Re: FAILED: patch "[PATCH] btrfs: send: emit file capabilities after chown" failed to apply to 4.4-stable tree

[Sasha Levin <sashal@kernel.org>]

On Thu, Jun 18, 2020 at 04:45:23PM +0200, gregkh@linuxfoundation.org wrote:
>
>The patch below does not apply to the 4.4-stable tree.
>If someone wants it applied there, or to any other stable or longterm
>tree, then please email the backport, including the original git commit
>id to <stable@vger.kernel.org>.
>
>thanks,
>
>greg k-h
>
>------------------ original commit in Linus's tree ------------------
>
>From 89efda52e6b6930f80f5adda9c3c9edfb1397191 Mon Sep 17 00:00:00 2001
>From: Marcos Paulo de Souza <mpdesouza@suse.com>
>Date: Sun, 10 May 2020 23:15:07 -0300
>Subject: [PATCH] btrfs: send: emit file capabilities after chown
>
>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 on 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 subvolume snapshot -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 subvolume snapshot -r fs1 fs1/snap_complete
>  $ btrfs subvolume snapshot -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
>
>To fix that, 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 workaround not needed anymore.
>
>Link: https://github.com/kdave/btrfs-progs/issues/202
>CC: stable@vger.kernel.org # 4.4+
>Suggested-by: Filipe Manana <fdmanana@suse.com>
>Reviewed-by: Filipe Manana <fdmanana@suse.com>
>Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
>Signed-off-by: David Sterba <dsterba@suse.com>

I took 1ec9a1ae1e30 ("Btrfs: fix unreplayable log after snapshot delete
+ parent dir fsync") to work around the conflict.

-- 
Thanks,
Sasha