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    Subject[PATCH 4.19 280/306] ALSA: usb-audio: Fix NULL dereference at parsing BADD
    Date
    From: Takashi Iwai <tiwai@suse.de>

    commit 9435f2bb66874a0c4dd25e7c978957a7ca2c93b1 upstream.

    snd_usb_mixer_controls_badd() that parses UAC3 BADD profiles misses a
    NULL check for the given interfaces. When a malformed USB descriptor
    is passed, this may lead to an Oops, as spotted by syzkaller.
    Skip the iteration if the interface doesn't exist for avoiding the
    crash.

    Fixes: 17156f23e93c ("ALSA: usb: add UAC3 BADD profiles support")
    Reported-by: syzbot+a36ab65c6653d7ccdd62@syzkaller.appspotmail.com
    Suggested-by: Dan Carpenter <dan.carpenter@oracle.com>
    Cc: <stable@vger.kernel.org>
    Link: https://lore.kernel.org/r/20191122112840.24797-1-tiwai@suse.de
    Signed-off-by: Takashi Iwai <tiwai@suse.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    sound/usb/mixer.c | 3 +++
    1 file changed, 3 insertions(+)

    --- a/sound/usb/mixer.c
    +++ b/sound/usb/mixer.c
    @@ -2949,6 +2949,9 @@ static int snd_usb_mixer_controls_badd(s
    continue;

    iface = usb_ifnum_to_if(dev, intf);
    + if (!iface)
    + continue;
    +
    num = iface->num_altsetting;

    if (num < 2)

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