From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757184Ab0JLJfN (ORCPT ); Tue, 12 Oct 2010 05:35:13 -0400 Received: from opensource.wolfsonmicro.com ([80.75.67.52]:43080 "EHLO opensource2.wolfsonmicro.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S932097Ab0JLJfK (ORCPT ); Tue, 12 Oct 2010 05:35:10 -0400 Date: Tue, 12 Oct 2010 10:35:07 +0100 From: Mark Brown To: Takashi Iwai Cc: Dan Carpenter , Liam Girdwood , Jaroslav Kysela , Peter Ujfalusi , Jassi Brar , alsa-devel@alsa-project.org, kernel-janitors@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [patch] ASoC: soc: snprintf() doesn't return negative Message-ID: <20101012093506.GB30933@rakim.wolfsonmicro.main> References: <20101011035416.GD5851@bicker> <20101011104009.GB9231@rakim.wolfsonmicro.main> <20101011164038.GE5851@bicker> <20101011185148.GB22355@opensource.wolfsonmicro.com> <20101011194502.GK5851@bicker> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Cookie: Words must be weighed, not counted. User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 11, 2010 at 10:57:40PM +0200, Takashi Iwai wrote: > Dan Carpenter wrote: > Well, actually we should fix either: > - check the return of snprintf() at each time properly, > > list_for_each_entry(dai, &dai_list, list) { > int len = snprintf(buf + ret, PAGE_SIZE - ret, "%s\n", dai->name); > if (len < 0) > return len; > ret += len; > } In this case we're deliberately eating the error since all these files are about getting diagnostics out - the code is intentionally soldiering on and trying to get as much data out as possible rather than giving up on error. > In either case, a negative check after for loop is superfluous. In those ones, yes - it's pretty much there for paranoia since the copy to userspace is more likely to explode than random memory corruption. > And, when no negative return value is assured (or filtered out like > above), there can't be overflow, too. snprintf() fills the string > at most the size including NUL-char. OTOH, it returns the size that > doesn't include NUL-char. Dan was saying that it would return sizes larger than the string it wrote (which is a behaviour of some implementations) which would be an issue since it would cause us to pass bad buffer pointers into subsequent snprintf() calls. I've not had time to look at this properly but Dan's analysis seems off.