[PATCH v6] vfs, security: Fix automount superblock LSM init problem, preventing NFS sb sharing

[David Howells]

David Howells <dhowells at redhat.com> wrote:

> IIRC, the issue is when you make a mount with an explicit context= setting and
> make another mount from some way down the export tree that doesn't have an
> explicit setting, e.g.:
> 
> 	mount carina:/ /mnt -o context=system_u:object_r:root_t:s0
> 	mount carina:/nfs/scratch /mnt2
> 
> and then cause an automount to walk from one to the other:
> 
> 	stat /mnt/nfs/scratch/foo

Actually, the order there isn't quite right.  The problem is with this order:

	# mount carina:/ /mnt -o context=system_u:object_r:root_t:s0
	# stat /mnt/nfs/scratch/bus
	  File: /mnt/nfs/scratch/bus
	  Size: 124160          Blocks: 248        IO Block: 1048576 regular file
	Device: 0,55    Inode: 131         Links: 1
	...
	# mount carina:/nfs/scratch /mnt2
	mount.nfs: /mnt2 is busy or already mounted or sharecache fail

with the error:

	SELinux: mount invalid.  Same superblock, different security settings for (dev 0:52, type nfs4)

David