linux-kernel - [PATCH 3.12 081/235] USB: gadgetfs: fix checks of wTotalLength in config descriptors

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Message-Id: <8e60e3f7a747b310e019312a761c145f10c6bb7d.1485514374.git.jslaby@suse.cz>
Date:   Fri, 27 Jan 2017 11:53:34 +0100
From:   Jiri Slaby <jslaby@...e.cz>
To:     stable@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Alan Stern <stern@...land.harvard.edu>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 081/235] USB: gadgetfs: fix checks of wTotalLength in config descriptors

From: Alan Stern <stern@...land.harvard.edu>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

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@...land.harvard.edu>
CC: Andrey Konovalov <andreyknvl@...gle.com>
Signed-off-by: Felipe Balbi <felipe.balbi@...ux.intel.com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 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 19e1efaeafa0..8fa7ba0f6beb 100644
--- a/drivers/usb/gadget/inode.c
+++ b/drivers/usb/gadget/inode.c
@@ -1829,10 +1829,12 @@ 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;
@@ -1874,7 +1876,8 @@ 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;
@@ -1883,7 +1886,8 @@ 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;
-- 
2.11.0