From 3452eecbcc954ef859b7d19309c121a78d6d0e31 Mon Sep 17 00:00:00 2001
From: Noah Orlando <Noah.Orlando@deshaw.com>
Date: Mon, 6 Jul 2026 14:26:01 -0400
Subject: [PATCH] selftests/filesystems: add mntns cleanup test

Verify that destroying a mount namespace keeps its mounts connected.

Signed-off-by: Noah Orlando <Noah.Orlando@deshaw.com>
Link: https://patch.msgid.link/20260706182559.2496448-4-Noah.Orlando@deshaw.com
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 tools/testing/selftests/Makefile              |  1 +
 .../filesystems/mntns_cleanup/.gitignore      |  2 +
 .../filesystems/mntns_cleanup/Makefile        |  6 ++
 .../mntns_cleanup/mntns_cleanup_test.c        | 58 +++++++++++++++++++
 4 files changed, 67 insertions(+)
 create mode 100644 tools/testing/selftests/filesystems/mntns_cleanup/.gitignore
 create mode 100644 tools/testing/selftests/filesystems/mntns_cleanup/Makefile
 create mode 100644 tools/testing/selftests/filesystems/mntns_cleanup/mntns_cleanup_test.c

diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index 8d4db2241cc2..023699f05e13 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -42,6 +42,7 @@ TARGETS += filesystems/fuse
 TARGETS += filesystems/move_mount
 TARGETS += filesystems/empty_mntns
 TARGETS += filesystems/fsmount_ns
+TARGETS += filesystems/mntns_cleanup
 TARGETS += firmware
 TARGETS += fpu
 TARGETS += ftrace
diff --git a/tools/testing/selftests/filesystems/mntns_cleanup/.gitignore b/tools/testing/selftests/filesystems/mntns_cleanup/.gitignore
new file mode 100644
index 000000000000..493fbcf8d9ec
--- /dev/null
+++ b/tools/testing/selftests/filesystems/mntns_cleanup/.gitignore
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+mntns_cleanup_test
diff --git a/tools/testing/selftests/filesystems/mntns_cleanup/Makefile b/tools/testing/selftests/filesystems/mntns_cleanup/Makefile
new file mode 100644
index 000000000000..0e09e7030a5c
--- /dev/null
+++ b/tools/testing/selftests/filesystems/mntns_cleanup/Makefile
@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0
+TEST_GEN_PROGS := mntns_cleanup_test
+
+CFLAGS += -Wall -O2 -g $(KHDR_INCLUDES)
+
+include ../../lib.mk
diff --git a/tools/testing/selftests/filesystems/mntns_cleanup/mntns_cleanup_test.c b/tools/testing/selftests/filesystems/mntns_cleanup/mntns_cleanup_test.c
new file mode 100644
index 000000000000..5209712568b1
--- /dev/null
+++ b/tools/testing/selftests/filesystems/mntns_cleanup/mntns_cleanup_test.c
@@ -0,0 +1,58 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h>
+#include <sched.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+#include "../../kselftest_harness.h"
+
+FIXTURE(mntns_cleanup) {
+};
+
+FIXTURE_SETUP(mntns_cleanup)
+{
+	if (geteuid() != 0)
+		SKIP(return, "test requires CAP_SYS_ADMIN");
+
+	ASSERT_EQ(unshare(CLONE_NEWNS), 0);
+	ASSERT_EQ(mount("", "/", NULL, MS_REC | MS_PRIVATE, NULL), 0);
+
+	rmdir("/mnt_dir");
+	ASSERT_EQ(mkdir("/mnt_dir", 0755), 0);
+	ASSERT_EQ(mount("tmpfs", "/mnt_dir", "tmpfs", 0, NULL), 0);
+	ASSERT_EQ(mkdir("/mnt_dir/hidden", 0755), 0);
+	ASSERT_EQ(mkdir("/mnt_dir/hidden/secret", 0755), 0);
+	ASSERT_EQ(mount("tmpfs", "/mnt_dir/hidden", "tmpfs", 0, NULL), 0);
+}
+
+FIXTURE_TEARDOWN(mntns_cleanup)
+{
+}
+
+/* Mounts must stay connected when a mount namespace is cleaned up. */
+TEST_F(mntns_cleanup, keeps_mounts_connected)
+{
+	int fd, sfd, err;
+
+	fd = open("/mnt_dir", O_PATH | O_DIRECTORY | O_CLOEXEC);
+	ASSERT_GE(fd, 0);
+
+	/* Destroy the namespace; the fd keeps /mnt_dir alive. */
+	ASSERT_EQ(unshare(CLONE_NEWNS), 0);
+
+	sfd = openat(fd, "hidden/secret", O_RDONLY);
+	err = errno;
+	if (sfd >= 0)
+		close(sfd);
+	close(fd);
+
+	ASSERT_LT(sfd, 0)
+		TH_LOG("mount namespace teardown revealed what the overmount covered");
+	ASSERT_EQ(err, ENOENT);
+}
+
+TEST_HARNESS_MAIN