On Tue, May 12, 2020 at 11:40:38AM -0300, Marcos Paulo de Souza wrote:
From: Marcos Paulo de Souza mpdesouza@suse.com
[PROBLEM] Whenever a chown is executed, all capabilities of the file being touched are lost. When doing incremental send with a file with capabilities, there is a situation where the capability can be lost in the receiving side. The sequence of actions bellow shows the problem:
$ mount /dev/sda fs1 $ mount /dev/sdb fs2
$ touch fs1/foo.bar $ setcap cap_sys_nice+ep fs1/foo.bar $ btrfs subvol snap -r fs1 fs1/snap_init $ btrfs send fs1/snap_init | btrfs receive fs2
$ chgrp adm fs1/foo.bar $ setcap cap_sys_nice+ep fs1/foo.bar
$ btrfs subvol snap -r fs1 fs1/snap_complete $ btrfs subvol snap -r fs1 fs1/snap_incremental
$ btrfs send fs1/snap_complete | btrfs receive fs2 $ btrfs send -p fs1/snap_init fs1/snap_incremental | btrfs receive fs2
At this point, only a chown was emitted by "btrfs send" since only the group was changed. This makes the cap_sys_nice capability to be dropped from fs2/snap_incremental/foo.bar
[FIX] Only emit capabilities after chown is emitted. The current code first checks for xattrs that are new/changed, emits them, and later emit the chown. Now, __process_new_xattr skips capabilities, letting only finish_inode_if_needed to emit them, if they exist, for the inode being processed.
This behavior was being worked around in "btrfs receive" side by caching the capability and only applying it after chown. Now, xattrs are only emmited _after_ chown, making that hack not needed anymore.
Link: https://github.com/kdave/btrfs-progs/issues/202 CC: stable@vger.kernel.org Suggested-by: Filipe Manana fdmanana@suse.com Reviewed-by: Filipe Manana fdmanana@suse.com Signed-off-by: Marcos Paulo de Souza mpdesouza@suse.com
Added to misc-next, thanks.