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=-0.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 2F65CC433E0 for ; Fri, 29 May 2020 02:04:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 09C212075F for ; Fri, 29 May 2020 02:04:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="CB8UJu43" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404781AbgE2CEt (ORCPT ); Thu, 28 May 2020 22:04:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37692 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390805AbgE2CEr (ORCPT ); Thu, 28 May 2020 22:04:47 -0400 Received: from mail-pg1-x541.google.com (mail-pg1-x541.google.com [IPv6:2607:f8b0:4864:20::541]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E3D49C08C5C6 for ; Thu, 28 May 2020 19:04:46 -0700 (PDT) Received: by mail-pg1-x541.google.com with SMTP id w20so560788pga.6 for ; Thu, 28 May 2020 19:04:46 -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; bh=LL/jvqQlSfNLPZ0wfLwjnZyalyTmqHTub54bRD3jbnQ=; b=CB8UJu43uLR+k80X1p0YZ9wcwqpXFIp4VKgWFtq1wfSf5yBA86r8kcWfxk2/wGwPFf R68/mqP6pQ024kpfNyySiA7+ISmOeIe+DkTDJYzjgAqJk9jrNmA03/SN56eC2ul+C+aM NoNeWf60hTtE7gEczG80K2ezDUc4RUceIbw3OgvIoUVG8UNngJpiiTXzHWGXb2MssrTv MKswTNXx2oIkkeLOl9hdnVnxZS5UnZ+f6k78vr/ygq0/fBSN3NVlmnsP2dWijbeakwtt /sduFzESsJOKOdRRVZm3PER+yZygU73bAdvp5jkNtNTi9gb9v/JwNk/EHiugFGzgniN/ midQ== 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; bh=LL/jvqQlSfNLPZ0wfLwjnZyalyTmqHTub54bRD3jbnQ=; b=DnOSFUeJ8UxX8paxyjQSx9cesfZm/bXLNTk0pIfAZpyinyqZ2kpjeZg+QRb7RA2WMZ XlomuQ6o3H5n82a6J4GA2jiZBcZ46XTJjUymX+MNSgkKIyPv0Q0T0c9u/UKPW6/f2czg Gt7iPQmqqe4h25OGLo96mPRY852PprzonMtPlRiuB0tLYzZk1EC/UPEKsWj/Drj/gd53 G0h2QlhQP9/1uiZmynnorKlCu2/EmB725IrCqgpP0dmRn9eHjlt0brN/cRADePOiHzU1 Bs/HB7277VQqwBHODcVZrd5dTns/SD+WdSQHsOfgL1U7NOj1Ems8BMxdG8AWK56nSiiw gbyw== X-Gm-Message-State: AOAM530NmXhqGi2/XGmTqX7cBUNliAMIvEsAl+Z+/UgEDWXdGYEupMQ8 sZ+oos2uY4aA3qDqBe4j1UQ= X-Google-Smtp-Source: ABdhPJxYKd9G2iMUvq8h6/VFZyECUotvwOyFG6LXUPPS7iZIRlv0J4GKSMkKoV7U7VL/1QFoms8DXw== X-Received: by 2002:a63:ea42:: with SMTP id l2mr4235540pgk.198.1590717886358; Thu, 28 May 2020 19:04:46 -0700 (PDT) Received: from localhost ([2409:10:2e40:5100:6e29:95ff:fe2d:8f34]) by smtp.gmail.com with ESMTPSA id q44sm6842027pja.29.2020.05.28.19.04.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 28 May 2020 19:04:45 -0700 (PDT) From: Sergey Senozhatsky X-Google-Original-From: Sergey Senozhatsky Date: Fri, 29 May 2020 11:04:42 +0900 To: Tetsuo Handa Cc: Sergey Senozhatsky , Petr Mladek , Andrew Morton , linux-kernel@vger.kernel.org, Dmitry Vyukov , Ondrej Mosnacek , Steven Rostedt Subject: Re: [PATCH] twist: allow converting pr_devel()/pr_debug() into printk(KERN_DEBUG) Message-ID: <20200529020442.GA526@jagdpanzerIV.localdomain> References: <20200524145034.10697-1-penguin-kernel@I-love.SAKURA.ne.jp> <20200525084218.GC5300@linux-b0ei> <20200525091157.GF755@jagdpanzerIV.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (20/05/25 19:43), Tetsuo Handa wrote: > >> On Sun 2020-05-24 23:50:34, Tetsuo Handa wrote: > >>> syzbot found a NULL pointer dereference bug inside mptcp_recvmsg() due to > >>> ssock == NULL, but this bug manifested inside selinux_socket_recvmsg() > >>> because pr_debug() was no-op [1]. > >>> > >>> pr_debug("fallback-read subflow=%p", > >>> mptcp_subflow_ctx(ssock->sk)); > >>> copied = sock_recvmsg(ssock, msg, flags); > >> > >> The NULL pointer deference was found even without this patch. > >> This patch would just cause that it will manifest itself on another > >> place. What is the benefit, please? > > It would help localizing the bug in this specific case. > > It's not only about %p, even %d can crash kernel or leak sensitive > info (if it happens after-free/out-of-bounds/uninit). Overall it > increases code coverage and allows to catch more bugs earlier. I don't know. Relying on random pr_debug()-s that can be added or removed any time. oops backtrace should help with that. You are not going to add pr_debug() all over the kernel, are you? -ss