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 074CAC433DB for ; Tue, 5 Jan 2021 09:29:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B4AC522AED for ; Tue, 5 Jan 2021 09:29:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728168AbhAEJ3D (ORCPT ); Tue, 5 Jan 2021 04:29:03 -0500 Received: from smtprelay0207.hostedemail.com ([216.40.44.207]:57022 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727853AbhAEJ3C (ORCPT ); Tue, 5 Jan 2021 04:29:02 -0500 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> Subject: deprecated.rst: deprecated strcpy ? (was: [PATCH] checkpatch: add a new check for strcpy/strlcpy uses) From: Joe Perches To: Dwaipayan Ray , Kees Cook , Jonathan Corbet Cc: linux-kernel-mentees@lists.linuxfoundation.org, linux-kernel , Lukas Bulwahn Date: Tue, 05 Jan 2021 01:28:18 -0800 In-Reply-To: References: <20210105082303.15310-1-dwaipayanray1@gmail.com> <50cc861121b62b3c1518222f24f679c3f72b868d.camel@perches.com> Content-Type: text/plain; charset="ISO-8859-1" User-Agent: Evolution 3.38.1-1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > > > >         strcpy(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=y` 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.