Merge tag 'idmapped-mounts-v5.12' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux

Pull idmapped mounts from Christian Brauner:
 "This introduces idmapped mounts which has been in the making for some
  time. Simply put, different mounts can expose the same file or
  directory with different ownership. This initial implementation comes
  with ports for fat, ext4 and with Christoph's port for xfs with more
  filesystems being actively worked on by independent people and
  maintainers.

  Idmapping mounts handle a wide range of long standing use-cases. Here
  are just a few:

   - Idmapped mounts make it possible to easily share files between
     multiple users or multiple machines especially in complex
     scenarios. For example, idmapped mounts will be used in the
     implementation of portable home directories in
     systemd-homed.service(8) where they allow users to move their home
     directory to an external storage device and use it on multiple
     computers where they are assigned different uids and gids. This
     effectively makes it possible to assign random uids and gids at
     login time.

   - It is possible to share files from the host with unprivileged
     containers without having to change ownership permanently through
     chown(2).

   - It is possible to idmap a container's rootfs and without having to
     mangle every file. For example, Chromebooks use it to share the
     user's Download folder with their unprivileged containers in their
     Linux subsystem.

   - It is possible to share files between containers with
     non-overlapping idmappings.

   - Filesystem that lack a proper concept of ownership such as fat can
     use idmapped mounts to implement discretionary access (DAC)
     permission checking.

   - They allow users to efficiently changing ownership on a per-mount
     basis without having to (recursively) chown(2) all files. In
     contrast to chown (2) changing ownership of large sets of files is
     instantenous with idmapped mounts. This is especially useful when
     ownership of a whole root filesystem of a virtual machine or
     container is changed. With idmapped mounts a single syscall
     mount_setattr syscall will be sufficient to change the ownership of
     all files.

   - Idmapped mounts always take the current ownership into account as
     idmappings specify what a given uid or gid is supposed to be mapped
     to. This contrasts with the chown(2) syscall which cannot by itself
     take the current ownership of the files it changes into account. It
     simply changes the ownership to the specified uid and gid. This is
     especially problematic when recursively chown(2)ing a large set of
     files which is commong with the aforementioned portable home
     directory and container and vm scenario.

   - Idmapped mounts allow to change ownership locally, restricting it
     to specific mounts, and temporarily as the ownership changes only
     apply as long as the mount exists.

  Several userspace projects have either already put up patches and
  pull-requests for this feature or will do so should you decide to pull
  this:

   - systemd: In a wide variety of scenarios but especially right away
     in their implementation of portable home directories.

         https://systemd.io/HOME_DIRECTORY/

   - container runtimes: containerd, runC, LXD:To share data between
     host and unprivileged containers, unprivileged and privileged
     containers, etc. The pull request for idmapped mounts support in
     containerd, the default Kubernetes runtime is already up for quite
     a while now: https://github.com/containerd/containerd/pull/4734

   - The virtio-fs developers and several users have expressed interest
     in using this feature with virtual machines once virtio-fs is
     ported.

   - ChromeOS: Sharing host-directories with unprivileged containers.

  I've tightly synced with all those projects and all of those listed
  here have also expressed their need/desire for this feature on the
  mailing list. For more info on how people use this there's a bunch of
  talks about this too. Here's just two recent ones:

      https://www.cncf.io/wp-content/uploads/2020/12/Rootless-Containers-in-Gitpod.pdf
      https://fosdem.org/2021/schedule/event/containers_idmap/

  This comes with an extensive xfstests suite covering both ext4 and
  xfs:

      https://git.kernel.org/brauner/xfstests-dev/h/idmapped_mounts

  It covers truncation, creation, opening, xattrs, vfscaps, setid
  execution, setgid inheritance and more both with idmapped and
  non-idmapped mounts. It already helped to discover an unrelated xfs
  setgid inheritance bug which has since been fixed in mainline. It will
  be sent for inclusion with the xfstests project should you decide to
  merge this.

  In order to support per-mount idmappings vfsmounts are marked with
  user namespaces. The idmapping of the user namespace will be used to
  map the ids of vfs objects when they are accessed through that mount.
  By default all vfsmounts are marked with the initial user namespace.
  The initial user namespace is used to indicate that a mount is not
  idmapped. All operations behave as before and this is verified in the
  testsuite.

  Based on prior discussions we want to attach the whole user namespace
  and not just a dedicated idmapping struct. This allows us to reuse all
  the helpers that already exist for dealing with idmappings instead of
  introducing a whole new range of helpers. In addition, if we decide in
  the future that we are confident enough to enable unprivileged users
  to setup idmapped mounts the permission checking can take into account
  whether the caller is privileged in the user namespace the mount is
  currently marked with.

  The user namespace the mount will be marked with can be specified by
  passing a file descriptor refering to the user namespace as an
  argument to the new mount_setattr() syscall together with the new
  MOUNT_ATTR_IDMAP flag. The system call follows the openat2() pattern
  of extensibility.

  The following conditions must be met in order to create an idmapped
  mount:

   - The caller must currently have the CAP_SYS_ADMIN capability in the
     user namespace the underlying filesystem has been mounted in.

   - The underlying filesystem must support idmapped mounts.

   - The mount must not already be idmapped. This also implies that the
     idmapping of a mount cannot be altered once it has been idmapped.

   - The mount must be a detached/anonymous mount, i.e. it must have
     been created by calling open_tree() with the OPEN_TREE_CLONE flag
     and it must not already have been visible in the filesystem.

  The last two points guarantee easier semantics for userspace and the
  kernel and make the implementation significantly simpler.

  By default vfsmounts are marked with the initial user namespace and no
  behavioral or performance changes are observed.

  The manpage with a detailed description can be found here:

      https://git.kernel.org/brauner/man-pages/c/1d7b902e2875a1ff342e036a9f866a995640aea8

  In order to support idmapped mounts, filesystems need to be changed
  and mark themselves with the FS_ALLOW_IDMAP flag in fs_flags. The
  patches to convert individual filesystem are not very large or
  complicated overall as can be seen from the included fat, ext4, and
  xfs ports. Patches for other filesystems are actively worked on and
  will be sent out separately. The xfstestsuite can be used to verify
  that port has been done correctly.

  The mount_setattr() syscall is motivated independent of the idmapped
  mounts patches and it's been around since July 2019. One of the most
  valuable features of the new mount api is the ability to perform
  mounts based on file descriptors only.

  Together with the lookup restrictions available in the openat2()
  RESOLVE_* flag namespace which we added in v5.6 this is the first time
  we are close to hardened and race-free (e.g. symlinks) mounting and
  path resolution.

  While userspace has started porting to the new mount api to mount
  proper filesystems and create new bind-mounts it is currently not
  possible to change mount options of an already existing bind mount in
  the new mount api since the mount_setattr() syscall is missing.

  With the addition of the mount_setattr() syscall we remove this last
  restriction and userspace can now fully port to the new mount api,
  covering every use-case the old mount api could. We also add the
  crucial ability to recursively change mount options for a whole mount
  tree, both removing and adding mount options at the same time. This
  syscall has been requested multiple times by various people and
  projects.

  There is a simple tool available at

      https://github.com/brauner/mount-idmapped

  that allows to create idmapped mounts so people can play with this
  patch series. I'll add support for the regular mount binary should you
  decide to pull this in the following weeks:

  Here's an example to a simple idmapped mount of another user's home
  directory:

	u1001@f2-vm:/$ sudo ./mount --idmap both:1000:1001:1 /home/ubuntu/ /mnt

	u1001@f2-vm:/$ ls -al /home/ubuntu/
	total 28
	drwxr-xr-x 2 ubuntu ubuntu 4096 Oct 28 22:07 .
	drwxr-xr-x 4 root   root   4096 Oct 28 04:00 ..
	-rw------- 1 ubuntu ubuntu 3154 Oct 28 22:12 .bash_history
	-rw-r--r-- 1 ubuntu ubuntu  220 Feb 25  2020 .bash_logout
	-rw-r--r-- 1 ubuntu ubuntu 3771 Feb 25  2020 .bashrc
	-rw-r--r-- 1 ubuntu ubuntu  807 Feb 25  2020 .profile
	-rw-r--r-- 1 ubuntu ubuntu    0 Oct 16 16:11 .sudo_as_admin_successful
	-rw------- 1 ubuntu ubuntu 1144 Oct 28 00:43 .viminfo

	u1001@f2-vm:/$ ls -al /mnt/
	total 28
	drwxr-xr-x  2 u1001 u1001 4096 Oct 28 22:07 .
	drwxr-xr-x 29 root  root  4096 Oct 28 22:01 ..
	-rw-------  1 u1001 u1001 3154 Oct 28 22:12 .bash_history
	-rw-r--r--  1 u1001 u1001  220 Feb 25  2020 .bash_logout
	-rw-r--r--  1 u1001 u1001 3771 Feb 25  2020 .bashrc
	-rw-r--r--  1 u1001 u1001  807 Feb 25  2020 .profile
	-rw-r--r--  1 u1001 u1001    0 Oct 16 16:11 .sudo_as_admin_successful
	-rw-------  1 u1001 u1001 1144 Oct 28 00:43 .viminfo

	u1001@f2-vm:/$ touch /mnt/my-file

	u1001@f2-vm:/$ setfacl -m u:1001:rwx /mnt/my-file

	u1001@f2-vm:/$ sudo setcap -n 1001 cap_net_raw+ep /mnt/my-file

	u1001@f2-vm:/$ ls -al /mnt/my-file
	-rw-rwxr--+ 1 u1001 u1001 0 Oct 28 22:14 /mnt/my-file

	u1001@f2-vm:/$ ls -al /home/ubuntu/my-file
	-rw-rwxr--+ 1 ubuntu ubuntu 0 Oct 28 22:14 /home/ubuntu/my-file

	u1001@f2-vm:/$ getfacl /mnt/my-file
	getfacl: Removing leading '/' from absolute path names
	# file: mnt/my-file
	# owner: u1001
	# group: u1001
	user::rw-
	user:u1001:rwx
	group::rw-
	mask::rwx
	other::r--

	u1001@f2-vm:/$ getfacl /home/ubuntu/my-file
	getfacl: Removing leading '/' from absolute path names
	# file: home/ubuntu/my-file
	# owner: ubuntu
	# group: ubuntu
	user::rw-
	user:ubuntu:rwx
	group::rw-
	mask::rwx
	other::r--"

* tag 'idmapped-mounts-v5.12' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux: (41 commits)
  xfs: remove the possibly unused mp variable in xfs_file_compat_ioctl
  xfs: support idmapped mounts
  ext4: support idmapped mounts
  fat: handle idmapped mounts
  tests: add mount_setattr() selftests
  fs: introduce MOUNT_ATTR_IDMAP
  fs: add mount_setattr()
  fs: add attr_flags_to_mnt_flags helper
  fs: split out functions to hold writers
  namespace: only take read lock in do_reconfigure_mnt()
  mount: make {lock,unlock}_mount_hash() static
  namespace: take lock_mount_hash() directly when changing flags
  nfs: do not export idmapped mounts
  overlayfs: do not mount on top of idmapped mounts
  ecryptfs: do not mount on top of idmapped mounts
  ima: handle idmapped mounts
  apparmor: handle idmapped mounts
  fs: make helpers idmap mount aware
  exec: handle idmapped mounts
  would_dump: handle idmapped mounts
  ...

6 files changed, 1437 insertions, 1 deletions

diff --git a/tools/include/uapi/asm-generic/unistd.h b/tools/include/uapi/asm-generic/unistd.h
index 728752917785..ce58cff99b66 100644
--- a/tools/include/uapi/asm-generic/unistd.h
+++ b/tools/include/uapi/asm-generic/unistd.h
@@ -861,9 +861,11 @@ __SYSCALL(__NR_faccessat2, sys_faccessat2)
 __SYSCALL(__NR_process_madvise, sys_process_madvise)
 #define __NR_epoll_pwait2 441
 __SC_COMP(__NR_epoll_pwait2, sys_epoll_pwait2, compat_sys_epoll_pwait2)
+#define __NR_mount_setattr 442
+__SYSCALL(__NR_mount_setattr, sys_mount_setattr)
 
