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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_RED 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 4F7BCC11F64 for ; Thu, 1 Jul 2021 20:06:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2A6BE61410 for ; Thu, 1 Jul 2021 20:06:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233119AbhGAUI3 (ORCPT ); Thu, 1 Jul 2021 16:08:29 -0400 Received: from out03.mta.xmission.com ([166.70.13.233]:42528 "EHLO out03.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231726AbhGAUI3 (ORCPT ); Thu, 1 Jul 2021 16:08:29 -0400 Received: from in02.mta.xmission.com ([166.70.13.52]:48706) by out03.mta.xmission.com with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1lz2wf-0051gb-7p; Thu, 01 Jul 2021 14:05:57 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95]:48610 helo=email.xmission.com) by in02.mta.xmission.com with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1lz2we-00BEc1-3d; Thu, 01 Jul 2021 14:05:56 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Alexey Gladkov Cc: Linus Torvalds , Linux Kernel Mailing List , Linux Containers References: <87fsx1vcr9.fsf@disp2133> <87czs4u0rm.fsf@disp2133> <87mtr8sjvr.fsf@disp2133> <87a6n8simq.fsf@disp2133> <20210701164144.u2dod4g2obfj4kit@example.org> Date: Thu, 01 Jul 2021 15:05:18 -0500 In-Reply-To: <20210701164144.u2dod4g2obfj4kit@example.org> (Alexey Gladkov's message of "Thu, 1 Jul 2021 18:41:44 +0200") Message-ID: <87o8blol4x.fsf@disp2133> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1lz2we-00BEc1-3d;;;mid=<87o8blol4x.fsf@disp2133>;;;hst=in02.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX186RRMiCoq2i2iZsr93Lu2GAzZej0SbQoQ= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [GIT PULL] ucounts: Count rlimits in each user namespace X-SA-Exim-Version: 4.2.1 (built Sat, 08 Feb 2020 21:53:50 +0000) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Alexey Gladkov writes: > On Tue, Jun 29, 2021 at 12:09:01PM -0500, Eric W. Biederman wrote: >> ebiederm@xmission.com (Eric W. Biederman) writes: >> >> > Linus Torvalds writes: >> > >> >> On Tue, Jun 29, 2021 at 8:52 AM Eric W. Biederman wrote: >> >>> >> >>> Linus Torvalds writes: >> >>> >> >>> > Why the "sigpending < LONG_MAX" test in that >> >>> > >> >>> > if (override_rlimit || (sigpending < LONG_MAX && sigpending <= >> >>> > task_rlimit(t, RLIMIT_SIGPENDING))) { >> >>> > thing? >> >>> >> >>> On second look that sigpending < LONG_MAX check is necessary. When >> >>> inc_rlimit_ucounts detects a problem it returns LONG_MAX. >> >> >> >> I saw that, but _without_ that test you'd be left with just that >> >> >> >> sigpending <= task_rlimit(t, RLIMIT_SIGPENDING) >> >> >> >> and if task_rlimit() is LONG_MAX, then that means "no limits", so it is all ok. >> > >> > It means no limits locally. The creator of your user namespace might >> > have had a limit which you are also bound by. >> > >> > The other possibility is that inc_rlimits_ucounts caused a sigpending >> > counter to overflow. In which case we need to fail and run >> > dec_rlimit_ucounts to keep the counter from staying overflowed. >> > >> > So I don't see a clever way to avoid the sigpending < LONG_MAX test. >> >> Hmm. I take that back. There is a simple clever way to satisfy all of >> the tests. >> >> - sigpending < LONG_MAX && sigpending <= task_rlimit(t, RLIMIT_SIGPENDING) >> + sigpending < task_rlimit(t, RLIMIT_SIGPENDING) >> >> That would just need a small comment to explain the subtleties. > > Is it because user.sigpending was atomic_t before this patch ? Apologies I was wrong. The replacement of "<=" with "<" is correct for the case where "task_rlimit(t, RLIMIT_SIGPENDING) == LONG_MAX". Unfortunately off by one for all other values of "task_rlimit(t, RLIMIT_SIGPENDING)". It completely breaks things for the case where RLIMIT_SIGPENDING == 1, where no signals are allowed to be queued. Today allowing 1 queued signal with a single task and a sender that does not send a second signal until the first is consumed will work reliably. That was just a brain fart on my part. Eric