linux-kernel - [PATCH] ALSA: usb-audio: fix set

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Date:   Fri, 20 Dec 2019 10:31:34 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     Jaroslav Kysela <perex@...ex.cz>, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org, Johan Hovold <johan@...nel.org>,
        stable <stable@...r.kernel.org>
Subject: [PATCH] ALSA: usb-audio: fix set_format altsetting sanity check

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@...r.kernel.org>     # 4.18
Signed-off-by: Johan Hovold <johan@...nel.org>
---
 sound/usb/pcm.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index 9c8930bb00c8..73dd9d21bb42 100644
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -506,9 +506,9 @@ static int set_format(struct snd_usb_substream *subs, struct audioformat *fmt)
 	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;
-- 
2.24.1