 #undef __NR_syscalls
-#define __NR_syscalls 442
+#define __NR_syscalls 443
 
 /*
  * 32 bit systems traditionally used different
diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index 41f0a0adbb80..6c575cf34a71 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -33,6 +33,7 @@ TARGETS += memfd
 TARGETS += memory-hotplug
 TARGETS += mincore
 TARGETS += mount
+TARGETS += mount_setattr
 TARGETS += mqueue
 TARGETS += nci
 TARGETS += net
diff --git a/tools/testing/selftests/mount_setattr/.gitignore b/tools/testing/selftests/mount_setattr/.gitignore
new file mode 100644
index 000000000000..5f74d8488472
--- /dev/null
+++ b/tools/testing/selftests/mount_setattr/.gitignore
@@ -0,0 +1 @@
+mount_setattr_test
diff --git a/tools/testing/selftests/mount_setattr/Makefile b/tools/testing/selftests/mount_setattr/Makefile
new file mode 100644
index 000000000000..2250f7dcb81e
--- /dev/null
+++ b/tools/testing/selftests/mount_setattr/Makefile
@@ -0,0 +1,7 @@
+# SPDX-License-Identifier: GPL-2.0
+# Makefile for mount selftests.
+CFLAGS = -g -I../../../../usr/include/ -Wall -O2 -pthread
+
+TEST_GEN_FILES += mount_setattr_test
+
+include ../lib.mk
diff --git a/tools/testing/selftests/mount_setattr/config b/tools/testing/selftests/mount_setattr/config
new file mode 100644
index 000000000000..416bd53ce982
--- /dev/null
+++ b/tools/testing/selftests/mount_setattr/config
@@ -0,0 +1 @@
+CONFIG_USER_NS=y
diff --git a/tools/testing/selftests/mount_setattr/mount_setattr_test.c b/tools/testing/selftests/mount_setattr/mount_setattr_test.c
new file mode 100644
index 000000000000..4e94e566e040
--- /dev/null
+++ b/tools/testing/selftests/mount_setattr/mount_setattr_test.c
@@ -0,0 +1,1424 @@
+// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+#include <sched.h>
+#include <stdio.h>
+#include <errno.h>
+#include <pthread.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/mount.h>
+#include <sys/wait.h>
+#include <sys/vfs.h>
+#include <sys/statvfs.h>
+#include <sys/sysinfo.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <grp.h>
+#include <stdbool.h>
+#include <stdarg.h>
+
+#include "../kselftest_harness.h"
+
+#ifndef CLONE_NEWNS
+#define CLONE_NEWNS 0x00020000
+#endif
+
+#ifndef CLONE_NEWUSER
+#define CLONE_NEWUSER 0x10000000
+#endif
+
+#ifndef MS_REC
+#define MS_REC 16384
+#endif
+
+#ifndef MS_RELATIME
+#define MS_RELATIME (1 << 21)
+#endif
+
+#ifndef MS_STRICTATIME
+#define MS_STRICTATIME (1 << 24)
+#endif
+
+#ifndef MOUNT_ATTR_RDONLY
+#define MOUNT_ATTR_RDONLY 0x00000001
+#endif
+
+#ifndef MOUNT_ATTR_NOSUID
+#define MOUNT_ATTR_NOSUID 0x00000002
+#endif
+
+#ifndef MOUNT_ATTR_NOEXEC
+#define MOUNT_ATTR_NOEXEC 0x00000008
+#endif
+
+#ifndef MOUNT_ATTR_NODIRATIME
+#define MOUNT_ATTR_NODIRATIME 0x00000080
+#endif
+
+#ifndef MOUNT_ATTR__ATIME
+#define MOUNT_ATTR__ATIME 0x00000070
+#endif
+
+#ifndef MOUNT_ATTR_RELATIME
+#define MOUNT_ATTR_RELATIME 0x00000000
+#endif
+
+#ifndef MOUNT_ATTR_NOATIME
+#define MOUNT_ATTR_NOATIME 0x00000010
+#endif
+
+#ifndef MOUNT_ATTR_STRICTATIME
+#define MOUNT_ATTR_STRICTATIME 0x00000020
+#endif
+
+#ifndef AT_RECURSIVE
+#define AT_RECURSIVE 0x8000
+#endif
+
+#ifndef MS_SHARED
+#define MS_SHARED (1 << 20)
+#endif
+
+#define DEFAULT_THREADS 4
+#define ptr_to_int(p) ((int)((intptr_t)(p)))
+#define int_to_ptr(u) ((void *)((intptr_t)(u)))
+
+#ifndef __NR_mount_setattr
+	#if defined __alpha__
+		#define __NR_mount_setattr 552
+	#elif defined _MIPS_SIM
+		#if _MIPS_SIM == _MIPS_SIM_ABI32	/* o32 */
+			#define __NR_mount_setattr (442 + 4000)
+		#endif
+		#if _MIPS_SIM == _MIPS_SIM_NABI32	/* n32 */
+			#define __NR_mount_setattr (442 + 6000)
+		#endif
+		#if _MIPS_SIM == _MIPS_SIM_ABI64	/* n64 */
+			#define __NR_mount_setattr (442 + 5000)
+		#endif
+	#elif defined __ia64__
+		#define __NR_mount_setattr (442 + 1024)
+	#else
+		#define __NR_mount_setattr 442
+	#endif
+
+struct mount_attr {
+	__u64 attr_set;
+	__u64 attr_clr;
+	__u64 propagation;
+	__u64 userns_fd;
+};
+#endif
+
+#ifndef __NR_open_tree
+	#if defined __alpha__
+		#define __NR_open_tree 538
+	#elif defined _MIPS_SIM
+		#if _MIPS_SIM == _MIPS_SIM_ABI32	/* o32 */
+			#define __NR_open_tree 4428
+		#endif
+		#if _MIPS_SIM == _MIPS_SIM_NABI32	/* n32 */
+			#define __NR_open_tree 6428
+		#endif
+		#if _MIPS_SIM == _MIPS_SIM_ABI64	/* n64 */
+			#define __NR_open_tree 5428
+		#endif
+	#elif defined __ia64__
+		#define __NR_open_tree (428 + 1024)
+	#else
+		#define __NR_open_tree 428
+	#endif
+#endif
+
+#ifndef MOUNT_ATTR_IDMAP
+#define MOUNT_ATTR_IDMAP 0x00100000
+#endif
+
+static inline int sys_mount_setattr(int dfd, const char *path, unsigned int flags,
+				    struct mount_attr *attr, size_t size)
+{
+	return syscall(__NR_mount_setattr, dfd, path, flags, attr, size);
+}
+
+#ifndef OPEN_TREE_CLONE
+#define OPEN_TREE_CLONE 1
+#endif
+
+#ifndef OPEN_TREE_CLOEXEC
+#define OPEN_TREE_CLOEXEC O_CLOEXEC
+#endif
+
+#ifndef AT_RECURSIVE
+#define AT_RECURSIVE 0x8000 /* Apply to the entire subtree */
+#endif
+
+static inline int sys_open_tree(int dfd, const char *filename, unsigned int flags)
+{
+	return syscall(__NR_open_tree, dfd, filename, flags);
+}
+
+static ssize_t write_nointr(int fd, const void *buf, size_t count)
+{
+	ssize_t ret;
+
+	do {
+		ret = write(fd, buf, count);
+	} while (ret < 0 && errno == EINTR);
+
+	return ret;
+}
+
+static int write_file(const char *path, const void *buf, size_t count)
+{
+	int fd;
+	ssize_t ret;
+
+	fd = open(path, O_WRONLY | O_CLOEXEC | O_NOCTTY | O_NOFOLLOW);
+	if (fd < 0)
+		return -1;
+
+	ret = write_nointr(fd, buf, count);
+	close(fd);
+	if (ret < 0 || (size_t)ret != count)
+		return -1;
+
+	return 0;
+}
+
+static int create_and_enter_userns(void)
+{
+	uid_t uid;
+	gid_t gid;
+	char map[100];
+
+	uid = getuid();
+	gid = getgid();
+
+	if (unshare(CLONE_NEWUSER))
+		return -1;
+
+	if (write_file("/proc/self/setgroups", "deny", sizeof("deny") - 1) &&
+	    errno != ENOENT)
+		return -1;
+
+	snprintf(map, sizeof(map), "0 %d 1", uid);
+	if (write_file("/proc/self/uid_map", map, strlen(map)))
+		return -1;
+
+
+	snprintf(map, sizeof(map), "0 %d 1", gid);
+	if (write_file("/proc/self/gid_map", map, strlen(map)))
+		return -1;
+
+	if (setgid(0))
+		return -1;
+
+	if (setuid(0))
+		return -1;
+
+	return 0;
+}
+
+static int prepare_unpriv_mountns(void)
+{
+	if (create_and_enter_userns())
+		return -1;
+
+	if (unshare(CLONE_NEWNS))
+		return -1;
+
+	if (mount(NULL, "/", NULL, MS_REC | MS_PRIVATE, 0))
+		return -1;
+
+	return 0;
+}
+
+static int read_mnt_flags(const char *path)
+{
+	int ret;
+	struct statvfs stat;
+	unsigned int mnt_flags;
+
+	ret = statvfs(path, &stat);
+	if (ret != 0)
+		return -EINVAL;
+
+	if (stat.f_flag &
+	    ~(ST_RDONLY | ST_NOSUID | ST_NODEV | ST_NOEXEC | ST_NOATIME |
