1 files changed, 129 insertions, 0 deletions
diff --git a/tools/testing/selftests/filesystems/empty_mntns/nullfs_atime_test.c b/tools/testing/selftests/filesystems/empty_mntns/nullfs_atime_test.c
new file mode 100644
index 000000000000..51e34f3c4f54
--- /dev/null
+++ b/tools/testing/selftests/filesystems/empty_mntns/nullfs_atime_test.c
@@ -0,0 +1,129 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * The root of every empty mount namespace is the same nullfs inode. A read
+ * of it by one user must not change the access time another user sees.
+ */
+#define _GNU_SOURCE
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <sched.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+
+#include "../../kselftest_harness.h"
+
+#ifndef UNSHARE_EMPTY_MNTNS
+#define UNSHARE_EMPTY_MNTNS	0x00100000
+#endif
+
+enum {
+	CHILD_OK,
+	CHILD_UNSUPPORTED,
+	CHILD_SETUP,
+	CHILD_CHANGED,
+};
+
+static int wait_byte(int fd)
+{
+	char c;
+
+	return read(fd, &c, 1) == 1 ? 0 : -1;
+}
+
+static int send_byte(int fd)
+{
+	return write(fd, "x", 1) == 1 ? 0 : -1;
+}
+
+static int empty_mntns(void)
+{
+	if (!unshare(UNSHARE_EMPTY_MNTNS))
+		return 0;
+	return errno == EINVAL ? CHILD_UNSUPPORTED : CHILD_SETUP;
+}
+
+/* the watcher: stats its root before and after the reader read its own */
+static int watcher(int to_reader, int from_reader)
+{
+	struct stat before, after;
+	int ret;
+
+	ret = empty_mntns();
+	if (ret)
+		return ret;
+	if (stat("/", &before))
+		return CHILD_SETUP;
+	if (send_byte(to_reader) || wait_byte(from_reader))
+		return CHILD_SETUP;
+	if (stat("/", &after))
+		return CHILD_SETUP;
+	if (before.st_atim.tv_sec != after.st_atim.tv_sec ||
+	    before.st_atim.tv_nsec != after.st_atim.tv_nsec)
+		return CHILD_CHANGED;
+	return CHILD_OK;
+}
+
+/* the reader: lists its own root, which is the same inode */
+static int reader(int to_watcher, int from_watcher)
+{
+	struct dirent *de;
+	DIR *d;
+	int ret;
+
+	ret = empty_mntns();
+	if (ret)
+		return ret;
+	if (wait_byte(from_watcher))
+		return CHILD_SETUP;
+	d = opendir("/");
+	if (!d)
+		return CHILD_SETUP;
+	while ((de = readdir(d)))
+		;
+	closedir(d);
+	return send_byte(to_watcher) ? CHILD_SETUP : CHILD_OK;
+}
+
+static int wait_child(pid_t pid)
+{
+	int status;
+
+	if (waitpid(pid, &status, 0) != pid || !WIFEXITED(status))
+		return -1;
+	return WEXITSTATUS(status);
+}
+
+TEST(empty_mntns_root_atime)
+{
+	int to_reader[2], to_watcher[2], w, r;
+	pid_t watcher_pid, reader_pid;
+
+	if (geteuid())
+		SKIP(return, "test requires root");
+	ASSERT_EQ(pipe(to_reader), 0);
+	ASSERT_EQ(pipe(to_watcher), 0);
+
+	watcher_pid = fork();
+	ASSERT_GE(watcher_pid, 0);
+	if (watcher_pid == 0)
+		_exit(watcher(to_reader[1], to_watcher[0]));
+	reader_pid = fork();
+	ASSERT_GE(reader_pid, 0);
+	if (reader_pid == 0)
+		_exit(reader(to_watcher[1], to_reader[0]));
+
+	r = wait_child(reader_pid);
+	w = wait_child(watcher_pid);
+	if (r == CHILD_UNSUPPORTED || w == CHILD_UNSUPPORTED)
+		SKIP(return, "UNSHARE_EMPTY_MNTNS not supported");
+	EXPECT_EQ(r, CHILD_OK);
+	EXPECT_EQ(w, CHILD_OK)
+		TH_LOG("the access time of the root changed while this namespace did nothing");
+}
+
+TEST_HARNESS_MAIN