[PATCH v3] ALSA: usb-audio: Fix potential out-of-bound accesses for Extigy and Mbox devices

["Benoît Sevens" <bsevens@google.com>]

A bogus device 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.

Signed-off-by: Benoît Sevens <bsevens@google.com>
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@kernel.org
---
v3:
 - First get the descriptor locally and only overwrite it if the check passes
 - Remove redundant dev->actconfig fetches
v2:
 - Also add sanity checks to snd_usb_mbox2_boot_quirk and
   snd_usb_mbox3_boot_quirk
---
 sound/usb/quirks.c | 27 +++++++++++++++++++++------
 1 file changed, 21 insertions(+), 6 deletions(-)

diff --git a/sound/usb/quirks.c b/sound/usb/quirks.c
index c5fd180357d1..8538fdfce353 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;
+	struct usb_device_descriptor new_device_descriptor;
 	int err;
 
 	if (le16_to_cpu(get_cfg_desc(config)->wTotalLength) == EXTIGY_FIRMWARE_SIZE_OLD ||
@@ -566,10 +567,14 @@ static int snd_usb_extigy_boot_quirk(struct usb_device *dev, struct usb_interfac
 		if (err < 0)
 			dev_dbg(&dev->dev, "error sending boot message: %d\n", err);
 		err = usb_get_descriptor(dev, USB_DT_DEVICE, 0,
-				&dev->descriptor, sizeof(dev->descriptor));
-		config = dev->actconfig;
+				&new_device_descriptor, sizeof(new_device_descriptor));
 		if (err < 0)
 			dev_dbg(&dev->dev, "error usb_get_descriptor: %d\n", err);
+		if (new_device_descriptor.bNumConfigurations > dev->descriptor.bNumConfigurations)
+			dev_dbg(&dev->dev, "error too large bNumConfigurations: %d\n",
+				new_device_descriptor.bNumConfigurations);
+		else
+			memcpy(&dev->descriptor, &new_device_descriptor, sizeof(dev->descriptor));
 		err = usb_reset_configuration(dev);
 		if (err < 0)
 			dev_dbg(&dev->dev, "error usb_reset_configuration: %d\n", err);
@@ -901,6 +906,7 @@ static void mbox2_setup_48_24_magic(struct usb_device *dev)
 static int snd_usb_mbox2_boot_quirk(struct usb_device *dev)
 {
 	struct usb_host_config *config = dev->actconfig;
+	struct usb_device_descriptor new_device_descriptor;
 	int err;
 	u8 bootresponse[0x12];
 	int fwsize;
@@ -936,10 +942,14 @@ static int snd_usb_mbox2_boot_quirk(struct usb_device *dev)
 	dev_dbg(&dev->dev, "device initialised!\n");
 
 	err = usb_get_descriptor(dev, USB_DT_DEVICE, 0,
-		&dev->descriptor, sizeof(dev->descriptor));
-	config = dev->actconfig;
+		&new_device_descriptor, sizeof(new_device_descriptor));
 	if (err < 0)
 		dev_dbg(&dev->dev, "error usb_get_descriptor: %d\n", err);
+	if (new_device_descriptor.bNumConfigurations > dev->descriptor.bNumConfigurations)
+		dev_dbg(&dev->dev, "error too large bNumConfigurations: %d\n",
+			new_device_descriptor.bNumConfigurations);
+	else
+		memcpy(&dev->descriptor, &new_device_descriptor, sizeof(dev->descriptor));
 
 	err = usb_reset_configuration(dev);
 	if (err < 0)
@@ -1249,6 +1259,7 @@ static void mbox3_setup_defaults(struct usb_device *dev)
 static int snd_usb_mbox3_boot_quirk(struct usb_device *dev)
 {
 	struct usb_host_config *config = dev->actconfig;
+	struct usb_device_descriptor new_device_descriptor;
 	int err;
 	int descriptor_size;
 
@@ -1262,10 +1273,14 @@ static int snd_usb_mbox3_boot_quirk(struct usb_device *dev)
 	dev_dbg(&dev->dev, "MBOX3: device initialised!\n");
 
 	err = usb_get_descriptor(dev, USB_DT_DEVICE, 0,
-		&dev->descriptor, sizeof(dev->descriptor));
-	config = dev->actconfig;
+		&new_device_descriptor, sizeof(new_device_descriptor));
 	if (err < 0)
 		dev_dbg(&dev->dev, "MBOX3: error usb_get_descriptor: %d\n", err);
+	if (new_device_descriptor.bNumConfigurations > dev->descriptor.bNumConfigurations)
+		dev_dbg(&dev->dev, "MBOX3: error too large bNumConfigurations: %d\n",
+			new_device_descriptor.bNumConfigurations);
+	else
+		memcpy(&dev->descriptor, &new_device_descriptor, sizeof(dev->descriptor));
 
 	err = usb_reset_configuration(dev);
 	if (err < 0)
-- 
2.47.0.338.g60cca15819-goog