CVE-2024-40938: landlock: Fix d_parent walk

[Greg Kroah-Hartman]

On Mon, Jul 15, 2024 at 01:17:10PM -0700, Kees Cook wrote:
> On Mon, Jul 15, 2024 at 08:04:21PM +0200, Mickaël Salaün wrote:
> > Yes, that's why we use WARN_ON_ONCE() to check cases that should never
> > happen (at the time of writting), but in practice it's useful to check
> > (with fuzzing) that this assertion is true.  However, if a
> > WARN_ON_ONCE() is reached, this doesn't mean that this is a security
> > issue, but just an unexpected case that kernel maintainers should be
> > notified with to fix it.
> 
> I leave CVE determinations to the CNA. :) I think the difficulty here is
> with having no way to trivially see which WARN is security sensitive and
> which isn't, and since WARNs may panic, all WARNs could be a DoS, and
> therefore may be a CVE for some deployment somewhere.

That is exactly correct, and why we must mark any way that userspace can
hit a WARN as needing a CVE.

thanks,

greg k-h