bpf: Add bpf_get_listener_sock(struct bpf_sock *sk) helper

Add a new helper "struct bpf_sock *bpf_get_listener_sock(struct bpf_sock *sk)"
which returns a bpf_sock in TCP_LISTEN state.  It will trace back to
the listener sk from a request_sock if possible.  It returns NULL
for all other cases.

No reference is taken because the helper ensures the sk is
in SOCK_RCU_FREE (where the TCP_LISTEN sock should be in).
Hence, bpf_sk_release() is unnecessary and the verifier does not
allow bpf_sk_release(listen_sk) to be called either.

The following is also allowed because the bpf_prog is run under
rcu_read_lock():

	sk = bpf_sk_lookup_tcp();
	/* if (!sk) { ... } */
	listen_sk = bpf_get_listener_sock(sk);
	/* if (!listen_sk) { ... } */
	bpf_sk_release(sk);
	src_port = listen_sk->src_port; /* Allowed */

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 21 insertions, 0 deletions

diff --git a/net/core/filter.c b/net/core/filter.c
index 36b6afacf83c..647c63a7b25b 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -5418,6 +5418,23 @@ static const struct bpf_func_proto bpf_tcp_sock_proto = {
 	.arg1_type	= ARG_PTR_TO_SOCK_COMMON,
 };
 
+BPF_CALL_1(bpf_get_listener_sock, struct sock *, sk)
+{
+	sk = sk_to_full_sk(sk);
+
+	if (sk->sk_state == TCP_LISTEN && sock_flag(sk, SOCK_RCU_FREE))
+		return (unsigned long)sk;
+
+	return (unsigned long)NULL;
+}
+
+static const struct bpf_func_proto bpf_get_listener_sock_proto = {
+	.func		= bpf_get_listener_sock,
+	.gpl_only	= false,
+	.ret_type	= RET_PTR_TO_SOCKET_OR_NULL,
+	.arg1_type	= ARG_PTR_TO_SOCK_COMMON,
+};
+
 BPF_CALL_1(bpf_skb_ecn_set_ce, struct sk_buff *, skb)
 {
 	unsigned int iphdr_len;
@@ -5603,6 +5620,8 @@ cg_skb_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 #ifdef CONFIG_INET
 	case BPF_FUNC_tcp_sock:
 		return &bpf_tcp_sock_proto;
+	case BPF_FUNC_get_listener_sock:
+		return &bpf_get_listener_sock_proto;
 	case BPF_FUNC_skb_ecn_set_ce:
 		return &bpf_skb_ecn_set_ce_proto;
 #endif
@@ -5698,6 +5717,8 @@ tc_cls_act_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_sk_release_proto;
 	case BPF_FUNC_tcp_sock:
 		return &bpf_tcp_sock_proto;
+	case BPF_FUNC_get_listener_sock:
+		return &bpf_get_listener_sock_proto;
 #endif
 	default:
 		return bpf_base_func_proto(func_id);