Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 5032 insertions, 0 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
new file mode 100644
index 0000000000..bfc5cff0e1
--- /dev/null
+++ b/fs/namespace.c
@@ -0,0 +1,5032 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  linux/fs/namespace.c
+ *
+ * (C) Copyright Al Viro 2000, 2001
+ *
+ * Based on code from fs/super.c, copyright Linus Torvalds and others.
+ * Heavily rewritten.
+ */
+
+#include <linux/syscalls.h>
+#include <linux/export.h>
+#include <linux/capability.h>
+#include <linux/mnt_namespace.h>
+#include <linux/user_namespace.h>
+#include <linux/namei.h>
+#include <linux/security.h>
+#include <linux/cred.h>
+#include <linux/idr.h>
+#include <linux/init.h>		/* init_rootfs */
+#include <linux/fs_struct.h>	/* get_fs_root et.al. */
+#include <linux/fsnotify.h>	/* fsnotify_vfsmount_delete */
+#include <linux/file.h>
+#include <linux/uaccess.h>
+#include <linux/proc_ns.h>
+#include <linux/magic.h>
+#include <linux/memblock.h>
+#include <linux/proc_fs.h>
+#include <linux/task_work.h>
+#include <linux/sched/task.h>
+#include <uapi/linux/mount.h>
+#include <linux/fs_context.h>
+#include <linux/shmem_fs.h>
+#include <linux/mnt_idmapping.h>
+
+#include "pnode.h"
+#include "internal.h"
+
+/* Maximum number of mounts in a mount namespace */
+static unsigned int sysctl_mount_max __read_mostly = 100000;
+
+static unsigned int m_hash_mask __read_mostly;
+static unsigned int m_hash_shift __read_mostly;
+static unsigned int mp_hash_mask __read_mostly;
+static unsigned int mp_hash_shift __read_mostly;
+
+static __initdata unsigned long mhash_entries;
+static int __init set_mhash_entries(char *str)
+{
+	if (!str)
+		return 0;
+	mhash_entries = simple_strtoul(str, &str, 0);
+	return 1;
+}
+__setup("mhash_entries=", set_mhash_entries);
+
+static __initdata unsigned long mphash_entries;
+static int __init set_mphash_entries(char *str)
+{
+	if (!str)
+		return 0;
+	mphash_entries = simple_strtoul(str, &str, 0);
+	return 1;
+}
+__setup("mphash_entries=", set_mphash_entries);
+
+static u64 event;
+static DEFINE_IDA(mnt_id_ida);
+static DEFINE_IDA(mnt_group_ida);
+
+static struct hlist_head *mount_hashtable __read_mostly;
+static struct hlist_head *mountpoint_hashtable __read_mostly;
+static struct kmem_cache *mnt_cache __read_mostly;
+static DECLARE_RWSEM(namespace_sem);
+static HLIST_HEAD(unmounted);	/* protected by namespace_sem */
+static LIST_HEAD(ex_mountpoints); /* protected by namespace_sem */
+
+struct mount_kattr {
+	unsigned int attr_set;
+	unsigned int attr_clr;
+	unsigned int propagation;
+	unsigned int lookup_flags;
+	bool recurse;
+	struct user_namespace *mnt_userns;
+	struct mnt_idmap *mnt_idmap;
+};
+
+/* /sys/fs */
+struct kobject *fs_kobj;
+EXPORT_SYMBOL_GPL(fs_kobj);
+
+/*
+ * vfsmount lock may be taken for read to prevent changes to the
+ * vfsmount hash, ie. during mountpoint lookups or walking back
+ * up the tree.
+ *
+ * It should be taken for write in all cases where the vfsmount
+ * tree or hash is modified or when a vfsmount structure is modified.
