On Mon, Jan 16, 2023 at 10:15:58AM +0000, Shinichiro Kawasaki wrote:
> I observe mount command with -o context option fails for btrfs, using mount
> command built from the latest util-linux master branch code (git hash
> dbf77f7a1).
>
> $ sudo mount -o context="system_u:object_r:root_t:s0" /dev/nullb1 /mnt
> mount: /mnt: wrong fs type, bad option, bad superblock on /dev/nullb1, missing codepage or helper program, or other error.
> dmesg(1) may have more information after failed mount system call.
>
> Kernel reports an SELinux error message:
>
> [565959.593054][T12131] SELinux: mount invalid. Same superblock, different security settings for (dev nullb1, type btrfs)
>
> Is this a known issue?
Not for me.
> Details:
>
> - Mount succeeds without the -o context option.
> - Ext4 succeeds to mount with the option.
> - Mount succeeds rolling back util-linux code to older git hash 8241fb005,
> which was committed on January 3rd. After this commit, a number of commits
> were merged to util-linux to use fsconfig syscall for mount in place of
> mount syscall.
>
> Then the new fsconfig syscall looks the trigger of the failure. I took a look in
> the code of mount path and saw that btrfs is not modified to use struct
> fs_context for the fsconfig syscall. The -o context option is parsed and kept in
> security field of fs_context, but it is not passed to btrfs_mount.
It's a serious issue if btrfs is not ready for the new kernel fsconfig
interface. I guess libmount cannot do anything else in this case
(well, we can switch back to classic mount(2), but it sounds as a
wrong solution).
Karel
--
Karel Zak <kzak@xxxxxxxxxx>
http://karelzak.blogspot.com
