From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751360AbaG3EGH (ORCPT ); Wed, 30 Jul 2014 00:06:07 -0400 Received: from mail-lb0-f176.google.com ([209.85.217.176]:42433 "EHLO mail-lb0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751020AbaG3EGE (ORCPT ); Wed, 30 Jul 2014 00:06:04 -0400 MIME-Version: 1.0 In-Reply-To: <87vbqhp4hf.fsf@x220.int.ebiederm.org> References: <1406296033-32693-1-git-send-email-drysdale@google.com> <1406296033-32693-12-git-send-email-drysdale@google.com> <87vbqhp4hf.fsf@x220.int.ebiederm.org> From: Andy Lutomirski Date: Tue, 29 Jul 2014 21:05:42 -0700 Message-ID: Subject: Re: [PATCH 11/11] seccomp: Add tgid and tid into seccomp_data To: "Eric W. Biederman" Cc: Kees Cook , Julien Tinnes , David Drysdale , Al Viro , Paolo Bonzini , LSM List , Greg Kroah-Hartman , Paul Moore , James Morris , Linux API , Meredydd Luff , Christoph Hellwig , "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 28, 2014 at 2:18 PM, Eric W. Biederman wrote: > Andy Lutomirski writes: > >> [cc: Eric Biederman] >> > >> Can we do one better and add a flag to prevent any non-self pid >> lookups? This might actually be easy on top of the pid namespace work >> (e.g. we could change the way that find_task_by_vpid works). >> >> It's far from just being signals. There's access_process_vm, ptrace, >> all the signal functions, clock_gettime (see CPUCLOCK_PID -- yes, this >> is ridiculous), and probably some others that I've forgotten about or >> never noticed in the first place. > > So here is the practical question. > > Are these processes that only can send signals to their thread group > allowed to call fork()? > > > If fork is allowed and all pid lookups are restricted to their own > thread group that wait, waitpid, and all of the rest of the wait family > will never return the pids of their children, and zombies will > accumulate. Aka the semantics are fundamentally broken. Good point. I can imagine at least three ways that fork() could continue working, though: 1. Allow lookups of immediate children, too. (I don't love this one.) 2. Allow non-self pids to be translated in but not out. This way P_ALL will continue working. 3. Have the kernel treat any PID-restricted process as though it were NOCLDWAIT. I think I like #3. Thoughts? > > If fork is not allowed pid namespaces already solve this problem. PID namespaces are fairly heavyweight. Julien pointed out that using PID namespaces requires a bunch of dummy PID 1 processes. --Andy From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andy Lutomirski Subject: Re: [PATCH 11/11] seccomp: Add tgid and tid into seccomp_data Date: Tue, 29 Jul 2014 21:05:42 -0700 Message-ID: References: <1406296033-32693-1-git-send-email-drysdale@google.com> <1406296033-32693-12-git-send-email-drysdale@google.com> <87vbqhp4hf.fsf@x220.int.ebiederm.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Return-path: In-Reply-To: <87vbqhp4hf.fsf-JOvCrm2gF+uungPnsOpG7nhyD016LWXt@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: "Eric W. Biederman" Cc: Kees Cook , Julien Tinnes , David Drysdale , Al Viro , Paolo Bonzini , LSM List , Greg Kroah-Hartman , Paul Moore , James Morris , Linux API , Meredydd Luff , Christoph Hellwig , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" List-Id: linux-api@vger.kernel.org On Mon, Jul 28, 2014 at 2:18 PM, Eric W. Biederman wrote: > Andy Lutomirski writes: > >> [cc: Eric Biederman] >> > >> Can we do one better and add a flag to prevent any non-self pid >> lookups? This might actually be easy on top of the pid namespace work >> (e.g. we could change the way that find_task_by_vpid works). >> >> It's far from just being signals. There's access_process_vm, ptrace, >> all the signal functions, clock_gettime (see CPUCLOCK_PID -- yes, this >> is ridiculous), and probably some others that I've forgotten about or >> never noticed in the first place. > > So here is the practical question. > > Are these processes that only can send signals to their thread group > allowed to call fork()? > > > If fork is allowed and all pid lookups are restricted to their own > thread group that wait, waitpid, and all of the rest of the wait family > will never return the pids of their children, and zombies will > accumulate. Aka the semantics are fundamentally broken. Good point. I can imagine at least three ways that fork() could continue working, though: 1. Allow lookups of immediate children, too. (I don't love this one.) 2. Allow non-self pids to be translated in but not out. This way P_ALL will continue working. 3. Have the kernel treat any PID-restricted process as though it were NOCLDWAIT. I think I like #3. Thoughts? > > If fork is not allowed pid namespaces already solve this problem. PID namespaces are fairly heavyweight. Julien pointed out that using PID namespaces requires a bunch of dummy PID 1 processes. --Andy