USB: cxacru: check data length is not negative

When attempting to read data that is not actually
an array of values, the length may be negative
which causes an Oops due to a likely access off
the end of the data array.

This bug should not occur under normal use unless
the device returns an invalid response.
Signed-off-by: NSimon Arlott <simon@fire.lp0.eu>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/usb/atm/cxacru.c

@@ -596,7 +596,7 @@ static int cxacru_cm_get_array(struct cxacru_data *instance, enum cxacru_cm_requ
 	len = ret / 4;
 	for (offb = 0; offb < len; ) {
 		int l = le32_to_cpu(buf[offb++]);
-		if (l > stride || l > (len - offb) / 2) {
+		if (l < 0 || l > stride || l > (len - offb) / 2) {
 			if (printk_ratelimit())
 				usb_err(instance->usbatm, "invalid data length from cm %#x: %d\n",
 					cm, l);