Subject: [PATCH net v2 3/3] selftests/bpf: Add mptcp test with sockmap

From: Jiayuan Chen <[email-masked]>
Date: Mon, 20 Oct 2025 14:04:48 +0800

Add test cases to verify that when MPTCP falls back to plain TCP sockets,
they can properly work with sockmap.

Additionally, add test cases to ensure that sockmap correctly rejects
MPTCP sockets as expected.

Signed-off-by: Jiayuan Chen <[email-masked]>
---
 .../testing/selftests/bpf/prog_tests/mptcp.c  | 136 ++++++++++++++++++
 .../selftests/bpf/progs/mptcp_sockmap.c       |  43 ++++++
 2 files changed, 179 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/mptcp_sockmap.c

diff --git a/tools/testing/selftests/bpf/prog_tests/mptcp.c b/tools/testing/selftests/bpf/prog_tests/mptcp.c
index f8eb7f9d4fd2..54459b385439 100644
--- a/tools/testing/selftests/bpf/prog_tests/mptcp.c
+++ b/tools/testing/selftests/bpf/prog_tests/mptcp.c
@@ -6,11 +6,14 @@
 #include <netinet/in.h>
 #include <test_progs.h>
 #include <unistd.h>
+#include <error.h>
 #include "cgroup_helpers.h"
 #include "network_helpers.h"
+#include "socket_helpers.h"
 #include "mptcp_sock.skel.h"
 #include "mptcpify.skel.h"
 #include "mptcp_subflow.skel.h"
+#include "mptcp_sockmap.skel.h"
 
 #define NS_TEST "mptcp_ns"
 #define ADDR_1	"10.0.1.1"
@@ -436,6 +439,137 @@ static void test_subflow(void)
 	close(cgroup_fd);
 }
 
