From 1c0edc3633b56000e18d82fc241e3995ca18a69e Mon Sep 17 00:00:00 2001
From: Alan Stern <stern@rowland.harvard.edu>
Date: Wed, 18 Oct 2017 12:49:38 -0400
Subject: [PATCH] USB: core: fix out-of-bounds access bug in
 usb_get_bos_descriptor()
Git-commit: 1c0edc3633b56000e18d82fc241e3995ca18a69e
Patch-mainline: v4.14-rc6
References: bsc#1066700 CVE-2017-16535

Andrey used the syzkaller fuzzer to find an out-of-bounds memory
access in usb_get_bos_descriptor().  The code wasn't checking that the
next usb_dev_cap_header structure could fit into the remaining buffer
space.

This patch fixes the error and also reduces the bNumDeviceCaps field
in the header to match the actual number of capabilities found, in
cases where there are fewer than expected.

Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Tested-by: Andrey Konovalov <andreyknvl@google.com>
CC: <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Oliver Neukum <oneukum@suse.com>
---
 drivers/usb/core/config.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/core/config.c b/drivers/usb/core/config.c
index 68b54bd88d1e..883549ee946c 100644
--- a/drivers/usb/core/config.c
+++ b/drivers/usb/core/config.c
@@ -960,10 +960,12 @@ int usb_get_bos_descriptor(struct usb_device *dev)
 	for (i = 0; i < num; i++) {
 		buffer += length;
 		cap = (struct usb_dev_cap_header *)buffer;
-		length = cap->bLength;
 
-		if (total_len < length)
+		if (total_len < sizeof(*cap) || total_len < cap->bLength) {
+			dev->bos->desc->bNumDeviceCaps = i;
 			break;
+		}
+		length = cap->bLength;
 		total_len -= length;
 
 		if (cap->bDescriptorType != USB_DT_DEVICE_CAPABILITY) {
-- 
2.13.6