[PATCH bpf-next v3 15/15] selftests/bpf: Add test for bpf_tcp_ops header option hooks

[Amery Hung <ameryhung@gmail.com>]

Add a test exercising the bpf_tcp_ops parse_hdr, hdr_opt_len and
write_hdr_opt members together with the header option helpers.

The struct_ops program (progs/bpf_tcp_ops_hdr.c) reserves space in
hdr_opt_len via bpf_reserve_hdr_opt(), writes an experimental option in
write_hdr_opt via bpf_store_hdr_opt(), and recovers it in parse_hdr via
bpf_load_hdr_opt() on the incoming skb. Each hook bumps a counter and the
parse hook records the option payload, so the three callbacks and all
three overloaded helpers are covered.

Signed-off-by: Amery Hung <ameryhung@gmail.com>
---
 .../bpf/prog_tests/bpf_tcp_ops_hdr.c          | 77 +++++++++++++++++
 .../selftests/bpf/progs/bpf_tcp_ops_hdr.c     | 83 +++++++++++++++++++
 2 files changed, 160 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/bpf_tcp_ops_hdr.c
 create mode 100644 tools/testing/selftests/bpf/progs/bpf_tcp_ops_hdr.c

diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ops_hdr.c b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ops_hdr.c
new file mode 100644
index 000000000000..244605e69e40
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ops_hdr.c
@@ -0,0 +1,77 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
+
+#include <test_progs.h>
+#include <network_helpers.h>
+#include "cgroup_helpers.h"
+#include "bpf_tcp_ops_hdr.skel.h"
+
+#define CGROUP_PATH	"/bpf_tcp_ops_hdr"
+#define TEST_NETNS	"bpf_tcp_ops_hdr"
+
+#define TEST_OPT_D0	0xAB
+#define TEST_OPT_D1	0xCD
+
+static void run_hdr_opt(void)
+{
+	struct bpf_tcp_ops_hdr *skel = NULL;
+	struct bpf_link *link = NULL;
+	struct netns_obj *ns = NULL;
+	int cgroup_fd, lfd = -1, fd = -1;
+
+	cgroup_fd = test__join_cgroup(CGROUP_PATH);
+	if (!ASSERT_GE(cgroup_fd, 0, "join_cgroup"))
+		return;
+
+	ns = netns_new(TEST_NETNS, true);
+	if (!ASSERT_OK_PTR(ns, "netns_new"))
+		goto done;
+
+	skel = bpf_tcp_ops_hdr__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "open_and_load"))
+		goto done;
+
+	link = bpf_map__attach_cgroup_opts(skel->maps.test_hdr_ops, cgroup_fd, NULL);
+	if (!ASSERT_OK_PTR(link, "attach_cgroup"))
+		goto done;
+
+	/*
+	 * One direction of data is enough to exercise all hooks: both peers
+	 * share the cgroup struct_ops, so the sender runs hdr_opt_len/write
+	 * and the receiver runs parse.
+	 */
+	lfd = start_server(AF_INET6, SOCK_STREAM, "::1", 0, 0);
+	if (!ASSERT_GE(lfd, 0, "start_server"))
+		goto done;
+
+	fd = connect_to_fd(lfd, 0);
+	if (!ASSERT_OK_FD(fd, "connect_to_fd"))
+		goto done;
+
+	if (!ASSERT_OK(send_recv_data(lfd, fd, 64), "send_recv_data"))
+		goto done;
+
+	/* Reserve + write hooks ran while sending. */
+	ASSERT_GT(skel->bss->hdr_opt_len_cnt, 0, "hdr_opt_len_cnt");
+	ASSERT_GT(skel->bss->write_cnt, 0, "write_cnt");
+	/* Parse hook ran and recovered our option on the receive side. */
+	ASSERT_GT(skel->bss->parse_cnt, 0, "parse_cnt");
