net/tcp: Separate tcp_md5sig_info allocation into tcp_md5sig_info_add()

Add a helper to allocate tcp_md5sig_info, that will help later to
do/allocate things when info allocated, once per socket.
Signed-off-by: Dmitry Safonov <dima@arista.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/tcp_ipv4.c

@@ -1161,6 +1161,24 @@ struct tcp_md5sig_key *tcp_v4_md5_lookup(const struct sock *sk,
 }
 EXPORT_SYMBOL(tcp_v4_md5_lookup);
 
+static int tcp_md5sig_info_add(struct sock *sk, gfp_t gfp)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct tcp_md5sig_info *md5sig;
+
+	if (rcu_dereference_protected(tp->md5sig_info, lockdep_sock_is_held(sk)))
+		return 0;
+
+	md5sig = kmalloc(sizeof(*md5sig), gfp);
+	if (!md5sig)
+		return -ENOMEM;
+
+	sk_gso_disable(sk);
+	INIT_HLIST_HEAD(&md5sig->head);
+	rcu_assign_pointer(tp->md5sig_info, md5sig);
+	return 0;
+}
+
 /* This can be called on a newly created socket, from other files */
 int tcp_md5_do_add(struct sock *sk, const union tcp_md5_addr *addr,
 		   int family, u8 prefixlen, int l3index, u8 flags,
@@ -1191,17 +1209,11 @@ int tcp_md5_do_add(struct sock *sk, const union tcp_md5_addr *addr,
 		return 0;
 	}
 
-	md5sig = rcu_dereference_protected(tp->md5sig_info,
-					   lockdep_sock_is_held(sk));
-	if (!md5sig) {
-		md5sig = kmalloc(sizeof(*md5sig), gfp);
-		if (!md5sig)
+	if (tcp_md5sig_info_add(sk, gfp))
 		return -ENOMEM;
 
-		sk_gso_disable(sk);
-		INIT_HLIST_HEAD(&md5sig->head);
-		rcu_assign_pointer(tp->md5sig_info, md5sig);
-	}
+	md5sig = rcu_dereference_protected(tp->md5sig_info,
+					   lockdep_sock_is_held(sk));
 
 	key = sock_kmalloc(sk, sizeof(*key), gfp | __GFP_ZERO);
 	if (!key)