Subject: [PATCH bpf-next 2/2] selftests/bpf: Cover TCP_NODELAY in hdr opt callback

From: KaFai Wan <[email-masked]>
Date: Tue, 14 Apr 2026 19:23:10 +0800

Add a sockops test program that enables
BPF_SOCK_OPS_WRITE_HDR_OPT_CB_FLAG on connection setup and calls
bpf_setsockopt(TCP_NODELAY) from BPF_SOCK_OPS_HDR_OPT_LEN_CB.

Exercise the connection by sending data after the socket is
established. Before the fix, this setup can recurse through
tcp_push_pending_frames() and bpf_skops_hdr_opt_len() until the
kernel hits a stack guard page. After the fix, the connection
continues to make forward progress and the data exchange completes.

Signed-off-by: KaFai Wan <[email-masked]>
---
 .../bpf/prog_tests/tcp_hdr_options.c          | 34 +++++++++++++++++++
 .../bpf/progs/test_misc_tcp_hdr_options.c     | 18 ++++++++++
 2 files changed, 52 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..f361f9c7bf59 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 +513,39 @@ 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;
+
+	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;
+	}
+
+	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;
+	}
+
+check_linum:
+	sk_fds_close(&sk_fds);
+	bpf_link__destroy(link);
+}
+
 struct test {
 	const char *desc;
 	void (*run)(void);
@@ -526,6 +559,7 @@ 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..e1dc7246193e 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
@@ -326,4 +326,22 @@ 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;
+
+	switch (skops->op) {
+	case BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB:
+	case BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB:
+		set_hdr_cb_flags(skops, 0);
+		break;
+	case BPF_SOCK_OPS_HDR_OPT_LEN_CB:
+		bpf_setsockopt(skops, SOL_TCP, TCP_NODELAY, &true_val, sizeof(true_val));
+		break;
+	}
+
+	return 0;
+}
+
 char _license[] SEC("license") = "GPL";
-- 
2.43.0