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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 9946EC433E0 for ; Thu, 11 Feb 2021 12:59:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5F76E64E2F for ; Thu, 11 Feb 2021 12:59:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230139AbhBKM73 (ORCPT ); Thu, 11 Feb 2021 07:59:29 -0500 Received: from mx2.suse.de ([195.135.220.15]:38904 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231487AbhBKM4N (ORCPT ); Thu, 11 Feb 2021 07:56:13 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1613048127; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=tDHyixPZc/hmwJlqM4MC2vKvRBa6s3jBQvaQGvjSoUI=; b=F3z/vrIEVhUfZGwqeG2qCI7qxZnhkSJOrLREdCB8mhjpdG2qgKYyEo/nzk/zyCtGBziZ3L /LS8n/HXbEMlAfueoiMfHhuvmIwReGag+vKuB4IB5Cxs0Nc55uMLZzYyWww2FjRuL2piMz X9XhAl7iTyZD3KcfraFKLVultoWxxi8= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id D483AAC69; Thu, 11 Feb 2021 12:55:26 +0000 (UTC) Date: Thu, 11 Feb 2021 13:55:25 +0100 From: Petr Mladek To: Richard Fitzgerald Cc: Andy Shevchenko , rostedt@goodmis.org, sergey.senozhatsky@gmail.com, linux@rasmusvillemoes.dk, shuah@kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, patches@opensource.cirrus.com Subject: Re: [PATCH v5 2/4] lib: vsprintf: Fix handling of number field widths in vsscanf Message-ID: References: <20210208140154.10964-1-rf@opensource.cirrus.com> <20210208140154.10964-2-rf@opensource.cirrus.com> <2f9f57a3-f0d6-1e07-36f9-682d65b481ad@opensource.cirrus.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2f9f57a3-f0d6-1e07-36f9-682d65b481ad@opensource.cirrus.com> Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org On Mon 2021-02-08 17:38:29, Richard Fitzgerald wrote: > On 08/02/2021 15:18, Andy Shevchenko wrote: > > On Mon, Feb 08, 2021 at 02:01:52PM +0000, Richard Fitzgerald wrote: > > > The existing code attempted to handle numbers by doing a strto[u]l(), > > > ignoring the field width, and then repeatedly dividing to extract the > > > field out of the full converted value. If the string contains a run of > > > valid digits longer than will fit in a long or long long, this would > > > overflow and no amount of dividing can recover the correct value. > > > > > > -unsigned long long simple_strtoull(const char *cp, char **endp, unsigned int base) > > > +static unsigned long long simple_strntoull(const char *startp, size_t max_chars, > > > + char **endp, unsigned int base) > > > { > > > - unsigned long long result; > > > + const char *cp; > > > + unsigned long long result = 0ULL; > > > unsigned int rv; > > > - cp = _parse_integer_fixup_radix(cp, &base); > > > - rv = _parse_integer(cp, base, &result); > > > + cp = _parse_integer_fixup_radix(startp, &base); > > > + if ((cp - startp) >= max_chars) { > > > + cp = startp + max_chars; > > > + goto out; > > > + } > > > + > > > + max_chars -= (cp - startp); > > > + rv = _parse_integer_limit(cp, base, &result, max_chars); > > > /* FIXME */ > > > cp += (rv & ~KSTRTOX_OVERFLOW); > > > +out: > > > if (endp) > > > *endp = (char *)cp; > > > return result; > > > } > > > > A nit-pick: What if we rewrite above as > > > > static unsigned long long simple_strntoull(const char *cp, size_t max_chars, > > char **endp, unsigned int base) > > { > > unsigned long long result = 0ULL; > > const char *startp = cp; > > unsigned int rv; > > size_t chars; > > > > cp = _parse_integer_fixup_radix(cp, &base); > > chars = cp - startp; > > if (chars >= max_chars) { > > /* We hit the limit */ > > cp = startp + max_chars; > > } else { > > rv = _parse_integer_limit(cp, base, &result, max_chars - chars); > > /* FIXME */ > > cp += (rv & ~KSTRTOX_OVERFLOW); > > } > > > > if (endp) > > *endp = (char *)cp; > > > > return result; > > } > > > > ... > > > I don't mind rewriting that code if you prefer that way. > I am used to working on other kernel subsytems where the preference is > to bail out on the error case so that the "normal" case flows without > nesting. Yeah. But in this case Andy's variant looks slightly better redable to me. ... > > > > > + val.s = simple_strntoll(str, > > > + field_width > 0 ? field_width : SIZE_MAX, > > > + &next, base); > > > > A nit-pick: Wouldn't be negative field_width "big enough" to just being used as > field_width is s16 so really should be sign-extended I guess that Andy just missed that it was a signed type. And it has to be because -1 means SIZE_MAX. > to make it "very > big". I think this would be less readable what the intention is and what > assumptions it is based on. There's a risk someone would look at > > (size_t)(long)field_width > > and think the (long) is redundant. > Perhaps change field_width to int? There I ask myself "if it can be an > int, why is it declared s16?" and worry there is something subtle in the > code. > > My personal preference is to avoid using tricks in code that isn't time > critical. I agree. Let's keep the check with signed type. > > is? Also, is field_width == 0 should be treated as "parse to the MAX"? filed_width == 0 actually means that no characters are read. I should return zero value. > > ... > > Earlier code terminates scanning if the width parsed from the format > string is <= 0. To make it clear what earlier code means. vsscanf() bail out earlier when field_width == 0. It is handled by this code: /* get field width */ field_width = -1; if (isdigit(*fmt)) { field_width = skip_atoi(&fmt); if (field_width <= 0) break; } > So field_width can only be -1 or > 0 here. But now you > point it out, that test would be better as field_width >= 0 ... so > it deals with 0 if it ever happened to sneak through to here > somehow. It might make sense to be proactive and change it to >= 0. But I would do it in a separate patch. The "< 0" condition matches the original code. Best Regards, Petr