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    Subject[PATCH 4.19 097/131] ALSA: usb-audio: Fix usb audio refcnt leak when getting spdif
    Date
    From: Xiyu Yang <xiyuyang19@fudan.edu.cn>

    commit 59e1947ca09ebd1cae147c08c7c41f3141233c84 upstream.

    snd_microii_spdif_default_get() invokes snd_usb_lock_shutdown(), which
    increases the refcount of the snd_usb_audio object "chip".

    When snd_microii_spdif_default_get() returns, local variable "chip"
    becomes invalid, so the refcount should be decreased to keep refcount
    balanced.

    The reference counting issue happens in several exception handling paths
    of snd_microii_spdif_default_get(). When those error scenarios occur
    such as usb_ifnum_to_if() returns NULL, the function forgets to decrease
    the refcnt increased by snd_usb_lock_shutdown(), causing a refcnt leak.

    Fix this issue by jumping to "end" label when those error scenarios
    occur.

    Fixes: 447d6275f0c2 ("ALSA: usb-audio: Add sanity checks for endpoint accesses")
    Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
    Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
    Cc: <stable@vger.kernel.org>
    Link: https://lore.kernel.org/r/1587617711-13200-1-git-send-email-xiyuyang19@fudan.edu.cn
    Signed-off-by: Takashi Iwai <tiwai@suse.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    sound/usb/mixer_quirks.c | 12 ++++++++----
    1 file changed, 8 insertions(+), 4 deletions(-)

    --- a/sound/usb/mixer_quirks.c
    +++ b/sound/usb/mixer_quirks.c
    @@ -1519,11 +1519,15 @@ static int snd_microii_spdif_default_get

    /* use known values for that card: interface#1 altsetting#1 */
    iface = usb_ifnum_to_if(chip->dev, 1);
    - if (!iface || iface->num_altsetting < 2)
    - return -EINVAL;
    + if (!iface || iface->num_altsetting < 2) {
    + err = -EINVAL;
    + goto end;
    + }
    alts = &iface->altsetting[1];
    - if (get_iface_desc(alts)->bNumEndpoints < 1)
    - return -EINVAL;
    + if (get_iface_desc(alts)->bNumEndpoints < 1) {
    + err = -EINVAL;
    + goto end;
    + }
    ep = get_endpoint(alts, 0)->bEndpointAddress;

    err = snd_usb_ctl_msg(chip->dev,

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