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 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 167B1C433E6 for ; Tue, 5 Jan 2021 09:28:29 +0000 (UTC) Received: from fraxinus.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 mail.kernel.org (Postfix) with ESMTPS id 6C98622A83 for ; Tue, 5 Jan 2021 09:28:28 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6C98622A83 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=perches.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linux-kernel-mentees-bounces@lists.linuxfoundation.org Received: from localhost (localhost [127.0.0.1]) by fraxinus.osuosl.org (Postfix) with ESMTP id 1517985CD0; Tue, 5 Jan 2021 09:28:28 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from fraxinus.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id UsKDjA5ZA_Uw; Tue, 5 Jan 2021 09:28:27 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by fraxinus.osuosl.org (Postfix) with ESMTP id 7730885C52; Tue, 5 Jan 2021 09:28:27 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 62892C0891; Tue, 5 Jan 2021 09:28:27 +0000 (UTC) Received: from silver.osuosl.org (smtp3.osuosl.org [140.211.166.136]) by lists.linuxfoundation.org (Postfix) with ESMTP id 4F4A4C013A for ; Tue, 5 Jan 2021 09:28:24 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by silver.osuosl.org (Postfix) with ESMTP id 1578220495 for ; Tue, 5 Jan 2021 09:28:24 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from silver.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id Z+9ZWgcn2JF0 for ; Tue, 5 Jan 2021 09:28:22 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from smtprelay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by silver.osuosl.org (Postfix) with ESMTPS id 9E0C6203ED for ; Tue, 5 Jan 2021 09:28:22 +0000 (UTC) Received: from filter.hostedemail.com (clb03-v110.bra.tucows.net [216.40.38.60]) by smtprelay01.hostedemail.com (Postfix) with ESMTP id 63E22100E7B46; Tue, 5 Jan 2021 09:28:20 +0000 (UTC) X-Session-Marker: 6A6F6540706572636865732E636F6D X-HE-Tag: books34_27150c3274d7 X-Filterd-Recvd-Size: 3489 Received: from [192.168.1.159] (unknown [47.151.137.21]) (Authenticated sender: joe@perches.com) by omf09.hostedemail.com (Postfix) with ESMTPA; Tue, 5 Jan 2021 09:28:19 +0000 (UTC) Message-ID: <3ffe616d8c3fb54833bfc4d86cb73427cf6c7add.camel@perches.com> From: Joe Perches To: Dwaipayan Ray , Kees Cook , Jonathan Corbet Date: Tue, 05 Jan 2021 01:28:18 -0800 In-Reply-To: References: <20210105082303.15310-1-dwaipayanray1@gmail.com> <50cc861121b62b3c1518222f24f679c3f72b868d.camel@perches.com> User-Agent: Evolution 3.38.1-1 MIME-Version: 1.0 Cc: linux-kernel-mentees@lists.linuxfoundation.org, linux-kernel Subject: [Linux-kernel-mentees] deprecated.rst: deprecated strcpy ? (was: [PATCH] checkpatch: add a new check for strcpy/strlcpy uses) X-BeenThere: linux-kernel-mentees@lists.linuxfoundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Errors-To: linux-kernel-mentees-bounces@lists.linuxfoundation.org Sender: "Linux-kernel-mentees" On Tue, 2021-01-05 at 14:29 +0530, Dwaipayan Ray wrote: > On Tue, Jan 5, 2021 at 2:14 PM Joe Perches wrote: > > = > > On Tue, 2021-01-05 at 13:53 +0530, Dwaipayan Ray wrote: > > > strcpy() performs no bounds checking on the destination buffer. > > > This could result in linear overflows beyond the end of the buffer. > > > = > > > strlcpy() reads the entire source buffer first. This read > > > may exceed the destination size limit. This can be both inefficient > > > and lead to linear read overflows. > > > = > > > The safe replacement to both of these is to use strscpy() instead. > > > Add a new checkpatch warning which alerts the user on finding usage of > > > strcpy() or strlcpy(). > > = > > I do not believe that strscpy is preferred over strcpy. > > = > > When the size of the output buffer is known to be larger > > than the input, strcpy is faster. > > = > > There are about 2k uses of strcpy. > > Is there a use where strcpy use actually matters? > > I don't know offhand... > > = > > But I believe compilers do not optimize away the uses of strscpy > > to a simple memcpy like they do for strcpy with a const from > > = > > =A0=A0=A0=A0=A0=A0=A0=A0strcpy(foo, "bar"); > > = > = > Yes the optimization here definitely helps. So in case the programmer > knows that the destination buffer is always larger, then strcpy() should = be > preferred? I think the documentation might have been too strict about > strcpy() uses here: > = > Documentation/process/deprecated.rst: > "strcpy() performs no bounds checking on the destination buffer. This > could result in linear overflows beyond the end of the buffer, leading to > all kinds of misbehaviors. While `CONFIG_FORTIFY_SOURCE=3Dy` and various > compiler flags help reduce the risk of using this function, there is > no good reason to add new uses of this function. The safe replacement > is strscpy(),..." Kees/Jonathan: Perhaps this text is overly restrictive. There are ~2k uses of strcpy in the kernel. About half of these are where the buffer length of foo is known and the use is 'strcpy(foo, "bar")' so the compiler converts/optimizes away the strcpy to memcpy and may not even put "bar" into the string table. I believe strscpy uses do not have this optimization. Is there a case where the runtime costs actually matters? I expect so. _______________________________________________ Linux-kernel-mentees mailing list Linux-kernel-mentees@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees