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Message-Id: <20251021-work-namespace-nstree-listns-v1-26-ad44261a8a5b@kernel.org>
Date: Tue, 21 Oct 2025 13:43:32 +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 26/50] selftests/namespaces: eigth active
reference count tests
Test that bind mounts keep namespaces in the tree even when inactive
Signed-off-by: Christian Brauner <brauner@...nel.org>
---
.../selftests/namespaces/ns_active_ref_test.c | 126 +++++++++++++++++++++
1 file changed, 126 insertions(+)
diff --git a/tools/testing/selftests/namespaces/ns_active_ref_test.c b/tools/testing/selftests/namespaces/ns_active_ref_test.c
index 6377f5d72ed9..66c9908d4977 100644
--- a/tools/testing/selftests/namespaces/ns_active_ref_test.c
+++ b/tools/testing/selftests/namespaces/ns_active_ref_test.c
@@ -883,4 +883,130 @@ TEST(ns_parent_always_reachable)
}
}
+/*
+ * Test that bind mounts keep namespaces in the tree even when inactive
+ */
+TEST(ns_bind_mount_keeps_in_tree)
+{
+ struct file_handle *handle;
+ int mount_id;
+ int ret;
+ int fd;
+ int pipefd[2];
+ pid_t pid;
+ int status;
+ char buf[sizeof(*handle) + MAX_HANDLE_SZ];
+ char tmpfile[] = "/tmp/ns-test-XXXXXX";
+ int tmpfd;
+
+ /* Create temporary file for bind mount */
+ tmpfd = mkstemp(tmpfile);
+ if (tmpfd < 0) {
+ SKIP(return, "Cannot create temporary file");
+ }
+ close(tmpfd);
+
+ ASSERT_EQ(pipe(pipefd), 0);
+
+ pid = fork();
+ ASSERT_GE(pid, 0);
+
+ if (pid == 0) {
+ /* Child process */
+ close(pipefd[0]);
+
+ /* Unshare mount namespace and make mounts private to avoid propagation */
+ ret = unshare(CLONE_NEWNS);
+ if (ret < 0) {
+ close(pipefd[1]);
+ unlink(tmpfile);
+ exit(1);
+ }
+ ret = mount(NULL, "/", NULL, MS_PRIVATE | MS_REC, NULL);
+ if (ret < 0) {
+ close(pipefd[1]);
+ unlink(tmpfile);
+ exit(1);
+ }
+
+ /* Create new network namespace */
+ ret = unshare(CLONE_NEWNET);
+ if (ret < 0) {
+ close(pipefd[1]);
+ unlink(tmpfile);
+ exit(1);
+ }
+
+ /* Bind mount the namespace */
+ ret = mount("/proc/self/ns/net", tmpfile, NULL, MS_BIND, NULL);
+ if (ret < 0) {
+ close(pipefd[1]);
+ unlink(tmpfile);
+ exit(1);
+ }
+
+ /* Get file handle */
+ fd = open("/proc/self/ns/net", O_RDONLY);
+ if (fd < 0) {
+ umount(tmpfile);
+ close(pipefd[1]);
+ unlink(tmpfile);
+ exit(1);
+ }
+
+ handle = (struct file_handle *)buf;
+ handle->handle_bytes = MAX_HANDLE_SZ;
+ ret = name_to_handle_at(fd, "", handle, &mount_id, AT_EMPTY_PATH);
+ close(fd);
+
+ if (ret < 0) {
+ umount(tmpfile);
+ close(pipefd[1]);
+ unlink(tmpfile);
+ exit(1);
+ }
+
+ /* Send handle to parent */
+ write(pipefd[1], buf, sizeof(*handle) + handle->handle_bytes);
+ close(pipefd[1]);
+ exit(0);
+ }
+
+ /* Parent */
+ close(pipefd[1]);
+ ret = read(pipefd[0], buf, sizeof(buf));
+ close(pipefd[0]);
+
+ waitpid(pid, &status, 0);
+ ASSERT_TRUE(WIFEXITED(status));
+
+ if (WEXITSTATUS(status) != 0) {
+ unlink(tmpfile);
+ SKIP(return, "Child failed to create namespace or bind mount");
+ }
+
+ ASSERT_GT(ret, 0);
+ handle = (struct file_handle *)buf;
+
+ /*
+ * Namespace should be inactive but still in tree due to bind mount.
+ * Reopening should fail with ENOENT (inactive) not ESTALE (not in tree).
+ */
+ fd = open_by_handle_at(FD_NSFS_ROOT, handle, O_RDONLY);
+ if (fd >= 0) {
+ /* Unexpected - namespace shouldn't be active */
+ close(fd);
+ TH_LOG("Warning: Namespace still active");
+ } else {
+ /* Should be ENOENT (inactive) since bind mount keeps it in tree */
+ if (errno != ENOENT && errno != ESTALE) {
+ TH_LOG("Unexpected error: %d", errno);
+ }
+ }
+
+ /* Cleanup */
+ umount(tmpfile);
+ unlink(tmpfile);
+}
+
TEST_HARNESS_MAIN
--
2.47.3
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