Commit 4fa0e81b authored Jan 08, 2012 by Xi Wang Committed by Takashi Iwai Jan 08, 2012

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 1024.

Suggested-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Xi Wang <xi.wang@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

parent fb65c2df

sound/usb/format.c

+7 −1

Original line number	Diff line number	Diff line
		@@ -209,6 +209,8 @@ 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
		@@ -226,7 +228,7 @@ 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 +255,10 @@ 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) {
		snd_printk(KERN_ERR "invalid uac2 rates\n");
		break;
		}

		/* avoid endless loop */
		if (res == 0)

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