From: Jakub Sitnicki <jakub@cloudflare.com>
Date: Thu, 17 Mar 2022 12:39:18 +0100
Subject: selftests/bpf: Check dst_port only on the client socket
Patch-mainline: v5.18-rc1
Git-commit: 2d2202ba858c112b03f84d546e260c61425831a1
References: jsc#PED-1377

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 egressing from the client socket in the
BPF program that tests 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>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20220317113920.1068535-3-jakub@cloudflare.com
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
 tools/testing/selftests/bpf/progs/test_sock_fields.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/tools/testing/selftests/bpf/progs/test_sock_fields.c
+++ b/tools/testing/selftests/bpf/progs/test_sock_fields.c
@@ -281,6 +281,10 @@ int read_sk_dst_port(struct __sk_buff *s
 	if (!sk)
 		RET_LOG();
 
+	/* Ignore everything but the SYN from the client socket */
+	if (sk->state != BPF_TCP_SYN_SENT)
+		return CG_OK;
+
 	if (!sk_dst_port__load_word(sk))
 		RET_LOG();
 	if (!sk_dst_port__load_half(sk))