+/* Test sockmap on MPTCP server handling non-mp-capable clients. */
+static void test_sockmap_with_mptcp_fallback(struct mptcp_sockmap *skel)
+{
+	int listen_fd = -1, client_fd1 = -1, client_fd2 = -1;
+	int server_fd1 = -1, server_fd2 = -1, sent, recvd;
+	char snd[9] = "123456789";
+	char rcv[10];
+
+	listen_fd = start_mptcp_server(AF_INET, NULL, 0, 0);
+	if (!ASSERT_OK_FD(listen_fd, "redirect:start_mptcp_server"))
+		return;
+
+	skel->bss->trace_port = ntohs(get_socket_local_port(listen_fd));
+	skel->bss->sk_index = 0;
+	client_fd1 = connect_to_fd_opts(listen_fd, NULL);
+	if (!ASSERT_OK_FD(client_fd1, "redirect:connect_to_fd"))
+		goto end;
+	server_fd1 = xaccept_nonblock(listen_fd, NULL, NULL);
+	skel->bss->sk_index = 1;
+	client_fd2 = connect_to_fd_opts(listen_fd, NULL);
+	if (!ASSERT_OK_FD(client_fd2, "redirect:connect_to_fd"))
+		goto end;
+	server_fd1 = xaccept_nonblock(listen_fd, NULL, NULL);
+	/* test normal redirect behavior: the data sent by client_fd1 can be
+	 * received by client_fd2
+	 */
+	skel->bss->redirect_idx = 1;
+	sent = xsend(client_fd1, snd, sizeof(snd), 0);
+	if (!ASSERT_EQ(sent, sizeof(snd), "redirect:xsend(client_fd1)"))
+		goto end;
+
+	/* try to recv more byte to avoid truncation check */
+	recvd = recv_timeout(client_fd2, rcv, sizeof(rcv), MSG_DONTWAIT, 2);
+	if (!ASSERT_EQ(recvd, sizeof(snd), "redirect:recv(client_fd2)"))
+		goto end;
+
+end:
+	if (client_fd1 > 1)
+		close(client_fd1);
+	if (client_fd2 > 1)
+		close(client_fd2);
+	if (server_fd1 > 0)
+		close(server_fd1);
+	if (server_fd2 > 0)
+		close(server_fd2);
+	close(listen_fd);
+}
+
+static void test_sockmap_reject_mptcp(struct mptcp_sockmap *skel)
+{
+	int listen_fd = -1, server_fd = -1;
+	int client_fd1 = -1, client_fd2 = -1;
+	int err, zero = 0;
+
+	listen_fd = start_mptcp_server(AF_INET, NULL, 0, 0);
+	if (!ASSERT_OK_FD(listen_fd, "start_mptcp_server"))
+		return;
+
+	skel->bss->trace_port = ntohs(get_socket_local_port(listen_fd));
+	skel->bss->sk_index = 0;
+	client_fd1 = connect_to_fd(listen_fd, 0);
+	if (!ASSERT_OK_FD(client_fd1, "connect_to_fd client_fd1"))
+		goto end;
+	/* sockmap helper called from sockops prog should reject mptcp sk */
+	if (ASSERT_EQ(skel->bss->helper_ret, -EOPNOTSUPP, "should reject"))
+		goto end;
+
+	/* skip sockops prog */
+	skel->bss->trace_port = -1;
+	client_fd2 = connect_to_fd(listen_fd, 0);
+	if (!ASSERT_OK_FD(client_fd2, "connect_to_fd client_fd2"))
+		goto end;
+
+	server_fd = xaccept_nonblock(listen_fd, NULL, NULL);
+	err = bpf_map_update_elem(bpf_map__fd(skel->maps.sock_map),
+				  &zero, &server_fd, BPF_NOEXIST);
+	if (ASSERT_EQ(err, -EOPNOTSUPP, "should reject"))
+		goto end;
+end:
+	if (client_fd1 > 0)
+		close(client_fd1);
+	if (client_fd2 > 0)
+		close(client_fd2);
+	if (server_fd > 0)
+		close(server_fd);
+	close(listen_fd);
+}
+
+static void test_mptcp_sockmap(void)
+{
+	struct mptcp_sockmap *skel;
+	struct netns_obj *netns;
+	int cgroup_fd, err;
+
+	cgroup_fd = test__join_cgroup("/mptcp_sockmap");
+	if (!ASSERT_OK_FD(cgroup_fd, "join_cgroup: mptcp_sockmap"))
+		return;
+
+	skel = mptcp_sockmap__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "skel_open_load: mptcp_sockmap"))
+		goto close_cgroup;
+
+	skel->links.mptcp_sockmap_inject =
+		bpf_program__attach_cgroup(skel->progs.mptcp_sockmap_inject, cgroup_fd);
+	if (!ASSERT_OK_PTR(skel->links.mptcp_sockmap_inject, "attach sockmap"))
+		goto skel_destroy;
+
+	err = bpf_prog_attach(bpf_program__fd(skel->progs.mptcp_sockmap_redirect),
+			      bpf_map__fd(skel->maps.sock_map),
+			      BPF_SK_SKB_STREAM_VERDICT, 0);
+	if (!ASSERT_OK(err, "bpf_prog_attach stream verdict"))
+		goto skel_destroy;
+
+	netns = netns_new(NS_TEST, true);
+	if (!ASSERT_OK_PTR(netns, "netns_new: mptcp_sockmap"))
+		goto skel_destroy;
+
+	if (endpoint_init("subflow") < 0)
+		goto close_netns;
+
+	test_sockmap_with_mptcp_fallback(skel);
+	test_sockmap_reject_mptcp(skel);
+
+close_netns:
+	netns_free(netns);
+skel_destroy:
+	mptcp_sockmap__destroy(skel);
+close_cgroup:
+	close(cgroup_fd);
+}
+
 void test_mptcp(void)
 {
 	if (test__start_subtest("base"))
@@ -444,4 +578,6 @@ void test_mptcp(void)
 		test_mptcpify();
 	if (test__start_subtest("subflow"))
 		test_subflow();
+	if (test__start_subtest("sockmap"))
+		test_mptcp_sockmap();
 }
diff --git a/tools/testing/selftests/bpf/progs/mptcp_sockmap.c b/tools/testing/selftests/bpf/progs/mptcp_sockmap.c
new file mode 100644
index 000000000000..d4eef0cbadb9
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/mptcp_sockmap.c
@@ -0,0 +1,43 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "bpf_tracing_net.h"
+
+char _license[] SEC("license") = "GPL";
+
+int sk_index;
+int redirect_idx;
+int trace_port;
+int helper_ret;
+struct {
+	__uint(type, BPF_MAP_TYPE_SOCKMAP);
+	__uint(key_size, sizeof(__u32));
+	__uint(value_size, sizeof(__u32));
+	__uint(max_entries, 100);
+} sock_map SEC(".maps");
+
+SEC("sockops")
+int mptcp_sockmap_inject(struct bpf_sock_ops *skops)
+{
+	struct bpf_sock *sk;
+
+	/* only accept specified connection */
+	if (skops->local_port != trace_port ||
+	    skops->op != BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB)
+		return 1;
+
+	sk = skops->sk;
+	if (!sk)
+		return 1;
+
+	/* update sk handler */
+	helper_ret = bpf_sock_map_update(skops, &sock_map, &sk_index, BPF_NOEXIST);
+
+	return 1;
+}
+
+SEC("sk_skb/stream_verdict")
+int mptcp_sockmap_redirect(struct __sk_buff *skb)
+{
+	/* redirect skb to the sk under sock_map[redirect_idx] */
+	return bpf_sk_redirect_map(skb, &sock_map, redirect_idx, 0);
+}
-- 
2.43.0