selftests: net: run reuseport in an isolated netns

The reuseport_* tests (bpf, bpf_cpu, bpf_numa, dualstack) currently use
a fixed port range. This can cause intermittent test failures when the
ports are already in use by other services:

  failed to bind receive socket: Address already in use

To avoid conflicts, run these tests in separate network namespaces using
unshare. Each test now has its own isolated network stack, preventing
port collisions with the host services.

Signed-off-by: Aleksei Oladko <aleksey.oladko@virtuozzo.com>
Link: https://patch.msgid.link/20260321215908.175465-2-aleksey.oladko@virtuozzo.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

4 files changed, 42 insertions, 0 deletions

diff --git a/tools/testing/selftests/net/reuseport_bpf.c b/tools/testing/selftests/net/reuseport_bpf.c
index b6634d6da3d6..12e48b97b862 100644
--- a/tools/testing/selftests/net/reuseport_bpf.c
+++ b/tools/testing/selftests/net/reuseport_bpf.c
@@ -23,6 +23,7 @@
 #include <sys/socket.h>
 #include <sys/resource.h>
 #include <unistd.h>
+#include <sched.h>
 
 #include "kselftest.h"
 
@@ -455,8 +456,18 @@ static __attribute__((destructor)) void main_dtor(void)
 	setrlimit(RLIMIT_MEMLOCK, &rlim_old);
 }
 
+static void setup_netns(void)
+{
+	if (unshare(CLONE_NEWNET))
+		error(1, errno, "failed to unshare netns");
+	if (system("ip link set lo up"))
+		error(1, 0, "failed to bring up lo interface in netns");
+}
+
 int main(void)
 {
+	setup_netns();
+
 	fprintf(stderr, "---- IPv4 UDP ----\n");
 	/* NOTE: UDP socket lookups traverse a different code path when there
 	 * are > 10 sockets in a group.  Run the bpf test through both paths.
diff --git a/tools/testing/selftests/net/reuseport_bpf_cpu.c b/tools/testing/selftests/net/reuseport_bpf_cpu.c
index 2d646174729f..ddfe92f6597a 100644
--- a/tools/testing/selftests/net/reuseport_bpf_cpu.c
+++ b/tools/testing/selftests/net/reuseport_bpf_cpu.c
@@ -228,10 +228,20 @@ static void test(int *rcv_fd, int len, int family, int proto)
 		close(rcv_fd[cpu]);
 }
 
+static void setup_netns(void)
+{
+	if (unshare(CLONE_NEWNET))
+		error(1, errno, "failed to unshare netns");
+	if (system("ip link set lo up"))
+		error(1, 0, "failed to bring up lo interface in netns");
+}
+
 int main(void)
 {
 	int *rcv_fd, cpus;
 
+	setup_netns();
+
 	cpus = sysconf(_SC_NPROCESSORS_ONLN);
 	if (cpus <= 0)
 		error(1, errno, "failed counting cpus");
diff --git a/tools/testing/selftests/net/reuseport_bpf_numa.c b/tools/testing/selftests/net/reuseport_bpf_numa.c
index 2ffd957ffb15..8ec52fc5ef41 100644
--- a/tools/testing/selftests/net/reuseport_bpf_numa.c
+++ b/tools/testing/selftests/net/reuseport_bpf_numa.c
@@ -230,10 +230,20 @@ static void test(int *rcv_fd, int len, int family, int proto)
 		close(rcv_fd[node]);
 }
 
+static void setup_netns(void)
+{
+	if (unshare(CLONE_NEWNET))
+		error(1, errno, "failed to unshare netns");
+	if (system("ip link set lo up"))
+		error(1, 0, "failed to bring up lo interface in netns");
+}
+
 int main(void)
 {
 	int *rcv_fd, nodes;
 
+	setup_netns();
+
 	if (numa_available() < 0)
 		ksft_exit_skip("no numa api support\n");
 
diff --git a/tools/testing/selftests/net/reuseport_dualstack.c b/tools/testing/selftests/net/reuseport_dualstack.c
index fb7a59ed759e..0eaf739d0c85 100644
--- a/tools/testing/selftests/net/reuseport_dualstack.c
+++ b/tools/testing/selftests/net/reuseport_dualstack.c
@@ -25,6 +25,7 @@
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <unistd.h>
+#include <sched.h>
 
 static const int PORT = 8888;
 
@@ -156,10 +157,20 @@ static void test(int *rcv_fds, int count, int proto)
 	close(epfd);
 }
 
+static void setup_netns(void)
+{
+	if (unshare(CLONE_NEWNET))
+		error(1, errno, "failed to unshare netns");
+	if (system("ip link set lo up"))
+		error(1, 0, "failed to bring up lo interface in netns");
+}
+
 int main(void)
 {
 	int rcv_fds[32], i;
 
+	setup_netns();
+
 	fprintf(stderr, "---- UDP IPv4 created before IPv6 ----\n");
 	build_rcv_fd(AF_INET, SOCK_DGRAM, rcv_fds, 5);
 	build_rcv_fd(AF_INET6, SOCK_DGRAM, &(rcv_fds[5]), 5);