linux-kernel - Re: [RESEND PATCH] prctl: add PR_[GS]ET_PDEATHSIG

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Date:   Tue, 03 Oct 2017 19:47:14 +0200
From:   Jürg Billeter <j@...ron.ch>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Filipe Brandenburger <filbranden@...gle.com>,
        David Wilcox <davidvsthegiant@...il.com>, hansecke@...il.com,
        linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH] prctl: add PR_[GS]ET_PDEATHSIG_PROC

On Tue, 2017-10-03 at 12:40 -0500, Eric W. Biederman wrote:
> Jürg Billeter <j@...ron.ch> writes:
> > What's actually the reason that CLONE_NEWPID requires CAP_SYS_ADMIN? 
> > Does CLONE_NEWPID pose any risks that don't exist for
> > CLONE_NEWUSER|CLONE_NEWPID?  Assuming we can't simply drop the
> > CAP_SYS_ADMIN requirement, do you see a better solution for this use
> > case?
> 
> CLONE_NEWPID without a permission check would allow runing a setuid root
> application in a pid namespace.  Off the top of my head I can't think of
> a really good exploit.  But when you mess up pid files, and hide
> information from a privileged application I can completely imagine
> forcing that application to misbehave in ways the attacker can control.
> Leading to bad things.

Could we allow unprivileged CLONE_NEWPID if the no_new_privs bit is
set?

Jürg