Test namespace lifecycle: create a namespace in a child process, get a
file handle while it's active, then try to reopen after the process
exits (namespace becomes inactive).

Signed-off-by: Christian Brauner <brauner@kernel.org>
---
 .../selftests/namespaces/ns_active_ref_test.c      | 89 ++++++++++++++++++++++
 1 file changed, 89 insertions(+)

diff --git a/tools/testing/selftests/namespaces/ns_active_ref_test.c b/tools/testing/selftests/namespaces/ns_active_ref_test.c
index 21514a537b26..f628b4a4a927 100644
--- a/tools/testing/selftests/namespaces/ns_active_ref_test.c
+++ b/tools/testing/selftests/namespaces/ns_active_ref_test.c
@@ -71,4 +71,93 @@ TEST(init_ns_always_active)
 	free(handle);
 }
 
+/*
+ * Test namespace lifecycle: create a namespace in a child process,
+ * get a file handle while it's active, then try to reopen after
+ * the process exits (namespace becomes inactive).
+ */
+TEST(ns_inactive_after_exit)
+{
+	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];
+
+	/* Create pipe for passing file handle from child */
+	ASSERT_EQ(pipe(pipefd), 0);
+
+	pid = fork();
+	ASSERT_GE(pid, 0);
+
+	if (pid == 0) {
+		/* Child process */
+		close(pipefd[0]);
+
+		/* Create new network namespace */
+		ret = unshare(CLONE_NEWNET);
+		if (ret < 0) {
+			close(pipefd[1]);
+			exit(1);
+		}
+
+		/* Open our new namespace */
+		fd = open("/proc/self/ns/net", O_RDONLY);
+		if (fd < 0) {
+			close(pipefd[1]);
+			exit(1);
+		}
+
+		/* Get file handle for the namespace */
+		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) {
+			close(pipefd[1]);
+			exit(1);
+		}
+
+		/* Send handle to parent */
+		write(pipefd[1], buf, sizeof(*handle) + handle->handle_bytes);
+		close(pipefd[1]);
+
+		/* Exit - namespace should become inactive */
+		exit(0);
+	}
+
+	/* Parent process */
+	close(pipefd[1]);
+
+	/* Read file handle from child */
+	ret = read(pipefd[0], buf, sizeof(buf));
+	close(pipefd[0]);
+
+	/* Wait for child to exit */
+	waitpid(pid, &status, 0);
+	ASSERT_TRUE(WIFEXITED(status));
+
+	if (WEXITSTATUS(status) != 0) {
+		SKIP(return, "Child failed to create namespace or get handle");
+	}
+
+	ASSERT_GT(ret, 0);
+	handle = (struct file_handle *)buf;
+
+	/* Try to reopen namespace - should fail with ENOENT since it's inactive */
+	fd = open_by_handle_at(FD_NSFS_ROOT, handle, O_RDONLY);
+	if (fd >= 0) {
+		/* Namespace is still active - this could happen if cleanup is slow */
+		TH_LOG("Warning: Namespace still active after process exit");
+		close(fd);
+	} else {
+		/* Should fail with ENOENT (namespace inactive) or ESTALE */
+		ASSERT_TRUE(errno == ENOENT || errno == ESTALE);
+	}
+}
+
 TEST_HARNESS_MAIN

-- 
2.47.3