release/4.8.18/USB-gadgetfs-fix-checks-of-wTotalLength-in-config-de.patch

From d5adc3b5cc8426e6236835424e623ad2f8e4174c Mon Sep 17 00:00:00 2001
From: Alan Stern <stern@rowland.harvard.edu>
Date: Fri, 9 Dec 2016 15:24:24 -0500
Subject: [PATCH] USB: gadgetfs: fix checks of wTotalLength in config
 descriptors

commit 1c069b057dcf64fada952eaa868d35f02bb0cfc2 upstream.

Andrey Konovalov's fuzz testing of gadgetfs showed that we should
improve the driver's checks for valid configuration descriptors passed
in by the user.  In particular, the driver needs to verify that the
wTotalLength value in the descriptor is not too short (smaller
than USB_DT_CONFIG_SIZE).  And the check for whether wTotalLength is
too large has to be changed, because the driver assumes there is
always enough room remaining in the buffer to hold a device descriptor
(at least USB_DT_DEVICE_SIZE bytes).

This patch adds the additional check and fixes the existing check.  It
may do a little more than strictly necessary, but one extra check
won't hurt.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: Andrey Konovalov <andreyknvl@google.com>
CC: <stable@vger.kernel.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/drivers/usb/gadget/legacy/inode.c b/drivers/usb/gadget/legacy/inode.c
index 9f090682518c..420fd2eedb71 100644
--- a/drivers/usb/gadget/legacy/inode.c
+++ b/drivers/usb/gadget/legacy/inode.c
@@ -1734,10 +1734,12 @@ static struct usb_gadget_driver gadgetfs_driver = {
  * such as configuration notifications.
  */
 
-static int is_valid_config (struct usb_config_descriptor *config)
+static int is_valid_config(struct usb_config_descriptor *config,
+		unsigned int total)
 {
 	return config->bDescriptorType == USB_DT_CONFIG
 		&& config->bLength == USB_DT_CONFIG_SIZE
+		&& total >= USB_DT_CONFIG_SIZE
 		&& config->bConfigurationValue != 0
 		&& (config->bmAttributes & USB_CONFIG_ATT_ONE) != 0
 		&& (config->bmAttributes & USB_CONFIG_ATT_WAKEUP) == 0;
@@ -1787,7 +1789,8 @@ dev_config (struct file *fd, const char __user *buf, size_t len, loff_t *ptr)
 	/* full or low speed config */
 	dev->config = (void *) kbuf;
 	total = le16_to_cpu(dev->config->wTotalLength);
-	if (!is_valid_config (dev->config) || total >= length)
+	if (!is_valid_config(dev->config, total) ||
+			total > length - USB_DT_DEVICE_SIZE)
 		goto fail;
 	kbuf += total;
 	length -= total;
@@ -1796,7 +1799,8 @@ dev_config (struct file *fd, const char __user *buf, size_t len, loff_t *ptr)
 	if (kbuf [1] == USB_DT_CONFIG) {
 		dev->hs_config = (void *) kbuf;
 		total = le16_to_cpu(dev->hs_config->wTotalLength);
-		if (!is_valid_config (dev->hs_config) || total >= length)
+		if (!is_valid_config(dev->hs_config, total) ||
+				total > length - USB_DT_DEVICE_SIZE)
 			goto fail;
 		kbuf += total;
 		length -= total;
-- 
2.10.1