+ */
+__cacheline_aligned_in_smp DEFINE_SEQLOCK(mount_lock);
+
+static inline void lock_mount_hash(void)
+{
+	write_seqlock(&mount_lock);
+}
+
+static inline void unlock_mount_hash(void)
+{
+	write_sequnlock(&mount_lock);
+}
+
+static inline struct hlist_head *m_hash(struct vfsmount *mnt, struct dentry *dentry)
+{
+	unsigned long tmp = ((unsigned long)mnt / L1_CACHE_BYTES);
+	tmp += ((unsigned long)dentry / L1_CACHE_BYTES);
+	tmp = tmp + (tmp >> m_hash_shift);
+	return &mount_hashtable[tmp & m_hash_mask];
+}
+
+static inline struct hlist_head *mp_hash(struct dentry *dentry)
+{
+	unsigned long tmp = ((unsigned long)dentry / L1_CACHE_BYTES);
+	tmp = tmp + (tmp >> mp_hash_shift);
+	return &mountpoint_hashtable[tmp & mp_hash_mask];
+}
+
+static int mnt_alloc_id(struct mount *mnt)
+{
+	int res = ida_alloc(&mnt_id_ida, GFP_KERNEL);
+
+	if (res < 0)
+		return res;
+	mnt->mnt_id = res;
+	return 0;
+}
+
+static void mnt_free_id(struct mount *mnt)
+{
+	ida_free(&mnt_id_ida, mnt->mnt_id);
+}
+
+/*
+ * Allocate a new peer group ID
+ */
+static int mnt_alloc_group_id(struct mount *mnt)
+{
+	int res = ida_alloc_min(&mnt_group_ida, 1, GFP_KERNEL);
+
+	if (res < 0)
+		return res;
+	mnt->mnt_group_id = res;
+	return 0;
+}
+
+/*
+ * Release a peer group ID
+ */
+void mnt_release_group_id(struct mount *mnt)
+{
+	ida_free(&mnt_group_ida, mnt->mnt_group_id);
+	mnt->mnt_group_id = 0;
+}
+
+/*
+ * vfsmount lock must be held for read
+ */
+static inline void mnt_add_count(struct mount *mnt, int n)
+{
+#ifdef CONFIG_SMP
+	this_cpu_add(mnt->mnt_pcp->mnt_count, n);
+#else
+	preempt_disable();
+	mnt->mnt_count += n;
+	preempt_enable();
+#endif
+}
+
+/*
+ * vfsmount lock must be held for write
+ */
+int mnt_get_count(struct mount *mnt)
+{
+#ifdef CONFIG_SMP
+	int count = 0;
+	int cpu;
+
+	for_each_possible_cpu(cpu) {
+		count += per_cpu_ptr(mnt->mnt_pcp, cpu)->mnt_count;
+	}
+
+	return count;
+#else
+	return mnt->mnt_count;
+#endif
+}
+
+static struct mount *alloc_vfsmnt(const char *name)
+{
+	struct mount *mnt = kmem_cache_zalloc(mnt_cache, GFP_KERNEL);
+	if (mnt) {
+		int err;
+
+		err = mnt_alloc_id(mnt);
+		if (err)
+			goto out_free_cache;
+
+		if (name) {
+			mnt->mnt_devname = kstrdup_const(name,
+							 GFP_KERNEL_ACCOUNT);
+			if (!mnt->mnt_devname)
+				goto out_free_id;
+		}
+
+#ifdef CONFIG_SMP
+		mnt->mnt_pcp = alloc_percpu(struct mnt_pcp);
+		if (!mnt->mnt_pcp)
+			goto out_free_devname;
+
+		this_cpu_add(mnt->mnt_pcp->mnt_count, 1);
+#else
+		mnt->mnt_count = 1;
+		mnt->mnt_writers = 0;
+#endif
+
+		INIT_HLIST_NODE(&mnt->mnt_hash);
+		INIT_LIST_HEAD(&mnt->mnt_child);
+		INIT_LIST_HEAD(&mnt->mnt_mounts);
+		INIT_LIST_HEAD(&mnt->mnt_list);
+		INIT_LIST_HEAD(&mnt->mnt_expire);
+		INIT_LIST_HEAD(&mnt->mnt_share);
+		INIT_LIST_HEAD(&mnt->mnt_slave_list);
+		INIT_LIST_HEAD(&mnt->mnt_slave);
+		INIT_HLIST_NODE(&mnt->mnt_mp_list);
+		INIT_LIST_HEAD(&mnt->mnt_umounting);
+		INIT_HLIST_HEAD(&mnt->mnt_stuck_children);
+		mnt->mnt.mnt_idmap = &nop_mnt_idmap;
+	}
+	return mnt;
+
+#ifdef CONFIG_SMP
+out_free_devname:
+	kfree_const(mnt->mnt_devname);
+#endif
+out_free_id:
+	mnt_free_id(mnt);
+out_free_cache:
+	kmem_cache_free(mnt_cache, mnt);
+	return NULL;
+}
+
+/*
+ * Most r/o checks on a fs are for operations that take
+ * discrete amounts of time, like a write() or unlink().
