[alsa-devel] [PATCH v2] ALSA: usb-audio: fix possible hang and overflow in parse_uac2_sample_rate_range()

[Takashi Iwai]

At Sun, 08 Jan 2012 09:02:52 -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 1024.
> 
> Suggested-by: Takashi Iwai <tiwai at suse.de>
> Signed-off-by: Xi Wang <xi.wang at gmail.com>

Thanks, applied now.


Takashi

> ---
>  sound/usb/format.c |    8 +++++++-
>  1 files changed, 7 insertions(+), 1 deletions(-)
> 
> diff --git a/sound/usb/format.c b/sound/usb/format.c
> index 89421d1..e09aba1 100644
> --- a/sound/usb/format.c
> +++ b/sound/usb/format.c
> @@ -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)
> -- 
> 1.7.5.4
> 
>