[PATCH v4 0/7] vfs: make immutable files actually immutable

[PATCH v4 0/7] vfs: make immutable files actually immutable

[Darrick J. Wong]

Hi all,

The chattr(1) manpage has this to say about the immutable bit that
system administrators can set on files:

"A file with the 'i' attribute cannot be modified: it cannot be deleted
or renamed, no link can be created to this file, most of the file's
metadata can not be modified, and the file can not be opened in write
mode."

Given the clause about how the file 'cannot be modified', it is
surprising that programs holding writable file descriptors can continue
to write to and truncate files after the immutable flag has been set,
but they cannot call other things such as utimes, fallocate, unlink,
link, setxattr, or reflink.

Since the immutable flag is only settable by administrators, resolve
this inconsistent behavior in favor of the documented behavior -- once
the flag is set, the file cannot be modified, period.  We presume that
administrators must be trusted to know what they're doing, and that
cutting off programs with writable fds will probably break them.

Therefore, add immutability checks to the relevant VFS functions, then
refactor the SETFLAGS and FSSETXATTR implementations to use common
argument checking functions so that we can then force pagefaults on all
the file data when setting immutability.

Note that various distro manpages points out the inconsistent behavior
of the various Linux filesystems w.r.t. immutable.  This fixes all that.

I also discovered that userspace programs can write and create writable
memory mappings to active swap files.  This is extremely bad because
this allows anyone with write privileges to corrupt system memory.  The
final patch in this series closes off that hole, at least for swap
files.

If you're going to start using this mess, you probably ought to just
pull from my git trees, which are linked below.

This has been lightly tested with fstests.  Enjoy!
Comments and questions are, as always, welcome.

--D

kernel git tree:
https://git.kernel.org/cgit/linux/kernel/git/djwong/xfs-linux.git/log/?h=immutable-files

fstests git tree:
https://git.kernel.org/cgit/linux/kernel/git/djwong/xfstests-dev.git/log/?h=immutable-files

[PATCH 1/7] mm/fs: don't allow writes to immutable files

[Darrick J. Wong]

From: Darrick J. Wong <darrick.wong@oracle.com>

The chattr manpage has this to say about immutable files:

"A file with the 'i' attribute cannot be modified: it cannot be deleted
or renamed, no link can be created to this file, most of the file's
metadata can not be modified, and the file can not be opened in write
mode."

Once the flag is set, it is enforced for quite a few file operations,
such as fallocate, fpunch, fzero, rm, touch, open, etc.  However, we
don't check for immutability when doing a write(), a PROT_WRITE mmap(),
a truncate(), or a write to a previously established mmap.

If a program has an open write fd to a file that the administrator
subsequently marks immutable, the program still can change the file
contents.  Weird!

The ability to write to an immutable file does not follow the manpage
promise that immutable files cannot be modified.  Worse yet it's
inconsistent with the behavior of other syscalls which don't allow
modifications of immutable files.

Therefore, add the necessary checks to make the write, mmap, and
truncate behavior consistent with what the manpage says and consistent
with other syscalls on filesystems which support IMMUTABLE.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
 fs/attr.c    |   13 ++++++-------
 mm/filemap.c |    3 +++
 mm/memory.c  |    3 +++
 mm/mmap.c    |    8 ++++++--
 4 files changed, 18 insertions(+), 9 deletions(-)


diff --git a/fs/attr.c b/fs/attr.c
index d22e8187477f..1fcfdcc5b367 100644
--- a/fs/attr.c
+++ b/fs/attr.c
@@ -233,19 +233,18 @@ int notify_change(struct dentry * dentry, struct iattr * attr, struct inode **de
 
 	WARN_ON_ONCE(!inode_is_locked(inode));
 
-	if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) {
-		if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
-			return -EPERM;
-	}
+	if (IS_IMMUTABLE(inode))
+		return -EPERM;
+
+	if ((ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) &&
+	    IS_APPEND(inode))
+		return -EPERM;
 
 	/*
 	 * If utimes(2) and friends are called with times == NULL (or both
 	 * times are UTIME_NOW), then we need to check for write permission
 	 */
 	if (ia_valid & ATTR_TOUCH) {
-		if (IS_IMMUTABLE(inode))
-			return -EPERM;
-
 		if (!inode_owner_or_capable(inode)) {
 			error = inode_permission(inode, MAY_WRITE);
 			if (error)
diff --git a/mm/filemap.c b/mm/filemap.c
index aac71aef4c61..dad85e10f5f8 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2935,6 +2935,9 @@ inline ssize_t generic_write_checks(struct kiocb *iocb, struct iov_iter *from)
 	loff_t count;
 	int ret;
 
+	if (IS_IMMUTABLE(inode))
+		return -EPERM;
+
 	if (!iov_iter_count(from))
 		return 0;
 
diff --git a/mm/memory.c b/mm/memory.c
index ddf20bd0c317..4311cfdade90 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2235,6 +2235,9 @@ static vm_fault_t do_page_mkwrite(struct vm_fault *vmf)
 
 	vmf->flags = FAULT_FLAG_WRITE|FAULT_FLAG_MKWRITE;
 
+	if (vmf->vma->vm_file && IS_IMMUTABLE(file_inode(vmf->vma->vm_file)))
+		return VM_FAULT_SIGBUS;
+
 	ret = vmf->vma->vm_ops->page_mkwrite(vmf);
 	/* Restore original flags so that caller is not surprised */
 	vmf->flags = old_flags;
diff --git a/mm/mmap.c b/mm/mmap.c
index 7e8c3e8ae75f..ac1e32205237 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1483,8 +1483,12 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
 		case MAP_SHARED_VALIDATE:
 			if (flags & ~flags_mask)
 				return -EOPNOTSUPP;
-			if ((prot&PROT_WRITE) && !(file->f_mode&FMODE_WRITE))
-				return -EACCES;
+			if (prot & PROT_WRITE) {
+				if (!(file->f_mode & FMODE_WRITE))
+					return -EACCES;
+				if (IS_IMMUTABLE(file_inode(file)))
+					return -EPERM;
+			}
 
 			/*
 			 * Make sure we don't allow writing to an append-only

Re: [PATCH 1/7] mm/fs: don't allow writes to immutable files

[Jan Kara]

On Fri 21-06-19 16:56:58, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> The chattr manpage has this to say about immutable files:
> 
> "A file with the 'i' attribute cannot be modified: it cannot be deleted
> or renamed, no link can be created to this file, most of the file's
> metadata can not be modified, and the file can not be opened in write
> mode."
> 
> Once the flag is set, it is enforced for quite a few file operations,
> such as fallocate, fpunch, fzero, rm, touch, open, etc.  However, we
> don't check for immutability when doing a write(), a PROT_WRITE mmap(),
> a truncate(), or a write to a previously established mmap.
> 
> If a program has an open write fd to a file that the administrator
> subsequently marks immutable, the program still can change the file
> contents.  Weird!
> 
> The ability to write to an immutable file does not follow the manpage
> promise that immutable files cannot be modified.  Worse yet it's
> inconsistent with the behavior of other syscalls which don't allow
> modifications of immutable files.
> 
> Therefore, add the necessary checks to make the write, mmap, and
> truncate behavior consistent with what the manpage says and consistent
> with other syscalls on filesystems which support IMMUTABLE.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

