Implement a new test program mptcpify: if the family is AF_INET or
AF_INET6, the type is SOCK_STREAM, and the protocol ID is 0 or
IPPROTO_TCP, set it to IPPROTO_MPTCP. It will be hooked in
update_socket_protocol().

Extend the MPTCP test base, add a selftest test_mptcpify() for the
mptcpify case. Open and load the mptcpify test prog to mptcpify the
TCP sockets dynamically, then use start_server() and connect_to_fd()
to create a TCP socket, but actually what's created is an MPTCP
socket, which can be verified through the outputs of 'ss' and 'nstat'
commands.

Reviewed-by: Matthieu Baerts <matthieu.bae...@tessares.net>
Signed-off-by: Geliang Tang <geliang.t...@suse.com>
---
 .../testing/selftests/bpf/prog_tests/mptcp.c  | 94 +++++++++++++++++++
 tools/testing/selftests/bpf/progs/mptcpify.c  | 25 +++++
 2 files changed, 119 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/mptcpify.c

diff --git a/tools/testing/selftests/bpf/prog_tests/mptcp.c 
b/tools/testing/selftests/bpf/prog_tests/mptcp.c
index 4407bd5c9e9a..caab3aa6a162 100644
--- a/tools/testing/selftests/bpf/prog_tests/mptcp.c
+++ b/tools/testing/selftests/bpf/prog_tests/mptcp.c
@@ -6,6 +6,7 @@
 #include "cgroup_helpers.h"
 #include "network_helpers.h"
 #include "mptcp_sock.skel.h"
+#include "mptcpify.skel.h"
 
 char NS_TEST[32];
 
@@ -195,8 +196,101 @@ static void test_base(void)
        close(cgroup_fd);
 }
 
+static void send_byte(int fd)
+{
+       char b = 0x55;
+
+       ASSERT_EQ(write(fd, &b, sizeof(b)), 1, "send single byte");
+}
+
+static int verify_mptcpify(void)
+{
+       char cmd[256];
+       int err = 0;
+
+       snprintf(cmd, sizeof(cmd),
+                "ip netns exec %s ss -tOni | grep -q '%s'",
+                NS_TEST, "tcp-ulp-mptcp");
+       if (!ASSERT_OK(system(cmd), "No tcp-ulp-mptcp found!"))
+               err++;
+
+       snprintf(cmd, sizeof(cmd),
+                "ip netns exec %s nstat -asz %s | awk '%s' | grep -q '%s'",
+                NS_TEST, "MPTcpExtMPCapableSYNACKRX",
+                "NR==1 {next} {print $2}", "1");
+       if (!ASSERT_OK(system(cmd), "No MPTcpExtMPCapableSYNACKRX found!"))
+               err++;
+
+       return err;
+}
+
+static int run_mptcpify(int cgroup_fd)
+{
+       int server_fd, client_fd, prog_fd, err = 0;
+       struct mptcpify *mptcpify_skel;
+
+       mptcpify_skel = mptcpify__open_and_load();
+       if (!ASSERT_OK_PTR(mptcpify_skel, "skel_open_load"))
+               return -EIO;
+
+       err = mptcpify__attach(mptcpify_skel);
+       if (!ASSERT_OK(err, "skel_attach"))
+               goto out;
+
+       prog_fd = bpf_program__fd(mptcpify_skel->progs.mptcpify);
+       if (!ASSERT_GE(prog_fd, 0, "bpf_program__fd")) {
+               err = -EIO;
+               goto out;
+       }
+
+       /* without MPTCP */
+       server_fd = start_server(AF_INET, SOCK_STREAM, NULL, 0, 0);
+       if (!ASSERT_GE(server_fd, 0, "start_server")) {
+               err = -EIO;
+               goto out;
+       }
+
+       client_fd = connect_to_fd(server_fd, 0);
+       if (!ASSERT_GE(client_fd, 0, "connect to fd")) {
+               err = -EIO;
+               goto close_server;
+       }
+
+       send_byte(client_fd);
+       err += verify_mptcpify();
+
+       close(client_fd);
+close_server:
+       close(server_fd);
+out:
+       mptcpify__destroy(mptcpify_skel);
+       return err;
+}
+
+static void test_mptcpify(void)
+{
+       struct nstoken *nstoken = NULL;
+       int cgroup_fd;
+
+       cgroup_fd = test__join_cgroup("/mptcpify");
+       if (!ASSERT_GE(cgroup_fd, 0, "test__join_cgroup"))
+               return;
+
+       nstoken = create_netns();
+       if (!ASSERT_OK_PTR(nstoken, "create_netns"))
+               goto fail;
+
+       ASSERT_OK(run_mptcpify(cgroup_fd), "run_mptcpify");
+
+fail:
+       cleanup_netns(nstoken);
+       close(cgroup_fd);
+}
+
 void test_mptcp(void)
 {
        if (test__start_subtest("base"))
                test_base();
+       if (test__start_subtest("mptcpify"))
+               test_mptcpify();
 }
diff --git a/tools/testing/selftests/bpf/progs/mptcpify.c 
b/tools/testing/selftests/bpf/progs/mptcpify.c
new file mode 100644
index 000000000000..9cf1febe982d
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/mptcpify.c
@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2023, SUSE. */
+
+#include <linux/bpf.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+#define        AF_INET         2
+#define        AF_INET6        10
+#define        SOCK_STREAM     1
+#define        IPPROTO_TCP     6
+#define        IPPROTO_MPTCP   262
+
+SEC("fmod_ret/update_socket_protocol")
+int BPF_PROG(mptcpify, int family, int type, int protocol)
+{
+       if ((family == AF_INET || family == AF_INET6) &&
+           type == SOCK_STREAM &&
+           (!protocol || protocol == IPPROTO_TCP)) {
+               return IPPROTO_MPTCP;
+       }
+
+       return protocol;
+}
-- 
2.35.3


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