+ * We must keep track of when those operations start
+ * (for permission checks) and when they end, so that
+ * we can determine when writes are able to occur to
+ * a filesystem.
+ */
+/*
+ * __mnt_is_readonly: check whether a mount is read-only
+ * @mnt: the mount to check for its write status
+ *
+ * This shouldn't be used directly ouside of the VFS.
+ * It does not guarantee that the filesystem will stay
+ * r/w, just that it is right *now*.  This can not and
+ * should not be used in place of IS_RDONLY(inode).
+ * mnt_want/drop_write() will _keep_ the filesystem
+ * r/w.
+ */
+bool __mnt_is_readonly(struct vfsmount *mnt)
+{
+	return (mnt->mnt_flags & MNT_READONLY) || sb_rdonly(mnt->mnt_sb);
+}
+EXPORT_SYMBOL_GPL(__mnt_is_readonly);
+
+static inline void mnt_inc_writers(struct mount *mnt)
+{
+#ifdef CONFIG_SMP
+	this_cpu_inc(mnt->mnt_pcp->mnt_writers);
+#else
+	mnt->mnt_writers++;
+#endif
+}
+
+static inline void mnt_dec_writers(struct mount *mnt)
+{
+#ifdef CONFIG_SMP
+	this_cpu_dec(mnt->mnt_pcp->mnt_writers);
+#else
+	mnt->mnt_writers--;
+#endif
+}
+
+static unsigned int mnt_get_writers(struct mount *mnt)
+{
+#ifdef CONFIG_SMP
+	unsigned int count = 0;
+	int cpu;
+
+	for_each_possible_cpu(cpu) {
+		count += per_cpu_ptr(mnt->mnt_pcp, cpu)->mnt_writers;
+	}
+
+	return count;
+#else
+	return mnt->mnt_writers;
+#endif
+}
+
+static int mnt_is_readonly(struct vfsmount *mnt)
+{
+	if (READ_ONCE(mnt->mnt_sb->s_readonly_remount))
+		return 1;
+	/*
+	 * The barrier pairs with the barrier in sb_start_ro_state_change()
+	 * making sure if we don't see s_readonly_remount set yet, we also will
+	 * not see any superblock / mount flag changes done by remount.
+	 * It also pairs with the barrier in sb_end_ro_state_change()
+	 * assuring that if we see s_readonly_remount already cleared, we will
+	 * see the values of superblock / mount flags updated by remount.
+	 */
+	smp_rmb();
+	return __mnt_is_readonly(mnt);
+}
+
+/*
+ * Most r/o & frozen checks on a fs are for operations that take discrete
+ * amounts of time, like a write() or unlink().  We must keep track of when
+ * those operations start (for permission checks) and when they end, so that we
+ * can determine when writes are able to occur to a filesystem.
+ */
+/**
+ * __mnt_want_write - get write access to a mount without freeze protection
+ * @m: the mount on which to take a write
+ *
+ * This tells the low-level filesystem that a write is about to be performed to
+ * it, and makes sure that writes are allowed (mnt it read-write) before
+ * returning success. This operation does not protect against filesystem being
+ * frozen. When the write operation is finished, __mnt_drop_write() must be
+ * called. This is effectively a refcount.
+ */
+int __mnt_want_write(struct vfsmount *m)
+{
+	struct mount *mnt = real_mount(m);
+	int ret = 0;
+
+	preempt_disable();
+	mnt_inc_writers(mnt);
+	/*
+	 * The store to mnt_inc_writers must be visible before we pass
+	 * MNT_WRITE_HOLD loop below, so that the slowpath can see our
+	 * incremented count after it has set MNT_WRITE_HOLD.
+	 */
+	smp_mb();
+	might_lock(&mount_lock.lock);
+	while (READ_ONCE(mnt->mnt.mnt_flags) & MNT_WRITE_HOLD) {
+		if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
+			cpu_relax();
+		} else {
+			/*
+			 * This prevents priority inversion, if the task
+			 * setting MNT_WRITE_HOLD got preempted on a remote
+			 * CPU, and it prevents life lock if the task setting
+			 * MNT_WRITE_HOLD has a lower priority and is bound to
+			 * the same CPU as the task that is spinning here.