Looks good to me. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> ---
>  fs/attr.c    |   13 ++++++-------
>  mm/filemap.c |    3 +++
>  mm/memory.c  |    3 +++
>  mm/mmap.c    |    8 ++++++--
>  4 files changed, 18 insertions(+), 9 deletions(-)
> 
> 
> diff --git a/fs/attr.c b/fs/attr.c
> index d22e8187477f..1fcfdcc5b367 100644
> --- a/fs/attr.c
> +++ b/fs/attr.c
> @@ -233,19 +233,18 @@ int notify_change(struct dentry * dentry, struct iattr * attr, struct inode **de
>  
>  	WARN_ON_ONCE(!inode_is_locked(inode));
>  
> -	if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) {
> -		if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
> -			return -EPERM;
> -	}
> +	if (IS_IMMUTABLE(inode))
> +		return -EPERM;
> +
> +	if ((ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) &&
> +	    IS_APPEND(inode))
> +		return -EPERM;
>  
>  	/*
>  	 * If utimes(2) and friends are called with times == NULL (or both
>  	 * times are UTIME_NOW), then we need to check for write permission
>  	 */
>  	if (ia_valid & ATTR_TOUCH) {
> -		if (IS_IMMUTABLE(inode))
> -			return -EPERM;
> -
>  		if (!inode_owner_or_capable(inode)) {
>  			error = inode_permission(inode, MAY_WRITE);
>  			if (error)
> diff --git a/mm/filemap.c b/mm/filemap.c
> index aac71aef4c61..dad85e10f5f8 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2935,6 +2935,9 @@ inline ssize_t generic_write_checks(struct kiocb *iocb, struct iov_iter *from)
>  	loff_t count;
>  	int ret;
>  
> +	if (IS_IMMUTABLE(inode))
> +		return -EPERM;
> +
>  	if (!iov_iter_count(from))
>  		return 0;
>  
> diff --git a/mm/memory.c b/mm/memory.c
> index ddf20bd0c317..4311cfdade90 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2235,6 +2235,9 @@ static vm_fault_t do_page_mkwrite(struct vm_fault *vmf)
>  
>  	vmf->flags = FAULT_FLAG_WRITE|FAULT_FLAG_MKWRITE;
>  
> +	if (vmf->vma->vm_file && IS_IMMUTABLE(file_inode(vmf->vma->vm_file)))
> +		return VM_FAULT_SIGBUS;
> +
>  	ret = vmf->vma->vm_ops->page_mkwrite(vmf);
>  	/* Restore original flags so that caller is not surprised */
>  	vmf->flags = old_flags;
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 7e8c3e8ae75f..ac1e32205237 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1483,8 +1483,12 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
>  		case MAP_SHARED_VALIDATE:
>  			if (flags & ~flags_mask)
>  				return -EOPNOTSUPP;
> -			if ((prot&PROT_WRITE) && !(file->f_mode&FMODE_WRITE))
> -				return -EACCES;
> +			if (prot & PROT_WRITE) {
> +				if (!(file->f_mode & FMODE_WRITE))
> +					return -EACCES;
> +				if (IS_IMMUTABLE(file_inode(file)))
> +					return -EPERM;
> +			}
>  
>  			/*
>  			 * Make sure we don't allow writing to an append-only
> 
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

[PATCH 2/7] vfs: flush and wait for io when setting the immutable flag via SETFLAGS

[Darrick J. Wong]

From: Darrick J. Wong <darrick.wong@oracle.com>

When we're using FS_IOC_SETFLAGS to set the immutable flag on a file, we
need to ensure that userspace can't continue to write the file after the
file becomes immutable.  To make that happen, we have to flush all the
dirty pagecache pages to disk to ensure that we can fail a page fault on
a mmap'd region, wait for pending directio to complete, and hope the
caller locked out any new writes by holding the inode lock.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
 fs/btrfs/ioctl.c       |    3 +++
 fs/efivarfs/file.c     |    5 +++++
 fs/ext2/ioctl.c        |    5 +++++
 fs/ext4/ioctl.c        |    3 +++
 fs/f2fs/file.c         |    3 +++
 fs/hfsplus/ioctl.c     |    3 +++
 fs/nilfs2/ioctl.c      |    3 +++
 fs/ocfs2/ioctl.c       |    3 +++
 fs/orangefs/file.c     |   11 ++++++++---
 fs/orangefs/protocol.h |    3 +++
 fs/reiserfs/ioctl.c    |    3 +++
 fs/ubifs/ioctl.c       |    3 +++
 include/linux/fs.h     |   48 ++++++++++++++++++++++++++++++++++++++++++++++++
 13 files changed, 93 insertions(+), 3 deletions(-)


diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 7ddda5b4b6a6..f431813b2454 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -214,6 +214,9 @@ static int btrfs_ioctl_setflags(struct file *file, void __user *arg)
 	fsflags = btrfs_mask_fsflags_for_type(inode, fsflags);
 	old_fsflags = btrfs_inode_flags_to_fsflags(binode->flags);
 	ret = vfs_ioc_setflags_check(inode, old_fsflags, fsflags);
+	if (ret)
+		goto out_unlock;
+	ret = vfs_ioc_setflags_flush_data(inode, fsflags);
 	if (ret)
 		goto out_unlock;
 
diff --git a/fs/efivarfs/file.c b/fs/efivarfs/file.c
index f4f6c1bec132..845016a67724 100644
--- a/fs/efivarfs/file.c
+++ b/fs/efivarfs/file.c
@@ -163,6 +163,11 @@ efivarfs_ioc_setxflags(struct file *file, void __user *arg)
 		return error;
 
 	inode_lock(inode);
+	error = vfs_ioc_setflags_flush_data(inode, flags);
+	if (error) {
+		inode_unlock(inode);
+		return error;
+	}
 	inode_set_flags(inode, i_flags, S_IMMUTABLE);
 	inode_unlock(inode);
 
diff --git a/fs/ext2/ioctl.c b/fs/ext2/ioctl.c
index 88b3b9720023..75f75619237c 100644
--- a/fs/ext2/ioctl.c
+++ b/fs/ext2/ioctl.c
@@ -65,6 +65,11 @@ long ext2_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 			inode_unlock(inode);
 			goto setflags_out;
 		}
+		ret = vfs_ioc_setflags_flush_data(inode, flags);
+		if (ret) {
+			inode_unlock(inode);
+			goto setflags_out;
+		}
 
 		flags = flags & EXT2_FL_USER_MODIFIABLE;
 		flags |= oldflags & ~EXT2_FL_USER_MODIFIABLE;
diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index 6aa1df1918f7..a05341b94d98 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -290,6 +290,9 @@ static int ext4_ioctl_setflags(struct inode *inode,
 	jflag = flags & EXT4_JOURNAL_DATA_FL;
 
 	err = vfs_ioc_setflags_check(inode, oldflags, flags);
+	if (err)
+		goto flags_out;
+	err = vfs_ioc_setflags_flush_data(inode, flags);
 	if (err)
 		goto flags_out;
 
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 183ed1ac60e1..d3cf4bdb8738 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -1681,6 +1681,9 @@ static int __f2fs_ioc_setflags(struct inode *inode, unsigned int flags)
 	oldflags = fi->i_flags;
 
 	err = vfs_ioc_setflags_check(inode, oldflags, flags);
+	if (err)
+		return err;
+	err = vfs_ioc_setflags_flush_data(inode, flags);
 	if (err)
 		return err;
 
diff --git a/fs/hfsplus/ioctl.c b/fs/hfsplus/ioctl.c
index 862a3c9481d7..f8295fa35237 100644
--- a/fs/hfsplus/ioctl.c
+++ b/fs/hfsplus/ioctl.c
@@ -104,6 +104,9 @@ static int hfsplus_ioctl_setflags(struct file *file, int __user *user_flags)
 	inode_lock(inode);
 
 	err = vfs_ioc_setflags_check(inode, oldflags, flags);
+	if (err)
+		goto out_unlock_inode;
+	err = vfs_ioc_setflags_flush_data(inode, flags);
 	if (err)
 		goto out_unlock_inode;
 
diff --git a/fs/nilfs2/ioctl.c b/fs/nilfs2/ioctl.c
index 0632336d2515..a3c200ab9f60 100644
--- a/fs/nilfs2/ioctl.c
+++ b/fs/nilfs2/ioctl.c
@@ -149,6 +149,9 @@ static int nilfs_ioctl_setflags(struct inode *inode, struct file *filp,
 	oldflags = NILFS_I(inode)->i_flags;
 
 	ret = vfs_ioc_setflags_check(inode, oldflags, flags);
+	if (ret)
+		goto out;
+	ret = vfs_ioc_setflags_flush_data(inode, flags);
 	if (ret)
 		goto out;
 
diff --git a/fs/ocfs2/ioctl.c b/fs/ocfs2/ioctl.c
index 467a2faf0305..e91ca0dad3d7 100644
--- a/fs/ocfs2/ioctl.c
+++ b/fs/ocfs2/ioctl.c
@@ -107,6 +107,9 @@ static int ocfs2_set_inode_attr(struct inode *inode, unsigned flags,
 	flags |= oldflags & ~mask;
 
 	status = vfs_ioc_setflags_check(inode, oldflags, flags);
+	if (status)
+		goto bail_unlock;
+	status = vfs_ioc_setflags_flush_data(inode, flags);
 	if (status)
 		goto bail_unlock;
 
diff --git a/fs/orangefs/file.c b/fs/orangefs/file.c
index a35c17017210..fec5dfbc3dac 100644
--- a/fs/orangefs/file.c
+++ b/fs/orangefs/file.c
@@ -389,6 +389,8 @@ static long orangefs_ioctl(struct file *file, unsigned int cmd, unsigned long ar
 			     (unsigned long long)uval);
 		return put_user(uval, (int __user *)arg);
 	} else if (cmd == FS_IOC_SETFLAGS) {
+		struct inode *inode = file_inode(file);
+
 		ret = 0;
 		if (get_user(uval, (int __user *)arg))
 			return -EFAULT;
@@ -399,11 +401,14 @@ static long orangefs_ioctl(struct file *file, unsigned int cmd, unsigned long ar
 		 * the flags and then updates the flags with some new
 		 * settings. So, we ignore it in the following edit. bligon.
 		 */
-		if ((uval & ~ORANGEFS_MIRROR_FL) &
-		    (~(FS_IMMUTABLE_FL | FS_APPEND_FL | FS_NOATIME_FL))) {
+		if ((uval & ~ORANGEFS_MIRROR_FL) & ~ORANGEFS_VFS_FL) {
 			gossip_err("orangefs_ioctl: the FS_IOC_SETFLAGS only supports setting one of FS_IMMUTABLE_FL|FS_APPEND_FL|FS_NOATIME_FL\n");
 			return -EINVAL;
 		}
+		ret = vfs_ioc_setflags_flush_data(inode,
+						  uval & ORANGEFS_VFS_FL);
+		if (ret)
+			goto out;
 		val = uval;
 		gossip_debug(GOSSIP_FILE_DEBUG,
 			     "orangefs_ioctl: FS_IOC_SETFLAGS: %llu\n",
@@ -412,7 +417,7 @@ static long orangefs_ioctl(struct file *file, unsigned int cmd, unsigned long ar
 					      "user.pvfs2.meta_hint",
 					      &val, sizeof(val), 0);
 	}
-
+out:
 	return ret;
 }
 
diff --git a/fs/orangefs/protocol.h b/fs/orangefs/protocol.h
index d403cf29a99b..3dbe1c4534ce 100644
--- a/fs/orangefs/protocol.h
+++ b/fs/orangefs/protocol.h
@@ -129,6 +129,9 @@ static inline void ORANGEFS_khandle_from(struct orangefs_khandle *kh,
 #define ORANGEFS_IMMUTABLE_FL FS_IMMUTABLE_FL
 #define ORANGEFS_APPEND_FL    FS_APPEND_FL
 #define ORANGEFS_NOATIME_FL   FS_NOATIME_FL
+#define ORANGEFS_VFS_FL				(FS_IMMUTABLE_FL | \
+						 FS_APPEND_FL | \
+						 FS_NOATIME_FL)
 #define ORANGEFS_MIRROR_FL    0x01000000ULL
 #define ORANGEFS_FS_ID_NULL       ((__s32)0)
 #define ORANGEFS_ATTR_SYS_UID                   (1 << 0)
diff --git a/fs/reiserfs/ioctl.c b/fs/reiserfs/ioctl.c
index 92bcb1ecd994..50494f54392c 100644
--- a/fs/reiserfs/ioctl.c
+++ b/fs/reiserfs/ioctl.c
@@ -77,6 +77,9 @@ long reiserfs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 			err = vfs_ioc_setflags_check(inode,
 						     REISERFS_I(inode)->i_attrs,
 						     flags);
+			if (err)
+				goto setflags_out;
+			err = vfs_ioc_setflags_flush_data(inode, flags);
 			if (err)
 				goto setflags_out;
 			if ((flags & REISERFS_NOTAIL_FL) &&
diff --git a/fs/ubifs/ioctl.c b/fs/ubifs/ioctl.c
index bdea836fc38b..ff4a43314599 100644
--- a/fs/ubifs/ioctl.c
+++ b/fs/ubifs/ioctl.c
@@ -110,6 +110,9 @@ static int setflags(struct inode *inode, int flags)
 	mutex_lock(&ui->ui_mutex);
 	oldflags = ubifs2ioctl(ui->flags);
 	err = vfs_ioc_setflags_check(inode, oldflags, flags);
+	if (err)
+		goto out_unlock;
+	err = vfs_ioc_setflags_flush_data(inode, flags);
 	if (err)
 		goto out_unlock;
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 0c3ef24afe22..ed9a74cf5ef3 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3557,7 +3557,55 @@ static inline struct sock *io_uring_get_socket(struct file *file)
 
 int vfs_ioc_setflags_check(struct inode *inode, int oldflags, int flags);
 
+/*
+ * Do we need to flush the file data before changing attributes?  When we're
+ * setting the immutable flag we must stop all directio writes and flush the
+ * dirty pages so that we can fail the page fault on the next write attempt.
+ */
+static inline bool vfs_ioc_setflags_need_flush(struct inode *inode, int flags)
+{
+	if (S_ISREG(inode->i_mode) && !IS_IMMUTABLE(inode) &&
+	    (flags & FS_IMMUTABLE_FL))
+		return true;
+
+	return false;
+}
+
+/*
+ * Flush file data before changing attributes.  Caller must hold any locks
+ * required to prevent further writes to this file until we're done setting
+ * flags.
+ */
+static inline int inode_flush_data(struct inode *inode)
+{
+	inode_dio_wait(inode);
+	return filemap_write_and_wait(inode->i_mapping);
+}
+
+/*
+ * Flush all pending IO and dirty mappings before setting S_IMMUTABLE on an
+ * inode via FS_IOC_SETFLAGS.  If the flush fails we'll clear the flag before
+ * returning error.
+ *
+ * Note: the caller should be holding i_mutex, or else be sure that
+ * they have exclusive access to the inode structure.
+ */
+static inline int vfs_ioc_setflags_flush_data(struct inode *inode, int flags)
+{
+	int ret;
+
+	if (!vfs_ioc_setflags_need_flush(inode, flags))
+		return 0;
+
+	inode_set_flags(inode, S_IMMUTABLE, S_IMMUTABLE);
+	ret = inode_flush_data(inode);
+	if (ret)
+		inode_set_flags(inode, 0, S_IMMUTABLE);
+	return ret;
+}
+
 int vfs_ioc_fssetxattr_check(struct inode *inode, const struct fsxattr *old_fa,
 			     struct fsxattr *fa);
 
+
 #endif /* _LINUX_FS_H */

Re: [PATCH 2/7] vfs: flush and wait for io when setting the immutable flag via SETFLAGS

[Jan Kara]

On Fri 21-06-19 16:57:07, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> When we're using FS_IOC_SETFLAGS to set the immutable flag on a file, we
> need to ensure that userspace can't continue to write the file after the
> file becomes immutable.  To make that happen, we have to flush all the
> dirty pagecache pages to disk to ensure that we can fail a page fault on
> a mmap'd region, wait for pending directio to complete, and hope the
> caller locked out any new writes by holding the inode lock.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

Seeing the way this worked out, is there a reason to have separate
vfs_ioc_setflags_flush_data() instead of folding the functionality in
vfs_ioc_setflags_check() (possibly renaming it to
vfs_ioc_setflags_prepare() to indicate it does already some changes)? I
don't see any place that would need these two separated...

> +/*
> + * Flush all pending IO and dirty mappings before setting S_IMMUTABLE on an
> + * inode via FS_IOC_SETFLAGS.  If the flush fails we'll clear the flag before
> + * returning error.
> + *
> + * Note: the caller should be holding i_mutex, or else be sure that
> + * they have exclusive access to the inode structure.
> + */
> +static inline int vfs_ioc_setflags_flush_data(struct inode *inode, int flags)
> +{
> +	int ret;
> +
> +	if (!vfs_ioc_setflags_need_flush(inode, flags))
> +		return 0;
> +
> +	inode_set_flags(inode, S_IMMUTABLE, S_IMMUTABLE);
> +	ret = inode_flush_data(inode);
> +	if (ret)
> +		inode_set_flags(inode, 0, S_IMMUTABLE);
> +	return ret;
> +}

Also this sets S_IMMUTABLE whenever vfs_ioc_setflags_need_flush() returns
true. That is currently the right thing but seems like a landmine waiting
to trip? So I'd just drop the vfs_ioc_setflags_need_flush() abstraction to
make it clear what's going on.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH 2/7] vfs: flush and wait for io when setting the immutable flag via SETFLAGS

[Darrick J. Wong]

On Mon, Jun 24, 2019 at 01:37:37PM +0200, Jan Kara wrote:
> On Fri 21-06-19 16:57:07, Darrick J. Wong wrote:
> > From: Darrick J. Wong <darrick.wong@oracle.com>
> > 
> > When we're using FS_IOC_SETFLAGS to set the immutable flag on a file, we
> > need to ensure that userspace can't continue to write the file after the
> > file becomes immutable.  To make that happen, we have to flush all the
> > dirty pagecache pages to disk to ensure that we can fail a page fault on
> > a mmap'd region, wait for pending directio to complete, and hope the
> > caller locked out any new writes by holding the inode lock.
> > 
> > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> 
> Seeing the way this worked out, is there a reason to have separate
> vfs_ioc_setflags_flush_data() instead of folding the functionality in
> vfs_ioc_setflags_check() (possibly renaming it to
> vfs_ioc_setflags_prepare() to indicate it does already some changes)? I
> don't see any place that would need these two separated...

XFS needs them to be separated.

If we even /think/ that we're going to be setting the immutable flag
then we need to grab the IOLOCK and the MMAPLOCK to prevent further
writes while we drain all the directio writes and dirty data.  IO
completions for the write draining can take the ILOCK, which means that
we can't have grabbed it yet.

Next, we grab the ILOCK so we can check the new flags against the inode
and then update the inode core.

For most filesystems I think it suffices to inode_lock and then do both,
though.

> > +/*
> > + * Flush all pending IO and dirty mappings before setting S_IMMUTABLE on an
> > + * inode via FS_IOC_SETFLAGS.  If the flush fails we'll clear the flag before
> > + * returning error.
> > + *
> > + * Note: the caller should be holding i_mutex, or else be sure that
> > + * they have exclusive access to the inode structure.
> > + */
> > +static inline int vfs_ioc_setflags_flush_data(struct inode *inode, int flags)
> > +{
> > +	int ret;
> > +
> > +	if (!vfs_ioc_setflags_need_flush(inode, flags))
> > +		return 0;
> > +
> > +	inode_set_flags(inode, S_IMMUTABLE, S_IMMUTABLE);
> > +	ret = inode_flush_data(inode);
> > +	if (ret)
> > +		inode_set_flags(inode, 0, S_IMMUTABLE);
> > +	return ret;
> > +}
> 
> Also this sets S_IMMUTABLE whenever vfs_ioc_setflags_need_flush() returns
> true. That is currently the right thing but seems like a landmine waiting
> to trip? So I'd just drop the vfs_ioc_setflags_need_flush() abstraction to
> make it clear what's going on.

Ok.

--D

> 
> 								Honza
> -- 
> Jan Kara <jack@suse.com>
> SUSE Labs, CR

Re: [Ocfs2-devel] [PATCH 2/7] vfs: flush and wait for io when setting the immutable flag via SETFLAGS

[Darrick J. Wong]

On Mon, Jun 24, 2019 at 02:58:17PM -0700, Darrick J. Wong wrote:
> On Mon, Jun 24, 2019 at 01:37:37PM +0200, Jan Kara wrote:
> > On Fri 21-06-19 16:57:07, Darrick J. Wong wrote:
> > > From: Darrick J. Wong <darrick.wong@oracle.com>
> > > 
> > > When we're using FS_IOC_SETFLAGS to set the immutable flag on a file, we
> > > need to ensure that userspace can't continue to write the file after the
> > > file becomes immutable.  To make that happen, we have to flush all the
> > > dirty pagecache pages to disk to ensure that we can fail a page fault on
> > > a mmap'd region, wait for pending directio to complete, and hope the
> > > caller locked out any new writes by holding the inode lock.
> > > 
> > > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > 
> > Seeing the way this worked out, is there a reason to have separate
> > vfs_ioc_setflags_flush_data() instead of folding the functionality in
> > vfs_ioc_setflags_check() (possibly renaming it to
> > vfs_ioc_setflags_prepare() to indicate it does already some changes)? I
> > don't see any place that would need these two separated...
> 
> XFS needs them to be separated.
> 
> If we even /think/ that we're going to be setting the immutable flag
> then we need to grab the IOLOCK and the MMAPLOCK to prevent further
> writes while we drain all the directio writes and dirty data.  IO
> completions for the write draining can take the ILOCK, which means that
> we can't have grabbed it yet.
> 
> Next, we grab the ILOCK so we can check the new flags against the inode
> and then update the inode core.
> 
> For most filesystems I think it suffices to inode_lock and then do both,
> though.

Heh, lol, that applies to fssetxattr, not to setflags, because xfs
setflags implementation open-codes the relevant fssetxattr pieces.
So for setflags we can combine both parts into a single _prepare
function.

--D

> > > +/*
> > > + * Flush all pending IO and dirty mappings before setting S_IMMUTABLE on an
> > > + * inode via FS_IOC_SETFLAGS.  If the flush fails we'll clear the flag before
> > > + * returning error.
> > > + *
> > > + * Note: the caller should be holding i_mutex, or else be sure that
> > > + * they have exclusive access to the inode structure.
> > > + */
> > > +static inline int vfs_ioc_setflags_flush_data(struct inode *inode, int flags)
> > > +{
> > > +	int ret;
> > > +
> > > +	if (!vfs_ioc_setflags_need_flush(inode, flags))
> > > +		return 0;
> > > +
> > > +	inode_set_flags(inode, S_IMMUTABLE, S_IMMUTABLE);
> > > +	ret = inode_flush_data(inode);
> > > +	if (ret)
> > > +		inode_set_flags(inode, 0, S_IMMUTABLE);
> > > +	return ret;
> > > +}
> > 
> > Also this sets S_IMMUTABLE whenever vfs_ioc_setflags_need_flush() returns
> > true. That is currently the right thing but seems like a landmine waiting
> > to trip? So I'd just drop the vfs_ioc_setflags_need_flush() abstraction to
> > make it clear what's going on.
> 
> Ok.
> 
> --D
> 
> > 
> > 								Honza
> > -- 
> > Jan Kara <jack@suse.com>
> > SUSE Labs, CR
> 
> _______________________________________________
> Ocfs2-devel mailing list
> Ocfs2-devel@oss.oracle.com
> https://oss.oracle.com/mailman/listinfo/ocfs2-devel