+	ASSERT_GT(skel->bss->found_cnt, 0, "found_cnt");
+	ASSERT_EQ(skel->bss->found_d0, TEST_OPT_D0, "found_d0");
+	ASSERT_EQ(skel->bss->found_d1, TEST_OPT_D1, "found_d1");
+
+done:
+	if (fd >= 0)
+		close(fd);
+	if (lfd >= 0)
+		close(lfd);
+	bpf_link__destroy(link);
+	bpf_tcp_ops_hdr__destroy(skel);
+	netns_free(ns);
+	close(cgroup_fd);
+}
+
+void test_bpf_tcp_ops_hdr(void)
+{
+	run_hdr_opt();
+}
diff --git a/tools/testing/selftests/bpf/progs/bpf_tcp_ops_hdr.c b/tools/testing/selftests/bpf/progs/bpf_tcp_ops_hdr.c
new file mode 100644
index 000000000000..46618a604d96
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bpf_tcp_ops_hdr.c
@@ -0,0 +1,83 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+/* Experimental option kind and payload written/parsed by this test. */
+#define TEST_OPT_KIND	0xFD
+#define TEST_OPT_LEN	4
+#define TEST_OPT_D0	0xAB
+#define TEST_OPT_D1	0xCD
+
+int hdr_opt_len_cnt;
+int write_cnt;
+int parse_cnt;
+int found_cnt;
+__u8 found_d0;
+__u8 found_d1;
+
+SEC("struct_ops")
+void BPF_PROG(test_hdr_opt_len, struct sock *sk, struct sk_buff *skb,
+	      struct request_sock *req, struct sk_buff *syn_skb,
+	      enum tcp_synack_type synack_type, unsigned int *remaining)
+{
+	hdr_opt_len_cnt++;
+
+	/* Reserve TEST_OPT_LEN bytes; the helper decrements *remaining. Stacks
+	 * with other progs in the cgroup hierarchy.
+	 */
+	bpf_reserve_hdr_opt(ctx, TEST_OPT_LEN, 0);
+}
+
+SEC("struct_ops")
+void BPF_PROG(test_write_hdr_opt, struct sock *sk, struct sk_buff *skb,
+	      struct request_sock *req, struct sk_buff *syn_skb,
+	      enum tcp_synack_type synack_type, __u32 opt_off)
+{
+	__u8 opt[TEST_OPT_LEN] = {
+		TEST_OPT_KIND, TEST_OPT_LEN, TEST_OPT_D0, TEST_OPT_D1,
+	};
+
+	/* bpf_store_hdr_opt() takes the program ctx (the kernel reads the
+	 * outgoing skb from it); it appends after any options already written
+	 * in the reserved window, rejects duplicates, and confines the write to
+	 * the header option scratch. Stacks across progs in the cgroup hierarchy.
+	 */
+	if (bpf_store_hdr_opt(ctx, opt, sizeof(opt), 0))
+		return;
+
+	write_cnt++;
+}
+
+SEC("struct_ops")
+void BPF_PROG(test_parse_hdr, struct sock *sk, struct sk_buff *skb)
+{
+	__u8 opt[TEST_OPT_LEN] = {
+		TEST_OPT_KIND, TEST_OPT_LEN, TEST_OPT_D0, TEST_OPT_D1,
+	};
+
+	parse_cnt++;
+
+	/* Look up the experimental option written by test_write_hdr_opt() in
+	 * the incoming skb. For an experimental kind the search matches on the
+	 * 2-byte magic in opt[2..3]; on a match the found option is copied back
+	 * into opt[].
+	 */
+	if (bpf_load_hdr_opt(ctx, opt, sizeof(opt), 0) < 0)
+		return;
+
+	found_d0 = opt[2];
+	found_d1 = opt[3];
+	found_cnt++;
+}
+
+SEC(".struct_ops.link")
+struct bpf_tcp_ops test_hdr_ops = {
+	.hdr_opt_len	= (void *)test_hdr_opt_len,
+	.write_hdr_opt	= (void *)test_write_hdr_opt,
+	.parse_hdr	= (void *)test_parse_hdr,
+};
+
+char _license[] SEC("license") = "GPL";
-- 
2.52.0