[PATCH 3.10 047/268] USB: gadgetfs: fix checks of wTotalLength in config descriptors

[Willy Tarreau]

From: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>

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@xxxxxxxxxxxxxxxxxxx>
CC: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Signed-off-by: Felipe Balbi <felipe.balbi@xxxxxxxxxxxxxxx>
Signed-off-by: Willy Tarreau <w@xxxxxx>
---
 drivers/usb/gadget/inode.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/gadget/inode.c b/drivers/usb/gadget/inode.c
index 3b4ef7c..c9e552b 100644
--- a/drivers/usb/gadget/inode.c
+++ b/drivers/usb/gadget/inode.c
@@ -1834,10 +1834,12 @@ static struct usb_gadget_driver probe_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;
@@ -1879,7 +1881,8 @@ 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;
@@ -1888,7 +1891,8 @@ 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;
-- 
2.8.0.rc2.1.gbe9624a