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 Received: from smtp4.osuosl.org (smtp4.osuosl.org [140.211.166.137]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 8808EC88E75 for ; Tue, 15 Sep 2026 19:00:24 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by smtp4.osuosl.org (Postfix) with ESMTP id 461CE404F4; Tue, 15 Sep 2026 19:00:24 +0000 (UTC) X-Virus-Scanned: amavis at osuosl.org Received: from smtp4.osuosl.org ([127.0.0.1]) by localhost (smtp4.osuosl.org [127.0.0.1]) (amavis, port 10024) with ESMTP id hmoz0UHN2rDL; Tue, 15 Sep 2026 19:00:23 +0000 (UTC) ARC-Filter: OpenARC Filter v1.3.0 smtp4.osuosl.org 96A20404EE Authentication-Results: smtp4.osuosl.org; arc=pass header.oldest-pass=0 smtp.remote-ip=140.211.166.142 ARC-Seal: i=2; d=osuosl.org; s=arc; a=rsa-sha256; cv=pass; t=1789498823; b=ec3CDuZ3dJtNwxpZ1PDUZYOTff1NE8duCHR/jpQey/aSSohDJOMOatYHskaC9z0895Cm D9iGgJ6IRi7bvwJ8Flcbk7NaVTlim8naTtHMYHHfw4Fq1/GoQtU275qu1UtIMsWPUTlL0 pbPp0/ZQNY8GctiKhQ/jKLagrra5rfREv5St0D7mkAv1DNeDRZExWD9XsQu/SA4C73Hyt t7k8Eao8ag+KsIsllrsVf1nnLxjOWsFWKeIHb/pFbmxNVEi3ewFkLQQ9SGXyELaApdmna fWAclo679Yz0gGcPX/6sHG+2Rlk5rRReqy6tDJkBBpU0XTAGrwfOA16YZw347QS1ziw== ARC-Message-Signature: i=2; d=osuosl.org; s=arc; a=rsa-sha256; c=relaxed/relaxed; t=1789498823; h=X-Comment:DKIM-Signature:X-Original-To:Delivered-To:Received: Received:X-Virus-Scanned:X-Spam-Flag:X-Spam-Score:X-Spam-Level: X-Spam-Status:Received:ARC-Filter:Received-SPF:Received:Received: Received:DKIM-Signature:Date:From:To:Cc:Subject:Message-ID:References: MIME-Version:Content-Type:Content-Disposition:In-Reply-To:X-BeenThere: X-Mailman-Version:Precedence:List-Id:List-Unsubscribe:List-Archive: List-Post:List-Help:List-Subscribe:Errors-To; bh=bH9D6fx46WAVM8PGx4wEKkSYBjKGmw5AvziupNUvWGk=; b=LZAp7V7KXE6izqE7FN3u9GTHN3ZTjb3ipLS9U4zH/KER8Z4KQkUDOEDhlAVTkb7Cj/gO wyO8p/V+GIi5jjGzIn367E+EwsIIu/uKqdSLOQ2rdVboXGOvmKHDeyRU+9ckt8LTnzLPZ GYapiNlHnTuvPQxXASw3egcIPl0CkoaB6E60ueXeCoKDNmYqZatEfPTwlvZqu2nFYnVHh jq3+jmCZV7LrtZ053+xn+XNI2i0VF2aFj3hquVr7sbgb3KoK3xIC0J2giwjAIF4QBqJ2N ui9yuNdW/2B1iW47ZCvkra+dVj0QBNS+nsUtpLgukmmLJCb9fGR2RcbI40Z+ELPqTOw== ARC-Authentication-Results: i=2; smtp4.osuosl.org; arc=pass header.oldest-pass=0 smtp.remote-ip=140.211.166.142 X-Comment: SPF check N/A for local connections - client-ip=140.211.166.142; helo=lists1.osuosl.org; envelope-from=intel-wired-lan-bounces@osuosl.org; receiver= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=osuosl.org; s=default; t=1789498823; bh=bH9D6fx46WAVM8PGx4wEKkSYBjKGmw5AvziupNUvWGk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-Id: List-Unsubscribe:List-Archive:List-Post:List-Help:List-Subscribe: From; b=d134uGPrvjgVMkKlABDTc4F/sYZHWqKnTMF60CYS1N/5skuwTjLSMhjBDB5VE6g1/ 0btxwWMqPWv8KuZTYnslxTFsqn9xTIEL32jmp3/o09G31jqdSjwcdRb3Dz1m4JCnWQ gXx/C7jPLva54iZtCEPR7Kh/nKp+92uRyV+h55g1trK4qsMkdHFO51EQf/M+B2crE5 Pn9POSjH9IdBe3rGO3TUh4rKcOTGxL69J/i4IiqKrMaD6U9WDuELWKIFssMZcDvuoG W/OIA5oV6ERt5ZCBvXORVC4uFmZPbSkxU/bZrEQkn5P+SzwVkRJd3BR1K9NpDhngXU VcbO9f+fjFigw== Received: from lists1.osuosl.org (lists1.osuosl.org [140.211.166.142]) by smtp4.osuosl.org (Postfix) with ESMTP id 96A20404EE; Tue, 15 Sep 2026 19:00:23 +0000 (UTC) Received: from smtp2.osuosl.org (smtp2.osuosl.org [IPv6:2605:bc80:3010::133]) by lists1.osuosl.org (Postfix) with ESMTP id A83F62D0 for ; Tue, 15 Sep 2026 19:00:22 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by smtp2.osuosl.org (Postfix) with ESMTP id 8E544400F3 for ; Tue, 