+			 */
+			preempt_enable();
+			lock_mount_hash();
+			unlock_mount_hash();
+			preempt_disable();
+		}
+	}
+	/*
+	 * The barrier pairs with the barrier sb_start_ro_state_change() making
+	 * sure that if we see MNT_WRITE_HOLD cleared, we will also see
+	 * s_readonly_remount set (or even SB_RDONLY / MNT_READONLY flags) in
+	 * mnt_is_readonly() and bail in case we are racing with remount
+	 * read-only.
+	 */
+	smp_rmb();
+	if (mnt_is_readonly(m)) {
+		mnt_dec_writers(mnt);
+		ret = -EROFS;
+	}
+	preempt_enable();
+
+	return ret;
+}
+
+/**
+ * mnt_want_write - get write access to a mount
+ * @m: the mount on which to take a write
+ *
+ * This tells the low-level filesystem that a write is about to be performed to
+ * it, and makes sure that writes are allowed (mount is read-write, filesystem
+ * is not frozen) before returning success.  When the write operation is
+ * finished, mnt_drop_write() must be called.  This is effectively a refcount.
+ */
+int mnt_want_write(struct vfsmount *m)
+{
+	int ret;
+
+	sb_start_write(m->mnt_sb);
+	ret = __mnt_want_write(m);
+	if (ret)
+		sb_end_write(m->mnt_sb);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(mnt_want_write);
+
+/**
+ * __mnt_want_write_file - get write access to a file's mount
+ * @file: the file who's mount on which to take a write
+ *
+ * This is like __mnt_want_write, but if the file is already open for writing it
+ * skips incrementing mnt_writers (since the open file already has a reference)
+ * and instead only does the check for emergency r/o remounts.  This must be
+ * paired with __mnt_drop_write_file.
+ */
+int __mnt_want_write_file(struct file *file)
+{
+	if (file->f_mode & FMODE_WRITER) {
+		/*
+		 * Superblock may have become readonly while there are still
+		 * writable fd's, e.g. due to a fs error with errors=remount-ro
+		 */
+		if (__mnt_is_readonly(file->f_path.mnt))
+			return -EROFS;
+		return 0;
+	}
+	return __mnt_want_write(file->f_path.mnt);
+}
+
+/**
+ * mnt_want_write_file - get write access to a file's mount
+ * @file: the file who's mount on which to take a write
+ *
+ * This is like mnt_want_write, but if the file is already open for writing it
+ * skips incrementing mnt_writers (since the open file already has a reference)
+ * and instead only does the freeze protection and the check for emergency r/o
+ * remounts.  This must be paired with mnt_drop_write_file.
+ */
+int mnt_want_write_file(struct file *file)
+{
+	int ret;
+
+	sb_start_write(file_inode(file)->i_sb);
+	ret = __mnt_want_write_file(file);
+	if (ret)
+		sb_end_write(file_inode(file)->i_sb);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(mnt_want_write_file);
+
+/**
+ * __mnt_drop_write - give up write access to a mount
+ * @mnt: the mount on which to give up write access
+ *
+ * Tells the low-level filesystem that we are done
+ * performing writes to it.  Must be matched with
+ * __mnt_want_write() call above.
+ */
+void __mnt_drop_write(struct vfsmount *mnt)
+{
+	preempt_disable();
+	mnt_dec_writers(real_mount(mnt));
+	preempt_enable();
+}
+
+/**
+ * mnt_drop_write - give up write access to a mount
+ * @mnt: the mount on which to give up write access
+ *
+ * Tells the low-level filesystem that we are done performing writes to it and
+ * also allows filesystem to be frozen again.  Must be matched with
+ * mnt_want_write() call above.
+ */
+void mnt_drop_write(struct vfsmount *mnt)
+{
+	__mnt_drop_write(mnt);
+	sb_end_write(mnt->mnt_sb);
+}
+EXPORT_SYMBOL_GPL(mnt_drop_write);
+
+void __mnt_drop_write_file(struct file *file)
+{
+	if (!(file->f_mode & FMODE_WRITER))
+		__mnt_drop_write(file->f_path.mnt);
+}
+
+void mnt_drop_write_file(struct file *file)
+{
+	__mnt_drop_write_file(file);
+	sb_end_write(file_inode(file)->i_sb);
+}
+EXPORT_SYMBOL(mnt_drop_write_file);
+
+/**
+ * mnt_hold_writers - prevent write access to the given mount
+ * @mnt: mnt to prevent write access to
+ *
+ * Prevents write access to @mnt if there are no active writers for @mnt.
