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    Subject[PATCH 4.4 58/77] ALSA: usb-audio: Fix an OOB bug in parse_audio_mixer_unit
    Date
    From: Hui Peng <benquike@gmail.com>

    commit daac07156b330b18eb5071aec4b3ddca1c377f2c upstream.

    The `uac_mixer_unit_descriptor` shown as below is read from the
    device side. In `parse_audio_mixer_unit`, `baSourceID` field is
    accessed from index 0 to `bNrInPins` - 1, the current implementation
    assumes that descriptor is always valid (the length of descriptor
    is no shorter than 5 + `bNrInPins`). If a descriptor read from
    the device side is invalid, it may trigger out-of-bound memory
    access.

    ```
    struct uac_mixer_unit_descriptor {
    __u8 bLength;
    __u8 bDescriptorType;
    __u8 bDescriptorSubtype;
    __u8 bUnitID;
    __u8 bNrInPins;
    __u8 baSourceID[];
    }
    ```

    This patch fixes the bug by add a sanity check on the length of
    the descriptor.

    Reported-by: Hui Peng <benquike@gmail.com>
    Reported-by: Mathias Payer <mathias.payer@nebelwelt.net>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: Hui Peng <benquike@gmail.com>
    Signed-off-by: Takashi Iwai <tiwai@suse.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    sound/usb/mixer.c | 1 +
    1 file changed, 1 insertion(+)

    --- a/sound/usb/mixer.c
    +++ b/sound/usb/mixer.c
    @@ -1647,6 +1647,7 @@ static int parse_audio_mixer_unit(struct
    int pin, ich, err;

    if (desc->bLength < 11 || !(input_pins = desc->bNrInPins) ||
    + desc->bLength < sizeof(*desc) + desc->bNrInPins ||
    !(num_outs = uac_mixer_unit_bNrChannels(desc))) {
    usb_audio_err(state->chip,
    "invalid MIXER UNIT descriptor %d\n",

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