linux-kernel - [PATCH] ALSA: usb-audio: avoid integer overflow in create_fixed_stream

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Date:	Tue, 14 Feb 2012 05:18:48 -0500
From:	Xi Wang <xi.wang@...il.com>
To:	Takashi Iwai <tiwai@...e.de>, Daniel Mack <zonque@...il.com>
Cc:	alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
	Xi Wang <xi.wang@...il.com>
Subject: [PATCH] ALSA: usb-audio: avoid integer overflow in create_fixed_stream_quirk()

A malicious USB device could feed in a large nr_rates value.  This would
cause the subsequent call to kmemdup() to allocate a smaller buffer than
expected, leading to out-of-bounds access.

This patch validates the nr_rates value and reuses the limit introduced
in commit 4fa0e81b ("ALSA: usb-audio: fix possible hang and overflow
in parse_uac2_sample_rate_range()").

Signed-off-by: Xi Wang <xi.wang@...il.com>
---
 sound/usb/card.h   |    1 +
 sound/usb/format.c |    4 +---
 sound/usb/quirks.c |    6 +++++-
 3 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/sound/usb/card.h b/sound/usb/card.h
index a39edcc..da5fa1a 100644
--- a/sound/usb/card.h
+++ b/sound/usb/card.h
@@ -1,6 +1,7 @@
 #ifndef __USBAUDIO_CARD_H
 #define __USBAUDIO_CARD_H
 
+#define MAX_NR_RATES	1024
 #define MAX_PACKS	20
 #define MAX_PACKS_HS	(MAX_PACKS * 8)	/* in high speed mode */
 #define MAX_URBS	8
diff --git a/sound/usb/format.c b/sound/usb/format.c
index e09aba1..ddfef57 100644
--- a/sound/usb/format.c
+++ b/sound/usb/format.c
@@ -209,8 +209,6 @@ static int parse_audio_format_rates_v1(struct snd_usb_audio *chip, struct audiof
 	return 0;
 }
 
-#define MAX_UAC2_NR_RATES 1024
-
 /*
  * Helper function to walk the array of sample rate triplets reported by
  * the device. The problem is that we need to parse whole array first to
@@ -255,7 +253,7 @@ static int parse_uac2_sample_rate_range(struct audioformat *fp, int nr_triplets,
 			fp->rates |= snd_pcm_rate_to_rate_bit(rate);
 
 			nr_rates++;
-			if (nr_rates >= MAX_UAC2_NR_RATES) {
+			if (nr_rates >= MAX_NR_RATES) {
 				snd_printk(KERN_ERR "invalid uac2 rates\n");
 				break;
 			}
diff --git a/sound/usb/quirks.c b/sound/usb/quirks.c
index a3ddac0..2781726 100644
--- a/sound/usb/quirks.c
+++ b/sound/usb/quirks.c
@@ -132,10 +132,14 @@ static int create_fixed_stream_quirk(struct snd_usb_audio *chip,
 	unsigned *rate_table = NULL;
 
 	fp = kmemdup(quirk->data, sizeof(*fp), GFP_KERNEL);
-	if (! fp) {
+	if (!fp) {
 		snd_printk(KERN_ERR "cannot memdup\n");
 		return -ENOMEM;
 	}
+	if (fp->nr_rates > MAX_NR_RATES) {
+		kfree(fp);
+		return -EINVAL;
+	}
 	if (fp->nr_rates > 0) {
 		rate_table = kmemdup(fp->rate_table,
 				     sizeof(int) * fp->nr_rates, GFP_KERNEL);
-- 
1.7.5.4

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