+	      ST_NODIRATIME | ST_RELATIME | ST_SYNCHRONOUS | ST_MANDLOCK))
+		return -EINVAL;
+
+	mnt_flags = 0;
+	if (stat.f_flag & ST_RDONLY)
+		mnt_flags |= MS_RDONLY;
+	if (stat.f_flag & ST_NOSUID)
+		mnt_flags |= MS_NOSUID;
+	if (stat.f_flag & ST_NODEV)
+		mnt_flags |= MS_NODEV;
+	if (stat.f_flag & ST_NOEXEC)
+		mnt_flags |= MS_NOEXEC;
+	if (stat.f_flag & ST_NOATIME)
+		mnt_flags |= MS_NOATIME;
+	if (stat.f_flag & ST_NODIRATIME)
+		mnt_flags |= MS_NODIRATIME;
+	if (stat.f_flag & ST_RELATIME)
+		mnt_flags |= MS_RELATIME;
+	if (stat.f_flag & ST_SYNCHRONOUS)
+		mnt_flags |= MS_SYNCHRONOUS;
+	if (stat.f_flag & ST_MANDLOCK)
+		mnt_flags |= ST_MANDLOCK;
+
+	return mnt_flags;
+}
+
+static char *get_field(char *src, int nfields)
+{
+	int i;
+	char *p = src;
+
+	for (i = 0; i < nfields; i++) {
+		while (*p && *p != ' ' && *p != '\t')
+			p++;
+
+		if (!*p)
+			break;
+
+		p++;
+	}
+
+	return p;
+}
+
+static void null_endofword(char *word)
+{
+	while (*word && *word != ' ' && *word != '\t')
+		word++;
+	*word = '\0';
+}
+
+static bool is_shared_mount(const char *path)
+{
+	size_t len = 0;
+	char *line = NULL;
+	FILE *f = NULL;
+
+	f = fopen("/proc/self/mountinfo", "re");
+	if (!f)
+		return false;
+
+	while (getline(&line, &len, f) != -1) {
+		char *opts, *target;
+
+		target = get_field(line, 4);
+		if (!target)
+			continue;
+
+		opts = get_field(target, 2);
+		if (!opts)
+			continue;
+
+		null_endofword(target);
+
+		if (strcmp(target, path) != 0)
+			continue;
+
+		null_endofword(opts);
+		if (strstr(opts, "shared:"))
+			return true;
+	}
+
+	free(line);
+	fclose(f);
+
+	return false;
+}
+
+static void *mount_setattr_thread(void *data)
+{
+	struct mount_attr attr = {
+		.attr_set	= MOUNT_ATTR_RDONLY | MOUNT_ATTR_NOSUID,
+		.attr_clr	= 0,
+		.propagation	= MS_SHARED,
+	};
+
+	if (sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, &attr, sizeof(attr)))
+		pthread_exit(int_to_ptr(-1));
+
+	pthread_exit(int_to_ptr(0));
+}
+
+/* Attempt to de-conflict with the selftests tree. */
+#ifndef SKIP
+#define SKIP(s, ...)	XFAIL(s, ##__VA_ARGS__)
+#endif
+
+static bool mount_setattr_supported(void)
+{
+	int ret;
+
+	ret = sys_mount_setattr(-EBADF, "", AT_EMPTY_PATH, NULL, 0);
+	if (ret < 0 && errno == ENOSYS)
+		return false;
+
+	return true;
+}
+
+FIXTURE(mount_setattr) {
+};
+
+FIXTURE_SETUP(mount_setattr)
+{
+	if (!mount_setattr_supported())
+		SKIP(return, "mount_setattr syscall not supported");
+
+	ASSERT_EQ(prepare_unpriv_mountns(), 0);
+
+	(void)umount2("/mnt", MNT_DETACH);
+	(void)umount2("/tmp", MNT_DETACH);
+
+	ASSERT_EQ(mount("testing", "/tmp", "tmpfs", MS_NOATIME | MS_NODEV,
+			"size=100000,mode=700"), 0);
+
+	ASSERT_EQ(mkdir("/tmp/B", 0777), 0);
+
+	ASSERT_EQ(mount("testing", "/tmp/B", "tmpfs", MS_NOATIME | MS_NODEV,
+			"size=100000,mode=700"), 0);
+
+	ASSERT_EQ(mkdir("/tmp/B/BB", 0777), 0);
+
+	ASSERT_EQ(mount("testing", "/tmp/B/BB", "tmpfs", MS_NOATIME | MS_NODEV,
+			"size=100000,mode=700"), 0);
+
+	ASSERT_EQ(mount("testing", "/mnt", "tmpfs", MS_NOATIME | MS_NODEV,
+			"size=100000,mode=700"), 0);
+
+	ASSERT_EQ(mkdir("/mnt/A", 0777), 0);
+
+	ASSERT_EQ(mount("testing", "/mnt/A", "tmpfs", MS_NOATIME | MS_NODEV,
+			"size=100000,mode=700"), 0);
+
+	ASSERT_EQ(mkdir("/mnt/A/AA", 0777), 0);
+
+	ASSERT_EQ(mount("/tmp", "/mnt/A/AA", NULL, MS_BIND | MS_REC, NULL), 0);
+
+	ASSERT_EQ(mkdir("/mnt/B", 0777), 0);
+
+	ASSERT_EQ(mount("testing", "/mnt/B", "ramfs",
+			MS_NOATIME | MS_NODEV | MS_NOSUID, 0), 0);
+
+	ASSERT_EQ(mkdir("/mnt/B/BB", 0777), 0);
+
+	ASSERT_EQ(mount("testing", "/tmp/B/BB", "devpts",
+			MS_RELATIME | MS_NOEXEC | MS_RDONLY, 0), 0);
+}
+
+FIXTURE_TEARDOWN(mount_setattr)
+{
+	if (!mount_setattr_supported())
+		SKIP(return, "mount_setattr syscall not supported");
+
+	(void)umount2("/mnt/A", MNT_DETACH);
+	(void)umount2("/tmp", MNT_DETACH);
+}
+
+TEST_F(mount_setattr, invalid_attributes)
+{
+	struct mount_attr invalid_attr = {
+		.attr_set = (1U << 31),
+	};
+
+	if (!mount_setattr_supported())
+		SKIP(return, "mount_setattr syscall not supported");
+
+	ASSERT_NE(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, &invalid_attr,
+				    sizeof(invalid_attr)), 0);
+
+	invalid_attr.attr_set	= 0;
+	invalid_attr.attr_clr	= (1U << 31);
+	ASSERT_NE(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, &invalid_attr,
+				    sizeof(invalid_attr)), 0);
+
+	invalid_attr.attr_clr		= 0;
+	invalid_attr.propagation	= (1U << 31);
+	ASSERT_NE(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, &invalid_attr,
+				    sizeof(invalid_attr)), 0);
+
+	invalid_attr.attr_set		= (1U << 31);
+	invalid_attr.attr_clr		= (1U << 31);
+	invalid_attr.propagation	= (1U << 31);
+	ASSERT_NE(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, &invalid_attr,
+				    sizeof(invalid_attr)), 0);
+
+	ASSERT_NE(sys_mount_setattr(-1, "mnt/A", AT_RECURSIVE, &invalid_attr,
+				    sizeof(invalid_attr)), 0);
+}
+
+TEST_F(mount_setattr, extensibility)
+{
+	unsigned int old_flags = 0, new_flags = 0, expected_flags = 0;
+	char *s = "dummy";
+	struct mount_attr invalid_attr = {};
+	struct mount_attr_large {
+		struct mount_attr attr1;
+		struct mount_attr attr2;
+		struct mount_attr attr3;
+	} large_attr = {};
+
+	if (!mount_setattr_supported())
+		SKIP(return, "mount_setattr syscall not supported");
+
+	old_flags = read_mnt_flags("/mnt/A");
+	ASSERT_GT(old_flags, 0);
+
+	ASSERT_NE(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, NULL,
+				    sizeof(invalid_attr)), 0);
+	ASSERT_EQ(errno, EFAULT);
+
+	ASSERT_NE(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, (void *)s,
+				    sizeof(invalid_attr)), 0);
+	ASSERT_EQ(errno, EINVAL);
+
+	ASSERT_NE(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, &invalid_attr, 0), 0);
+	ASSERT_EQ(errno, EINVAL);
+
+	ASSERT_NE(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, &invalid_attr,
+				    sizeof(invalid_attr) / 2), 0);
+	ASSERT_EQ(errno, EINVAL);
+
+	ASSERT_NE(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, &invalid_attr,
+				    sizeof(invalid_attr) / 2), 0);
+	ASSERT_EQ(errno, EINVAL);
+
+	ASSERT_EQ(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE,
+				    (void *)&large_attr, sizeof(large_attr)), 0);
+
+	large_attr.attr3.attr_set = MOUNT_ATTR_RDONLY;
+	ASSERT_NE(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE,
+				    (void *)&large_attr, sizeof(large_attr)), 0);
+
+	large_attr.attr3.attr_set = 0;
+	large_attr.attr1.attr_set = MOUNT_ATTR_RDONLY;
+	ASSERT_EQ(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE,
+				    (void *)&large_attr, sizeof(large_attr)), 0);
+
+	expected_flags = old_flags;
+	expected_flags |= MS_RDONLY;
+
+	new_flags = read_mnt_flags("/mnt/A");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	new_flags = read_mnt_flags("/mnt/A/AA");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	new_flags = read_mnt_flags("/mnt/A/AA/B");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	new_flags = read_mnt_flags("/mnt/A/AA/B/BB");
+	ASSERT_EQ(new_flags, expected_flags);
+}
+
+TEST_F(mount_setattr, basic)
+{
+	unsigned int old_flags = 0, new_flags = 0, expected_flags = 0;
+	struct mount_attr attr = {
+		.attr_set	= MOUNT_ATTR_RDONLY | MOUNT_ATTR_NOEXEC | MOUNT_ATTR_RELATIME,
+		.attr_clr	= MOUNT_ATTR__ATIME,
+	};
+
+	if (!mount_setattr_supported())
+		SKIP(return, "mount_setattr syscall not supported");
+
+	old_flags = read_mnt_flags("/mnt/A");
+	ASSERT_GT(old_flags, 0);
+
+	ASSERT_EQ(sys_mount_setattr(-1, "/mnt/A", 0, &attr, sizeof(attr)), 0);
+
+	expected_flags = old_flags;
+	expected_flags |= MS_RDONLY;
+	expected_flags |= MS_NOEXEC;
+	expected_flags &= ~MS_NOATIME;
+	expected_flags |= MS_RELATIME;
+
+	new_flags = read_mnt_flags("/mnt/A");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	new_flags = read_mnt_flags("/mnt/A/AA");
+	ASSERT_EQ(new_flags, old_flags);
+
+	new_flags = read_mnt_flags("/mnt/A/AA/B");
+	ASSERT_EQ(new_flags, old_flags);
+
+	new_flags = read_mnt_flags("/mnt/A/AA/B/BB");
+	ASSERT_EQ(new_flags, old_flags);
+}
+
+TEST_F(mount_setattr, basic_recursive)
+{
+	int fd;
+	unsigned int old_flags = 0, new_flags = 0, expected_flags = 0;
+	struct mount_attr attr = {
+		.attr_set	= MOUNT_ATTR_RDONLY | MOUNT_ATTR_NOEXEC | MOUNT_ATTR_RELATIME,
+		.attr_clr	= MOUNT_ATTR__ATIME,
+	};
+
+	if (!mount_setattr_supported())
+		SKIP(return, "mount_setattr syscall not supported");
+
+	old_flags = read_mnt_flags("/mnt/A");
+	ASSERT_GT(old_flags, 0);
+
+	ASSERT_EQ(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, &attr, sizeof(attr)), 0);
+
+	expected_flags = old_flags;
+	expected_flags |= MS_RDONLY;
+	expected_flags |= MS_NOEXEC;
+	expected_flags &= ~MS_NOATIME;
+	expected_flags |= MS_RELATIME;
+
+	new_flags = read_mnt_flags("/mnt/A");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	new_flags = read_mnt_flags("/mnt/A/AA");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	new_flags = read_mnt_flags("/mnt/A/AA/B");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	new_flags = read_mnt_flags("/mnt/A/AA/B/BB");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	memset(&attr, 0, sizeof(attr));
+	attr.attr_clr = MOUNT_ATTR_RDONLY;
+	attr.propagation = MS_SHARED;
+	ASSERT_EQ(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, &attr, sizeof(attr)), 0);
+
+	expected_flags &= ~MS_RDONLY;
+	new_flags = read_mnt_flags("/mnt/A");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	ASSERT_EQ(is_shared_mount("/mnt/A"), true);
+
+	new_flags = read_mnt_flags("/mnt/A/AA");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	ASSERT_EQ(is_shared_mount("/mnt/A/AA"), true);
+
+	new_flags = read_mnt_flags("/mnt/A/AA/B");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	ASSERT_EQ(is_shared_mount("/mnt/A/AA/B"), true);
+
+	new_flags = read_mnt_flags("/mnt/A/AA/B/BB");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	ASSERT_EQ(is_shared_mount("/mnt/A/AA/B/BB"), true);
+
+	fd = open("/mnt/A/AA/B/b", O_RDWR | O_CLOEXEC | O_CREAT | O_EXCL, 0777);
+	ASSERT_GE(fd, 0);
+
+	/*
+	 * We're holding a fd open for writing so this needs to fail somewhere
+	 * in the middle and the mount options need to be unchanged.
+	 */
+	attr.attr_set = MOUNT_ATTR_RDONLY;
+	ASSERT_LT(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, &attr, sizeof(attr)), 0);
+
+	new_flags = read_mnt_flags("/mnt/A");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	ASSERT_EQ(is_shared_mount("/mnt/A"), true);
+
+	new_flags = read_mnt_flags("/mnt/A/AA");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	ASSERT_EQ(is_shared_mount("/mnt/A/AA"), true);
+
+	new_flags = read_mnt_flags("/mnt/A/AA/B");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	ASSERT_EQ(is_shared_mount("/mnt/A/AA/B"), true);
+
+	new_flags = read_mnt_flags("/mnt/A/AA/B/BB");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	ASSERT_EQ(is_shared_mount("/mnt/A/AA/B/BB"), true);
+
+	EXPECT_EQ(close(fd), 0);
+}
+
+TEST_F(mount_setattr, mount_has_writers)
+{
+	int fd, dfd;
+	unsigned int old_flags = 0, new_flags = 0;
+	struct mount_attr attr = {
+		.attr_set	= MOUNT_ATTR_RDONLY | MOUNT_ATTR_NOEXEC | MOUNT_ATTR_RELATIME,
+		.attr_clr	= MOUNT_ATTR__ATIME,
+		.propagation	= MS_SHARED,
+	};
+
+	if (!mount_setattr_supported())
+		SKIP(return, "mount_setattr syscall not supported");
+
+	old_flags = read_mnt_flags("/mnt/A");
+	ASSERT_GT(old_flags, 0);
+
+	fd = open("/mnt/A/AA/B/b", O_RDWR | O_CLOEXEC | O_CREAT | O_EXCL, 0777);
+	ASSERT_GE(fd, 0);
+
+	/*
+	 * We're holding a fd open to a mount somwhere in the middle so this
+	 * needs to fail somewhere in the middle. After this the mount options
+	 * need to be unchanged.
+	 */
+	ASSERT_LT(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, &attr, sizeof(attr)), 0);
+
+	new_flags = read_mnt_flags("/mnt/A");
+	ASSERT_EQ(new_flags, old_flags);
+
+	ASSERT_EQ(is_shared_mount("/mnt/A"), false);
+
+	new_flags = read_mnt_flags("/mnt/A/AA");
+	ASSERT_EQ(new_flags, old_flags);
+
+	ASSERT_EQ(is_shared_mount("/mnt/A/AA"), false);
+
+	new_flags = read_mnt_flags("/mnt/A/AA/B");
+	ASSERT_EQ(new_flags, old_flags);
+
+	ASSERT_EQ(is_shared_mount("/mnt/A/AA/B"), false);
+
+	new_flags = read_mnt_flags("/mnt/A/AA/B/BB");
+	ASSERT_EQ(new_flags, old_flags);
+
+	ASSERT_EQ(is_shared_mount("/mnt/A/AA/B/BB"), false);
+
+	dfd = open("/mnt/A/AA/B", O_DIRECTORY | O_CLOEXEC);
+	ASSERT_GE(dfd, 0);
+	EXPECT_EQ(fsync(dfd), 0);
+	EXPECT_EQ(close(dfd), 0);
+
+	EXPECT_EQ(fsync(fd), 0);
+	EXPECT_EQ(close(fd), 0);
+
+	/* All writers are gone so this should succeed. */
+	ASSERT_EQ(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, &attr, sizeof(attr)), 0);
+}
+
+TEST_F(mount_setattr, mixed_mount_options)
+{
+	unsigned int old_flags1 = 0, old_flags2 = 0, new_flags = 0, expected_flags = 0;
+	struct mount_attr attr = {
+		.attr_clr = MOUNT_ATTR_RDONLY | MOUNT_ATTR_NOSUID | MOUNT_ATTR_NOEXEC | MOUNT_ATTR__ATIME,
+		.attr_set = MOUNT_ATTR_RELATIME,
+	};
+
+	if (!mount_setattr_supported())
+		SKIP(return, "mount_setattr syscall not supported");
+
+	old_flags1 = read_mnt_flags("/mnt/B");
+	ASSERT_GT(old_flags1, 0);
+
+	old_flags2 = read_mnt_flags("/mnt/B/BB");
+	ASSERT_GT(old_flags2, 0);
+
+	ASSERT_EQ(sys_mount_setattr(-1, "/mnt/B", AT_RECURSIVE, &attr, sizeof(attr)), 0);
+
+	expected_flags = old_flags2;
+	expected_flags &= ~(MS_RDONLY | MS_NOEXEC | MS_NOATIME | MS_NOSUID);
+	expected_flags |= MS_RELATIME;
+
+	new_flags = read_mnt_flags("/mnt/B");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	expected_flags = old_flags2;
