bpf: tcp: Add bpf_skops_established()

In tcp_init_transfer(), it currently calls the bpf prog to give it a
chance to handle the just "ESTABLISHED" event (e.g. do setsockopt
on the newly established sk).  Right now, it is done by calling the
general purpose tcp_call_bpf().

In the later patch, it also needs to pass the just-received skb which
concludes the 3 way handshake. E.g. the SYNACK received at the active side.
The bpf prog can then learn some specific header options written by the
peer's bpf-prog and potentially do setsockopt on the newly established sk.
Thus, instead of reusing the general purpose tcp_call_bpf(), a new function
bpf_skops_established() is added to allow passing the "skb" to the bpf
prog.  The actual skb passing from bpf_skops_established() to the bpf prog
will happen together in a later patch which has the necessary bpf pieces.

A "skb" arg is also added to tcp_init_transfer() such that
it can then be passed to bpf_skops_established().

Calling the new bpf_skops_established() instead of tcp_call_bpf()
should be a noop in this patch.

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20200820190039.2884750-1-kafai@fb.com

include/net/tcp.h

@@ -394,7 +394,7 @@ void tcp_metrics_init(void);
 bool tcp_peer_is_proven(struct request_sock *req, struct dst_entry *dst);
 void tcp_close(struct sock *sk, long timeout);
 void tcp_init_sock(struct sock *sk);
-void tcp_init_transfer(struct sock *sk, int bpf_op);
+void tcp_init_transfer(struct sock *sk, int bpf_op, struct sk_buff *skb);
 __poll_t tcp_poll(struct file *file, struct socket *sock,
 		      struct poll_table_struct *wait);
 int tcp_getsockopt(struct sock *sk, int level, int optname,

net/ipv4/tcp_fastopen.c

@@ -295,7 +295,7 @@ static struct sock *tcp_fastopen_create_child(struct sock *sk,
 	refcount_set(&req->rsk_refcnt, 2);
 
 	/* Now finish processing the fastopen child socket. */
-	tcp_init_transfer(child, BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB);
+	tcp_init_transfer(child, BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB, skb);
 
 	tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
 

net/ipv4/tcp_input.c

@@ -138,6 +138,29 @@ void clean_acked_data_flush(void)
 EXPORT_SYMBOL_GPL(clean_acked_data_flush);
 #endif
 
+#ifdef CONFIG_CGROUP_BPF
+static void bpf_skops_established(struct sock *sk, int bpf_op,
+				  struct sk_buff *skb)
+{
+	struct bpf_sock_ops_kern sock_ops;
+
+	sock_owned_by_me(sk);
+
+	memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp));
+	sock_ops.op = bpf_op;
+	sock_ops.is_fullsock = 1;
+	sock_ops.sk = sk;
+	/* skb will be passed to the bpf prog in a later patch. */
+
+	BPF_CGROUP_RUN_PROG_SOCK_OPS(&sock_ops);
+}
+#else
+static void bpf_skops_established(struct sock *sk, int bpf_op,
+				  struct sk_buff *skb)
+{
+}
+#endif
+
 static void tcp_gro_dev_warn(struct sock *sk, const struct sk_buff *skb,
 			     unsigned int len)
 {
@@ -5808,7 +5831,7 @@ void tcp_rcv_established(struct sock *sk, struct sk_buff *skb)
 }
 EXPORT_SYMBOL(tcp_rcv_established);
 
-void tcp_init_transfer(struct sock *sk, int bpf_op)
+void tcp_init_transfer(struct sock *sk, int bpf_op, struct sk_buff *skb)
 {
 	struct inet_connection_sock *icsk = inet_csk(sk);
 	struct tcp_sock *tp = tcp_sk(sk);
@@ -5829,7 +5852,7 @@ void tcp_init_transfer(struct sock *sk, int bpf_op)
 		tp->snd_cwnd = tcp_init_cwnd(tp, __sk_dst_get(sk));
 	tp->snd_cwnd_stamp = tcp_jiffies32;
 
-	tcp_call_bpf(sk, bpf_op, 0, NULL);
+	bpf_skops_established(sk, bpf_op, skb);
 	tcp_init_congestion_control(sk);
 	tcp_init_buffer_space(sk);
 }
@@ -5848,7 +5871,7 @@ void tcp_finish_connect(struct sock *sk, struct sk_buff *skb)
 		sk_mark_napi_id(sk, skb);
 	}
 
-	tcp_init_transfer(sk, BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB);
+	tcp_init_transfer(sk, BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB, skb);
 
 	/* Prevent spurious tcp_cwnd_restart() on first data
 	 * packet.
@@ -6320,7 +6343,8 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
 		} else {
 			tcp_try_undo_spurious_syn(sk);
 			tp->retrans_stamp = 0;
-			tcp_init_transfer(sk, BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB);
+			tcp_init_transfer(sk, BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB,
+					  skb);
 			WRITE_ONCE(tp->copied_seq, tp->rcv_nxt);
 		}
 		smp_mb();