CVE-2024-40938: landlock: Fix d_parent walk

[Kees Cook]

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.

-- 
Kees Cook