IB/rxe: Fix mem_check_range integer overflow

Update the range check to avoid integer-overflow in edge case.
Resolves CVE 2016-8636.

Signed-off-by: Eyal Itkin <eyal.itkin@gmail.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/sw/rxe/rxe_mr.c

@@ -59,9 +59,11 @@ int mem_check_range(struct rxe_mem *mem, u64 iova, size_t length)
 
 	case RXE_MEM_TYPE_MR:
 	case RXE_MEM_TYPE_FMR:
-		return ((iova < mem->iova) ||
-			((iova + length) > (mem->iova + mem->length))) ?
-			-EFAULT : 0;
+		if (iova < mem->iova ||
+		    length > mem->length ||
+		    iova > mem->iova + mem->length - length)
+			return -EFAULT;
+		return 0;
 
 	default:
 		return -EFAULT;