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

commit 1c0edc3633b56000e18d82fc241e3995ca18a69e upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/usb/core/config.c b/drivers/usb/core/config.c
index ac5b2efcb9d02f59cc7df3cdc2b72ea73c123a63..ea15bccf30a7b59f127c0f9cd4e4e478e40dee68 100644 (file)
--- a/drivers/usb/core/config.c
+++ b/drivers/usb/core/config.c
@@ -931,10 +931,12 @@ 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) {