tree d61f4c65bc51e6455f0cb5a3d03fab41d0f83169
parent 2ad18bdf3b8f84c85c7da7e4de365f7c5701fb3f
author Eric Paris <eparis@redhat.com> 1299186554 -0500
committer Eric Paris <eparis@redhat.com> 1299186747 -0500

LSM: Pass -o remount options to the LSM

The VFS mount code passes the mount options to the LSM.  The LSM will remove
options it understands from the data and the VFS will then pass the remaining
options onto the underlying filesystem.  This is how options like the
SELinux context= work.  The problem comes in that -o remount never calls
into LSM code.  So if you include an LSM specific option it will get passed
to the filesystem and will cause the remount to fail.  An example of where
this is a problem is the 'seclabel' option.  The SELinux LSM hook will
print this word in /proc/mounts if the filesystem is being labeled using
xattrs.  If you pass this word on mount it will be silently stripped and
ignored.  But if you pass this word on remount the LSM never gets called
and it will be passed to the FS.  The FS doesn't know what seclabel means
and thus should fail the mount.  For example an ext3 fs mounted over loop

# mount -o loop /tmp/fs /mnt/tmp
# cat /proc/mounts | grep /mnt/tmp
/dev/loop0 /mnt/tmp ext3 rw,seclabel,relatime,errors=continue,barrier=0,data=ordered 0 0
# mount -o remount /mnt/tmp
mount: /mnt/tmp not mounted already, or bad option
# dmesg
EXT3-fs (loop0): error: unrecognized mount option "seclabel" or missing value

This patch passes the remount mount options to an new LSM hook.

Signed-off-by: Eric Paris <eparis@redhat.com>
Reviewed-by: James Morris <jmorris@namei.org>