Re: [PATCH 3/7] vfs: Add a mount-notification facility

From: David Howells
Date: Wed May 29 2019 - 07:04:28 EST

Jann Horn <jannh@xxxxxxxxxx> wrote:

> > +void post_mount_notification(struct mount *changed,
> > + struct mount_notification *notify)
> > +{
> > + const struct cred *cred = current_cred();
> This current_cred() looks bogus to me. Can't mount topology changes
> come from all sorts of places? For example, umount_mnt() from
> umount_tree() from dissolve_on_fput() from __fput(), which could
> happen pretty much anywhere depending on where the last reference gets
> dropped?

IIRC, that's what Casey argued is the right thing to do from a security PoV.

Maybe I should pass in NULL creds in the case that an event is being generated
because an object is being destroyed due to the last usage[*] being removed.

[*] Usage, not ref - Superblocks are a bit weird in their accounting.