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=-2.1 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, 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 5D7F2C33C9E for ; Thu, 30 Jan 2020 05:17:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 24AA520707 for ; Thu, 30 Jan 2020 05:17:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="ldzUaWK/" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726353AbgA3FRP (ORCPT ); Thu, 30 Jan 2020 00:17:15 -0500 Received: from mail-pg1-f196.google.com ([209.85.215.196]:36002 "EHLO mail-pg1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725280AbgA3FRP (ORCPT ); Thu, 30 Jan 2020 00:17:15 -0500 Received: by mail-pg1-f196.google.com with SMTP id k3so1031364pgc.3 for ; Wed, 29 Jan 2020 21:17:14 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=HgVZcNLI9NFyQNxv0grkqLVxwVjlyBQNZusKb8xDpmo=; b=ldzUaWK/BlIpCBJzVfT/KbsvEQDmYvr3UqS6Bi3Sc6uie9C1260aSogN9UPqCoPeDI EvgWQ2+IEFNgGeHAbgxIXDy1deJ4918PPB9y1eNDt/5HkfwgNhYULZWRs4+EfUUTlnHl /tyixm8lr0pP9afMBokhGcKA4kQmzm6CEL/SwBEKSl29oq5VkflaQoF3jDsXNiBQbzRt GjCUu0TMIBK7p/j4Bak5haimgfcAqduptWUiOpG/5KkpfRbBZjRgeE6YNejVbfAVtVaq xkdxL1sLFGFOosKyocqk2f5RPUnDIsDIJ3CJeSeDOA2xeo7pTGaVYGBXZs8N76YKSyBD gOcg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=HgVZcNLI9NFyQNxv0grkqLVxwVjlyBQNZusKb8xDpmo=; b=R4tPMsQaSt9G8LDkDNR2DYIOoSuPKA2PWjgTWUUVqj/VVOMcfzF3MI3v+Ivnl/0EtG 9znxwtqdDNxPCQLF6FZSpF1UDRRt5w0OJn4UkNC/J3d/eFBh0bv784qlaltgjSa/A8hv fbPcBcuy9oxx/KyQLB3mAoR+m2JvNSb+f51mRL2MzS4IYtJ3rYkt50WYaGL54rdltwuD f7Kvu/5wuRSnuP5MlSNdktvhoGZ96MoOJI/6mmEQEc4vJDQiHakAHAa2nconZkhK65T2 sLjH8Z2ydtyTaHjW7L87TJmi6oyDIplyreXdLj0XN+k/d+1wo53jNPTP5wWvKyWmc2DR n4qQ== X-Gm-Message-State: APjAAAUizd95HLIj+DCk/f0N2c59qtbOvgYyo2EgSIgomIaWPon35+zt WTZuH1kSRJB0dP94Q93kQ1k= X-Google-Smtp-Source: APXvYqzBlV9usWBUCUJC/gWjduVXKp/hPnU4LUo7jNqRqvKfeQkw4uMWeyihHAVO8A2+MiG9ovv85g== X-Received: by 2002:a62:830c:: with SMTP id h12mr3442357pfe.162.1580361434515; Wed, 29 Jan 2020 21:17:14 -0800 (PST) Received: from localhost ([2401:fa00:8f:203:5bbb:c872:f2b1:f53b]) by smtp.gmail.com with ESMTPSA id x22sm4782205pgc.2.2020.01.29.21.17.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 29 Jan 2020 21:17:13 -0800 (PST) Date: Thu, 30 Jan 2020 14:17:11 +0900 From: Sergey Senozhatsky To: Nathan Chancellor Cc: Petr Mladek , Sergey Senozhatsky , Steven Rostedt , linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com Subject: Re: -Wfortify-source in kernel/printk/printk.c Message-ID: <20200130051711.GF115889@google.com> References: <20200130021648.GA32309@ubuntu-x2-xlarge-x86> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200130021648.GA32309@ubuntu-x2-xlarge-x86> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (20/01/29 19:16), Nathan Chancellor wrote: > Hi all, > > After commit 6d485ff455e ("Improve static checks for sprintf and > __builtin___sprintf_chk") in clang [1], the following warning appears > when CONFIG_PRINTK is disabled (e.g. allnoconfig): > > ../kernel/printk/printk.c:2416:10: warning: 'sprintf' will always > overflow; destination buffer has size 0, but format string expands > to at least 33 [-Wfortify-source] > len = sprintf(text, > ^ > 1 warning generated. > > Specifically referring to > https://elixir.bootlin.com/linux/v5.5/source/kernel/printk/printk.c#L2416. Good catch. > It isn't wrong, given that when CONFIG_PRINTK is disabled, text's length > is 0 (LOG_LINE_MAX and PREFIX_MAX are both zero). How should this > warning be dealt this? I am not familiar enough with the printk code to > say myself. It's not wrong. Unless I'm missing something completely obvious: with disabled printk() we don't have any functions that can append messages to the logbuf, hence we can't overflow it. So the error in question should never trigger. - Normal printk() is void, so kernel cannot append messages; - dev_printk() is void, so drivers cannot append messages and dicts; - devkmsg_write() is void, so user space cannot write to logbuf. So I think we should never trigger that overflow (assuming that I didn't miss something) message. In any case feel free to submit a patch - switch it to snprintf(). -ss