctxlen points to the place to put the length of @ctx.
>    *
> + * Security hooks for the general notification queue:
> + *
> + * @watch_key:
> + *	Check to see if a process is allowed to watch for event notifications
> + *	from a key or keyring.
> + *	@watch: The watch object
> + *	@key: The key to watch.
> + *
> + * @watch_devices:
> + *	Check to see if a process is allowed to watch for event notifications
> + *	from devices (as a global set).
> + *	@watch: The watch object

It is difficult to evaluate these without at least one implementation of 
each hook.  I am unclear as to how any security module would use the 
watch argument, since it has no security field/blob and does not appear 
to contain any information that would be relevant to deciding whether or 
not to permit the watch to be set.

> + *
> + *
>    * Security hooks for using the eBPF maps and programs functionalities through
>    * eBPF syscalls.
>    *
> @@ -1688,6 +1702,10 @@ 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 (*watch_key)(struct watch *watch, struct key *key);
> +	int (*watch_devices)(struct watch *watch);
> +#endif /* CONFIG_WATCH_QUEUE */
>   
>   #ifdef CONFIG_SECURITY_NETWORK
>   	int (*unix_stream_connect)(struct sock *sock, struct sock *other,
> @@ -1964,6 +1982,10 @@ 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 watch_key;
> +	struct hlist_head watch_devices;
> +#endif /* CONFIG_WATCH_QUEUE */
>   #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 659071c2e57c..540863678355 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -57,6 +57,7 @@ struct mm_struct;
>   struct fs_context;
>   struct fs_parameter;
>   enum fs_value_type;
> +struct watch;
>   
>   /* Default (no) options for the capable function */
>   #define CAP_OPT_NONE 0x0
> @@ -392,6 +393,10 @@ 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_watch_key(struct watch *watch, struct key *key);
> +int security_watch_devices(struct watch *watch);
> +#endif /* CONFIG_WATCH_QUEUE */
>   #else /* CONFIG_SECURITY */
>   
>   static inline int call_lsm_notifier(enum lsm_event event, void *data)
> @@ -1204,6 +1209,16 @@ static inline int security_inode_getsecctx(struct inode *inode, void **ctx, u32
>   {
>   	return -EOPNOTSUPP;
>   }
> +#ifdef CONFIG_WATCH_QUEUE
> +static inline int security_watch_key(struct watch *watch, struct key *key)
> +{
> +	return 0;
> +}
> +static inline int security_watch_devices(struct watch *watch)
> +{
> +	return 0;
> +}
> +#endif /* CONFIG_WATCH_QUEUE */
>   #endif	/* CONFIG_SECURITY */
>   
>   #ifdef CONFIG_SECURITY_NETWORK
> diff --git a/security/security.c b/security/security.c
> index 613a5c00e602..2c9919226ad1 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -1917,6 +1917,19 @@ int security_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen)
>   }
>   EXPORT_SYMBOL(security_inode_getsecctx);
>   
> +#ifdef CONFIG_WATCH_QUEUE
> +int security_watch_key(struct watch *watch, struct key *key)
> +{
> +	return call_int_hook(watch_key, 0, watch, key);
> +}
> +
> +int security_watch_devices(struct watch *watch)
> +{
> +	return call_int_hook(watch_devices, 0, watch);
> +}
> +
> +#endif /* CONFIG_WATCH_QUEUE */
> +
>   #ifdef CONFIG_SECURITY_NETWORK
>   
>   int security_unix_stream_connect(struct sock *sock, struct sock *other, struct sock *newsk)
> 

Re: [PATCH 3/9] security: Add a hook for the point of notification insertion [ver #5]

[Stephen Smalley]

On 6/28/19 11:49 AM, David Howells wrote:
> Add a security hook that allows an LSM to rule on whether a notification
> message is allowed to be inserted into a particular watch queue.
> 
> The hook is given the following information:
> 
>   (1) The credentials of the triggerer (which may be init_cred for a system
>       notification, eg. a hardware error).
> 
>   (2) The credentials of the whoever set the watch.
> 
>   (3) The notification message.

