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 53168C4740A for ; Tue, 10 Sep 2019 14:28:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2A4BD20872 for ; Tue, 10 Sep 2019 14:28:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387618AbfIJO2K (ORCPT ); Tue, 10 Sep 2019 10:28:10 -0400 Received: from mx1.redhat.com ([209.132.183.28]:25301 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726066AbfIJO2K (ORCPT ); Tue, 10 Sep 2019 10:28:10 -0400 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id AE7B63175A20; Tue, 10 Sep 2019 14:28:09 +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 24D9560C5E; Tue, 10 Sep 2019 14:27:36 +0000 (UTC) Date: Tue, 10 Sep 2019 15:27:07 +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: <20190910142707.GQ4960@asgard.redhat.com> References: <20190910115711.GA3755@asgard.redhat.com> <20190910124440.GA25647@redhat.com> <20190910130935.jxqxbt7wop3ostob@wittgenstein> <20190910131048.e7xr52az2zej4p4v@wittgenstein> <20190910132701.s5o5nidewyo5zl7h@wittgenstein> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190910132701.s5o5nidewyo5zl7h@wittgenstein> User-Agent: Mutt/1.5.23 (2014-03-12) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.41]); Tue, 10 Sep 2019 14:28:09 +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 03:27:02PM +0200, 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(). There's also a discrepancy between CSIGNAL (0xff) and _NSIG, used in valid_signal (which is between 32 and 128, depending on architecture), it seems it doesn't break thread_group_leader, but definitely allows passing some invalid signal numbers via legacy clone-like syscalls—I'm not sure if that's important. > Christian