tcp/dccp: fix inet_reuseport_add_sock()

David Ahern reported panics in __inet_hash() caused by my recent commit.

The reason is inet_reuseport_add_sock() was still using
sk_nulls_for_each_rcu() instead of sk_for_each_rcu().
SO_REUSEPORT enabled listeners were causing an instant crash.

While chasing this bug, I found that I forgot to clear SOCK_RCU_FREE
flag, as it is inherited from the parent at clone time.

Fixes: 3b24d854 ("tcp/dccp: do not touch listener sk_refcnt under synflood")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: David Ahern <dsa@cumulusnetworks.com>
Tested-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/inet_connection_sock.c

@@ -661,6 +661,9 @@ struct sock *inet_csk_clone_lock(const struct sock *sk,
 		inet_sk(newsk)->inet_sport = htons(inet_rsk(req)->ir_num);
 		newsk->sk_write_space = sk_stream_write_space;
 
+		/* listeners have SOCK_RCU_FREE, not the children */
+		sock_reset_flag(newsk, SOCK_RCU_FREE);
+
 		newsk->sk_mark = inet_rsk(req)->ir_mark;
 		atomic64_set(&newsk->sk_cookie,
 			     atomic64_read(&inet_rsk(req)->ir_cookie));

net/ipv4/inet_hashtables.c

@@ -439,10 +439,9 @@ static int inet_reuseport_add_sock(struct sock *sk,
 						     bool match_wildcard))
 {
 	struct sock *sk2;
-	struct hlist_nulls_node *node;
 	kuid_t uid = sock_i_uid(sk);
 
-	sk_nulls_for_each_rcu(sk2, node, &ilb->head) {
+	sk_for_each_rcu(sk2, &ilb->head) {
 		if (sk2 != sk &&
 		    sk2->sk_family == sk->sk_family &&
 		    ipv6_only_sock(sk2) == ipv6_only_sock(sk) &&