[PATCH bpf-next v3 2/4] selftests/bpf: Check dst_port only on the client socket

From: Jakub Sitnicki <jakub@cloudflare.com>
To: bpf@vger.kernel.org
Cc: netdev@vger.kernel.org, Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	kernel-team@cloudflare.com, Ilya Leoshkevich <iii@linux.ibm.com>,
	Martin KaFai Lau <kafai@fb.com>
Subject: [PATCH bpf-next v3 2/4] selftests/bpf: Check dst_port only on the client socket
Date: Thu, 17 Mar 2022 12:39:18 +0100	[thread overview]
Message-ID: <20220317113920.1068535-3-jakub@cloudflare.com> (raw)
In-Reply-To: <20220317113920.1068535-1-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 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>
---
 tools/testing/selftests/bpf/progs/test_sock_fields.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/test_sock_fields.c b/tools/testing/selftests/bpf/progs/test_sock_fields.c
index 3e2e3ee51cc9..43b31aa1fcf7 100644
--- 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 *skb)
 	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))
-- 
2.35.1

