inet: fix request sock refcounting

While testing last patch series, I found req sock refcounting was wrong.

We must set skc_refcnt to 1 for all request socks added in hashes,
but also on request sockets created by FastOpen or syncookies.

It is tricky because we need to defer this initialization so that
future RCU lookups do not try to take a refcount on a not yet
fully initialized request socket.

Also get rid of ireq_refcnt alias.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Fixes: 13854e5a6046 ("inet: add proper refcounting to request sock")
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/inet_connection_sock.h

@@ -275,11 +275,6 @@ static inline void inet_csk_reqsk_queue_add(struct sock *sk,
 					    struct sock *child)
 {
 	reqsk_queue_add(&inet_csk(sk)->icsk_accept_queue, req, sk, child);
-	/* before letting lookups find us, make sure all req fields
-	 * are committed to memory.
-	 */
-	smp_wmb();
-	atomic_set(&req->rsk_refcnt, 1);
 }
 
 void inet_csk_reqsk_queue_hash_add(struct sock *sk, struct request_sock *req,

include/net/inet_sock.h

@@ -81,7 +81,6 @@ struct inet_request_sock {
 #define ir_cookie		req.__req_common.skc_cookie
 #define ireq_net		req.__req_common.skc_net
 #define ireq_state		req.__req_common.skc_state
-#define ireq_refcnt		req.__req_common.skc_refcnt
 #define ireq_family		req.__req_common.skc_family
 
 	kmemcheck_bitfield_begin(flags);

include/net/request_sock.h

@@ -77,6 +77,11 @@ reqsk_alloc(const struct request_sock_ops *ops, struct sock *sk_listener)
 		req->rsk_ops = ops;
 		sock_hold(sk_listener);
 		req->rsk_listener = sk_listener;
+
+		/* Following is temporary. It is coupled with debugging
+		 * helpers in reqsk_put() & reqsk_free()
+		 */
+		atomic_set(&req->rsk_refcnt, 0);
 	}
 	return req;
 }
@@ -292,6 +297,12 @@ static inline void reqsk_queue_hash_req(struct request_sock_queue *queue,
 	req->sk = NULL;
 	req->dl_next = lopt->syn_table[hash];
 
+	/* before letting lookups find us, make sure all req fields
+	 * are committed to memory and refcnt initialized.
+	 */
+	smp_wmb();
+	atomic_set(&req->rsk_refcnt, 1);
+
 	write_lock(&queue->syn_wait_lock);
 	lopt->syn_table[hash] = req;
 	write_unlock(&queue->syn_wait_lock);

net/ipv4/syncookies.c

@@ -227,11 +227,12 @@ static struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb,
 	struct sock *child;
 
 	child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst);
-	if (child)
+	if (child) {
+		atomic_set(&req->rsk_refcnt, 1);
 		inet_csk_reqsk_queue_add(sk, req, child);
-	else
+	} else {
 		reqsk_free(req);
-
+	}
 	return child;
 }
 
@@ -356,7 +357,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
 	ireq->opt = tcp_v4_save_options(skb);
 
 	if (security_inet_conn_request(sk, skb, req)) {
-		reqsk_put(req);
+		reqsk_free(req);
 		goto out;
 	}
 
@@ -377,7 +378,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
 	security_req_classify_flow(req, flowi4_to_flowi(&fl4));
 	rt = ip_route_output_key(sock_net(sk), &fl4);
 	if (IS_ERR(rt)) {
-		reqsk_put(req);
+		reqsk_free(req);
 		goto out;
 	}
 

net/ipv4/tcp_fastopen.c

@@ -169,6 +169,7 @@ static bool tcp_fastopen_create_child(struct sock *sk,
 	inet_csk_reset_xmit_timer(child, ICSK_TIME_RETRANS,
 				  TCP_TIMEOUT_INIT, TCP_RTO_MAX);
 
+	atomic_set(&req->rsk_refcnt, 1);
 	/* Add the child socket directly into the accept queue */
 	inet_csk_reqsk_queue_add(sk, req, child);
 

net/ipv4/tcp_input.c

@@ -5981,10 +5981,6 @@ struct request_sock *inet_reqsk_alloc(const struct request_sock_ops *ops,
 		ireq->ireq_state = TCP_NEW_SYN_RECV;
 		write_pnet(&ireq->ireq_net, sock_net(sk_listener));
 
-		/* Following is temporary. It is coupled with debugging
-		 * helpers in reqsk_put() & reqsk_free()
-		 */
-		atomic_set(&ireq->ireq_refcnt, 0);
 	}
 
 	return req;

net/ipv6/syncookies.c

@@ -49,11 +49,12 @@ static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb,
 	struct sock *child;
 
 	child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst);
-	if (child)
+	if (child) {
+		atomic_set(&req->rsk_refcnt, 1);
 		inet_csk_reqsk_queue_add(sk, req, child);
-	else
+	} else {
 		reqsk_free(req);
-
+	}
 	return child;
 }