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    Subject[PATCH v2] 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>
    ---
    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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