inet: Extract helper for selecting socket from reuseport group

Prepare for calling into reuseport from __inet_lookup_listener as well.

Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200717103536.397595-4-jakub@cloudflare.com

net/ipv4/inet_hashtables.c

@@ -246,6 +246,21 @@ static inline int compute_score(struct sock *sk, struct net *net,
 	return score;
 }
 
+static inline struct sock *lookup_reuseport(struct net *net, struct sock *sk,
+					    struct sk_buff *skb, int doff,
+					    __be32 saddr, __be16 sport,
+					    __be32 daddr, unsigned short hnum)
+{
+	struct sock *reuse_sk = NULL;
+	u32 phash;
+
+	if (sk->sk_reuseport) {
+		phash = inet_ehashfn(net, daddr, hnum, saddr, sport);
+		reuse_sk = reuseport_select_sock(sk, phash, skb, doff);
+	}
+	return reuse_sk;
+}
+
 /*
  * Here are some nice properties to exploit here. The BSD API
  * does not allow a listening sock to specify the remote port nor the
@@ -265,21 +280,17 @@ static struct sock *inet_lhash2_lookup(struct net *net,
 	struct inet_connection_sock *icsk;
 	struct sock *sk, *result = NULL;
 	int score, hiscore = 0;
-	u32 phash = 0;
 
 	inet_lhash2_for_each_icsk_rcu(icsk, &ilb2->head) {
 		sk = (struct sock *)icsk;
 		score = compute_score(sk, net, hnum, daddr,
 				      dif, sdif, exact_dif);
 		if (score > hiscore) {
-			if (sk->sk_reuseport) {
-				phash = inet_ehashfn(net, daddr, hnum,
-						     saddr, sport);
-				result = reuseport_select_sock(sk, phash,
-							       skb, doff);
-				if (result)
-					return result;
-			}
+			result = lookup_reuseport(net, sk, skb, doff,
+						  saddr, sport, daddr, hnum);
+			if (result)
+				return result;
+
 			result = sk;
 			hiscore = score;
 		}