Re: [Ocfs2-devel] [PATCH 2/7] vfs: flush and wait for io when setting the immutable flag via SETFLAGS

[Jan Kara]

On Mon 24-06-19 20:04:39, Darrick J. Wong wrote:
> On Mon, Jun 24, 2019 at 02:58:17PM -0700, Darrick J. Wong wrote:
> > On Mon, Jun 24, 2019 at 01:37:37PM +0200, Jan Kara wrote:
> > > On Fri 21-06-19 16:57:07, Darrick J. Wong wrote:
> > > > From: Darrick J. Wong <darrick.wong@oracle.com>
> > > > 
> > > > When we're using FS_IOC_SETFLAGS to set the immutable flag on a file, we
> > > > need to ensure that userspace can't continue to write the file after the
> > > > file becomes immutable.  To make that happen, we have to flush all the
> > > > dirty pagecache pages to disk to ensure that we can fail a page fault on
> > > > a mmap'd region, wait for pending directio to complete, and hope the
> > > > caller locked out any new writes by holding the inode lock.
> > > > 
> > > > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > > 
> > > Seeing the way this worked out, is there a reason to have separate
> > > vfs_ioc_setflags_flush_data() instead of folding the functionality in
> > > vfs_ioc_setflags_check() (possibly renaming it to
> > > vfs_ioc_setflags_prepare() to indicate it does already some changes)? I
> > > don't see any place that would need these two separated...
> > 
> > XFS needs them to be separated.
> > 
> > If we even /think/ that we're going to be setting the immutable flag
> > then we need to grab the IOLOCK and the MMAPLOCK to prevent further
> > writes while we drain all the directio writes and dirty data.  IO
> > completions for the write draining can take the ILOCK, which means that
> > we can't have grabbed it yet.
> > 
> > Next, we grab the ILOCK so we can check the new flags against the inode
> > and then update the inode core.
> > 
> > For most filesystems I think it suffices to inode_lock and then do both,
> > though.
> 
> Heh, lol, that applies to fssetxattr, not to setflags, because xfs
> setflags implementation open-codes the relevant fssetxattr pieces.
> So for setflags we can combine both parts into a single _prepare
> function.

Yeah. Also for fssetxattr we could use the prepare helper at least for
ext4, f2fs, and btrfs where the situation isn't so complex as for xfs to
save some boilerplate code.

								Honza

> > > > +/*
> > > > + * Flush all pending IO and dirty mappings before setting S_IMMUTABLE on an
> > > > + * inode via FS_IOC_SETFLAGS.  If the flush fails we'll clear the flag before
> > > > + * returning error.
> > > > + *
> > > > + * Note: the caller should be holding i_mutex, or else be sure that
> > > > + * they have exclusive access to the inode structure.
> > > > + */
> > > > +static inline int vfs_ioc_setflags_flush_data(struct inode *inode, int flags)
> > > > +{
> > > > +	int ret;
> > > > +
> > > > +	if (!vfs_ioc_setflags_need_flush(inode, flags))
> > > > +		return 0;
> > > > +
> > > > +	inode_set_flags(inode, S_IMMUTABLE, S_IMMUTABLE);
> > > > +	ret = inode_flush_data(inode);
> > > > +	if (ret)
> > > > +		inode_set_flags(inode, 0, S_IMMUTABLE);
> > > > +	return ret;
> > > > +}
> > > 
> > > Also this sets S_IMMUTABLE whenever vfs_ioc_setflags_need_flush() returns
> > > true. That is currently the right thing but seems like a landmine waiting
> > > to trip? So I'd just drop the vfs_ioc_setflags_need_flush() abstraction to
> > > make it clear what's going on.
> > 
> > Ok.
> > 
> > --D
> > 
> > > 
> > > 								Honza
> > > -- 
> > > Jan Kara <jack@suse.com>
> > > SUSE Labs, CR
> > 
> > _______________________________________________
> > Ocfs2-devel mailing list
> > Ocfs2-devel@oss.oracle.com
> > https://oss.oracle.com/mailman/listinfo/ocfs2-devel
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH 2/7] vfs: flush and wait for io when setting the immutable flag via SETFLAGS

[Jan Kara]

On Fri 21-06-19 16:57:07, Darrick J. Wong wrote:
> +/*
> + * Flush file data before changing attributes.  Caller must hold any locks
> + * required to prevent further writes to this file until we're done setting
> + * flags.
> + */
> +static inline int inode_flush_data(struct inode *inode)
> +{
> +	inode_dio_wait(inode);
> +	return filemap_write_and_wait(inode->i_mapping);
> +}

BTW, how about calling this function inode_drain_writes() instead? The
'flush_data' part is more a detail of implementation of write draining than
what we need to do to set immutable flag.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH 2/7] vfs: flush and wait for io when setting the immutable flag via SETFLAGS

[Darrick J. Wong]

On Mon, Jun 24, 2019 at 05:33:58PM +0200, Jan Kara wrote:
> On Fri 21-06-19 16:57:07, Darrick J. Wong wrote:
> > +/*
> > + * Flush file data before changing attributes.  Caller must hold any locks
> > + * required to prevent further writes to this file until we're done setting
> > + * flags.
> > + */
> > +static inline int inode_flush_data(struct inode *inode)
> > +{
> > +	inode_dio_wait(inode);
> > +	return filemap_write_and_wait(inode->i_mapping);
> > +}
> 
> BTW, how about calling this function inode_drain_writes() instead? The
> 'flush_data' part is more a detail of implementation of write draining than
> what we need to do to set immutable flag.

Ok, that's a much better description of what the function does.

--D

> 
> 								Honza
> -- 
> Jan Kara <jack@suse.com>
> SUSE Labs, CR

[PATCH 3/7] vfs: flush and wait for io when setting the immutable flag via FSSETXATTR

[Darrick J. Wong]

From: Darrick J. Wong <darrick.wong@oracle.com>

When we're using FS_IOC_FSSETXATTR to set the immutable flag on a file,
we need to ensure that userspace can't continue to write the file after
the file becomes immutable.  To make that happen, we have to flush all
the dirty pagecache pages to disk to ensure that we can fail a page
fault on a mmap'd region, wait for pending directio to complete, and
hope the caller locked out any new writes by holding the inode lock.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
 fs/btrfs/ioctl.c   |    3 +++
 fs/ext4/ioctl.c    |    3 +++
 fs/f2fs/file.c     |    3 +++
 fs/xfs/xfs_ioctl.c |   39 +++++++++++++++++++++++++++++++++------
 include/linux/fs.h |   37 +++++++++++++++++++++++++++++++++++++
 5 files changed, 79 insertions(+), 6 deletions(-)


diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index f431813b2454..63a9281e6ce0 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -432,6 +432,9 @@ static int btrfs_ioctl_fssetxattr(struct file *file, void __user *arg)
 
 	__btrfs_ioctl_fsgetxattr(binode, &old_fa);
 	ret = vfs_ioc_fssetxattr_check(inode, &old_fa, &fa);
+	if (ret)
+		goto out_unlock;
+	ret = vfs_ioc_fssetxattr_flush_data(inode, &fa);
 	if (ret)
 		goto out_unlock;
 
diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index a05341b94d98..6037585c1520 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -1115,6 +1115,9 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		inode_lock(inode);
 		ext4_fsgetxattr(inode, &old_fa);
 		err = vfs_ioc_fssetxattr_check(inode, &old_fa, &fa);
+		if (err)
+			goto out;
+		err = vfs_ioc_fssetxattr_flush_data(inode, &fa);
 		if (err)
 			goto out;
 		flags = (ei->i_flags & ~EXT4_FL_XFLAG_VISIBLE) |
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index d3cf4bdb8738..97f4bb36540f 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -2832,6 +2832,9 @@ static int f2fs_ioc_fssetxattr(struct file *filp, unsigned long arg)
 
