--- /dev/null
+// SPDX-License-Identifier: GPL-2.0-or-later
+// Copyright (c) 2025 Miklos Szeredi <miklos@szeredi.hu>
+
+#define _GNU_SOURCE
+#include <fcntl.h>
+#include <sched.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/mount.h>
+#include <linux/fanotify.h>
+#include <unistd.h>
+#include <sys/fanotify.h>
+#include <sys/syscall.h>
+
+#include "../../kselftest_harness.h"
+#include "../statmount/statmount.h"
+
+#ifndef FAN_MNT_ATTACH
+struct fanotify_event_info_mnt {
+ struct fanotify_event_info_header hdr;
+ __u64 mnt_id;
+};
+#define FAN_MNT_ATTACH 0x01000000 /* Mount was attached */
+#endif
+
+#ifndef FAN_MNT_DETACH
+#define FAN_MNT_DETACH 0x02000000 /* Mount was detached */
+#endif
+
+#ifndef FAN_REPORT_MNT
+#define FAN_REPORT_MNT 0x00004000 /* Report mount events */
+#endif
+
+#ifndef FAN_MARK_MNTNS
+#define FAN_MARK_MNTNS 0x00000110
+#endif
+
+static uint64_t get_mnt_id(struct __test_metadata *const _metadata,
+ const char *path)
+{
+ struct statx sx;
+
+ ASSERT_EQ(statx(AT_FDCWD, path, 0, STATX_MNT_ID_UNIQUE, &sx), 0);
+ ASSERT_TRUE(!!(sx.stx_mask & STATX_MNT_ID_UNIQUE));
+ return sx.stx_mnt_id;
+}
+
+static const char root_mntpoint_templ[] = "/tmp/mount-notify_test_root.XXXXXX";
+
+FIXTURE(fanotify) {
+ int fan_fd;
+ char buf[256];
+ unsigned int rem;
+ void *next;
+ char root_mntpoint[sizeof(root_mntpoint_templ)];
+ int orig_root;
+ int ns_fd;
+ uint64_t root_id;
+};
+
+FIXTURE_SETUP(fanotify)
+{
+ int ret;
+
+ ASSERT_EQ(unshare(CLONE_NEWNS), 0);
+
+ self->ns_fd = open("/proc/self/ns/mnt", O_RDONLY);
+ ASSERT_GE(self->ns_fd, 0);
+
+ ASSERT_EQ(mount("", "/", NULL, MS_REC|MS_PRIVATE, NULL), 0);
+
+ strcpy(self->root_mntpoint, root_mntpoint_templ);
+ ASSERT_NE(mkdtemp(self->root_mntpoint), NULL);
+
+ self->orig_root = open("/", O_PATH | O_CLOEXEC);
+ ASSERT_GE(self->orig_root, 0);
+
+ ASSERT_EQ(mount("tmpfs", self->root_mntpoint, "tmpfs", 0, NULL), 0);
+
+ ASSERT_EQ(chroot(self->root_mntpoint), 0);
+
+ ASSERT_EQ(chdir("/"), 0);
+
+ ASSERT_EQ(mkdir("a", 0700), 0);
+
+ ASSERT_EQ(mkdir("b", 0700), 0);
+
+ self->root_id = get_mnt_id(_metadata, "/");
+ ASSERT_NE(self->root_id, 0);
+
+ self->fan_fd = fanotify_init(FAN_REPORT_MNT, 0);
+ ASSERT_GE(self->fan_fd, 0);
+
+ ret = fanotify_mark(self->fan_fd, FAN_MARK_ADD | FAN_MARK_MNTNS,
+ FAN_MNT_ATTACH | FAN_MNT_DETACH, self->ns_fd, NULL);
+ ASSERT_EQ(ret, 0);
+
+ self->rem = 0;
+}
+
+FIXTURE_TEARDOWN(fanotify)
+{
+ ASSERT_EQ(self->rem, 0);
+ close(self->fan_fd);
+
+ ASSERT_EQ(fchdir(self->orig_root), 0);
+
+ ASSERT_EQ(chroot("."), 0);
+
+ EXPECT_EQ(umount2(self->root_mntpoint, MNT_DETACH), 0);
+ EXPECT_EQ(chdir(self->root_mntpoint), 0);
+ EXPECT_EQ(chdir("/"), 0);
+ EXPECT_EQ(rmdir(self->root_mntpoint), 0);
+}
+
+static uint64_t expect_notify(struct __test_metadata *const _metadata,
+ FIXTURE_DATA(fanotify) *self,
+ uint64_t *mask)
+{
+ struct fanotify_event_metadata *meta;
+ struct fanotify_event_info_mnt *mnt;
+ unsigned int thislen;
+
+ if (!self->rem) {
+ ssize_t len = read(self->fan_fd, self->buf, sizeof(self->buf));
+ ASSERT_GT(len, 0);
+
+ self->rem = len;
+ self->next = (void *) self->buf;
+ }
+
+ meta = self->next;
+ ASSERT_TRUE(FAN_EVENT_OK(meta, self->rem));
+
+ thislen = meta->event_len;
+ self->rem -= thislen;
+ self->next += thislen;
+
+ *mask = meta->mask;
+ thislen -= sizeof(*meta);
+
+ mnt = ((void *) meta) + meta->event_len - thislen;
+
+ ASSERT_EQ(thislen, sizeof(*mnt));
+
+ return mnt->mnt_id;
+}
+
+static void expect_notify_n(struct __test_metadata *const _metadata,
+ FIXTURE_DATA(fanotify) *self,
+ unsigned int n, uint64_t mask[], uint64_t mnts[])
+{
+ unsigned int i;
+
+ for (i = 0; i < n; i++)
+ mnts[i] = expect_notify(_metadata, self, &mask[i]);
+}
+
+static uint64_t expect_notify_mask(struct __test_metadata *const _metadata,
+ FIXTURE_DATA(fanotify) *self,
+ uint64_t expect_mask)
+{
+ uint64_t mntid, mask;
+
+ mntid = expect_notify(_metadata, self, &mask);
+ ASSERT_EQ(expect_mask, mask);
+
+ return mntid;
+}
+
+
+static void expect_notify_mask_n(struct __test_metadata *const _metadata,
+ FIXTURE_DATA(fanotify) *self,
+ uint64_t mask, unsigned int n, uint64_t mnts[])
+{
+ unsigned int i;
+
+ for (i = 0; i < n; i++)
+ mnts[i] = expect_notify_mask(_metadata, self, mask);
+}
+
+static void verify_mount_ids(struct __test_metadata *const _metadata,
+ const uint64_t list1[], const uint64_t list2[],
+ size_t num)
+{
+ unsigned int i, j;
+
+ // Check that neither list has any duplicates
+ for (i = 0; i < num; i++) {
+ for (j = 0; j < num; j++) {
+ if (i != j) {
+ ASSERT_NE(list1[i], list1[j]);
+ ASSERT_NE(list2[i], list2[j]);
+ }
+ }
+ }
+ // Check that all list1 memebers can be found in list2. Together with
+ // the above it means that the list1 and list2 represent the same sets.
+ for (i = 0; i < num; i++) {
+ for (j = 0; j < num; j++) {
+ if (list1[i] == list2[j])
+ break;
+ }
+ ASSERT_NE(j, num);
+ }
+}
+
+static void check_mounted(struct __test_metadata *const _metadata,
+ const uint64_t mnts[], size_t num)
+{
+ ssize_t ret;
+ uint64_t *list;
+
+ list = malloc((num + 1) * sizeof(list[0]));
+ ASSERT_NE(list, NULL);
+
+ ret = listmount(LSMT_ROOT, 0, 0, list, num + 1, 0);
+ ASSERT_EQ(ret, num);
+
+ verify_mount_ids(_metadata, mnts, list, num);
+
+ free(list);
+}
+
+static void setup_mount_tree(struct __test_metadata *const _metadata,
+ int log2_num)
+{
+ int ret, i;
+
+ ret = mount("", "/", NULL, MS_SHARED, NULL);
+ ASSERT_EQ(ret, 0);
+
+ for (i = 0; i < log2_num; i++) {
+ ret = mount("/", "/", NULL, MS_BIND, NULL);
+ ASSERT_EQ(ret, 0);
+ }
+}
+
+TEST_F(fanotify, bind)
+{
+ int ret;
+ uint64_t mnts[2] = { self->root_id };
+
+ ret = mount("/", "/", NULL, MS_BIND, NULL);
+ ASSERT_EQ(ret, 0);
+
+ mnts[1] = expect_notify_mask(_metadata, self, FAN_MNT_ATTACH);
+ ASSERT_NE(mnts[0], mnts[1]);
+
+ check_mounted(_metadata, mnts, 2);
+
+ // Cleanup
+ uint64_t detach_id;
+ ret = umount("/");
+ ASSERT_EQ(ret, 0);
+
