security.capability xattr missing after btrfs send/receive

security.capability xattr missing after btrfs send/receive

[Jan Andres]

I found that the security.capability xattr gets lost when cloning a
subvolume via btrfs send | btrfs receive. This is easy to reproduce
(currently on 3.19.0-rc6, x86_64, with btrfs-progs 3.18.1):

Have two btrfs file systems, "/fs1" and "/fs2".

# btrfs sub create /fs1/test
# touch /fs1/test/foo
# setcap cap_net_admin+ep /fs1/test/foo
# getcap /fs1/test/foo
/fs1/test/foo = cap_net_admin+ep
# btrfs prop set /fs1/test ro true
# btrfs send /fs1/test | btrfs receive /fs2
# getcap /fs2/test/foo
[reports nothing]


The cause of the problem seems to be that BTRFS_SEND_C_SET_XATTR comes
before BTRFS_SEND_C_CHMOD in the send stream, so that the receiving end
will first correctly restore all the xattrs of the file, and after that,
perform an lchown() which will cause the kernel to reset the
file's capabilities.

I don't know how to fix this correctly (especially in the case of
incremental sends), so I don't have a patch, but figured it might be
useful to share what I found.

Regards,
Jan

-- 
Jan Andres <jandres@gmx.net>

Re: security.capability xattr missing after btrfs send/receive

[Juan Orti]

El dom, 01-02-2015 a las 13:13 +0100, Jan Andres escribió:
> I found that the security.capability xattr gets lost when cloning a
> subvolume via btrfs send | btrfs receive. This is easy to reproduce
> (currently on 3.19.0-rc6, x86_64, with btrfs-progs 3.18.1):
> 
> Have two btrfs file systems, "/fs1" and "/fs2".
> 
> # btrfs sub create /fs1/test
> # touch /fs1/test/foo
> # setcap cap_net_admin+ep /fs1/test/foo
> # getcap /fs1/test/foo
> /fs1/test/foo = cap_net_admin+ep
> # btrfs prop set /fs1/test ro true
> # btrfs send /fs1/test | btrfs receive /fs2
> # getcap /fs2/test/foo
> [reports nothing]
> 
> 
> The cause of the problem seems to be that BTRFS_SEND_C_SET_XATTR comes
> before BTRFS_SEND_C_CHMOD in the send stream, so that the receiving end
> will first correctly restore all the xattrs of the file, and after that,
> perform an lchown() which will cause the kernel to reset the
> file's capabilities.
> 
> I don't know how to fix this correctly (especially in the case of
> incremental sends), so I don't have a patch, but figured it might be
> useful to share what I found.

https://bugzilla.kernel.org/show_bug.cgi?id=68891

-- 
Juan Orti
https://miceliux.com

Re: security.capability xattr missing after btrfs send/receive

[Chris Murphy]

Looks like security.capabilities also has tripped up tar.
https://bugzilla.redhat.com/show_bug.cgi?id=771927

There's a suggestion that security.capabilities are "non standard
attributes"? Also, comment 28 is interesting. Anyway it seems a big
messy to support them in any case.