+ * This function needs to be called and return successfully before changing
+ * properties of @mnt that need to remain stable for callers with write access
+ * to @mnt.
+ *
+ * After this functions has been called successfully callers must pair it with
+ * a call to mnt_unhold_writers() in order to stop preventing write access to
+ * @mnt.
+ *
+ * Context: This function expects lock_mount_hash() to be held serializing
+ *          setting MNT_WRITE_HOLD.
+ * Return: On success 0 is returned.
+ *	   On error, -EBUSY is returned.
+ */
+static inline int mnt_hold_writers(struct mount *mnt)
+{
+	mnt->mnt.mnt_flags |= MNT_WRITE_HOLD;
+	/*
+	 * After storing MNT_WRITE_HOLD, we'll read the counters. This store
+	 * should be visible before we do.
+	 */
+	smp_mb();
+
+	/*
+	 * With writers on hold, if this value is zero, then there are
+	 * definitely no active writers (although held writers may subsequently
+	 * increment the count, they'll have to wait, and decrement it after
+	 * seeing MNT_READONLY).
+	 *
+	 * It is OK to have counter incremented on one CPU and decremented on
+	 * another: the sum will add up correctly. The danger would be when we
+	 * sum up each counter, if we read a counter before it is incremented,
+	 * but then read another CPU's count which it has been subsequently
+	 * decremented from -- we would see more decrements than we should.
+	 * MNT_WRITE_HOLD protects against this scenario, because
+	 * mnt_want_write first increments count, then smp_mb, then spins on
+	 * MNT_WRITE_HOLD, so it can't be decremented by another CPU while
+	 * we're counting up here.
+	 */
+	if (mnt_get_writers(mnt) > 0)
+		return -EBUSY;
+
+	return 0;
+}
+
+/**
+ * mnt_unhold_writers - stop preventing write access to the given mount
+ * @mnt: mnt to stop preventing write access to
+ *
+ * Stop preventing write access to @mnt allowing callers to gain write access
+ * to @mnt again.
+ *
+ * This function can only be called after a successful call to
+ * mnt_hold_writers().
+ *
+ * Context: This function expects lock_mount_hash() to be held.
+ */
+static inline void mnt_unhold_writers(struct mount *mnt)
+{
+	/*
+	 * MNT_READONLY must become visible before ~MNT_WRITE_HOLD, so writers
+	 * that become unheld will see MNT_READONLY.
+	 */
+	smp_wmb();
+	mnt->mnt.mnt_flags &= ~MNT_WRITE_HOLD;
+}
+
+static int mnt_make_readonly(struct mount *mnt)
+{
+	int ret;
+
+	ret = mnt_hold_writers(mnt);
+	if (!ret)
+		mnt->mnt.mnt_flags |= MNT_READONLY;
+	mnt_unhold_writers(mnt);
+	return ret;
+}
+
+int sb_prepare_remount_readonly(struct super_block *sb)
+{
+	struct mount *mnt;
+	int err = 0;
+
+	/* Racy optimization.  Recheck the counter under MNT_WRITE_HOLD */
+	if (atomic_long_read(&sb->s_remove_count))
+		return -EBUSY;
+
+	lock_mount_hash();
+	list_for_each_entry(mnt, &sb->s_mounts, mnt_instance) {
+		if (!(mnt->mnt.mnt_flags & MNT_READONLY)) {
+			err = mnt_hold_writers(mnt);
+			if (err)
+				break;
+		}
+	}
+	if (!err && atomic_long_read(&sb->s_remove_count))
+		err = -EBUSY;
+
+	if (!err)
+		sb_start_ro_state_change(sb);
+	list_for_each_entry(mnt, &sb->s_mounts, mnt_instance) {