 	__f2fs_ioc_fsgetxattr(inode, &old_fa);
 	err = vfs_ioc_fssetxattr_check(inode, &old_fa, &fa);
+	if (err)
+		goto out;
+	err = vfs_ioc_fssetxattr_flush_data(inode, &fa);
 	if (err)
 		goto out;
 	flags = (fi->i_flags & ~F2FS_FL_XFLAG_VISIBLE) |
diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index b494e7e881e3..88583b3e1e76 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -1014,6 +1014,28 @@ xfs_diflags_to_linux(
 #endif
 }
 
+/*
+ * Lock the inode against file io and page faults, then flush all dirty pages
+ * and wait for writeback and direct IO operations to finish.  Returns with
+ * the relevant inode lock flags set in @join_flags.  Caller is responsible for
+ * unlocking even on error return.
+ */
+static int
+xfs_ioctl_setattr_flush(
+	struct xfs_inode	*ip,
+	int			*join_flags)
+{
+	/* Already locked the inode from IO?  Assume we're done. */
+	if (((*join_flags) & (XFS_IOLOCK_EXCL | XFS_MMAPLOCK_EXCL)) ==
+			     (XFS_IOLOCK_EXCL | XFS_MMAPLOCK_EXCL))
+		return 0;
+
+	/* Lock and flush all mappings and IO in preparation for flag change */
+	*join_flags = XFS_IOLOCK_EXCL | XFS_MMAPLOCK_EXCL;
+	xfs_ilock(ip, *join_flags);
+	return inode_flush_data(VFS_I(ip));
+}
+
 static int
 xfs_ioctl_setattr_xflags(
 	struct xfs_trans	*tp,
@@ -1099,23 +1121,22 @@ xfs_ioctl_setattr_dax_invalidate(
 	if (!(fa->fsx_xflags & FS_XFLAG_DAX) && !IS_DAX(inode))
 		return 0;
 
-	if (S_ISDIR(inode->i_mode))
+	if (!S_ISREG(inode->i_mode))
 		return 0;
 
-	/* lock, flush and invalidate mapping in preparation for flag change */
-	xfs_ilock(ip, XFS_MMAPLOCK_EXCL | XFS_IOLOCK_EXCL);
-	error = filemap_write_and_wait(inode->i_mapping);
+	error = xfs_ioctl_setattr_flush(ip, join_flags);
 	if (error)
 		goto out_unlock;
 	error = invalidate_inode_pages2(inode->i_mapping);
 	if (error)
 		goto out_unlock;
 
-	*join_flags = XFS_MMAPLOCK_EXCL | XFS_IOLOCK_EXCL;
 	return 0;
 
 out_unlock:
-	xfs_iunlock(ip, XFS_MMAPLOCK_EXCL | XFS_IOLOCK_EXCL);
+	if (*join_flags)
+		xfs_iunlock(ip, *join_flags);
+	*join_flags = 0;
 	return error;
 
 }
@@ -1337,6 +1358,12 @@ xfs_ioctl_setattr(
 	if (code)
 		goto error_free_dquots;
 
+	if (!join_flags && vfs_ioc_fssetxattr_need_flush(VFS_I(ip), fa)) {
+		code = xfs_ioctl_setattr_flush(ip, &join_flags);
+		if (code)
+			goto error_free_dquots;
+	}
+
 	tp = xfs_ioctl_setattr_get_trans(ip, join_flags);
 	if (IS_ERR(tp)) {
 		code = PTR_ERR(tp);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index ed9a74cf5ef3..b4553d01e254 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3607,5 +3607,42 @@ static inline int vfs_ioc_setflags_flush_data(struct inode *inode, int flags)
 int vfs_ioc_fssetxattr_check(struct inode *inode, const struct fsxattr *old_fa,
 			     struct fsxattr *fa);
 
+/*
+ * Do we need to flush the file data before changing attributes?  When we're
+ * setting the immutable flag we must stop all directio writes and flush the
+ * dirty pages so that we can fail the page fault on the next write attempt.
+ */
+static inline bool vfs_ioc_fssetxattr_need_flush(struct inode *inode,
+						 struct fsxattr *fa)
+{
+	if (S_ISREG(inode->i_mode) && !IS_IMMUTABLE(inode) &&
+	    (fa->fsx_xflags & FS_XFLAG_IMMUTABLE))
+		return true;
+
+	return false;
+}
+
+/*
+ * Flush all pending IO and dirty mappings before setting S_IMMUTABLE on an
+ * inode via FS_IOC_SETXATTR.  If the flush fails we'll clear the flag before
+ * returning error.
+ *
+ * Note: the caller should be holding i_mutex, or else be sure that
+ * they have exclusive access to the inode structure.
+ */
+static inline int vfs_ioc_fssetxattr_flush_data(struct inode *inode,
+						struct fsxattr *fa)
+{
+	int ret;
+
+	if (!vfs_ioc_fssetxattr_need_flush(inode, fa))
+		return 0;
+
+	inode_set_flags(inode, S_IMMUTABLE, S_IMMUTABLE);
+	ret = inode_flush_data(inode);
+	if (ret)
+		inode_set_flags(inode, 0, S_IMMUTABLE);
+	return ret;
+}
 
 #endif /* _LINUX_FS_H */

[PATCH 4/7] vfs: don't allow most setxattr to immutable files

[Darrick J. Wong]

From: Darrick J. Wong <darrick.wong@oracle.com>

The chattr manpage has this to say about immutable files:

"A file with the 'i' attribute cannot be modified: it cannot be deleted
or renamed, no link can be created to this file, most of the file's
metadata can not be modified, and the file can not be opened in write
mode."

However, we don't actually check the immutable flag in the setattr code,
which means that we can update inode flags and project ids and extent
size hints on supposedly immutable files.  Therefore, reject setflags
and fssetxattr calls on an immutable file if the file is immutable and
will remain that way.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
 fs/inode.c |   27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)


diff --git a/fs/inode.c b/fs/inode.c
index 6374ad2ef25b..220caefc31f7 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -2204,6 +2204,14 @@ int vfs_ioc_setflags_check(struct inode *inode, int oldflags, int flags)
 	    !capable(CAP_LINUX_IMMUTABLE))
 		return -EPERM;
 
+	/*
+	 * We aren't allowed to change any other flags if the immutable flag is
+	 * already set and is not being unset.
+	 */
+	if ((oldflags & FS_IMMUTABLE_FL) && (flags & FS_IMMUTABLE_FL) &&
+	    oldflags != flags)
+		return -EPERM;
+
 	return 0;
 }
 EXPORT_SYMBOL(vfs_ioc_setflags_check);
@@ -2246,6 +2254,25 @@ int vfs_ioc_fssetxattr_check(struct inode *inode, const struct fsxattr *old_fa,
 	    !S_ISREG(inode->i_mode) && !S_ISDIR(inode->i_mode))
 		return -EINVAL;
 
+	/*
+	 * We aren't allowed to change any fields if the immutable flag is
+	 * already set and is not being unset.
+	 */
+	if ((old_fa->fsx_xflags & FS_XFLAG_IMMUTABLE) &&
+	    (fa->fsx_xflags & FS_XFLAG_IMMUTABLE)) {
+		if (old_fa->fsx_xflags != fa->fsx_xflags)
+			return -EPERM;
+		if (old_fa->fsx_projid != fa->fsx_projid)
+			return -EPERM;
+		if ((fa->fsx_xflags & (FS_XFLAG_EXTSIZE |
+				       FS_XFLAG_EXTSZINHERIT)) &&
+		    old_fa->fsx_extsize != fa->fsx_extsize)
+			return -EPERM;
+		if ((old_fa->fsx_xflags & FS_XFLAG_COWEXTSIZE) &&
+		    old_fa->fsx_cowextsize != fa->fsx_cowextsize)
+			return -EPERM;
+	}
+
 	/* Extent size hints of zero turn off the flags. */
 	if (fa->fsx_extsize == 0)
 		fa->fsx_xflags &= ~(FS_XFLAG_EXTSIZE | FS_XFLAG_EXTSZINHERIT);