15 Sep 2026 19:00:22 +0000 (UTC) X-Virus-Scanned: amavis at osuosl.org Received: from smtp2.osuosl.org ([127.0.0.1]) by localhost (smtp2.osuosl.org [127.0.0.1]) (amavis, port 10024) with ESMTP id fhpE2heJ2lAJ for ; Tue, 15 Sep 2026 19:00:22 +0000 (UTC) ARC-Filter: OpenARC Filter v1.3.0 smtp2.osuosl.org B4B7C400C5 Authentication-Results: smtp2.osuosl.org; arc=none smtp.remote-ip=172.105.4.254 ARC-Seal: i=1; d=osuosl.org; s=arc; a=rsa-sha256; cv=none; t=1789498821; b=M5v2R8IIYkRj0CFZ7eE+PX3q03MIQ9YvFsQ3bd6hlKEcGoZAptREibj0Ca5qw0K1is8I kW10vRYMLYL14jSi5sjxj53Du5eEe4Qd6GmGfx79AyqoQrApLRXXJ0bLA0dWY6DVpCSzO ocaveqI5/BYAwNnpgGw7S+VLm/kPVKxEPHQs2kdFzhK7RAqJ/8HiLWAWEg71YoTCEkWnF qw6YQfwCxzJaW1bzYf1l2KlH6iM+2pbV2RSD3IM2jGJgwRFpG0r/qnGi9q/oGbkJD+r1O DqPCoJxD2BVahHK7Rghgkiq3ah9sDy7WCRZZqHMxkfJpFuul/XfUu07U0wVmAnhxZ7g== ARC-Message-Signature: i=1; d=osuosl.org; s=arc; a=rsa-sha256; c=relaxed/relaxed; t=1789498821; h=Received-SPF:Received:Received:DKIM-Signature:Date:From:To:Cc: Subject:Message-ID:References:MIME-Version:Content-Type: Content-Disposition:In-Reply-To; bh=bH9D6fx46WAVM8PGx4wEKkSYBjKGmw5AvziupNUvWGk=; b=TxolV3LG8rbRMWx9W5Juph7WNcgA8jbrVWh94IoZyBcuHWnD6b2xRmRbVpBkpbBUewPU c6YbwHfV+wtCG5dsAgEGF5DWHxtSzcX5Cofv4QzM0N3xrsMNJmbQ8+YMb0wxANJiNEsD4 PLFkLlMgtjlcRvqxwkts3N402Es40Qou7KYMKi71Uxsxxpmz886K2wizFeAjx7VlVr4UI gEVwQa20Jmcq9elk3+EyKfB+hkHGYkZNYt25I+EXQsVgaZqtYnxM5APGGNzMrtSdK3Kik oB1SlV+lJm30eRml4FM7/6eenthwW+WqTcjvPtEZiWY6FUL5oazIy81sO8SW+pv1twA== ARC-Authentication-Results: i=1; smtp2.osuosl.org; dmarc=pass header.from=kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=j0iSBaet; arc=none smtp.remote-ip=172.105.4.254 Received-SPF: Pass (mailfrom) identity=mailfrom; client-ip=172.105.4.254; helo=tor.source.kernel.org; envelope-from=kees@kernel.org; receiver= Authentication-Results: smtp2.osuosl.org; dmarc=pass (p=quarantine dis=none) header.from=kernel.org Authentication-Results: smtp2.osuosl.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=j0iSBaet Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by smtp2.osuosl.org (Postfix) with ESMTPS id B4B7C400C5 for ; Tue, 15 Sep 2026 19:00:21 +0000 (UTC) Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 9D122602C3; Tue, 15 Sep 2026 19:00:19 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4C7C11F00899; Tue, 15 Sep 2026 19:00:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789498819; bh=bH9D6fx46WAVM8PGx4wEKkSYBjKGmw5AvziupNUvWGk=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=j0iSBaetC/3YCi18xNuSeB+n+7VnOF+QOgAvJx7ktLSNyWzdoyXHzZ/YPBs5rtm+n WA6gaCeYDOM7G68qSWfRsHvbbAN1voKYHzwbAYckQsRPEBWlfdZePBmdFPmQ1OMU/N sUCxn5+r/cR7FN5oCIcXoHFsLztawdQ7lZ2pVlHqL5qvTKh/9Qqc0Ta8A275Irt74k zf/eAGrgknulaZr5ylmpMNiuL5cL1xjelXuos4e0Xj/d9MPGQhh5E4WSCnRmy8X7rs HaD3mC4eIWM8qko0PgiUDZhDxobQu7+Yi4Weeos/5iSyNoUm6TMJqr9E5mfS6sKjxo y4BshIH81fNpw== Date: Tue, 15 Sep 2026 12:00:19 -0700 From: Kees Cook To: Bill Wendling Cc: linux-kernel@vger.kernel.org, codemender-patching+linux@google.com, Russell King , Huacai Chen , WANG Xuerui , Thomas Bogendoerfer , "James E.J. Bottomley" , Helge Deller , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Ian Abbott , H Hartley Sweeten , Tony Luck , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Matthew Brost , Thomas =?iso-8859-1?Q?Hellstr=F6m?= , Rodrigo Vivi , Dmitry Torokhov , Matthias Schwarzott , Mauro Carvalho Chehab , Tony Nguyen , Przemek Kitszel , Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Arend van Spriel , Rob Herring , Saravana Kannan , Krzysztof Kozlowski , Sylwester Nawrocki , Peter Griffin , Alim Akhtar , Linus Walleij , Anil Gurumurthy , Sudarsana Kalluru , "Martin K. Petersen" , Trond Myklebust , Anna Schumaker , Mike Marshall , Martin Brandenburg , Jiri Pirko , Simon Horman , Chuck Lever , Jeff Layton , NeilBrown , Olga Kornievskaia , Dai Ngo , Tom Talpey , Jaroslav Kysela , Takashi Iwai , Andrew Morton , "Mike Rapoport (Microsoft)" , Kanglong Wang , Tiezhu Yang , Qiang Ma , Randy Dunlap , Pengpeng Hou , Ard Biesheuvel , Breno Leitao , Thorsten Blum , Harshit Mogalapalli , Greg Kroah-Hartman , Lyude Paul , Ashutosh Desai , Imre Deak , Dmitry Baryshkov , Johan Hovold , Johannes Berg , Miri Korenblit , Alexander Stein , Cryolitia PukNgae , Jiaming Zhang , Will Porter , Cen Zhang , =?iso-8859-1?Q?C=E1ssio?= Gabriel , Rong Zhang , Arun Raghavan , linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linux-edac@vger.kernel.org, dri-devel@lists.freedesktop.org, intel-xe@lists.freedesktop.org, linux-input@vger.kernel.org, linux-media@vger.kernel.org, intel-wired-lan@lists.osuosl.org, netdev@vger.kernel.org, linux-wireless@vger.kernel.org, brcm80211@lists.linux.dev, brcm80211-dev-list.pdl@broadcom.com, devicetree@vger.kernel.org, linux-samsung-soc@vger.kernel.org, linux-gpio@vger.kernel.org, linux-scsi@vger.kernel.org, linux-nfs@vger.kernel.org, devel@lists.orangefs.org, linux-hardening@vger.kernel.org, linux-sound@vger.kernel.org Subject: Re: [PATCH 03/28] ARM: atags: Replace strlcat() with snprintf() for cmdline extend Message-ID: <202609151155.CC22827@keescook> References: <20260915081910.4142719-1-morbo@google.com> <20260915081910.4142719-4-morbo@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260915081910.4142719-4-morbo@google.com> X-BeenThere: intel-wired-lan@osuosl.org X-Mailman-Version: 2.1.30 Precedence: list List-Id: Intel Wired Ethernet Linux Kernel Driver Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-wired-lan-bounces@osuosl.org On Tue, Sep 15, 2026 at 08:18:20AM +0000, Bill Wendling wrote: > --- a/arch/arm/kernel/atags_parse.c > +++ b/arch/arm/kernel/atags_parse.c > @@ -121,9 +121,10 @@ __tagtable(ATAG_REVISION, parse_tag_revision); > static int __init parse_tag_cmdline(const struct tag *tag) > { > #if defined(CONFIG_CMDLINE_EXTEND) > - strlcat(default_command_line, " ", COMMAND_LINE_SIZE); > - strlcat(default_command_line, tag->u.cmdline.cmdline, > - COMMAND_LINE_SIZE); > + size_t len = strlen(default_command_line); > + > + snprintf(default_command_line + len, COMMAND_LINE_SIZE - len, > + " %s", tag->u.cmdline.cmdline); > #elif defined(CONFIG_CMDLINE_FORCE) > pr_warn("Ignoring tag cmdline (using the default kernel command line)\n"); > #else It's pretty clear we have a pattern of "simple append" that is needed, and while strlcat() does that, it's horrible. I feel like we need an appending scnprintf(), and it needs to return like strscpy() does (i.e. -E2BIG on truncation). My goal would be: - don't open-code string length math - never leave the destination unterminated - allow for format strings - yes/no return indication for "did this truncate?" Initializing a whole seq_buf struct for these small cases is too much overhead... For both cases (small without seq_buf, large with seq_buf), it is also frequently needed to know the resulting strlen. seq_buf doesn't do this right today, and a strscpy-style return value also doesn't tell us. :( -- Kees Cook