From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754192AbbINJQ7 (ORCPT ); Mon, 14 Sep 2015 05:16:59 -0400 Received: from mx1.redhat.com ([209.132.183.28]:6424 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752588AbbINJQ6 (ORCPT ); Mon, 14 Sep 2015 05:16:58 -0400 From: Vitaly Kuznetsov To: James Bottomley Cc: "akpm\@linux-foundation.org" , "linux\@rasmusvillemoes.dk" , "andriy.shevchenko\@linux.intel.com" , "linux-kernel\@vger.kernel.org" , "kys\@microsoft.com" Subject: Re: [PATCH] lib/string_helpers.c: fix infinite loop in string_get_size() References: <1441371393-15030-1-git-send-email-vkuznets@redhat.com> <20150910160815.30d56ee48bbfdf5eed783c53@linux-foundation.org> <1441996263.6276.4.camel@Odin.com> Date: Mon, 14 Sep 2015 11:16:55 +0200 In-Reply-To: <1441996263.6276.4.camel@Odin.com> (James Bottomley's message of "Fri, 11 Sep 2015 18:31:07 +0000") Message-ID: <87d1xl1htk.fsf@vitty.brq.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org James Bottomley writes: > On Thu, 2015-09-10 at 16:08 -0700, Andrew Morton wrote: >> On Fri, 4 Sep 2015 14:56:33 +0200 Vitaly Kuznetsov wrote: >> >> > string_get_size(1, 512, 0, ..., ...) call results in an infinite loop. The >> > problem is that if size == 0 when we start calculating sf_cap this loop >> > will never end. >> > >> > The caller causing the issue is sd_read_capacity(), the problem was noticed >> > on Hyper-V. >> >> When fixing bugs, please provide enough info for others to be able to >> understand which kernel version(s) need the fix. In this case: what >> end-user action triggers this bug? (iow, how does sdkp->capacity >> become zero?) > > Any more details. The attached programme, which is cut straight out of > the algorithm in string_helpers.c and modified for a C environment > slightly (only in do_div and the typedefs) produces this > > hello > STRING IS 512 B > > With your input, so I don't think the problem is where you think it > is. Sorry for delayed reply, I was traveling. Please change string_get_size(1, 512, STRING_UNITS_2, buf, sizeof(buf)); to string_get_size(1, 512, STRING_UNITS_10, buf, sizeof(buf)); in your test.c program to see the issue, it will enter the infinite loop as well. Regardless to Hyper-V I think such library function shouldn't do such nasty things (but I'll try to investigate why such small size was reported). -- Vitaly