[PATCH 5/7] xfs: refactor setflags to use setattr code directly

[Darrick J. Wong]

From: Darrick J. Wong <darrick.wong@oracle.com>

Refactor the SETFLAGS implementation to use the SETXATTR code directly
instead of partially constructing a struct fsxattr and calling bits and
pieces of the setxattr code.  This reduces code size and becomes
necessary in the next patch to maintain the behavior of allowing
userspace to set immutable on an immutable file so long as nothing
/else/ about the attributes change.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
 fs/xfs/xfs_ioctl.c |   40 +++-------------------------------------
 1 file changed, 3 insertions(+), 37 deletions(-)


diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index 88583b3e1e76..7b19ba2956ad 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -1491,11 +1491,8 @@ xfs_ioc_setxflags(
 	struct file		*filp,
 	void			__user *arg)
 {
-	struct xfs_trans	*tp;
 	struct fsxattr		fa;
-	struct fsxattr		old_fa;
 	unsigned int		flags;
-	int			join_flags = 0;
 	int			error;
 
 	if (copy_from_user(&flags, arg, sizeof(flags)))
@@ -1506,44 +1503,13 @@ xfs_ioc_setxflags(
 		      FS_SYNC_FL))
 		return -EOPNOTSUPP;
 
-	fa.fsx_xflags = xfs_merge_ioc_xflags(flags, xfs_ip2xflags(ip));
+	__xfs_ioc_fsgetxattr(ip, false, &fa);
+	fa.fsx_xflags = xfs_merge_ioc_xflags(flags, fa.fsx_xflags);
 
 	error = mnt_want_write_file(filp);
 	if (error)
 		return error;
-
-	/*
-	 * Changing DAX config may require inode locking for mapping
-	 * invalidation. These need to be held all the way to transaction commit
-	 * or cancel time, so need to be passed through to
-	 * xfs_ioctl_setattr_get_trans() so it can apply them to the join call
-	 * appropriately.
-	 */
-	error = xfs_ioctl_setattr_dax_invalidate(ip, &fa, &join_flags);
-	if (error)
-		goto out_drop_write;
-
-	tp = xfs_ioctl_setattr_get_trans(ip, join_flags);
-	if (IS_ERR(tp)) {
-		error = PTR_ERR(tp);
-		goto out_drop_write;
-	}
-
-	__xfs_ioc_fsgetxattr(ip, false, &old_fa);
-	error = vfs_ioc_fssetxattr_check(VFS_I(ip), &old_fa, &fa);
-	if (error) {
-		xfs_trans_cancel(tp);
-		goto out_drop_write;
-	}
-
-	error = xfs_ioctl_setattr_xflags(tp, ip, &fa);
-	if (error) {
-		xfs_trans_cancel(tp);
-		goto out_drop_write;
-	}
-
-	error = xfs_trans_commit(tp);
-out_drop_write:
+	error = xfs_ioctl_setattr(ip, &fa);
 	mnt_drop_write_file(filp);
 	return error;
 }

[PATCH 6/7] xfs: clean up xfs_merge_ioc_xflags

[Darrick J. Wong]

From: Darrick J. Wong <darrick.wong@oracle.com>

Clean up the calling convention since we're editing the fsxattr struct
anyway.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
 fs/xfs/xfs_ioctl.c |   32 ++++++++++++++------------------
 1 file changed, 14 insertions(+), 18 deletions(-)


diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index 7b19ba2956ad..a67bc9afdd0b 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -829,35 +829,31 @@ xfs_ioc_ag_geometry(
  * Linux extended inode flags interface.
  */
 
-STATIC unsigned int
+static inline void
 xfs_merge_ioc_xflags(
-	unsigned int	flags,
-	unsigned int	start)
+	struct fsxattr	*fa,
+	unsigned int	flags)
 {
-	unsigned int	xflags = start;
-
 	if (flags & FS_IMMUTABLE_FL)
-		xflags |= FS_XFLAG_IMMUTABLE;
+		fa->fsx_xflags |= FS_XFLAG_IMMUTABLE;
 	else
-		xflags &= ~FS_XFLAG_IMMUTABLE;
+		fa->fsx_xflags &= ~FS_XFLAG_IMMUTABLE;
 	if (flags & FS_APPEND_FL)
-		xflags |= FS_XFLAG_APPEND;
+		fa->fsx_xflags |= FS_XFLAG_APPEND;
 	else
-		xflags &= ~FS_XFLAG_APPEND;
+		fa->fsx_xflags &= ~FS_XFLAG_APPEND;
 	if (flags & FS_SYNC_FL)
-		xflags |= FS_XFLAG_SYNC;
+		fa->fsx_xflags |= FS_XFLAG_SYNC;
 	else
-		xflags &= ~FS_XFLAG_SYNC;
+		fa->fsx_xflags &= ~FS_XFLAG_SYNC;
 	if (flags & FS_NOATIME_FL)
-		xflags |= FS_XFLAG_NOATIME;
+		fa->fsx_xflags |= FS_XFLAG_NOATIME;
 	else
-		xflags &= ~FS_XFLAG_NOATIME;
+		fa->fsx_xflags &= ~FS_XFLAG_NOATIME;
 	if (flags & FS_NODUMP_FL)
-		xflags |= FS_XFLAG_NODUMP;
+		fa->fsx_xflags |= FS_XFLAG_NODUMP;
 	else
-		xflags &= ~FS_XFLAG_NODUMP;
-
-	return xflags;
+		fa->fsx_xflags &= ~FS_XFLAG_NODUMP;
 }
 
 STATIC unsigned int
@@ -1504,7 +1500,7 @@ xfs_ioc_setxflags(
 		return -EOPNOTSUPP;
 
 	__xfs_ioc_fsgetxattr(ip, false, &fa);
-	fa.fsx_xflags = xfs_merge_ioc_xflags(flags, fa.fsx_xflags);
+	xfs_merge_ioc_xflags(&fa, flags);
 
 	error = mnt_want_write_file(filp);
 	if (error)

[PATCH 7/7] vfs: don't allow writes to swap files

[Darrick J. Wong]

From: Darrick J. Wong <darrick.wong@oracle.com>

Don't let userspace write to an active swap file because the kernel
effectively has a long term lease on the storage and things could get
seriously corrupted if we let this happen.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
 fs/attr.c     |    3 +++
 mm/filemap.c  |    3 +++
 mm/memory.c   |    4 +++-
 mm/mmap.c     |    2 ++
 mm/swapfile.c |   15 +++++++++++++--
 5 files changed, 24 insertions(+), 3 deletions(-)


diff --git a/fs/attr.c b/fs/attr.c
index 1fcfdcc5b367..42f4d4fb0631 100644
--- a/fs/attr.c
+++ b/fs/attr.c
@@ -236,6 +236,9 @@ int notify_change(struct dentry * dentry, struct iattr * attr, struct inode **de
 	if (IS_IMMUTABLE(inode))
 		return -EPERM;
 
+	if (IS_SWAPFILE(inode))
+		return -ETXTBSY;
+
 	if ((ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID | ATTR_TIMES_SET)) &&
 	    IS_APPEND(inode))
 		return -EPERM;
diff --git a/mm/filemap.c b/mm/filemap.c
index dad85e10f5f8..fd80bc20e30a 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2938,6 +2938,9 @@ inline ssize_t generic_write_checks(struct kiocb *iocb, struct iov_iter *from)
 	if (IS_IMMUTABLE(inode))
 		return -EPERM;
 
