Commit b5c40d59 authored May 22, 2018 by Omar Sandoval Committed by David Sterba May 29, 2018

Btrfs: fix clone vs chattr NODATASUM race



In btrfs_clone_files(), we must check the NODATASUM flag while the
inodes are locked. Otherwise, it's possible that btrfs_ioctl_setflags()
will change the flags after we check and we can end up with a party
checksummed file.

The race window is only a few instructions in size, between the if and
the locks which is:

3834         if (S_ISDIR(src->i_mode) || S_ISDIR(inode->i_mode))
3835                 return -EISDIR;

where the setflags must be run and toggle the NODATASUM flag (provided
the file size is 0).  The clone will block on the inode lock, segflags
takes the inode lock, changes flags, releases log and clone continues.

Not impossible but still needs a lot of bad luck to hit unintentionally.

Fixes: 0e7b824c ("Btrfs: don't make a file partly checksummed through file clone")
CC: stable@vger.kernel.org # 4.4+
Signed-off-by: Omar Sandoval <osandov@fb.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ update changelog ]
Signed-off-by: David Sterba <dsterba@suse.com>

parent b89311ef

fs/btrfs/ioctl.c

+7 −5

Original line number	Diff line number	Diff line
		@@ -3808,11 +3808,6 @@ static noinline int btrfs_clone_files(struct file file, struct file file_src,
		src->i_sb != inode->i_sb)
		return -EXDEV;

		/* don't make the dst file partly checksummed */
		if ((BTRFS_I(src)->flags & BTRFS_INODE_NODATASUM) !=
		(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM))
		return -EINVAL;

		if (S_ISDIR(src->i_mode) \|\| S_ISDIR(inode->i_mode))
		return -EISDIR;

		@@ -3822,6 +3817,13 @@ static noinline int btrfs_clone_files(struct file file, struct file file_src,
		inode_lock(src);
		}

		/* don't make the dst file partly checksummed */
		if ((BTRFS_I(src)->flags & BTRFS_INODE_NODATASUM) !=
		(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) {
		ret = -EINVAL;
		goto out_unlock;
		}

		/* determine range to clone */
		ret = -EINVAL;
		if (off + len > src->i_size \|\| off + len < off)

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