[NET]: sanitize kernel_accept() error path

If kernel_accept() returns an error, it may pass back a pointer to
freed memory (which the caller should ignore).  Make it pass back NULL
instead for better safety.
Signed-off-by: Tony Battersby <tonyb@cybernetics.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/socket.c

@@ -2235,6 +2235,7 @@ int kernel_accept(struct socket *sock, struct socket **newsock, int flags)
 	err = sock->ops->accept(sock, *newsock, flags);
 	if (err < 0) {
 		sock_release(*newsock);
+		*newsock = NULL;
 		goto done;
 	}