+		if (mnt->mnt.mnt_flags & MNT_WRITE_HOLD)
+			mnt->mnt.mnt_flags &= ~MNT_WRITE_HOLD;
+	}
+	unlock_mount_hash();
+
+	return err;
+}
+
+static void free_vfsmnt(struct mount *mnt)
+{
+	mnt_idmap_put(mnt_idmap(&mnt->mnt));
+	kfree_const(mnt->mnt_devname);
+#ifdef CONFIG_SMP
+	free_percpu(mnt->mnt_pcp);
+#endif
+	kmem_cache_free(mnt_cache, mnt);
+}
+
+static void delayed_free_vfsmnt(struct rcu_head *head)
+{
+	free_vfsmnt(container_of(head, struct mount, mnt_rcu));
+}
+
+/* call under rcu_read_lock */
+int __legitimize_mnt(struct vfsmount *bastard, unsigned seq)
+{
+	struct mount *mnt;
+	if (read_seqretry(&mount_lock, seq))
+		return 1;
+	if (bastard == NULL)
+		return 0;
+	mnt = real_mount(bastard);
+	mnt_add_count(mnt, 1);
+	smp_mb();			// see mntput_no_expire()
+	if (likely(!read_seqretry(&mount_lock, seq)))
+		return 0;
+	if (bastard->mnt_flags & MNT_SYNC_UMOUNT) {
+		mnt_add_count(mnt, -1);
+		return 1;
+	}
+	lock_mount_hash();
+	if (unlikely(bastard->mnt_flags & MNT_DOOMED)) {
+		mnt_add_count(mnt, -1);
+		unlock_mount_hash();
+		return 1;
+	}
+	unlock_mount_hash();
+	/* caller will mntput() */
+	return -1;
+}
+
+/* call under rcu_read_lock */
+static bool legitimize_mnt(struct vfsmount *bastard, unsigned seq)
+{
+	int res = __legitimize_mnt(bastard, seq);
+	if (likely(!res))
+		return true;
+	if (unlikely(res < 0)) {
+		rcu_read_unlock();
+		mntput(bastard);
+		rcu_read_lock();
+	}
+	return false;
+}
+
+/**
+ * __lookup_mnt - find first child mount
+ * @mnt:	parent mount
+ * @dentry:	mountpoint
+ *
+ * If @mnt has a child mount @c mounted @dentry find and return it.
+ *
+ * Note that the child mount @c need not be unique. There are cases
+ * where shadow mounts are created. For example, during mount
+ * propagation when a source mount @mnt whose root got overmounted by a
+ * mount @o after path lookup but before @namespace_sem could be
+ * acquired gets copied and propagated. So @mnt gets copied including
+ * @o. When @mnt is propagated to a destination mount @d that already
+ * has another mount @n mounted at the same mountpoint then the source
+ * mount @mnt will be tucked beneath @n, i.e., @n will be mounted on
+ * @mnt and @mnt mounted on @d. Now both @n and @o are mounted at @mnt
+ * on @dentry.
+ *
+ * Return: The first child of @mnt mounted @dentry or NULL.
+ */
+struct mount *__lookup_mnt(struct vfsmount *mnt, struct dentry *dentry)
+{
+	struct hlist_head *head = m_hash(mnt, dentry);
+	struct mount *p;
+
+	hlist_for_each_entry_rcu(p, head, mnt_hash)
+		if (&p->mnt_parent->mnt == mnt && p->mnt_mountpoint == dentry)
+			return p;
+	return NULL;
+}
+
+/*
+ * lookup_mnt - Return the first child mount mounted at path
+ *
+ * "First" means first mounted chronologically.  If you create the
+ * following mounts:
+ *
+ * mount /dev/sda1 /mnt
+ * mount /dev/sda2 /mnt
+ * mount /dev/sda3 /mnt
+ *
+ * Then lookup_mnt() on the base /mnt dentry in the root mount will
+ * return successively the root dentry and vfsmount of /dev/sda1, then
+ * /dev/sda2, then /dev/sda3, then NULL.
+ *
+ * lookup_mnt takes a reference to the found vfsmount.
