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

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>
(cherry picked from commit 1c0edc3633b56000e18d82fc241e3995ca18a69e)

Orabug: 27207955
CVE: CVE-2017-16535

Signed-off-by: Kirtikar Kashyap <kirtikar.kashyap@oracle.com>
Reviewed-by: Jack Vogel <jack.vogel@oracle.com>

diff --git a/drivers/usb/core/config.c b/drivers/usb/core/config.c
index b9ddf0c1ffe5993893d5bd0d4f3ffe3f313ed435..bc5fb347eabc7fe2bf4cec60c29c67a85572ee84 100644 (file)
--- 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) {