+	expected_flags &= ~(MS_RDONLY | MS_NOEXEC | MS_NOATIME | MS_NOSUID);
+	expected_flags |= MS_RELATIME;
+
+	new_flags = read_mnt_flags("/mnt/B/BB");
+	ASSERT_EQ(new_flags, expected_flags);
+}
+
+TEST_F(mount_setattr, time_changes)
+{
+	unsigned int old_flags = 0, new_flags = 0, expected_flags = 0;
+	struct mount_attr attr = {
+		.attr_set	= MOUNT_ATTR_NODIRATIME | MOUNT_ATTR_NOATIME,
+	};
+
+	if (!mount_setattr_supported())
+		SKIP(return, "mount_setattr syscall not supported");
+
+	ASSERT_NE(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, &attr, sizeof(attr)), 0);
+
+	attr.attr_set = MOUNT_ATTR_STRICTATIME;
+	ASSERT_NE(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, &attr, sizeof(attr)), 0);
+
+	attr.attr_set = MOUNT_ATTR_STRICTATIME | MOUNT_ATTR_NOATIME;
+	ASSERT_NE(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, &attr, sizeof(attr)), 0);
+
+	attr.attr_set = MOUNT_ATTR_STRICTATIME | MOUNT_ATTR_NOATIME;
+	attr.attr_clr = MOUNT_ATTR__ATIME;
+	ASSERT_NE(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, &attr, sizeof(attr)), 0);
+
+	attr.attr_set = 0;
+	attr.attr_clr = MOUNT_ATTR_STRICTATIME;
+	ASSERT_NE(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, &attr, sizeof(attr)), 0);
+
+	attr.attr_clr = MOUNT_ATTR_NOATIME;
+	ASSERT_NE(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, &attr, sizeof(attr)), 0);
+
+	old_flags = read_mnt_flags("/mnt/A");
+	ASSERT_GT(old_flags, 0);
+
+	attr.attr_set = MOUNT_ATTR_NODIRATIME | MOUNT_ATTR_NOATIME;
+	attr.attr_clr = MOUNT_ATTR__ATIME;
+	ASSERT_EQ(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, &attr, sizeof(attr)), 0);
+
+	expected_flags = old_flags;
+	expected_flags |= MS_NOATIME;
+	expected_flags |= MS_NODIRATIME;
+
+	new_flags = read_mnt_flags("/mnt/A");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	new_flags = read_mnt_flags("/mnt/A/AA");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	new_flags = read_mnt_flags("/mnt/A/AA/B");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	new_flags = read_mnt_flags("/mnt/A/AA/B/BB");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	memset(&attr, 0, sizeof(attr));
+	attr.attr_set &= ~MOUNT_ATTR_NOATIME;
+	attr.attr_set |= MOUNT_ATTR_RELATIME;
+	attr.attr_clr |= MOUNT_ATTR__ATIME;
+	ASSERT_EQ(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, &attr, sizeof(attr)), 0);
+
+	expected_flags &= ~MS_NOATIME;
+	expected_flags |= MS_RELATIME;
+
+	new_flags = read_mnt_flags("/mnt/A");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	new_flags = read_mnt_flags("/mnt/A/AA");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	new_flags = read_mnt_flags("/mnt/A/AA/B");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	new_flags = read_mnt_flags("/mnt/A/AA/B/BB");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	memset(&attr, 0, sizeof(attr));
+	attr.attr_set &= ~MOUNT_ATTR_RELATIME;
+	attr.attr_set |= MOUNT_ATTR_STRICTATIME;
+	attr.attr_clr |= MOUNT_ATTR__ATIME;
+	ASSERT_EQ(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, &attr, sizeof(attr)), 0);
+
+	expected_flags &= ~MS_RELATIME;
+
+	new_flags = read_mnt_flags("/mnt/A");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	new_flags = read_mnt_flags("/mnt/A/AA");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	new_flags = read_mnt_flags("/mnt/A/AA/B");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	new_flags = read_mnt_flags("/mnt/A/AA/B/BB");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	memset(&attr, 0, sizeof(attr));
+	attr.attr_set &= ~MOUNT_ATTR_STRICTATIME;
+	attr.attr_set |= MOUNT_ATTR_NOATIME;
+	attr.attr_clr |= MOUNT_ATTR__ATIME;
+	ASSERT_EQ(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, &attr, sizeof(attr)), 0);
+
+	expected_flags |= MS_NOATIME;
+	new_flags = read_mnt_flags("/mnt/A");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	new_flags = read_mnt_flags("/mnt/A/AA");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	new_flags = read_mnt_flags("/mnt/A/AA/B");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	new_flags = read_mnt_flags("/mnt/A/AA/B/BB");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	memset(&attr, 0, sizeof(attr));
+	ASSERT_EQ(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, &attr, sizeof(attr)), 0);
+
+	new_flags = read_mnt_flags("/mnt/A");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	new_flags = read_mnt_flags("/mnt/A/AA");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	new_flags = read_mnt_flags("/mnt/A/AA/B");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	new_flags = read_mnt_flags("/mnt/A/AA/B/BB");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	memset(&attr, 0, sizeof(attr));
+	attr.attr_clr = MOUNT_ATTR_NODIRATIME;
+	ASSERT_EQ(sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, &attr, sizeof(attr)), 0);
+
+	expected_flags &= ~MS_NODIRATIME;
+
+	new_flags = read_mnt_flags("/mnt/A");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	new_flags = read_mnt_flags("/mnt/A/AA");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	new_flags = read_mnt_flags("/mnt/A/AA/B");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	new_flags = read_mnt_flags("/mnt/A/AA/B/BB");
+	ASSERT_EQ(new_flags, expected_flags);
+}
+
+TEST_F(mount_setattr, multi_threaded)
+{
+	int i, j, nthreads, ret = 0;
+	unsigned int old_flags = 0, new_flags = 0, expected_flags = 0;
+	pthread_attr_t pattr;
+	pthread_t threads[DEFAULT_THREADS];
+
+	if (!mount_setattr_supported())
+		SKIP(return, "mount_setattr syscall not supported");
+
+	old_flags = read_mnt_flags("/mnt/A");
+	ASSERT_GT(old_flags, 0);
+
+	/* Try to change mount options from multiple threads. */
+	nthreads = get_nprocs_conf();
+	if (nthreads > DEFAULT_THREADS)
+		nthreads = DEFAULT_THREADS;
+
+	pthread_attr_init(&pattr);
+	for (i = 0; i < nthreads; i++)
+		ASSERT_EQ(pthread_create(&threads[i], &pattr, mount_setattr_thread, NULL), 0);
+
+	for (j = 0; j < i; j++) {
+		void *retptr = NULL;
+
+		EXPECT_EQ(pthread_join(threads[j], &retptr), 0);
+
+		ret += ptr_to_int(retptr);
+		EXPECT_EQ(ret, 0);
+	}
+	pthread_attr_destroy(&pattr);
+
+	ASSERT_EQ(ret, 0);
+
+	expected_flags = old_flags;
+	expected_flags |= MS_RDONLY;
+	expected_flags |= MS_NOSUID;
+	new_flags = read_mnt_flags("/mnt/A");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	ASSERT_EQ(is_shared_mount("/mnt/A"), true);
+
+	new_flags = read_mnt_flags("/mnt/A/AA");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	ASSERT_EQ(is_shared_mount("/mnt/A/AA"), true);
+
+	new_flags = read_mnt_flags("/mnt/A/AA/B");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	ASSERT_EQ(is_shared_mount("/mnt/A/AA/B"), true);
+
+	new_flags = read_mnt_flags("/mnt/A/AA/B/BB");
+	ASSERT_EQ(new_flags, expected_flags);
+
+	ASSERT_EQ(is_shared_mount("/mnt/A/AA/B/BB"), true);
+}
+
+TEST_F(mount_setattr, wrong_user_namespace)
+{
+	int ret;
+	struct mount_attr attr = {
+		.attr_set = MOUNT_ATTR_RDONLY,
+	};
+
+	if (!mount_setattr_supported())
+		SKIP(return, "mount_setattr syscall not supported");
+
+	EXPECT_EQ(create_and_enter_userns(), 0);
+	ret = sys_mount_setattr(-1, "/mnt/A", AT_RECURSIVE, &attr, sizeof(attr));
+	ASSERT_LT(ret, 0);
+	ASSERT_EQ(errno, EPERM);
+}
+
+TEST_F(mount_setattr, wrong_mount_namespace)
+{
+	int fd, ret;
+	struct mount_attr attr = {
+		.attr_set = MOUNT_ATTR_RDONLY,
+	};
+
+	if (!mount_setattr_supported())
+		SKIP(return, "mount_setattr syscall not supported");
+
+	fd = open("/mnt/A", O_DIRECTORY | O_CLOEXEC);
+	ASSERT_GE(fd, 0);
+
+	ASSERT_EQ(unshare(CLONE_NEWNS), 0);
+
+	ret = sys_mount_setattr(fd, "", AT_EMPTY_PATH | AT_RECURSIVE, &attr, sizeof(attr));
+	ASSERT_LT(ret, 0);
+	ASSERT_EQ(errno, EINVAL);
+}
+
+FIXTURE(mount_setattr_idmapped) {
+};
+
+FIXTURE_SETUP(mount_setattr_idmapped)
+{
+	int img_fd = -EBADF;
+
+	ASSERT_EQ(unshare(CLONE_NEWNS), 0);
+
+	ASSERT_EQ(mount(NULL, "/", NULL, MS_REC | MS_PRIVATE, 0), 0);
+
+	(void)umount2("/mnt", MNT_DETACH);
+	(void)umount2("/tmp", MNT_DETACH);
+
+	ASSERT_EQ(mount("testing", "/tmp", "tmpfs", MS_NOATIME | MS_NODEV,
+			"size=100000,mode=700"), 0);
+
+	ASSERT_EQ(mkdir("/tmp/B", 0777), 0);
+	ASSERT_EQ(mknodat(-EBADF, "/tmp/B/b", S_IFREG | 0644, 0), 0);
+	ASSERT_EQ(chown("/tmp/B/b", 0, 0), 0);
+
+	ASSERT_EQ(mount("testing", "/tmp/B", "tmpfs", MS_NOATIME | MS_NODEV,
+			"size=100000,mode=700"), 0);
+
+	ASSERT_EQ(mkdir("/tmp/B/BB", 0777), 0);
+	ASSERT_EQ(mknodat(-EBADF, "/tmp/B/BB/b", S_IFREG | 0644, 0), 0);
+	ASSERT_EQ(chown("/tmp/B/BB/b", 0, 0), 0);
+
+	ASSERT_EQ(mount("testing", "/tmp/B/BB", "tmpfs", MS_NOATIME | MS_NODEV,
+			"size=100000,mode=700"), 0);
+
+	ASSERT_EQ(mount("testing", "/mnt", "tmpfs", MS_NOATIME | MS_NODEV,
+			"size=100000,mode=700"), 0);
+
+	ASSERT_EQ(mkdir("/mnt/A", 0777), 0);
+
+	ASSERT_EQ(mount("testing", "/mnt/A", "tmpfs", MS_NOATIME | MS_NODEV,
+			"size=100000,mode=700"), 0);
+
+	ASSERT_EQ(mkdir("/mnt/A/AA", 0777), 0);
+
+	ASSERT_EQ(mount("/tmp", "/mnt/A/AA", NULL, MS_BIND | MS_REC, NULL), 0);
+
+	ASSERT_EQ(mkdir("/mnt/B", 0777), 0);
+
+	ASSERT_EQ(mount("testing", "/mnt/B", "ramfs",
+			MS_NOATIME | MS_NODEV | MS_NOSUID, 0), 0);
+
+	ASSERT_EQ(mkdir("/mnt/B/BB", 0777), 0);
+
+	ASSERT_EQ(mount("testing", "/tmp/B/BB", "devpts",
+			MS_RELATIME | MS_NOEXEC | MS_RDONLY, 0), 0);
+
+	ASSERT_EQ(mkdir("/mnt/C", 0777), 0);
+	ASSERT_EQ(mkdir("/mnt/D", 0777), 0);
+	img_fd = openat(-EBADF, "/mnt/C/ext4.img", O_CREAT | O_WRONLY, 0600);
+	ASSERT_GE(img_fd, 0);
+	ASSERT_EQ(ftruncate(img_fd, 1024 * 2048), 0);
+	ASSERT_EQ(system("mkfs.ext4 -q /mnt/C/ext4.img"), 0);
+	ASSERT_EQ(system("mount -o loop -t ext4 /mnt/C/ext4.img /mnt/D/"), 0);
+	ASSERT_EQ(close(img_fd), 0);
+}
+
+FIXTURE_TEARDOWN(mount_setattr_idmapped)
+{
+	(void)umount2("/mnt/A", MNT_DETACH);
+	(void)umount2("/tmp", MNT_DETACH);
+}
+
+/**
+ * Validate that negative fd values are rejected.
+ */
+TEST_F(mount_setattr_idmapped, invalid_fd_negative)
+{
+	struct mount_attr attr = {
+		.attr_set	= MOUNT_ATTR_IDMAP,
+		.userns_fd	= -EBADF,
+	};
+
+	if (!mount_setattr_supported())
+		SKIP(return, "mount_setattr syscall not supported");
+
+	ASSERT_NE(sys_mount_setattr(-1, "/", 0, &attr, sizeof(attr)), 0) {
+		TH_LOG("failure: created idmapped mount with negative fd");
+	}
+}
+
+/**
+ * Validate that excessively large fd values are rejected.
+ */
+TEST_F(mount_setattr_idmapped, invalid_fd_large)
+{
+	struct mount_attr attr = {
+		.attr_set	= MOUNT_ATTR_IDMAP,
+		.userns_fd	= INT64_MAX,
+	};
+
+	if (!mount_setattr_supported())
+		SKIP(return, "mount_setattr syscall not supported");
+
+	ASSERT_NE(sys_mount_setattr(-1, "/", 0, &attr, sizeof(attr)), 0) {
+		TH_LOG("failure: created idmapped mount with too large fd value");
+	}
+}
+
+/**
+ * Validate that closed fd values are rejected.
+ */
+TEST_F(mount_setattr_idmapped, invalid_fd_closed)
+{
+	int fd;
+	struct mount_attr attr = {
+		.attr_set = MOUNT_ATTR_IDMAP,
+	};
+
+	if (!mount_setattr_supported())
+		SKIP(return, "mount_setattr syscall not supported");
+
+	fd = open("/dev/null", O_RDONLY | O_CLOEXEC);
+	ASSERT_GE(fd, 0);
+	ASSERT_GE(close(fd), 0);
+
+	attr.userns_fd = fd;
+	ASSERT_NE(sys_mount_setattr(-1, "/", 0, &attr, sizeof(attr)), 0) {
+		TH_LOG("failure: created idmapped mount with closed fd");
+	}
+}
+
+/**
+ * Validate that the initial user namespace is rejected.
+ */
+TEST_F(mount_setattr_idmapped, invalid_fd_initial_userns)
+{
+	int open_tree_fd = -EBADF;
+	struct mount_attr attr = {
+		.attr_set = MOUNT_ATTR_IDMAP,
+	};
+
+	if (!mount_setattr_supported())
+		SKIP(return, "mount_setattr syscall not supported");
+
+	open_tree_fd = sys_open_tree(-EBADF, "/mnt/D",
+				     AT_NO_AUTOMOUNT |
+				     AT_SYMLINK_NOFOLLOW |
+				     OPEN_TREE_CLOEXEC | OPEN_TREE_CLONE);
+	ASSERT_GE(open_tree_fd, 0);
+
+	attr.userns_fd = open("/proc/1/ns/user", O_RDONLY | O_CLOEXEC);
+	ASSERT_GE(attr.userns_fd, 0);
+	ASSERT_NE(sys_mount_setattr(open_tree_fd, "", AT_EMPTY_PATH, &attr, sizeof(attr)), 0);
+	ASSERT_EQ(errno, EPERM);
+	ASSERT_EQ(close(attr.userns_fd), 0);
+	ASSERT_EQ(close(open_tree_fd), 0);
+}
+
+static int map_ids(pid_t pid, unsigned long nsid, unsigned long hostid,
+		   unsigned long range)
+{
+	char map[100], procfile[256];
+
+	snprintf(procfile, sizeof(procfile), "/proc/%d/uid_map", pid);
+	snprintf(map, sizeof(map), "%lu %lu %lu", nsid, hostid, range);
+	if (write_file(procfile, map, strlen(map)))
+		return -1;
+
+
+	snprintf(procfile, sizeof(procfile), "/proc/%d/gid_map", pid);
+	snprintf(map, sizeof(map), "%lu %lu %lu", nsid, hostid, range);
+	if (write_file(procfile, map, strlen(map)))
+		return -1;
+
+	return 0;
+}
+
+#define __STACK_SIZE (8 * 1024 * 1024)
+static pid_t do_clone(int (*fn)(void *), void *arg, int flags)
+{
+	void *stack;
+
+	stack = malloc(__STACK_SIZE);
+	if (!stack)
+		return -ENOMEM;
+
+#ifdef __ia64__
+	return __clone2(fn, stack, __STACK_SIZE, flags | SIGCHLD, arg, NULL);
+#else
+	return clone(fn, stack + __STACK_SIZE, flags | SIGCHLD, arg, NULL);
+#endif
+}
+
+static int get_userns_fd_cb(void *data)
+{
+	return kill(getpid(), SIGSTOP);
+}
+
+static int wait_for_pid(pid_t pid)
+{
+	int status, ret;
+
+again:
+	ret = waitpid(pid, &status, 0);
+	if (ret == -1) {
+		if (errno == EINTR)
+			goto again;
+
+		return -1;
+	}
+
+	if (!WIFEXITED(status))
+		return -1;
+
+	return WEXITSTATUS(status);
+}
+
+static int get_userns_fd(unsigned long nsid, unsigned long hostid, unsigned long range)
+{
+	int ret;
