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Message-Id: <20251021-work-namespace-nstree-listns-v1-39-ad44261a8a5b@kernel.org>
Date: Tue, 21 Oct 2025 13:43:45 +0200
From: Christian Brauner <brauner@...nel.org>
To: linux-fsdevel@...r.kernel.org, Josef Bacik <josef@...icpanda.com>,
Jeff Layton <jlayton@...nel.org>
Cc: Jann Horn <jannh@...gle.com>, Mike Yuan <me@...dnzj.com>,
Zbigniew Jędrzejewski-Szmek <zbyszek@...waw.pl>,
Lennart Poettering <mzxreary@...inter.de>,
Daan De Meyer <daan.j.demeyer@...il.com>, Aleksa Sarai <cyphar@...har.com>,
Amir Goldstein <amir73il@...il.com>, Tejun Heo <tj@...nel.org>,
Johannes Weiner <hannes@...xchg.org>, Thomas Gleixner <tglx@...utronix.de>,
Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>,
linux-kernel@...r.kernel.org, cgroups@...r.kernel.org, bpf@...r.kernel.org,
Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
netdev@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
Christian Brauner <brauner@...nel.org>
Subject: [PATCH RFC DRAFT 39/50] selftests/namespaces: fifth listns() test
Test that listns() only returns active namespaces.
Create a namespace, let it become inactive, verify it's not listed.
Signed-off-by: Christian Brauner <brauner@...nel.org>
---
tools/testing/selftests/namespaces/listns_test.c | 126 +++++++++++++++++++++++
1 file changed, 126 insertions(+)
diff --git a/tools/testing/selftests/namespaces/listns_test.c b/tools/testing/selftests/namespaces/listns_test.c
index 457298cb4c64..e854794abe56 100644
--- a/tools/testing/selftests/namespaces/listns_test.c
+++ b/tools/testing/selftests/namespaces/listns_test.c
@@ -201,4 +201,130 @@ TEST(listns_current_user)
TH_LOG(" [%zd] ns_id: %llu", i, (unsigned long long)ns_ids[i]);
}
+/*
+ * Test that listns() only returns active namespaces.
+ * Create a namespace, let it become inactive, verify it's not listed.
+ */
+TEST(listns_only_active)
+{
+ struct ns_id_req req = {
+ .size = sizeof(req),
+ .spare = 0,
+ .ns_id = 0,
+ .ns_type = CLONE_NEWNET,
+ .spare2 = 0,
+ .user_ns_id = 0,
+ };
+ __u64 ns_ids_before[100], ns_ids_after[100];
+ ssize_t ret_before, ret_after;
+ int pipefd[2];
+ pid_t pid;
+ __u64 new_ns_id = 0;
+ int status;
+
+ /* Get initial list */
+ ret_before = sys_listns(&req, ns_ids_before, ARRAY_SIZE(ns_ids_before), 0);
+ if (ret_before < 0) {
+ if (errno == ENOSYS)
+ SKIP(return, "listns() not supported");
+ TH_LOG("listns failed: %s (errno=%d)", strerror(errno), errno);
+ ASSERT_TRUE(false);
+ }
+ ASSERT_GE(ret_before, 0);
+
+ TH_LOG("Before: %zd active network namespaces", ret_before);
+
+ /* Create a new namespace in a child process and get its ID */
+ ASSERT_EQ(pipe(pipefd), 0);
+
+ pid = fork();
+ ASSERT_GE(pid, 0);
+
+ if (pid == 0) {
+ int fd;
+ __u64 ns_id;
+
+ close(pipefd[0]);
+
+ /* Create new network namespace */
+ if (unshare(CLONE_NEWNET) < 0) {
+ close(pipefd[1]);
+ exit(1);
+ }
+
+ /* Get its ID */
+ fd = open("/proc/self/ns/net", O_RDONLY);
+ if (fd < 0) {
+ close(pipefd[1]);
+ exit(1);
+ }
+
+ if (ioctl(fd, NS_GET_ID, &ns_id) < 0) {
+ close(fd);
+ close(pipefd[1]);
+ exit(1);
+ }
+ close(fd);
+
+ /* Send ID to parent */
+ write(pipefd[1], &ns_id, sizeof(ns_id));
+ close(pipefd[1]);
+
+ /* Keep namespace active briefly */
+ usleep(100000);
+ exit(0);
+ }
+
+ /* Parent reads the new namespace ID */
+ {
+ int bytes;
+
+ close(pipefd[1]);
+ bytes = read(pipefd[0], &new_ns_id, sizeof(new_ns_id));
+ close(pipefd[0]);
+
+ if (bytes == sizeof(new_ns_id)) {
+ __u64 ns_ids_during[100];
+ int ret_during;
+
+ TH_LOG("Child created namespace with ID %llu", (unsigned long long)new_ns_id);
+
+ /* List namespaces while child is still alive - should see new one */
+ ret_during = sys_listns(&req, ns_ids_during, ARRAY_SIZE(ns_ids_during), 0);
+ ASSERT_GE(ret_during, 0);
+ TH_LOG("During: %d active network namespaces", ret_during);
+
+ /* Should have more namespaces than before */
+ ASSERT_GE(ret_during, ret_before);
+ }
+ }
+
+ /* Wait for child to exit */
+ waitpid(pid, &status, 0);
+
+ /* Give time for namespace to become inactive */
+ usleep(100000);
+
+ /* List namespaces after child exits - should not see new one */
+ ret_after = sys_listns(&req, ns_ids_after, ARRAY_SIZE(ns_ids_after), 0);
+ ASSERT_GE(ret_after, 0);
+ TH_LOG("After: %zd active network namespaces", ret_after);
+
+ /* Verify the new namespace ID is not in the after list */
+ if (new_ns_id != 0) {
+ bool found = false;
+
+ for (ssize_t i = 0; i < ret_after; i++) {
+ if (ns_ids_after[i] == new_ns_id) {
+ found = true;
+ break;
+ }
+ }
+ if (found) {
+ TH_LOG("Warning: Namespace %llu still active after process exit",
+ (unsigned long long)new_ns_id);
+ }
+ }
+}
+
TEST_HARNESS_MAIN
--
2.47.3
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