+ detach_id = expect_notify_mask(_metadata, self, FAN_MNT_DETACH);
+ ASSERT_EQ(detach_id, mnts[1]);
+
+ check_mounted(_metadata, mnts, 1);
+}
+
+TEST_F(fanotify, move)
+{
+ int ret;
+ uint64_t mnts[2] = { self->root_id };
+ uint64_t move_id;
+
+ ret = mount("/", "/a", NULL, MS_BIND, NULL);
+ ASSERT_EQ(ret, 0);
+
+ mnts[1] = expect_notify_mask(_metadata, self, FAN_MNT_ATTACH);
+ ASSERT_NE(mnts[0], mnts[1]);
+
+ check_mounted(_metadata, mnts, 2);
+
+ ret = move_mount(AT_FDCWD, "/a", AT_FDCWD, "/b", 0);
+ ASSERT_EQ(ret, 0);
+
+ move_id = expect_notify_mask(_metadata, self, FAN_MNT_ATTACH | FAN_MNT_DETACH);
+ ASSERT_EQ(move_id, mnts[1]);
+
+ // Cleanup
+ ret = umount("/b");
+ ASSERT_EQ(ret, 0);
+
+ check_mounted(_metadata, mnts, 1);
+}
+
+TEST_F(fanotify, propagate)
+{
+ const unsigned int log2_num = 4;
+ const unsigned int num = (1 << log2_num);
+ uint64_t mnts[num];
+
+ setup_mount_tree(_metadata, log2_num);
+
+ expect_notify_mask_n(_metadata, self, FAN_MNT_ATTACH, num - 1, mnts + 1);
+
+ mnts[0] = self->root_id;
+ check_mounted(_metadata, mnts, num);
+
+ // Cleanup
+ int ret;
+ uint64_t mnts2[num];
+ ret = umount2("/", MNT_DETACH);
+ ASSERT_EQ(ret, 0);
+
+ ret = mount("", "/", NULL, MS_PRIVATE, NULL);
+ ASSERT_EQ(ret, 0);
+
+ mnts2[0] = self->root_id;
+ expect_notify_mask_n(_metadata, self, FAN_MNT_DETACH, num - 1, mnts2 + 1);
+ verify_mount_ids(_metadata, mnts, mnts2, num);
+
+ check_mounted(_metadata, mnts, 1);
+}
+
+TEST_F(fanotify, fsmount)
+{
+ int ret, fs, mnt;
+ uint64_t mnts[2] = { self->root_id };
+
+ fs = fsopen("tmpfs", 0);
+ ASSERT_GE(fs, 0);
+
+ ret = fsconfig(fs, FSCONFIG_CMD_CREATE, 0, 0, 0);
+ ASSERT_EQ(ret, 0);
+
+ mnt = fsmount(fs, 0, 0);
+ ASSERT_GE(mnt, 0);
+
+ close(fs);
+
+ ret = move_mount(mnt, "", AT_FDCWD, "/a", MOVE_MOUNT_F_EMPTY_PATH);
+ ASSERT_EQ(ret, 0);
+
+ close(mnt);
+
+ mnts[1] = expect_notify_mask(_metadata, self, FAN_MNT_ATTACH);
+ ASSERT_NE(mnts[0], mnts[1]);
+
+ check_mounted(_metadata, mnts, 2);
+
+ // Cleanup
+ uint64_t detach_id;
+ ret = umount("/a");
+ ASSERT_EQ(ret, 0);
+
+ detach_id = expect_notify_mask(_metadata, self, FAN_MNT_DETACH);
+ ASSERT_EQ(detach_id, mnts[1]);
+
+ check_mounted(_metadata, mnts, 1);
+}
+
+TEST_F(fanotify, reparent)
+{
+ uint64_t mnts[6] = { self->root_id };
+ uint64_t dmnts[3];
+ uint64_t masks[3];
+ unsigned int i;
+ int ret;
+
+ // Create setup with a[1] -> b[2] propagation
+ ret = mount("/", "/a", NULL, MS_BIND, NULL);
+ ASSERT_EQ(ret, 0);
+
+ ret = mount("", "/a", NULL, MS_SHARED, NULL);
+ ASSERT_EQ(ret, 0);
+
+ ret = mount("/a", "/b", NULL, MS_BIND, NULL);
+ ASSERT_EQ(ret, 0);
+
+ ret = mount("", "/b", NULL, MS_SLAVE, NULL);
+ ASSERT_EQ(ret, 0);
+
+ expect_notify_mask_n(_metadata, self, FAN_MNT_ATTACH, 2, mnts + 1);
+
+ check_mounted(_metadata, mnts, 3);
+
+ // Mount on a[3], which is propagated to b[4]
+ ret = mount("/", "/a", NULL, MS_BIND, NULL);
+ ASSERT_EQ(ret, 0);
+
+ expect_notify_mask_n(_metadata, self, FAN_MNT_ATTACH, 2, mnts + 3);
