bpf, sockmap: Allow skipping sk_skb parser program

Currently, we often run with a nop parser namely one that just does
this, 'return skb->len'. This happens when either our verdict program
can handle streaming data or it is only looking at socket data such
as IP addresses and other metadata associated with the flow. The second
case is common for a L3/L4 proxy for instance.

So lets allow loading programs without the parser then we can skip
the stream parser logic and avoid having to add a BPF program that
is effectively a nop.

Signed-off-by: John Fastabend <[e-mail]>
Signed-off-by: Alexei Starovoitov <[e-mail]>
Link: https://lore.kernel.org/bpf/160239297866.8495.13345662302749219672.stgit@john-Precision-5820-Tower

include/linux/skmsg.h

···
 int sk_psock_init_strp(struct sock *sk, struct sk_psock *psock);
 void sk_psock_start_strp(struct sock *sk, struct sk_psock *psock);
 void sk_psock_stop_strp(struct sock *sk, struct sk_psock *psock);
+void sk_psock_start_verdict(struct sock *sk, struct sk_psock *psock);
+void sk_psock_stop_verdict(struct sock *sk, struct sk_psock *psock);
 
 int sk_psock_msg_verdict(struct sock *sk, struct sk_psock *psock,
 			 struct sk_msg *msg);

net/core/skmsg.c

···
 	rcu_assign_sk_user_data(sk, NULL);
 	if (psock->progs.skb_parser)
 		sk_psock_stop_strp(sk, psock);
+	else if (psock->progs.skb_verdict)
+		sk_psock_stop_verdict(sk, psock);
 	write_unlock_bh(&sk->sk_callback_lock);
 	sk_psock_clear_state(psock, SK_PSOCK_TX_ENABLED);
 
···
 	rcu_read_unlock();
 }
 
+static int sk_psock_verdict_recv(read_descriptor_t *desc, struct sk_buff *skb,
+				 unsigned int offset, size_t orig_len)
+{
+	struct sock *sk = (struct sock *)desc->arg.data;
+	struct sk_psock *psock;
+	struct bpf_prog *prog;
+	int ret = __SK_DROP;
+	int len = skb->len;
+
+	/* clone here so sk_eat_skb() in tcp_read_sock does not drop our data */
+	skb = skb_clone(skb, GFP_ATOMIC);
+	if (!skb) {
+		desc->error = -ENOMEM;
+		return 0;
+	}
+
+	rcu_read_lock();
+	psock = sk_psock(sk);
+	if (unlikely(!psock)) {
+		len = 0;
+		kfree_skb(skb);
+		goto out;
+	}
+	skb_set_owner_r(skb, sk);
+	prog = READ_ONCE(psock->progs.skb_verdict);
+	if (likely(prog)) {
+		tcp_skb_bpf_redirect_clear(skb);
+		ret = sk_psock_bpf_run(psock, prog, skb);
+		ret = sk_psock_map_verd(ret, tcp_skb_bpf_redirect_fetch(skb));
+	}
+	sk_psock_verdict_apply(psock, skb, ret);
+out:
+	rcu_read_unlock();
+	return len;
+}
+
+static void sk_psock_verdict_data_ready(struct sock *sk)
+{
+	struct socket *sock = sk->sk_socket;
+	read_descriptor_t desc;
+
+	if (unlikely(!sock || !sock->ops || !sock->ops->read_sock))
+		return;
+
+	desc.arg.data = sk;
+	desc.error = 0;
+	desc.count = 1;
+
+	sock->ops->read_sock(sk, &desc, sk_psock_verdict_recv);
+}
+
 static void sk_psock_write_space(struct sock *sk)
 {
 	struct sk_psock *psock;
···
 	return strp_init(&psock->parser.strp, sk, &cb);
 }
 
+void sk_psock_start_verdict(struct sock *sk, struct sk_psock *psock)
+{
+	struct sk_psock_parser *parser = &psock->parser;
+
+	if (parser->enabled)
+		return;
+
+	parser->saved_data_ready = sk->sk_data_ready;
+	sk->sk_data_ready = sk_psock_verdict_data_ready;
+	sk->sk_write_space = sk_psock_write_space;
+	parser->enabled = true;
+}
+
 void sk_psock_start_strp(struct sock *sk, struct sk_psock *psock)
 {
 	struct sk_psock_parser *parser = &psock->parser;
···
 	sk->sk_data_ready = parser->saved_data_ready;
 	parser->saved_data_ready = NULL;
 	strp_stop(&parser->strp);
+	parser->enabled = false;
+}
+
+void sk_psock_stop_verdict(struct sock *sk, struct sk_psock *psock)
+{
+	struct sk_psock_parser *parser = &psock->parser;
+
+	if (!parser->enabled)
+		return;
+
+	sk->sk_data_ready = parser->saved_data_ready;
+	parser->saved_data_ready = NULL;
 	parser->enabled = false;
 }

net/core/sock_map.c

···
 static void sock_map_del_link(struct sock *sk,
 			      struct sk_psock *psock, void *link_raw)
 {
+	bool strp_stop = false, verdict_stop = false;
 	struct sk_psock_link *link, *tmp;
-	bool strp_stop = false;
 
 	spin_lock_bh(&psock->link_lock);
 	list_for_each_entry_safe(link, tmp, &psock->link, list) {
···
 							     map);
 			if (psock->parser.enabled && stab->progs.skb_parser)
 				strp_stop = true;
+			if (psock->parser.enabled && stab->progs.skb_verdict)
+				verdict_stop = true;
 			list_del(&link->list);
 			sk_psock_free_link(link);
 		}
 	}
 	spin_unlock_bh(&psock->link_lock);
-	if (strp_stop) {
+	if (strp_stop || verdict_stop) {
 		write_lock_bh(&sk->sk_callback_lock);
-		sk_psock_stop_strp(sk, psock);
+		if (strp_stop)
+			sk_psock_stop_strp(sk, psock);
+		else
+			sk_psock_stop_verdict(sk, psock);
 		write_unlock_bh(&sk->sk_callback_lock);
 	}
 }
···
 	write_lock_bh(&sk->sk_callback_lock);
 	if (skb_parser && skb_verdict && !psock->parser.enabled) {
 		ret = sk_psock_init_strp(sk, psock);
-		if (ret) {
-			write_unlock_bh(&sk->sk_callback_lock);
-			goto out_drop;
-		}
+		if (ret)
+			goto out_unlock_drop;
 		psock_set_prog(&psock->progs.skb_verdict, skb_verdict);
 		psock_set_prog(&psock->progs.skb_parser, skb_parser);
 		sk_psock_start_strp(sk, psock);
+	} else if (!skb_parser && skb_verdict && !psock->parser.enabled) {
+		psock_set_prog(&psock->progs.skb_verdict, skb_verdict);
+		sk_psock_start_verdict(sk,psock);
 	}
 	write_unlock_bh(&sk->sk_callback_lock);
 	return 0;
+out_unlock_drop:
+	write_unlock_bh(&sk->sk_callback_lock);
 out_drop:
 	sk_psock_put(sk, psock);
 out_progs: