[PATCH] ALSA: usb-audio: Fix potential out-of-bound accesses for Extigy devices

[Benoit Sevens <bsevens@google.com>]

A bogus devices can provide a bNumConfigurations value that exceeds the
initial value used in usb_get_configuration for allocating dev->config.

This can lead to out-of-bounds accesses later, e.g. in
usb_destroy_configuration.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@kernel.org
Signed-off-by: Benoit Sevens <bsevens@google.com>
---
 sound/usb/quirks.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/sound/usb/quirks.c b/sound/usb/quirks.c
index c5fd180357d1..970d36d13ad8 100644
--- a/sound/usb/quirks.c
+++ b/sound/usb/quirks.c
@@ -555,6 +555,7 @@ int snd_usb_create_quirk(struct snd_usb_audio *chip,
 static int snd_usb_extigy_boot_quirk(struct usb_device *dev, struct usb_interface *intf)
 {
 	struct usb_host_config *config = dev->actconfig;
+	int num_configs;
 	int err;
 
 	if (le16_to_cpu(get_cfg_desc(config)->wTotalLength) == EXTIGY_FIRMWARE_SIZE_OLD ||
@@ -565,8 +566,11 @@ static int snd_usb_extigy_boot_quirk(struct usb_device *dev, struct usb_interfac
 				      0x10, 0x43, 0x0001, 0x000a, NULL, 0);
 		if (err < 0)
 			dev_dbg(&dev->dev, "error sending boot message: %d\n", err);
+		num_configs = dev->descriptor.bNumConfigurations;
 		err = usb_get_descriptor(dev, USB_DT_DEVICE, 0,
 				&dev->descriptor, sizeof(dev->descriptor));
+		if (dev->descriptor.bNumConfigurations > num_configs)
+			dev->descriptor.bNumConfigurations = num_configs;
 		config = dev->actconfig;
 		if (err < 0)
 			dev_dbg(&dev->dev, "error usb_get_descriptor: %d\n", err);
-- 
2.47.0.338.g60cca15819-goog