From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4F3B1C49ED7 for ; Tue, 10 Sep 2019 15:18:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 30EDB208E4 for ; Tue, 10 Sep 2019 15:18:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2393905AbfIJPSi (ORCPT ); Tue, 10 Sep 2019 11:18:38 -0400 Received: from mx1.redhat.com ([209.132.183.28]:49842 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726060AbfIJPSi (ORCPT ); Tue, 10 Sep 2019 11:18:38 -0400 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id A34B230821A3; Tue, 10 Sep 2019 15:18:37 +0000 (UTC) Received: from asgard.redhat.com (ovpn-112-20.ams2.redhat.com [10.36.112.20]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3CA491001B01; Tue, 10 Sep 2019 15:18:29 +0000 (UTC) Date: Tue, 10 Sep 2019 16:18:01 +0100 From: Eugene Syromiatnikov To: Christian Brauner Cc: Oleg Nesterov , linux-kernel@vger.kernel.org, Christian Brauner , Andrew Morton , "Peter Zijlstra (Intel)" , Ingo Molnar , "Dmitry V. Levin" , Eric Biederman Subject: Re: [PATCH] fork: fail on non-zero higher 32 bits of args.exit_signal Message-ID: <20190910151801.GR4960@asgard.redhat.com> References: <20190910115711.GA3755@asgard.redhat.com> <20190910124440.GA25647@redhat.com> <20190910130935.jxqxbt7wop3ostob@wittgenstein> <20190910131048.e7xr52az2zej4p4v@wittgenstein> <20190910132701.s5o5nidewyo5zl7h@wittgenstein> <20190910143943.GC25647@redhat.com> <20190910144614.qsisdvm46vlc4bl7@wittgenstein> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190910144614.qsisdvm46vlc4bl7@wittgenstein> User-Agent: Mutt/1.5.23 (2014-03-12) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.47]); Tue, 10 Sep 2019 15:18:37 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 10, 2019 at 04:46:15PM +0200, Christian Brauner wrote: > On Tue, Sep 10, 2019 at 04:39:44PM +0200, Oleg Nesterov wrote: > > On 09/10, Christian Brauner wrote: > > > On Tue, Sep 10, 2019 at 03:10:48PM +0200, Christian Brauner wrote: > > > > On Tue, Sep 10, 2019 at 03:09:35PM +0200, Christian Brauner wrote: > > > > > On Tue, Sep 10, 2019 at 02:44:41PM +0200, Oleg Nesterov wrote: > > > > > > On 09/10, Eugene Syromiatnikov wrote: > > > > > > > > > > > > > > --- a/kernel/fork.c > > > > > > > +++ b/kernel/fork.c > > > > > > > @@ -2562,6 +2562,9 @@ noinline static int copy_clone_args_from_user(struct kernel_clone_args *kargs, > > > > > > > if (copy_from_user(&args, uargs, size)) > > > > > > > return -EFAULT; > > > > > > > > > > > > > > + if (unlikely(((unsigned int)args.exit_signal) != args.exit_signal)) > > > > > > > + return -EINVAL; > > > > > > > > > > > > Hmm. Unless I am totally confused you found a serious bug... > > > > > > > > > > > > Without CLONE_THREAD/CLONE_PARENT copy_process() blindly does > > > > > > > > > > > > p->exit_signal = args->exit_signal; > > > > > > > > > > > > the valid_signal(sig) check in do_notify_parent() mostly saves us, but we > > > > > > must not allow child->exit_signal < 0, if nothing else this breaks > > > > > > thread_group_leader(). > > > > > > > > > > > > And afaics this patch doesn't fix this? I think we need the valid_signal() > > > > > > check... > > > > > > > > > > Thanks for sending this patch so quickly after our conversation > > > > > yesterday, Eugene! > > > > > We definitely want valid_signal() to verify the signal is ok. > > > > > > So we could do your check in copy_clone_args_from_user(), and then we do > > > another valid_signal() check in clone3_args_valid()? We could do the > > > latter in copy_clone_args_from_user() too but it's nicer to do it along > > > the other checks in clone3_args_valid(). > > > > I am fine either way. Sure, we can add valid_signal() into clone3_args_valid(), > > but then I'd ask to simplify the "overflow" check above. Something like > > > > if (args.exit_signal > UINT_MAX) > > return -EINVAL; > > > > looks much more readable to me. > > > > > > Or we can simply do > > > > if (args.exit_signal & ~((u64)CSIGNAL)) > > return -EINVAL; > > > > in copy_clone_args_from_user() and forget about all problems. > > Both are fine with me. The latter might have the advantage that we catch > both legacy clone and clone3. I think Eugene prefers this as well. Unfortunately, it doesn't. I think, the best place for the check is either in _do_fork or copy_process itself; however, it's quite messy as that way it's detached from the other checks, but, at the same time, there are a lot of code paths (like the one in arch/x86/ia32/sys_ia32.c), and it's kinda obscure that the caller of _do_fork has to check that exit_syscall is positive itself. > Christian