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

KaFai Wan
2026-04-14T11:24:21Z

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 <kafai.wan@linux.dev>
---
.../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