rds: Integer overflow in RDS cmsg handling

In rds_cmsg_rdma_args(), the user-provided args->nr_local value is
restricted to less than UINT_MAX.  This seems to need a tighter upper
bound, since the calculation of total iov_size can overflow, resulting
in a small sock_kmalloc() allocation.  This would probably just result
in walking off the heap and crashing when calling rds_rdma_pages() with
a high count value.  If it somehow doesn't crash here, then memory
corruption could occur soon after.
Signed-off-by: NDan Rosenberg <drosenberg@vsecurity.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/rds/rdma.c

@@ -567,7 +567,7 @@ int rds_cmsg_rdma_args(struct rds_sock *rs, struct rds_message *rm,
 		goto out;
 	}
 
-	if (args->nr_local > (u64)UINT_MAX) {
+	if (args->nr_local > UIO_MAXIOV) {
 		ret = -EMSGSIZE;
 		goto out;
 	}