linux-kernel - [PATCH] ALSA: usb-audio: fix possible hang and overflow in parse_uac2_sample_rate

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Message-Id: <1325698749-5353-1-git-send-email-xi.wang@gmail.com>
Date:	Wed,  4 Jan 2012 12:39:09 -0500
From:	Xi Wang <xi.wang@...il.com>
To:	Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.de>,
	Clemens Ladisch <clemens@...isch.de>,
	Daniel Mack <zonque@...il.com>,
	Wolfgang Breyha <wbreyha@....net>
Cc:	alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
	Xi Wang <xi.wang@...il.com>
Subject: [PATCH] ALSA: usb-audio: fix possible hang and overflow in parse_uac2_sample_rate_range()

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 <xi.wang@...il.com>
---
 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

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