From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752227Ab2AHJJU (ORCPT ); Sun, 8 Jan 2012 04:09:20 -0500 Received: from cantor2.suse.de ([195.135.220.15]:38232 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751727Ab2AHJJQ (ORCPT ); Sun, 8 Jan 2012 04:09:16 -0500 Date: Sun, 08 Jan 2012 10:09:11 +0100 Message-ID: From: Takashi Iwai To: Xi Wang Cc: Jaroslav Kysela , Clemens Ladisch , Daniel Mack , Wolfgang Breyha , alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] ALSA: usb-audio: fix possible hang and overflow in parse_uac2_sample_rate_range() In-Reply-To: <1325698749-5353-1-git-send-email-xi.wang@gmail.com> References: <1325698749-5353-1-git-send-email-xi.wang@gmail.com> User-Agent: Wanderlust/2.15.6 (Almost Unreal) SEMI/1.14.6 (Maruoka) FLIM/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL/10.7 Emacs/23.3 (x86_64-suse-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka") Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org At Wed, 4 Jan 2012 12:39:09 -0500, Xi Wang wrote: > > A malicious USB device may feed in carefully crafted min/max/res values, > so that the inner loop in parse_uac2_sample_rate_range() could run for > a long time or even never terminate, e.g., given max = INT_MAX. > > Also nr_rates could be a large integer, which causes an integer overflow > in the subsequent call to kmalloc() in parse_audio_format_rates_v2(). > Thus, kmalloc() would allocate a smaller buffer than expected, leading > to a memory corruption. > > To exploit the two vulnerabilities, an attacker needs physical access > to the machine to plug in a malicious USB device. > > This patch makes two changes. > > 1) The type of "rate" is changed to unsigned int, so that the loop could > stop once "rate" is larger than INT_MAX. > > 2) Limit nr_rates to avoid overflow. > > Signed-off-by: Xi Wang Thanks for the patch. As of now, I have little time to evaluate, so I might have missed something, but I wonder whether /* avoid overflow */ if (nr_rates == KMALLOC_MAX_SIZE / sizeof(int)) break; is the best way to check. This looks ugly to me. If we need to limit the number of rates, better to define some proper numbers as the upper limit. And then, it should warn, not only breaking loop. Anyway I'll check this tomorrow in more details. thanks, Takashi > --- > sound/usb/format.c | 5 ++++- > 1 files changed, 4 insertions(+), 1 deletions(-) > > diff --git a/sound/usb/format.c b/sound/usb/format.c > index 89421d1..a99de67 100644 > --- a/sound/usb/format.c > +++ b/sound/usb/format.c > @@ -226,7 +226,7 @@ static int parse_uac2_sample_rate_range(struct audioformat *fp, int nr_triplets, > int min = combine_quad(&data[2 + 12 * i]); > int max = combine_quad(&data[6 + 12 * i]); > int res = combine_quad(&data[10 + 12 * i]); > - int rate; > + unsigned int rate; > > if ((max < 0) || (min < 0) || (res < 0) || (max < min)) > continue; > @@ -253,6 +253,9 @@ static int parse_uac2_sample_rate_range(struct audioformat *fp, int nr_triplets, > fp->rates |= snd_pcm_rate_to_rate_bit(rate); > > nr_rates++; > + /* avoid overflow */ > + if (nr_rates == KMALLOC_MAX_SIZE / sizeof(int)) > + break; > > /* avoid endless loop */ > if (res == 0) > -- > 1.7.5.4 > From mboxrd@z Thu Jan 1 00:00:00 1970 From: Takashi Iwai Subject: Re: [PATCH] ALSA: usb-audio: fix possible hang and overflow in parse_uac2_sample_rate_range() Date: Sun, 08 Jan 2012 10:09:11 +0100 Message-ID: References: <1325698749-5353-1-git-send-email-xi.wang@gmail.com> Mime-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka") Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mx2.suse.de (cantor2.suse.de [195.135.220.15]) by alsa0.perex.cz (Postfix) with ESMTP id B8C1F1038B4 for ; Sun, 8 Jan 2012 10:09:14 +0100 (CET) In-Reply-To: <1325698749-5353-1-git-send-email-xi.wang@gmail.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: alsa-devel-bounces@alsa-project.org Errors-To: alsa-devel-bounces@alsa-project.org To: Xi Wang Cc: alsa-devel@alsa-project.org, Clemens Ladisch , linux-kernel@vger.kernel.org, Daniel Mack , Wolfgang Breyha List-Id: alsa-devel@alsa-project.org At Wed, 4 Jan 2012 12:39:09 -0500, Xi Wang wrote: > > A malicious USB device may feed in carefully crafted min/max/res values, > so that the inner loop in parse_uac2_sample_rate_range() could run for > a long time or even never terminate, e.g., given max = INT_MAX. > > Also nr_rates could be a large integer, which causes an integer overflow > in the subsequent call to kmalloc() in parse_audio_format_rates_v2(). > Thus, kmalloc() would allocate a smaller buffer than expected, leading > to a memory corruption. > > To exploit the two vulnerabilities, an attacker needs physical access > to the machine to plug in a malicious USB device. > > This patch makes two changes. > > 1) The type of "rate" is changed to unsigned int, so that the loop could > stop once "rate" is larger than INT_MAX. > > 2) Limit nr_rates to avoid overflow. > > Signed-off-by: Xi Wang Thanks for the patch. As of now, I have little time to evaluate, so I might have missed something, but I wonder whether /* avoid overflow */ if (nr_rates == KMALLOC_MAX_SIZE / sizeof(int)) break; is the best way to check. This looks ugly to me. If we need to limit the number of rates, better to define some proper numbers as the upper limit. And then, it should warn, not only breaking loop. Anyway I'll check this tomorrow in more details. thanks, Takashi > --- > sound/usb/format.c | 5 ++++- > 1 files changed, 4 insertions(+), 1 deletions(-) > > diff --git a/sound/usb/format.c b/sound/usb/format.c > index 89421d1..a99de67 100644 > --- a/sound/usb/format.c > +++ b/sound/usb/format.c > @@ -226,7 +226,7 @@ static int parse_uac2_sample_rate_range(struct audioformat *fp, int nr_triplets, > int min = combine_quad(&data[2 + 12 * i]); > int max = combine_quad(&data[6 + 12 * i]); > int res = combine_quad(&data[10 + 12 * i]); > - int rate; > + unsigned int rate; > > if ((max < 0) || (min < 0) || (res < 0) || (max < min)) > continue; > @@ -253,6 +253,9 @@ static int parse_uac2_sample_rate_range(struct audioformat *fp, int nr_triplets, > fp->rates |= snd_pcm_rate_to_rate_bit(rate); > > nr_rates++; > + /* avoid overflow */ > + if (nr_rates == KMALLOC_MAX_SIZE / sizeof(int)) > + break; > > /* avoid endless loop */ > if (res == 0) > -- > 1.7.5.4 >