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=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 5D4E4C43381 for ; Sat, 16 Mar 2019 14:14:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2977C21903 for ; Sat, 16 Mar 2019 14:14:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="sEwSdhqc" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727063AbfCPOOQ (ORCPT ); Sat, 16 Mar 2019 10:14:16 -0400 Received: from mail-pg1-f196.google.com ([209.85.215.196]:37315 "EHLO mail-pg1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726064AbfCPOOQ (ORCPT ); Sat, 16 Mar 2019 10:14:16 -0400 Received: by mail-pg1-f196.google.com with SMTP id q206so8387632pgq.4 for ; Sat, 16 Mar 2019 07:14:15 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:date:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=iqSv3VwnLzmUHJiY0agWx/Nu4MIVi/KllnQytijL1sA=; b=sEwSdhqcWBnBdue9yoCAG8iy9LoqbGzhrJZyOXZDEyL0dCzFBPk51I5xld/wKLMvNU DuY6RKuhnwcnhjQWpKODUN8paX1O+xp8OavRy8X20VMA8b1Q+egEM5IogkOSY/9GrdC0 ltrBJOG0eSVYb7arN9NxMfa9QQNQbxgQF8wQ7p/OVVrdbW/5X28bxlQoDofn5Yk0Pf/T CoevqKMI8hDO5XxEAuBuyTiAjLElk0S8xno84AOg/9psHHK/0h50bZDUUACIMTzlUB06 F45M9uquIiEg5hMOEYZbdcTfiKPkmSGi4+576zLzCmqNEVRURLj7Ska40y8ksUsPur06 DwvA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:date:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=iqSv3VwnLzmUHJiY0agWx/Nu4MIVi/KllnQytijL1sA=; b=VMYkVyP56sRqnaUqc1z3Gle774WY0jinQOCDOaUrEIaNb1keYwLXElu4duKh0Cvfy1 cmvu6UWg2kyGe9vKqbkNjF8JJYuIPfXHmABSvfLmctHtBv2BivK1Js4L/blEUC9Ed9lX PJk3C/y6FXklV/2Sz5jEgh1A37kmeBoApSCdim9MkaSfnd9Cds98pMOX0Xr30SxcWhOz 26sWPfoRPMPawx7guknT/JeezxGTJ4rzm1cWtFCuYAr86pOMyQ6enAx3HyV9spI0cLT7 A7OCE+TTv7XENscvBLQBebpvGcMrEHxEobyC2lXiA3u5FzgnXTrk0GBcom5uMrdluFR+ b1Cw== X-Gm-Message-State: APjAAAWBO8u46ruGw1ZaIQWV45+sOmF0QZzNwdf6Gdqz+TU7rYk7tMVm jbRXcw9Y+NC8h6yofGDOksA= X-Google-Smtp-Source: APXvYqyrcR+RSB9zCTyOO8OTYON9M50iwxPHDr0JXvaRH54yTiVL7/JTqbsu3wCJYCSvavJrEnzGcw== X-Received: by 2002:aa7:885a:: with SMTP id k26mr9622649pfo.70.1552745655023; Sat, 16 Mar 2019 07:14:15 -0700 (PDT) Received: from localhost ([121.137.63.184]) by smtp.gmail.com with ESMTPSA id z6sm6147159pgp.8.2019.03.16.07.14.13 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sat, 16 Mar 2019 07:14:13 -0700 (PDT) From: Sergey Senozhatsky X-Google-Original-From: Sergey Senozhatsky Date: Sat, 16 Mar 2019 23:14:10 +0900 To: Tetsuo Handa Cc: Dmitry Vyukov , Petr Mladek , Sergey Senozhatsky , Sergey Senozhatsky , LKML , syzkaller Subject: Re: [syzbot? printk?] no WARN_ON() messages printed before "Kernel panic - not syncing: panic_on_warn set ..." Message-ID: <20190316141410.GA18654@tigerII.localdomain> References: <0a0d282b-6757-5f42-b888-ef52b040aaa1@i-love.sakura.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.11.4 (2019-03-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (03/16/19 19:18), Tetsuo Handa wrote: > On 2019/03/16 18:11, Dmitry Vyukov wrote: > > Such reports showed up always with low frequency. For all that I > > looked at we also always had a normal non-truncated version, so I was > > never too worried. > > > > If something would write from userspace, that would show up in the > > output, or not? > > > > Perhaps syzkaller somehow manages to lower console output level? > > panic() calls console_verbose() before calling > > pr_emerg("Kernel panic - not syncing: %s\n", buf); > > line. Then, someone might have changed console_loglevel enough to > suppress printk() output. Hmm... sysctl, may be? > > I figured out that we should restrict it from doing > > syslog(SYSLOG_ACTION_CONSOLE_OFF). And I also restricted its access o > > /dev/console. But maybe there is something else? It _should_ not be > > able to write to random sysctl's. > > Maybe try running with "ignore_loglevel" kernel command line option added? Right, that's something I would expect 0-day and syzkaller to do. -ss