+ */
+struct vfsmount *lookup_mnt(const struct path *path)
+{
+	struct mount *child_mnt;
+	struct vfsmount *m;
+	unsigned seq;
+
+	rcu_read_lock();
+	do {
+		seq = read_seqbegin(&mount_lock);
+		child_mnt = __lookup_mnt(path->mnt, path->dentry);
+		m = child_mnt ? &child_mnt->mnt : NULL;
+	} while (!legitimize_mnt(m, seq));
+	rcu_read_unlock();
+	return m;
+}
+
+static inline void lock_ns_list(struct mnt_namespace *ns)
+{
+	spin_lock(&ns->ns_lock);
+}
+
+static inline void unlock_ns_list(struct mnt_namespace *ns)
+{
+	spin_unlock(&ns->ns_lock);
+}
+
+static inline bool mnt_is_cursor(struct mount *mnt)
+{
+	return mnt->mnt.mnt_flags & MNT_CURSOR;
+}
+
+/*
+ * __is_local_mountpoint - Test to see if dentry is a mountpoint in the
+ *                         current mount namespace.
+ *
+ * The common case is dentries are not mountpoints at all and that
+ * test is handled inline.  For the slow case when we are actually
+ * dealing with a mountpoint of some kind, walk through all of the
+ * mounts in the current mount namespace and test to see if the dentry
+ * is a mountpoint.
+ *
+ * The mount_hashtable is not usable in the context because we
+ * need to identify all mounts that may be in the current mount
+ * namespace not just a mount that happens to have some specified
+ * parent mount.
+ */
+bool __is_local_mountpoint(struct dentry *dentry)
+{
+	struct mnt_namespace *ns = current->nsproxy->mnt_ns;
+	struct mount *mnt;
+	bool is_covered = false;
+
+	down_read(&namespace_sem);
+	lock_ns_list(ns);
+	list_for_each_entry(mnt, &ns->list, mnt_list) {
+		if (mnt_is_cursor(mnt))
+			continue;
+		is_covered = (mnt->mnt_mountpoint == dentry);
+		if (is_covered)
+			break;
+	}
+	unlock_ns_list(ns);
+	up_read(&namespace_sem);
+
+	return is_covered;
+}
+
+static struct mountpoint *lookup_mountpoint(struct dentry *dentry)
+{
+	struct hlist_head *chain = mp_hash(dentry);
+	struct mountpoint *mp;
+
+	hlist_for_each_entry(mp, chain, m_hash) {
+		if (mp->m_dentry == dentry) {
+			mp->m_count++;
+			return mp;
+		}
+	}
+	return NULL;
+}
+
+static struct mountpoint *get_mountpoint(struct dentry *dentry)
+{
+	struct mountpoint *mp, *new = NULL;
+	int ret;
+
+	if (d_mountpoint(dentry)) {
+		/* might be worth a WARN_ON() */
+		if (d_unlinked(dentry))
+			return ERR_PTR(-ENOENT);
+mountpoint:
+		read_seqlock_excl(&mount_lock);
+		mp = lookup_mountpoint(dentry);
+		read_sequnlock_excl(&mount_lock);
+		if (mp)
+			goto done;
+	}
+
+	if (!new)
+		new = kmalloc(sizeof(struct mountpoint), GFP_KERNEL);
+	if (!new)
+		return ERR_PTR(-ENOMEM);
+
+
+	/* Exactly one processes may set d_mounted */
+	ret = d_set_mounted(dentry);
+
+	/* Someone else set d_mounted? */
+	if (ret == -EBUSY)
+		goto mountpoint;
+
+	/* The dentry is not available as a mountpoint? */
+	mp = ERR_PTR(ret);
+	if (ret)
+		goto done;
+
+	/* Add the new mountpoint to the hash table */
+	read_seqlock_excl(&mount_lock);
+	new->m_dentry = dget(dentry);
+	new->m_count = 1;
+	hlist_add_head(&new->m_hash, mp_hash(dentry));
+	INIT_HLIST_HEAD(&new->m_list);
+	read_sequnlock_excl(&mount_lock);
+
+	mp = new;
+	new = NULL;
+done:
+	kfree(new);
+	return mp;
+}
+
+/*
+ * vfsmount lock must be held.  Additionally, the caller is responsible
+ * for serializing calls for given disposal list.
