[PATCH 4.19 043/115] ALSA: usb-audio: fix set_format altsetting sanity check

Greg Kroah-Hartman
2020-01-07T21:07:20Z

From: Johan Hovold <johan@kernel.org>

commit 0141254b0a74b37aa7eb13d42a56adba84d51c73 upstream.

Make sure to check the return value of usb_altnum_to_altsetting() to
avoid dereferencing a NULL pointer when the requested alternate settings
is missing.

The format altsetting number may come from a quirk table and there does
not seem to be any other validation of it (the corresponding index is
checked however).

Fixes: b099b9693d23 ("ALSA: usb-audio: Avoid superfluous usb_set_interface() calls")
Cc: stable <stable@vger.kernel.org> # 4.18
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20191220093134.1248-1-johan@kernel.org
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
sound/usb/pcm.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -513,9 +513,9 @@ static int set_format(struct snd_usb_sub
if (WARN_ON(!iface))
return -EINVAL;
alts = usb_altnum_to_altsetting(iface, fmt->altsetting);
- altsd = get_iface_desc(alts);
- if (WARN_ON(altsd->bAlternateSetting != fmt->altsetting))
+ if (WARN_ON(!alts))
return -EINVAL;
+ altsd = get_iface_desc(alts);

if (fmt == subs->cur_audiofmt)
return 0;