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

From: David Howells
Date: Fri Aug 04 2023 - 11:23:43 EST

David Howells <dhowells@xxxxxxxxxx> 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)