linux-kernel - Re: [PATCH v2 1/4] capabilities: Add user namespace capabilities

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Date: Sat, 15 Jun 2024 10:19:08 -0500
From: "Serge E. Hallyn" <serge@...lyn.com>
To: Jonathan Calmels <jcalmels@...0.net>
Cc: "Serge E. Hallyn" <serge@...lyn.com>, Andrew Morgan <morgan@...nel.org>,
	brauner@...nel.org, ebiederm@...ssion.com,
	Jonathan Corbet <corbet@....net>, Paul Moore <paul@...l-moore.com>,
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Subject: Re: [PATCH v2 1/4] capabilities: Add user namespace capabilities

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