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

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Date:	Wed, 15 Feb 2012 15:00:37 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	Xi Wang <xi.wang@...il.com>
Cc:	Daniel Mack <zonque@...il.com>, alsa-devel@...a-project.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ALSA: usb-audio: avoid integer overflow in create_fixed_stream_quirk()

At Tue, 14 Feb 2012 05:18:48 -0500,
Xi Wang wrote:
> 
> 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>

Thanks, applied now.


Takashi

> ---
>  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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