[PATCH 3.2 035/115] ALSA: usb-audio: Fix NULL dereference in create_fixed_stream_quirk()

[Ben Hutchings]

3.2.80-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Takashi Iwai <tiwai@xxxxxxx>

commit 0f886ca12765d20124bd06291c82951fd49a33be upstream.

create_fixed_stream_quirk() may cause a NULL-pointer dereference by
accessing the non-existing endpoint when a USB device with a malformed
USB descriptor is used.

This patch avoids it simply by adding a sanity check of bNumEndpoints
before the accesses.

Bugzilla: https://bugzilla.suse.com/show_bug.cgi?id=971125
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
[bwh: Backported to 3.2:
 - There's no altsd variable
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 sound/usb/quirks.c | 6 ++++++
 1 file changed, 6 insertions(+)

--- a/sound/usb/quirks.c
+++ b/sound/usb/quirks.c
@@ -165,6 +165,12 @@ static int create_fixed_stream_quirk(str
 		return -EINVAL;
 	}
 	alts = &iface->altsetting[fp->altset_idx];
+	if (get_iface_desc(alts)->bNumEndpoints < 1) {
+		kfree(fp);
+		kfree(rate_table);
+		return -EINVAL;
+	}
+
 	fp->datainterval = snd_usb_parse_datainterval(chip, alts);
 	fp->maxpacksize = le16_to_cpu(get_endpoint(alts, 0)->wMaxPacketSize);
 	usb_set_interface(chip->dev, fp->iface, 0);