[PATCH] USB: core: fix out-of-bounds access bug in usb_get_bos_descriptor()

[Paolo Pisati]

From: Alan Stern <stern at rowland.harvard.edu>

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 at google.com>
Signed-off-by: Alan Stern <stern at rowland.harvard.edu>
Tested-by: Andrey Konovalov <andreyknvl at google.com>
CC: <stable at vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
(cherry picked from commit 1c0edc3633b56000e18d82fc241e3995ca18a69e)
Signed-off-by: Paolo Pisati <paolo.pisati at canonical.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 755d82f..4cf67fc 100644
--- a/drivers/usb/core/config.c
+++ b/drivers/usb/core/config.c
@@ -830,10 +830,12 @@ 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) {
-- 
2.7.4