+	pid_t pid;
+	char path[256];
+
+	pid = do_clone(get_userns_fd_cb, NULL, CLONE_NEWUSER);
+	if (pid < 0)
+		return -errno;
+
+	ret = map_ids(pid, nsid, hostid, range);
+	if (ret < 0)
+		return ret;
+
+	snprintf(path, sizeof(path), "/proc/%d/ns/user", pid);
+	ret = open(path, O_RDONLY | O_CLOEXEC);
+	kill(pid, SIGKILL);
+	wait_for_pid(pid);
+	return ret;
+}
+
+/**
+ * Validate that an attached mount in our mount namespace can be idmapped.
+ * (The kernel enforces that the mount's mount namespace and the caller's mount
+ *  namespace match.)
+ */
+TEST_F(mount_setattr_idmapped, attached_mount_inside_current_mount_namespace)
+{
+	int open_tree_fd = -EBADF;
+	struct mount_attr attr = {
+		.attr_set = MOUNT_ATTR_IDMAP,
+	};
+
+	if (!mount_setattr_supported())
+		SKIP(return, "mount_setattr syscall not supported");
+
+	open_tree_fd = sys_open_tree(-EBADF, "/mnt/D",
+				     AT_EMPTY_PATH |
+				     AT_NO_AUTOMOUNT |
+				     AT_SYMLINK_NOFOLLOW |
+				     OPEN_TREE_CLOEXEC);
+	ASSERT_GE(open_tree_fd, 0);
+
+	attr.userns_fd	= get_userns_fd(0, 10000, 10000);
+	ASSERT_GE(attr.userns_fd, 0);
+	ASSERT_EQ(sys_mount_setattr(open_tree_fd, "", AT_EMPTY_PATH, &attr, sizeof(attr)), 0);
+	ASSERT_EQ(close(attr.userns_fd), 0);
+	ASSERT_EQ(close(open_tree_fd), 0);
+}
+
+/**
+ * Validate that idmapping a mount is rejected if the mount's mount namespace
+ * and our mount namespace don't match.
+ * (The kernel enforces that the mount's mount namespace and the caller's mount
+ *  namespace match.)
+ */
+TEST_F(mount_setattr_idmapped, attached_mount_outside_current_mount_namespace)
+{
+	int open_tree_fd = -EBADF;
+	struct mount_attr attr = {
+		.attr_set = MOUNT_ATTR_IDMAP,
+	};
+
+	if (!mount_setattr_supported())
+		SKIP(return, "mount_setattr syscall not supported");
+
+	open_tree_fd = sys_open_tree(-EBADF, "/mnt/D",
+				     AT_EMPTY_PATH |
+				     AT_NO_AUTOMOUNT |
+				     AT_SYMLINK_NOFOLLOW |
+				     OPEN_TREE_CLOEXEC);
+	ASSERT_GE(open_tree_fd, 0);
+
+	ASSERT_EQ(unshare(CLONE_NEWNS), 0);
+
+	attr.userns_fd	= get_userns_fd(0, 10000, 10000);
+	ASSERT_GE(attr.userns_fd, 0);
+	ASSERT_NE(sys_mount_setattr(open_tree_fd, "", AT_EMPTY_PATH, &attr,
+				    sizeof(attr)), 0);
+	ASSERT_EQ(close(attr.userns_fd), 0);
+	ASSERT_EQ(close(open_tree_fd), 0);
+}
+
+/**
+ * Validate that an attached mount in our mount namespace can be idmapped.
+ */
+TEST_F(mount_setattr_idmapped, detached_mount_inside_current_mount_namespace)
+{
+	int open_tree_fd = -EBADF;
+	struct mount_attr attr = {
+		.attr_set = MOUNT_ATTR_IDMAP,
+	};
+
+	if (!mount_setattr_supported())
+		SKIP(return, "mount_setattr syscall not supported");
+
+	open_tree_fd = sys_open_tree(-EBADF, "/mnt/D",
+				     AT_EMPTY_PATH |
+				     AT_NO_AUTOMOUNT |
+				     AT_SYMLINK_NOFOLLOW |
+				     OPEN_TREE_CLOEXEC |
+				     OPEN_TREE_CLONE);
+	ASSERT_GE(open_tree_fd, 0);
+
+	/* Changing mount properties on a detached mount. */
+	attr.userns_fd	= get_userns_fd(0, 10000, 10000);
+	ASSERT_GE(attr.userns_fd, 0);
+	ASSERT_EQ(sys_mount_setattr(open_tree_fd, "",
+				    AT_EMPTY_PATH, &attr, sizeof(attr)), 0);
+	ASSERT_EQ(close(attr.userns_fd), 0);
+	ASSERT_EQ(close(open_tree_fd), 0);
+}
+
+/**
+ * Validate that a detached mount not in our mount namespace can be idmapped.
+ */
+TEST_F(mount_setattr_idmapped, detached_mount_outside_current_mount_namespace)
+{
+	int open_tree_fd = -EBADF;
+	struct mount_attr attr = {
+		.attr_set = MOUNT_ATTR_IDMAP,
+	};
+
+	if (!mount_setattr_supported())
+		SKIP(return, "mount_setattr syscall not supported");
+
+	open_tree_fd = sys_open_tree(-EBADF, "/mnt/D",
+				     AT_EMPTY_PATH |
+				     AT_NO_AUTOMOUNT |
+				     AT_SYMLINK_NOFOLLOW |
+				     OPEN_TREE_CLOEXEC |
+				     OPEN_TREE_CLONE);
+	ASSERT_GE(open_tree_fd, 0);
+
+	ASSERT_EQ(unshare(CLONE_NEWNS), 0);
+
+	/* Changing mount properties on a detached mount. */
+	attr.userns_fd	= get_userns_fd(0, 10000, 10000);
+	ASSERT_GE(attr.userns_fd, 0);
+	ASSERT_EQ(sys_mount_setattr(open_tree_fd, "",
+				    AT_EMPTY_PATH, &attr, sizeof(attr)), 0);
+	ASSERT_EQ(close(attr.userns_fd), 0);
+	ASSERT_EQ(close(open_tree_fd), 0);
+}
+
+/**
+ * Validate that currently changing the idmapping of an idmapped mount fails.
+ */
+TEST_F(mount_setattr_idmapped, change_idmapping)
+{
+	int open_tree_fd = -EBADF;
+	struct mount_attr attr = {
+		.attr_set = MOUNT_ATTR_IDMAP,
+	};
+
+	if (!mount_setattr_supported())
+		SKIP(return, "mount_setattr syscall not supported");
+
+	open_tree_fd = sys_open_tree(-EBADF, "/mnt/D",
+				     AT_EMPTY_PATH |
+				     AT_NO_AUTOMOUNT |
+				     AT_SYMLINK_NOFOLLOW |
+				     OPEN_TREE_CLOEXEC |
+				     OPEN_TREE_CLONE);
+	ASSERT_GE(open_tree_fd, 0);
+
+	attr.userns_fd	= get_userns_fd(0, 10000, 10000);
+	ASSERT_GE(attr.userns_fd, 0);
+	ASSERT_EQ(sys_mount_setattr(open_tree_fd, "",
+				    AT_EMPTY_PATH, &attr, sizeof(attr)), 0);
+	ASSERT_EQ(close(attr.userns_fd), 0);
+
+	/* Change idmapping on a detached mount that is already idmapped. */
+	attr.userns_fd	= get_userns_fd(0, 20000, 10000);
+	ASSERT_GE(attr.userns_fd, 0);
+	ASSERT_NE(sys_mount_setattr(open_tree_fd, "", AT_EMPTY_PATH, &attr, sizeof(attr)), 0);
+	ASSERT_EQ(close(attr.userns_fd), 0);
+	ASSERT_EQ(close(open_tree_fd), 0);
+}
+
+static bool expected_uid_gid(int dfd, const char *path, int flags,
+			     uid_t expected_uid, gid_t expected_gid)
+{
+	int ret;
+	struct stat st;
+
+	ret = fstatat(dfd, path, &st, flags);
+	if (ret < 0)
+		return false;
+
+	return st.st_uid == expected_uid && st.st_gid == expected_gid;
+}
+
+TEST_F(mount_setattr_idmapped, idmap_mount_tree_invalid)
+{
+	int open_tree_fd = -EBADF;
+	struct mount_attr attr = {
+		.attr_set = MOUNT_ATTR_IDMAP,
+	};
+
+	if (!mount_setattr_supported())
+		SKIP(return, "mount_setattr syscall not supported");
+
+	ASSERT_EQ(expected_uid_gid(-EBADF, "/tmp/B/b", 0, 0, 0), 0);
+	ASSERT_EQ(expected_uid_gid(-EBADF, "/tmp/B/BB/b", 0, 0, 0), 0);
+
+	open_tree_fd = sys_open_tree(-EBADF, "/mnt/A",
+				     AT_RECURSIVE |
+				     AT_EMPTY_PATH |
+				     AT_NO_AUTOMOUNT |
+				     AT_SYMLINK_NOFOLLOW |
+				     OPEN_TREE_CLOEXEC |
+				     OPEN_TREE_CLONE);
+	ASSERT_GE(open_tree_fd, 0);
+
+	attr.userns_fd	= get_userns_fd(0, 10000, 10000);
+	ASSERT_GE(attr.userns_fd, 0);
+	ASSERT_NE(sys_mount_setattr(open_tree_fd, "", AT_EMPTY_PATH, &attr, sizeof(attr)), 0);
+	ASSERT_EQ(close(attr.userns_fd), 0);
+	ASSERT_EQ(close(open_tree_fd), 0);
+
+	ASSERT_EQ(expected_uid_gid(-EBADF, "/tmp/B/b", 0, 0, 0), 0);
+	ASSERT_EQ(expected_uid_gid(-EBADF, "/tmp/B/BB/b", 0, 0, 0), 0);
+	ASSERT_EQ(expected_uid_gid(open_tree_fd, "B/b", 0, 0, 0), 0);
+	ASSERT_EQ(expected_uid_gid(open_tree_fd, "B/BB/b", 0, 0, 0), 0);
+}
+
+TEST_HARNESS_MAIN