From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xi Wang Subject: [PATCH] ALSA: usb-audio: fix possible hang and overflow in parse_uac2_sample_rate_range() Date: Wed, 4 Jan 2012 12:39:09 -0500 Message-ID: <1325698749-5353-1-git-send-email-xi.wang@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail-qy0-f179.google.com (mail-qy0-f179.google.com [209.85.216.179]) by alsa0.perex.cz (Postfix) with ESMTP id 063D52439C for ; Wed, 4 Jan 2012 18:40:57 +0100 (CET) Received: by qcol42 with SMTP id l42so11004376qco.38 for ; Wed, 04 Jan 2012 09:40:57 -0800 (PST) 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: Jaroslav Kysela , Takashi Iwai , Clemens Ladisch , Daniel Mack , Wolfgang Breyha Cc: alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org, Xi Wang List-Id: alsa-devel@alsa-project.org 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 --- 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