selftests/bpf: run mptcp in a dedicated netns

The current mptcp test is run in init netns. If the user or default
system config disabled mptcp, the test will fail. Let's run the mptcp
test in a dedicated netns to avoid none kernel default mptcp setting.
Suggested-by: Martin KaFai Lau <martin.lau@linux.dev>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Acked-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Link: https://lore.kernel.org/r/20230224061343.506571-3-liuhangbin@gmail.comSigned-off-by: Martin KaFai Lau <martin.lau@kernel.org>

tools/testing/selftests/bpf/prog_tests/mptcp.c

@@ -7,6 +7,8 @@
 #include "network_helpers.h"
 #include "mptcp_sock.skel.h"
 
+#define NS_TEST "mptcp_ns"
+
 #ifndef TCP_CA_NAME_MAX
 #define TCP_CA_NAME_MAX	16
 #endif
@@ -138,12 +140,20 @@ static int run_test(int cgroup_fd, int server_fd, bool is_mptcp)
 
 static void test_base(void)
 {
+	struct nstoken *nstoken = NULL;
 	int server_fd, cgroup_fd;
 
 	cgroup_fd = test__join_cgroup("/mptcp");
 	if (!ASSERT_GE(cgroup_fd, 0, "test__join_cgroup"))
 		return;
 
+	SYS(fail, "ip netns add %s", NS_TEST);
+	SYS(fail, "ip -net %s link set dev lo up", NS_TEST);
+
+	nstoken = open_netns(NS_TEST);
+	if (!ASSERT_OK_PTR(nstoken, "open_netns"))
+		goto fail;
+
 	/* without MPTCP */
 	server_fd = start_server(AF_INET, SOCK_STREAM, NULL, 0, 0);
 	if (!ASSERT_GE(server_fd, 0, "start_server"))
@@ -157,13 +167,18 @@ static void test_base(void)
 	/* with MPTCP */
 	server_fd = start_mptcp_server(AF_INET, NULL, 0, 0);
 	if (!ASSERT_GE(server_fd, 0, "start_mptcp_server"))
-		goto close_cgroup_fd;
+		goto fail;
 
 	ASSERT_OK(run_test(cgroup_fd, server_fd, true), "run_test mptcp");
 
 	close(server_fd);
 
-close_cgroup_fd:
+fail:
+	if (nstoken)
+		close_netns(nstoken);
+
+	SYS_NOFAIL("ip netns del " NS_TEST " &> /dev/null");
+
 	close(cgroup_fd);
 }