[PATCH bpf-next v2 2/3] selftests/bpf: Check dst_port only on the client socket

[Jakub Sitnicki <jakub@cloudflare.com>]

cgroup_skb/egress programs which sock_fields test installs process packets
flying in both directions, from the client to the server, and in reverse
direction.

Recently added dst_port check relies on the fact that destination
port (remote peer port) of the socket which sends the packet is known ahead
of time. This holds true only for the client socket, which connects to the
known server port.

Filter out any traffic that is not bound to be egressing from the client
socket in the test program for reading the dst_port.

Fixes: 8f50f16ff39d ("selftests/bpf: Extend verifier and bpf_sock tests for dst_port loads")
Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
---
 .../testing/selftests/bpf/progs/test_sock_fields.c  | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/bpf/progs/test_sock_fields.c b/tools/testing/selftests/bpf/progs/test_sock_fields.c
index 3e2e3ee51cc9..186fed1deaab 100644
--- a/tools/testing/selftests/bpf/progs/test_sock_fields.c
+++ b/tools/testing/selftests/bpf/progs/test_sock_fields.c
@@ -42,6 +42,11 @@ struct {
 	__type(value, struct bpf_spinlock_cnt);
 } sk_pkt_out_cnt10 SEC(".maps");
 
+enum {
+	TCP_SYN_SENT = 2,
+	TCP_LISTEN = 10,
+};
+
 struct bpf_tcp_sock listen_tp = {};
 struct sockaddr_in6 srv_sa6 = {};
 struct bpf_tcp_sock cli_tp = {};
@@ -138,7 +143,7 @@ int egress_read_sock_fields(struct __sk_buff *skb)
 	 * TCP_LISTEN (10) socket will be copied at the ingress side.
 	 */
 	if (sk->family != AF_INET6 || !is_loopback6(sk->src_ip6) ||
-	    sk->state == 10)
+	    sk->state == TCP_LISTEN)
 		return CG_OK;
 
 	if (sk->src_port == bpf_ntohs(srv_sa6.sin6_port)) {
@@ -233,7 +238,7 @@ int ingress_read_sock_fields(struct __sk_buff *skb)
 		return CG_OK;
 
 	/* Only interested in TCP_LISTEN */
-	if (sk->state != 10)
+	if (sk->state != TCP_LISTEN)
 		return CG_OK;
 
 	/* It must be a fullsock for cgroup_skb/ingress prog */
@@ -281,6 +286,10 @@ int read_sk_dst_port(struct __sk_buff *skb)
 	if (!sk)
 		RET_LOG();
 
+	/* Ignore everything but the SYN from the client socket */
+	if (sk->state != TCP_SYN_SENT)
+		return CG_OK;
+
 	if (!sk_dst_port__load_word(sk))
 		RET_LOG();
 	if (!sk_dst_port__load_half(sk))
-- 
2.35.1