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 A6B18C433E6 for ; Thu, 27 Aug 2020 22:45:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8E4DE20848 for ; Thu, 27 Aug 2020 22:45:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727892AbgH0WpX (ORCPT ); Thu, 27 Aug 2020 18:45:23 -0400 Received: from smtprelay0094.hostedemail.com ([216.40.44.94]:36066 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726826AbgH0WpV (ORCPT ); Thu, 27 Aug 2020 18:45:21 -0400 Received: from filter.hostedemail.com (clb03-v110.bra.tucows.net [216.40.38.60]) by smtprelay05.hostedemail.com (Postfix) with ESMTP id DB2FD180339CD; Thu, 27 Aug 2020 22:45:20 +0000 (UTC) X-Session-Marker: 6A6F6540706572636865732E636F6D X-HE-Tag: pies81_1b16d5127070 X-Filterd-Recvd-Size: 3013 Received: from XPS-9350.home (unknown [47.151.133.149]) (Authenticated sender: joe@perches.com) by omf15.hostedemail.com (Postfix) with ESMTPA; Thu, 27 Aug 2020 22:45:19 +0000 (UTC) Message-ID: <5ebe5c2737b59d04f1b8a46008cd3159c638f9d0.camel@perches.com> Subject: Re: [Cocci] [PATCH] usb: atm: don't use snprintf() for sysfs attrs From: Joe Perches To: Kees Cook , Denis Efremov Cc: Julia Lawall , "Gustavo A. R. Silva" , Greg Kroah-Hartman , linux-usb@vger.kernel.org, Rasmus Villemoes , linux-kernel@vger.kernel.org, cocci , Alex Dewar Date: Thu, 27 Aug 2020 15:45:17 -0700 In-Reply-To: <202008271517.ECC1F1F8F@keescook> References: <20200824222322.22962-1-alex.dewar90@gmail.com> <48f2dc90-7852-eaf1-55d7-2c85cf954688@rasmusvillemoes.dk> <20200827071537.GA168593@kroah.com> <20200827131819.7rcl2f5js3hkoqj2@lenovo-laptop> <20200827144846.yauuttjaqtxaldxg@lenovo-laptop> <5d1dfb9b031130d4d20763ec621233a19d6a88a2.camel@perches.com> <5853c58e-7d26-2cf9-6cbf-698ecd93cbf9@linux.com> <202008271517.ECC1F1F8F@keescook> Content-Type: text/plain; charset="ISO-8859-1" User-Agent: Evolution 3.36.4-0ubuntu1 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-usb-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org On Thu, 2020-08-27 at 15:20 -0700, Kees Cook wrote: > On Fri, Aug 28, 2020 at 12:01:34AM +0300, Denis Efremov wrote: > > Just FYI, I've send an addition to the device_attr_show.cocci script[1] to turn > > simple cases of snprintf (e.g. "%i") to sprintf. Looks like many developers would > > like it more than changing snprintf to scnprintf. As for me, I don't like the idea > > of automated altering of the original logic from bounded snprint to unbouded one > > with sprintf. > > Agreed. This just makes me cringe. If the API design declares that when > a show() callback starts, buf has been allocated with PAGE_SIZE bytes, > then that's how the logic should proceed, and it should be using > scnprintf... > > show(...) { > size_t remaining = PAGE_SIZE; > > ... > remaining -= scnprintf(buf, remaining, "fmt", var args ...); > remaining -= scnprintf(buf, remaining, "fmt", var args ...); > remaining -= scnprintf(buf, remaining, "fmt", var args ...); > > return PAGE_SIZE - remaining; > } It seems likely that coccinelle could do those transform with any of sprintf/snprintf/scnprint too. Though my bikeshed would use a single function and have that function know the maximum output size Something like: With single line use: return sysfs_emit(buf, buf, fmt, ...) - buf; and multi-line use: char *pos = buf; pos = sysfs_emit(buf, pos, fmt1, ...); pos = sysfs_emit(buf, pos, fmt2, ...); ... return pos - buf;