+
+ check_mounted(_metadata, mnts, 5);
+
+ // Mount on b[5], not propagated
+ ret = mount("/", "/b", NULL, MS_BIND, NULL);
+ ASSERT_EQ(ret, 0);
+
+ mnts[5] = expect_notify_mask(_metadata, self, FAN_MNT_ATTACH);
+
+ check_mounted(_metadata, mnts, 6);
+
+ // Umount a[3], which is propagated to b[4], but not b[5]
+ // This will result in b[5] "falling" on b[2]
+ ret = umount("/a");
+ ASSERT_EQ(ret, 0);
+
+ expect_notify_n(_metadata, self, 3, masks, dmnts);
+ verify_mount_ids(_metadata, mnts + 3, dmnts, 3);
+
+ for (i = 0; i < 3; i++) {
+ if (dmnts[i] == mnts[5]) {
+ ASSERT_EQ(masks[i], FAN_MNT_ATTACH | FAN_MNT_DETACH);
+ } else {
+ ASSERT_EQ(masks[i], FAN_MNT_DETACH);
+ }
+ }
+
+ mnts[3] = mnts[5];
+ check_mounted(_metadata, mnts, 4);
+
+ // Cleanup
+ ret = umount("/b");
+ ASSERT_EQ(ret, 0);
+
+ ret = umount("/a");
+ ASSERT_EQ(ret, 0);
+
+ ret = umount("/b");
+ ASSERT_EQ(ret, 0);
+
+ expect_notify_mask_n(_metadata, self, FAN_MNT_DETACH, 3, dmnts);
+ verify_mount_ids(_metadata, mnts + 1, dmnts, 3);
+
+ check_mounted(_metadata, mnts, 1);
+}
+
+TEST_F(fanotify, rmdir)
+{
+ uint64_t mnts[3] = { self->root_id };
+ int ret;
+
+ ret = mount("/", "/a", NULL, MS_BIND, NULL);
+ ASSERT_EQ(ret, 0);
+
+ ret = mount("/", "/a/b", NULL, MS_BIND, NULL);
+ ASSERT_EQ(ret, 0);
+
+ expect_notify_mask_n(_metadata, self, FAN_MNT_ATTACH, 2, mnts + 1);
+
+ check_mounted(_metadata, mnts, 3);
+
+ ret = chdir("/a");
+ ASSERT_EQ(ret, 0);
+
+ ret = fork();
+ ASSERT_GE(ret, 0);
+
+ if (ret == 0) {
+ chdir("/");
+ unshare(CLONE_NEWNS);
+ mount("", "/", NULL, MS_REC|MS_PRIVATE, NULL);
+ umount2("/a", MNT_DETACH);
+ // This triggers a detach in the other namespace
+ rmdir("/a");
+ exit(0);
+ }
+ wait(NULL);
+
+ expect_notify_mask_n(_metadata, self, FAN_MNT_DETACH, 2, mnts + 1);
+ check_mounted(_metadata, mnts, 1);
+
+ // Cleanup
+ ret = chdir("/");
+ ASSERT_EQ(ret, 0);
+}
+
+TEST_F(fanotify, pivot_root)
+{
+ uint64_t mnts[3] = { self->root_id };
+ uint64_t mnts2[3];
+ int ret;
+
+ ret = mount("tmpfs", "/a", "tmpfs", 0, NULL);
+ ASSERT_EQ(ret, 0);
+
+ mnts[2] = expect_notify_mask(_metadata, self, FAN_MNT_ATTACH);
+
+ ret = mkdir("/a/new", 0700);
+ ASSERT_EQ(ret, 0);
+
+ ret = mkdir("/a/old", 0700);
+ ASSERT_EQ(ret, 0);
+
+ ret = mount("/a", "/a/new", NULL, MS_BIND, NULL);
+ ASSERT_EQ(ret, 0);
+
+ mnts[1] = expect_notify_mask(_metadata, self, FAN_MNT_ATTACH);
+ check_mounted(_metadata, mnts, 3);
+
+ ret = syscall(SYS_pivot_root, "/a/new", "/a/new/old");
+ ASSERT_EQ(ret, 0);
+
+ expect_notify_mask_n(_metadata, self, FAN_MNT_ATTACH | FAN_MNT_DETACH, 2, mnts2);
+ verify_mount_ids(_metadata, mnts, mnts2, 2);
+ check_mounted(_metadata, mnts, 3);
+
+ // Cleanup
+ ret = syscall(SYS_pivot_root, "/old", "/old/a/new");
+ ASSERT_EQ(ret, 0);
+
+ ret = umount("/a/new");
+ ASSERT_EQ(ret, 0);
+
+ ret = umount("/a");
+ ASSERT_EQ(ret, 0);
+
+ check_mounted(_metadata, mnts, 1);
+}
+
+TEST_HARNESS_MAIN
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