bpf: Refactor sockmap redirect code so its easy to reuse

We will need this block of code called from tls context shortly
lets refactor the redirect logic so its easy to use. This also
cleans up the switch stmt so we have fewer fallthrough cases.

No logic changes are intended.

Fixes: d829e9c4 ("tls: convert to generic sk_msg interface")
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/159079360110.5745.7024009076049029819.stgit@john-Precision-5820-TowerSigned-off-by: Alexei Starovoitov <ast@kernel.org>

net/core/skmsg.c

@@ -682,13 +682,43 @@ static struct sk_psock *sk_psock_from_strp(struct strparser *strp)
 	return container_of(parser, struct sk_psock, parser);
 }
 
-static void sk_psock_verdict_apply(struct sk_psock *psock,
-				   struct sk_buff *skb, int verdict)
+static void sk_psock_skb_redirect(struct sk_psock *psock, struct sk_buff *skb)
 {
 	struct sk_psock *psock_other;
 	struct sock *sk_other;
 	bool ingress;
 
+	sk_other = tcp_skb_bpf_redirect_fetch(skb);
+	if (unlikely(!sk_other)) {
+		kfree_skb(skb);
+		return;
+	}
+	psock_other = sk_psock(sk_other);
+	if (!psock_other || sock_flag(sk_other, SOCK_DEAD) ||
+	    !sk_psock_test_state(psock_other, SK_PSOCK_TX_ENABLED)) {
+		kfree_skb(skb);
+		return;
+	}
+
+	ingress = tcp_skb_bpf_ingress(skb);
+	if ((!ingress && sock_writeable(sk_other)) ||
+	    (ingress &&
+	     atomic_read(&sk_other->sk_rmem_alloc) <=
+	     sk_other->sk_rcvbuf)) {
+		if (!ingress)
+			skb_set_owner_w(skb, sk_other);
+		skb_queue_tail(&psock_other->ingress_skb, skb);
+		schedule_work(&psock_other->work);
+	} else {
+		kfree_skb(skb);
+	}
+}
+
+static void sk_psock_verdict_apply(struct sk_psock *psock,
+				   struct sk_buff *skb, int verdict)
+{
+	struct sock *sk_other;
+
 	switch (verdict) {
 	case __SK_PASS:
 		sk_other = psock->sk;
@@ -707,25 +737,8 @@ static void sk_psock_verdict_apply(struct sk_psock *psock,
 		}
 		goto out_free;
 	case __SK_REDIRECT:
-		sk_other = tcp_skb_bpf_redirect_fetch(skb);
-		if (unlikely(!sk_other))
-			goto out_free;
-		psock_other = sk_psock(sk_other);
-		if (!psock_other || sock_flag(sk_other, SOCK_DEAD) ||
-		    !sk_psock_test_state(psock_other, SK_PSOCK_TX_ENABLED))
-			goto out_free;
-		ingress = tcp_skb_bpf_ingress(skb);
-		if ((!ingress && sock_writeable(sk_other)) ||
-		    (ingress &&
-		     atomic_read(&sk_other->sk_rmem_alloc) <=
-		     sk_other->sk_rcvbuf)) {
-			if (!ingress)
-				skb_set_owner_w(skb, sk_other);
-			skb_queue_tail(&psock_other->ingress_skb, skb);
-			schedule_work(&psock_other->work);
-			break;
-		}
-		/* fall-through */
+		sk_psock_skb_redirect(psock, skb);
+		break;
 	case __SK_DROP:
 		/* fall-through */
 	default: