Subject: [PATCH bpf v2 2/2] selftests/bpf: Test TCP_NODELAY in TCP hdr opt callbacks

From: KaFai Wan <[email-masked]>
Date: Thu, 16 Apr 2026 19:23:08 +0800

Add a sockops selftest for the TCP_NODELAY restriction in
BPF_SOCK_OPS_HDR_OPT_LEN_CB and BPF_SOCK_OPS_WRITE_HDR_OPT_CB.

The test program calls bpf_setsockopt(TCP_NODELAY) from
ACTIVE_ESTABLISHED_CB and PASSIVE_ESTABLISHED_CB to verify that it is
still allowed outside the TCP header option callbacks.

It then enables BPF_SOCK_OPS_WRITE_HDR_OPT_CB_FLAG, sends data to
exercise the TCP header option path, and checks that
bpf_setsockopt(TCP_NODELAY) returns -EOPNOTSUPP from both
BPF_SOCK_OPS_HDR_OPT_LEN_CB and BPF_SOCK_OPS_WRITE_HDR_OPT_CB while the
connection continues to make forward progress.

Signed-off-by: KaFai Wan <[email-masked]>
---
 .../bpf/prog_tests/tcp_hdr_options.c          | 54 +++++++++++++++++++
 .../bpf/progs/test_misc_tcp_hdr_options.c     | 40 ++++++++++++++
 2 files changed, 94 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/tcp_hdr_options.c b/tools/testing/selftests/bpf/prog_tests/tcp_hdr_options.c
index 56685fc03c7e..2d738c0c4259 100644
--- a/tools/testing/selftests/bpf/prog_tests/tcp_hdr_options.c
+++ b/tools/testing/selftests/bpf/prog_tests/tcp_hdr_options.c
@@ -513,6 +513,59 @@ static void misc(void)
 	bpf_link__destroy(link);
 }
 
+static void hdr_sockopt(void)
+{
+	const char send_msg[] = "MISC!!!";
+	char recv_msg[sizeof(send_msg)];
+	const unsigned int nr_data = 2;
+	struct bpf_link *link;
+	struct sk_fds sk_fds;
+	int i, ret, true_val = 1;
+
+	lport_linum_map_fd = bpf_map__fd(misc_skel->maps.lport_linum_map);
+
+	link = bpf_program__attach_cgroup(misc_skel->progs.misc_hdr_sockopt, cg_fd);
+	if (!ASSERT_OK_PTR(link, "attach_cgroup(misc_hdr_sockopt)"))
+		return;
+
+	if (sk_fds_connect(&sk_fds, false)) {
+		bpf_link__destroy(link);
+		return;
+	}
+
+	ret = setsockopt(sk_fds.active_fd, SOL_TCP, TCP_NODELAY, &true_val, sizeof(true_val));
+	if (!ASSERT_OK(ret, "setsockopt(TCP_NODELAY) active"))
+		goto check_linum;
+
+	ret = setsockopt(sk_fds.passive_fd, SOL_TCP, TCP_NODELAY, &true_val, sizeof(true_val));
+	if (!ASSERT_OK(ret, "setsockopt(TCP_NODELAY) passive"))
+		goto check_linum;
+
+	for (i = 0; i < nr_data; i++) {
+		ret = send(sk_fds.active_fd, send_msg, sizeof(send_msg), 0);
+		if (!ASSERT_EQ(ret, sizeof(send_msg), "send(msg)"))
+			goto check_linum;
+
+		ret = read(sk_fds.passive_fd, recv_msg, sizeof(recv_msg));
+		if (!ASSERT_EQ(ret, sizeof(send_msg), "read(msg)"))
+			goto check_linum;
+	}
+
+	ASSERT_NEQ(misc_skel->bss->nr_hdr_sockopt_estab, 0, "nr_hdr_sockopt_estab");
+	ASSERT_EQ(misc_skel->bss->nr_hdr_sockopt_estab_err, 0, "nr_hdr_sockopt_estab_err");
+
+	ASSERT_NEQ(misc_skel->bss->nr_hdr_sockopt_len, 0, "nr_hdr_sockopt_len");
+	ASSERT_EQ(misc_skel->bss->nr_hdr_sockopt_len_err, 0, "nr_hdr_sockopt_len_err");
+
+	ASSERT_NEQ(misc_skel->bss->nr_hdr_sockopt_write, 0, "nr_hdr_sockopt_write");
+	ASSERT_EQ(misc_skel->bss->nr_hdr_sockopt_write_err, 0, "nr_hdr_sockopt_write_err");
+
+check_linum:
+	ASSERT_FALSE(check_error_linum(&sk_fds), "check_error_linum");
+	sk_fds_close(&sk_fds);
+	bpf_link__destroy(link);
+}
+
 struct test {
 	const char *desc;
 	void (*run)(void);
@@ -526,6 +579,7 @@ static struct test tests[] = {
 	DEF_TEST(fastopen_estab),
 	DEF_TEST(fin),
 	DEF_TEST(misc),
+	DEF_TEST(hdr_sockopt),
 };
 
 void test_tcp_hdr_options(void)
diff --git a/tools/testing/selftests/bpf/progs/test_misc_tcp_hdr_options.c b/tools/testing/selftests/bpf/progs/test_misc_tcp_hdr_options.c
index d487153a839d..a8cf7c4e7ed2 100644
--- a/tools/testing/selftests/bpf/progs/test_misc_tcp_hdr_options.c
+++ b/tools/testing/selftests/bpf/progs/test_misc_tcp_hdr_options.c
@@ -28,6 +28,12 @@ unsigned int nr_data = 0;
 unsigned int nr_syn = 0;
 unsigned int nr_fin = 0;
 unsigned int nr_hwtstamp = 0;
+unsigned int nr_hdr_sockopt_estab = 0;
+unsigned int nr_hdr_sockopt_estab_err = 0;
+unsigned int nr_hdr_sockopt_len = 0;
+unsigned int nr_hdr_sockopt_len_err = 0;
+unsigned int nr_hdr_sockopt_write = 0;
+unsigned int nr_hdr_sockopt_write_err = 0;
 
 /* Check the header received from the active side */
 static int __check_active_hdr_in(struct bpf_sock_ops *skops, bool check_syn)
@@ -326,4 +332,38 @@ int misc_estab(struct bpf_sock_ops *skops)
 	return CG_OK;
 }
 
+SEC("sockops")
+int misc_hdr_sockopt(struct bpf_sock_ops *skops)
+{
+	int true_val = 1;
+	int ret;
+
+	switch (skops->op) {
+	case BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB:
+	case BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB:
+		nr_hdr_sockopt_estab++;
+		set_hdr_cb_flags(skops, 0);
+		ret = bpf_setsockopt(skops, SOL_TCP, TCP_NODELAY, &true_val, sizeof(true_val));
+		if (ret)
+			nr_hdr_sockopt_estab_err++;
+		break;
+	case BPF_SOCK_OPS_HDR_OPT_LEN_CB:
+		nr_hdr_sockopt_len++;
+		ret = bpf_setsockopt(skops, SOL_TCP, TCP_NODELAY, &true_val, sizeof(true_val));
+		if (ret != -EOPNOTSUPP)
+			nr_hdr_sockopt_len_err++;
+		/* just trigger BPF_SOCK_OPS_WRITE_HDR_OPT_CB */
+		bpf_reserve_hdr_opt(skops, 12, 0);
+		break;
+	case BPF_SOCK_OPS_WRITE_HDR_OPT_CB:
+		nr_hdr_sockopt_write++;
+		ret = bpf_setsockopt(skops, SOL_TCP, TCP_NODELAY, &true_val, sizeof(true_val));
+		if (ret != -EOPNOTSUPP)
+			nr_hdr_sockopt_write_err++;
+		break;
+	}
+
+	return CG_OK;
+}
+
 char _license[] SEC("license") = "GPL";
-- 
2.43.0