+	if (IS_SWAPFILE(inode))
+		return -ETXTBSY;
+
 	if (!iov_iter_count(from))
 		return 0;
 
diff --git a/mm/memory.c b/mm/memory.c
index 4311cfdade90..c04c6a689995 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2235,7 +2235,9 @@ static vm_fault_t do_page_mkwrite(struct vm_fault *vmf)
 
 	vmf->flags = FAULT_FLAG_WRITE|FAULT_FLAG_MKWRITE;
 
-	if (vmf->vma->vm_file && IS_IMMUTABLE(file_inode(vmf->vma->vm_file)))
+	if (vmf->vma->vm_file &&
+	    (IS_IMMUTABLE(file_inode(vmf->vma->vm_file)) ||
+	     IS_SWAPFILE(file_inode(vmf->vma->vm_file))))
 		return VM_FAULT_SIGBUS;
 
 	ret = vmf->vma->vm_ops->page_mkwrite(vmf);
diff --git a/mm/mmap.c b/mm/mmap.c
index ac1e32205237..031807339869 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1488,6 +1488,8 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
 					return -EACCES;
 				if (IS_IMMUTABLE(file_inode(file)))
 					return -EPERM;
+				if (IS_SWAPFILE(file_inode(file)))
+					return -ETXTBSY;
 			}
 
 			/*
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 596ac98051c5..390859785558 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3165,6 +3165,19 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 	if (error)
 		goto bad_swap;
 
+	/*
+	 * Flush any pending IO and dirty mappings before we start using this
+	 * swap file.
+	 */
+	if (S_ISREG(inode->i_mode)) {
+		inode->i_flags |= S_SWAPFILE;
+		error = inode_flush_data(inode);
+		if (error) {
+			inode->i_flags &= ~S_SWAPFILE;
+			goto bad_swap;
+		}
+	}
+
 	mutex_lock(&swapon_mutex);
 	prio = -1;
 	if (swap_flags & SWAP_FLAG_PREFER)
@@ -3185,8 +3198,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 	atomic_inc(&proc_poll_event);
 	wake_up_interruptible(&proc_poll_wait);
 
-	if (S_ISREG(inode->i_mode))
-		inode->i_flags |= S_SWAPFILE;
 	error = 0;
 	goto out;
 bad_swap:

Re: [PATCH v4 0/7] vfs: make immutable files actually immutable

[Christoph Hellwig]

On Fri, Jun 21, 2019 at 04:56:50PM -0700, Darrick J. Wong wrote:
> Hi all,
> 
> The chattr(1) manpage has this to say about the immutable bit that
> system administrators can set on files:
> 
> "A file with the 'i' attribute cannot be modified: it cannot be deleted
> or renamed, no link can be created to this file, most of the file's
> metadata can not be modified, and the file can not be opened in write
> mode."
> 
> Given the clause about how the file 'cannot be modified', it is
> surprising that programs holding writable file descriptors can continue
> to write to and truncate files after the immutable flag has been set,
> but they cannot call other things such as utimes, fallocate, unlink,
> link, setxattr, or reflink.

I still think living code beats documentation.  And as far as I can
tell the immutable bit never behaved as documented or implemented
in this series on Linux, and it originated on Linux.

If you want  hard cut off style immutable flag it should really be a
new API, but I don't really see the point.  It isn't like the usual
workload is to set the flag on a file actively in use.

Re: [PATCH v4 0/7] vfs: make immutable files actually immutable

[Darrick J. Wong]

On Tue, Jun 25, 2019 at 03:36:31AM -0700, Christoph Hellwig wrote:
> On Fri, Jun 21, 2019 at 04:56:50PM -0700, Darrick J. Wong wrote:
> > Hi all,
> > 
> > The chattr(1) manpage has this to say about the immutable bit that
> > system administrators can set on files:
> > 
> > "A file with the 'i' attribute cannot be modified: it cannot be deleted
> > or renamed, no link can be created to this file, most of the file's
> > metadata can not be modified, and the file can not be opened in write
> > mode."
> > 
> > Given the clause about how the file 'cannot be modified', it is
> > surprising that programs holding writable file descriptors can continue
> > to write to and truncate files after the immutable flag has been set,
> > but they cannot call other things such as utimes, fallocate, unlink,
> > link, setxattr, or reflink.
> 
> I still think living code beats documentation.  And as far as I can
> tell the immutable bit never behaved as documented or implemented
> in this series on Linux, and it originated on Linux.

The behavior has never been consistent -- since the beginning you can
keep write()ing to a fd after the file becomes immutable, but you can't
ftruncate() it.  I would really like to make the behavior consistent.
Since the authors of nearly every new system call and ioctl since the
late 1990s have interpreted S_IMMUTABLE to mean "immutable takes effect
everywhere immediately" I resolved the inconsistency in favor of that
interpretation.

I asked Ted what he thought that that userspace having the ability to
continue writing to an immutable file, and he thought it was an
implementation bug that had been there for 25 years.  Even he thought
that immutable should take effect immediately everywhere.

> If you want  hard cut off style immutable flag it should really be a
> new API, but I don't really see the point.  It isn't like the usual
> workload is to set the flag on a file actively in use.

FWIW Ted also thought that since it's rare for admins to set +i on a
file actively in use we could just change it without forcing everyone
onto a new api.

--D

Re: [PATCH v4 0/7] vfs: make immutable files actually immutable

[Andreas Dilger]

[-- Attachment #1: Type: text/plain, Size: 2850 bytes --]

On Jun 25, 2019, at 12:03 PM, Darrick J. Wong <darrick.wong@oracle.com> wrote:
> 
> On Tue, Jun 25, 2019 at 03:36:31AM -0700, Christoph Hellwig wrote:
>> On Fri, Jun 21, 2019 at 04:56:50PM -0700, Darrick J. Wong wrote:
>>> Hi all,
>>> 
>>> The chattr(1) manpage has this to say about the immutable bit that
>>> system administrators can set on files:
>>> 
>>> "A file with the 'i' attribute cannot be modified: it cannot be deleted
>>> or renamed, no link can be created to this file, most of the file's
>>> metadata can not be modified, and the file can not be opened in write
>>> mode."
>>> 
>>> Given the clause about how the file 'cannot be modified', it is
>>> surprising that programs holding writable file descriptors can continue
>>> to write to and truncate files after the immutable flag has been set,
>>> but they cannot call other things such as utimes, fallocate, unlink,
>>> link, setxattr, or reflink.
>> 
>> I still think living code beats documentation.  And as far as I can
>> tell the immutable bit never behaved as documented or implemented
>> in this series on Linux, and it originated on Linux.
> 
> The behavior has never been consistent -- since the beginning you can
> keep write()ing to a fd after the file becomes immutable, but you can't
> ftruncate() it.  I would really like to make the behavior consistent.
> Since the authors of nearly every new system call and ioctl since the
> late 1990s have interpreted S_IMMUTABLE to mean "immutable takes effect
> everywhere immediately" I resolved the inconsistency in favor of that
> interpretation.
> 
> I asked Ted what he thought that that userspace having the ability to
> continue writing to an immutable file, and he thought it was an
> implementation bug that had been there for 25 years.  Even he thought
> that immutable should take effect immediately everywhere.
> 
>> If you want  hard cut off style immutable flag it should really be a
>> new API, but I don't really see the point.  It isn't like the usual
>> workload is to set the flag on a file actively in use.
> 
> FWIW Ted also thought that since it's rare for admins to set +i on a
> file actively in use we could just change it without forcing everyone
> onto a new api.

On the flip side, it is possible to continue to write to an open fd
after removing the write permission, and this is a problem we've hit
in the real world with NFS export, so real applications do this.

It may be the same case with immutable files, where an application sets
the immutable flag immediately after creation, but continues to write
until it closes the file, so that the file can't be modified by other
processes, and there isn't a risk that the file is missing the immutable
flag if the writing process dies before setting it at the end.

Cheers, Andreas






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