Test user namespace active ref tracking via credential lifecycle.

Signed-off-by: Christian Brauner <brauner@kernel.org>
---
 .../selftests/namespaces/ns_active_ref_test.c      | 97 ++++++++++++++++++++++
 1 file changed, 97 insertions(+)

diff --git a/tools/testing/selftests/namespaces/ns_active_ref_test.c b/tools/testing/selftests/namespaces/ns_active_ref_test.c
index 63233f22517a..b9836693f5ec 100644
--- a/tools/testing/selftests/namespaces/ns_active_ref_test.c
+++ b/tools/testing/selftests/namespaces/ns_active_ref_test.c
@@ -288,4 +288,101 @@ TEST(ns_active_with_multiple_processes)
 	ASSERT_TRUE(WIFEXITED(status));
 }
 
+/*
+ * Test user namespace active ref tracking via credential lifecycle
+ */
+TEST(userns_active_ref_lifecycle)
+{
+	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];
+
+	ASSERT_EQ(pipe(pipefd), 0);
+
+	pid = fork();
+	ASSERT_GE(pid, 0);
+
+	if (pid == 0) {
+		/* Child process */
+		close(pipefd[0]);
+
+		/* Create new user namespace */
+		ret = unshare(CLONE_NEWUSER);
+		if (ret < 0) {
+			close(pipefd[1]);
+			exit(1);
+		}
+
+		/* Set up uid/gid mappings */
+		int uid_map_fd = open("/proc/self/uid_map", O_WRONLY);
+		int gid_map_fd = open("/proc/self/gid_map", O_WRONLY);
+		int setgroups_fd = open("/proc/self/setgroups", O_WRONLY);
+
+		if (uid_map_fd >= 0 && gid_map_fd >= 0 && setgroups_fd >= 0) {
+			write(setgroups_fd, "deny", 4);
+			close(setgroups_fd);
+
+			char mapping[64];
+			snprintf(mapping, sizeof(mapping), "0 %d 1", getuid());
+			write(uid_map_fd, mapping, strlen(mapping));
+			close(uid_map_fd);
+
+			snprintf(mapping, sizeof(mapping), "0 %d 1", getgid());
+			write(gid_map_fd, mapping, strlen(mapping));
+			close(gid_map_fd);
+		}
+
+		/* Get file handle */
+		fd = open("/proc/self/ns/user", O_RDONLY);
+		if (fd < 0) {
+			close(pipefd[1]);
+			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) {
+			close(pipefd[1]);
+			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) {
+		SKIP(return, "Child failed to create user namespace");
+	}
+
+	ASSERT_GT(ret, 0);
+	handle = (struct file_handle *)buf;
+
+	/* Namespace should be inactive after all tasks exit */
+	fd = open_by_handle_at(FD_NSFS_ROOT, handle, O_RDONLY);
+	if (fd >= 0) {
+		TH_LOG("Warning: User namespace still active after process exit");
+		close(fd);
+	} else {
+		ASSERT_TRUE(errno == ENOENT || errno == ESTALE);
+	}
+}
+
 TEST_HARNESS_MAIN

-- 
2.47.3