[PATCH v2 1/4] capabilities: Add user namespace capabilities

[Serge E. Hallyn]

On Tue, Jun 11, 2024 at 01:20:40AM -0700, Jonathan Calmels wrote:
> On Mon, Jun 10, 2024 at 08:00:57AM GMT, Serge E. Hallyn wrote:
> > 
> > Now, one thing that does occur to me here is that there is a
> > very mild form of sendmail-capabilities vulnerability that
> > could happen here.  Unpriv user joe can drop CAP_SYS_ADMIN
> > from cap_userns, then run a setuid-root program which starts
> > a container which expects CAP_SYS_ADMIN.  This could be a
> > shared container, and so joe could be breaking expected
> > behavior there.
> > 
> > I *think* we want to say we don't care about this case, but
> > if we did, I suppose we could say that the normal cap raise
> > rules on setuid should apply to cap_userns?
> > 
> 
> Right, good catch. If we do want to fix it, we could just check for
> setuid no? Or do we want to follow the normal root inheritance rules
> too? Essentially something like this:
> 
> pU' = is_suid(root) ? X : pU

Yeah, I think that makes sense.  Thanks.

-serge