Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Tue, 7 Jul 2020 23:27:39 +0300
From:   Cyrill Gorcunov <gorcunov@gmail.com>
To:     Christian Brauner <christian.brauner@ubuntu.com>
Cc:     Nicolas Viennot <Nicolas.Viennot@twosigma.com>,
        Jann Horn <jannh@google.com>, Paul Moore <paul@paul-moore.com>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        Adrian Reber <areber@redhat.com>,
        Eric Biederman <ebiederm@xmission.com>,
        Pavel Emelyanov <ovzxemul@gmail.com>,
        Oleg Nesterov <oleg@redhat.com>,
        Dmitry Safonov <0x7f454c46@gmail.com>,
        Andrei Vagin <avagin@gmail.com>,
        =?utf-8?B?TWljaGHFgiBDxYJhcGnFhHNraQ==?= <mclapinski@google.com>,
        Kamil Yurtsever <kyurtsever@google.com>,
        Dirk Petersen <dipeit@gmail.com>,
        Christine Flood <chf@redhat.com>,
        Casey Schaufler <casey@schaufler-ca.com>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Radostin Stoyanov <rstoyanov1@gmail.com>,
        Stephen Smalley <stephen.smalley.work@gmail.com>,
        Sargun Dhillon <sargun@sargun.me>,
        Arnd Bergmann <arnd@arndb.de>,
        "linux-security-module@vger.kernel.org" 
        <linux-security-module@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "selinux@vger.kernel.org" <selinux@vger.kernel.org>,
        Eric Paris <eparis@parisplace.org>,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH v4 3/3] prctl: Allow ptrace capable processes to change
 /proc/self/exe
Message-ID: <20200707202739.GB1999@grain>
References: <20200701064906.323185-1-areber@redhat.com>
 <20200701064906.323185-4-areber@redhat.com>
 <20200702211647.GB3283@mail.hallyn.com>
 <CAHC9VhQZ=cwiOay6OMMdM1UHm69wDaga9HBkyTbx8-1OU=aBvA@mail.gmail.com>
 <a2b4deacfc7541e3adea2f36a6f44262@EXMBDFT11.ad.twosigma.com>
 <20200706174437.zpshxlul7rl3vmmq@wittgenstein>
 <20200707154504.aknxmw6qavpjkr24@wittgenstein>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20200707154504.aknxmw6qavpjkr24@wittgenstein>
User-Agent: Mutt/1.14.5 (2020-06-23)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, Jul 07, 2020 at 05:45:04PM +0200, Christian Brauner wrote:
...
> 
> Ok, so the original patch proposal was presented in [4] in 2014. The
> final version of that patch added the PR_SET_MM_MAP we know today. The
> initial version presented in [4] did not require _any_ privilege.
> 

True. I still think that relyng on /proc/<pid>/exe being immutable (or
guarded by caps) in a sake of security is a bit misleading, this link
only a hint without any guarantees of what code is being executed once
we pass cs:rip to userspace right after exec is completed. Nowadays I rather
think we might need to call audit_log() here or something similar to point
that exe link is changed (by criu or someone else) and simply notify
node's administrator, that's all. But as you pointed tomoyo may be
affected if we simply drops all caps from here. Thus I agree that
the new cap won't make situation worse.

Still I'm not in touch with kernel code for a couple of years already
and might be missing something obvious here.