Messages in this thread | | | Date | Sun, 08 Jan 2012 16:04:21 +0100 | From | Takashi Iwai <> | Subject | Re: [PATCH v2] ALSA: usb-audio: fix possible hang and overflow in parse_uac2_sample_rate_range() |
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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@suse.de> > Signed-off-by: Xi Wang <xi.wang@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 > >
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