As with the other proposed hooks, it is difficult to evaluate this hook 
without at least one implementation of the hook.  Since Casey is the 
only one requesting this hook, a Smack implementation would be the 
natural choice; I do not intend to implement this hook for SELinux. 
However, by providing this hook, you are in effect taking a position wrt 
the earlier controversy over it, i.e. that application developers must 
deal with the possibility that notifications can be dropped if a 
security module does not permit the triggerer to post the notification 
to the watcher, without any indication to either the triggerer or the 
watcher.  This is a choice you are making by providing this hook.  The 
alternative is to require that permission to set a watch imply the 
ability to receive all notifications for the watched object.  Aside from 
friendliness to application developers, the latter also yields stable, 
sane policy and better performance.

> 
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: Casey Schaufler <casey@schaufler-ca.com>
> cc: Stephen Smalley <sds@tycho.nsa.gov>
> cc: linux-security-module@vger.kernel.org
> ---
> 
>   include/linux/lsm_hooks.h |   10 ++++++++++
>   include/linux/security.h  |   10 ++++++++++
>   security/security.c       |    6 ++++++
>   3 files changed, 26 insertions(+)
> 
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index f9d31f6445e4..fd4b2b14e7d0 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -1426,6 +1426,12 @@
>    *	from devices (as a global set).
>    *	@watch: The watch object
>    *
> + * @post_notification:
> + *	Check to see if a watch notification can be posted to a particular
> + *	queue.
> + *	@w_cred: The credentials of the whoever set the watch.
> + *	@cred: The event-triggerer's credentials
> + *	@n: The notification being posted
>    *
>    * Security hooks for using the eBPF maps and programs functionalities through
>    * eBPF syscalls.
> @@ -1705,6 +1711,9 @@ union security_list_options {
>   #ifdef CONFIG_WATCH_QUEUE
>   	int (*watch_key)(struct watch *watch, struct key *key);
>   	int (*watch_devices)(struct watch *watch);
> +	int (*post_notification)(const struct cred *w_cred,
> +				 const struct cred *cred,
> +				 struct watch_notification *n);
>   #endif /* CONFIG_WATCH_QUEUE */
>   
>   #ifdef CONFIG_SECURITY_NETWORK
> @@ -1985,6 +1994,7 @@ struct security_hook_heads {
>   #ifdef CONFIG_WATCH_QUEUE
>   	struct hlist_head watch_key;
>   	struct hlist_head watch_devices;
> +	struct hlist_head post_notification;
>   #endif /* CONFIG_WATCH_QUEUE */
>   #ifdef CONFIG_SECURITY_NETWORK
>   	struct hlist_head unix_stream_connect;
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 540863678355..5c074bf18bea 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 watch;
> +struct watch_notification;
>   
>   /* Default (no) options for the capable function */
>   #define CAP_OPT_NONE 0x0
> @@ -396,6 +397,9 @@ int security_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen);
>   #ifdef CONFIG_WATCH_QUEUE
>   int security_watch_key(struct watch *watch, struct key *key);
>   int security_watch_devices(struct watch *watch);
> +int security_post_notification(const struct cred *w_cred,
> +			       const struct cred *cred,
> +			       struct watch_notification *n);
>   #endif /* CONFIG_WATCH_QUEUE */
>   #else /* CONFIG_SECURITY */
>   
> @@ -1218,6 +1222,12 @@ static inline int security_watch_devices(struct watch *watch)
>   {
>   	return 0;
>   }
> +static inline int security_post_notification(const struct cred *w_cred,
> +					     const struct cred *cred,
> +					     struct watch_notification *n)
> +{
> +	return 0;
> +}
>   #endif /* CONFIG_WATCH_QUEUE */
>   #endif	/* CONFIG_SECURITY */
>   
> diff --git a/security/security.c b/security/security.c
> index 2c9919226ad1..459e87d55ac9 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -1928,6 +1928,12 @@ int security_watch_devices(struct watch *watch)
>   	return call_int_hook(watch_devices, 0, watch);
>   }
>   
> +int security_post_notification(const struct cred *w_cred,
> +			       const struct cred *cred,
> +			       struct watch_notification *n)
> +{
> +	return call_int_hook(post_notification, 0, w_cred, cred, n);
> +}
>   #endif /* CONFIG_WATCH_QUEUE */
>   
>   #ifdef CONFIG_SECURITY_NETWORK
>