+ */
+static void __put_mountpoint(struct mountpoint *mp, struct list_head *list)
+{
+	if (!--mp->m_count) {
+		struct dentry *dentry = mp->m_dentry;
+		BUG_ON(!hlist_empty(&mp->m_list));
+		spin_lock(&dentry->d_lock);
+		dentry->d_flags &= ~DCACHE_MOUNTED;
+		spin_unlock(&dentry->d_lock);
+		dput_to_list(dentry, list);
+		hlist_del(&mp->m_hash);
+		kfree(mp);
+	}
+}
+
+/* called with namespace_lock and vfsmount lock */
+static void put_mountpoint(struct mountpoint *mp)
+{
+	__put_mountpoint(mp, &ex_mountpoints);
+}
+
+static inline int check_mnt(struct mount *mnt)
+{
+	return mnt->mnt_ns == current->nsproxy->mnt_ns;
+}
+
+/*
+ * vfsmount lock must be held for write
+ */
+static void touch_mnt_namespace(struct mnt_namespace *ns)
+{
+	if (ns) {
+		ns->event = ++event;
+		wake_up_interruptible(&ns->poll);
+	}
+}
+
+/*
+ * vfsmount lock must be held for write
+ */
+static void __touch_mnt_namespace(struct mnt_namespace *ns)
+{
+	if (ns && ns->event != event) {
+		ns->event = event;
+		wake_up_interruptible(&ns->poll);
+	}
+}
+
+/*
+ * vfsmount lock must be held for write
+ */
+static struct mountpoint *unhash_mnt(struct mount *mnt)
+{
+	struct mountpoint *mp;
+	mnt->mnt_parent = mnt;
+	mnt->mnt_mountpoint = mnt->mnt.mnt_root;
+	list_del_init(&mnt->mnt_child);
+	hlist_del_init_rcu(&mnt->mnt_hash);
+	hlist_del_init(&mnt->mnt_mp_list);
+	mp = mnt->mnt_mp;
+	mnt->mnt_mp = NULL;
+	return mp;
+}
+
+/*
+ * vfsmount lock must be held for write
+ */
+static void umount_mnt(struct mount *mnt)
+{
+	put_mountpoint(unhash_mnt(mnt));
+}
+
+/*
+ * vfsmount lock must be held for write
+ */
+void mnt_set_mountpoint(struct mount *mnt,
+			struct mountpoint *mp,
+			struct mount *child_mnt)
+{
+	mp->m_count++;
+	mnt_add_count(mnt, 1);	/* essentially, that's mntget */
+	child_mnt->mnt_mountpoint = mp->m_dentry;
+	child_mnt->mnt_parent = mnt;
+	child_mnt->mnt_mp = mp;
+	hlist_add_head(&child_mnt->mnt_mp_list, &mp->m_list);
+}
+
+/**
+ * mnt_set_mountpoint_beneath - mount a mount beneath another one
+ *
+ * @new_parent: the source mount
+ * @top_mnt:    the mount beneath which @new_parent is mounted
+ * @new_mp:     the new mountpoint of @top_mnt on @new_parent
+ *
+ * Remove @top_mnt from its current mountpoint @top_mnt->mnt_mp and
+ * parent @top_mnt->mnt_parent and mount it on top of @new_parent at
+ * @new_mp. And mount @new_parent on the old parent and old
+ * mountpoint of @top_mnt.
+ *
+ * Context: This function expects namespace_lock() and lock_mount_hash()
+ *          to have been acquired in that order.
+ */
+static void mnt_set_mountpoint_beneath(struct mount *new_parent,
+				       struct mount *top_mnt,
+				       struct mountpoint *new_mp)
+{
+	struct mount *old_top_parent = top_mnt->mnt_parent;
+	struct mountpoint *old_top_mp = top_mnt->mnt_mp;
+
+	mnt_set_mountpoint(old_top_parent, old_top_mp, new_parent);
+	mnt_change_mountpoint(new_parent, new_mp, top_mnt);
+}
+
+
+static void __attach_mnt(struct mount *mnt, struct mount *parent)
+{
+	hlist_add_head_rcu(&mnt->mnt_hash,
+			   m_hash(&parent->mnt, mnt->mnt_mountpoint));
+	list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
+}
+
+/**
+ * attach_mnt - mount a mount, attach to @mount_hashtable and parent's
+ *              list of child mounts
+ * @parent:  the parent
+ * @mnt:     the new mount
+ * @mp:      the new mountpoint
+ * @beneath: whether to mount @mnt beneath or on top of @parent
+ *
+ * If @beneath is false, mount @mnt at @mp on @parent. Then attach @mnt
+ * to @parent's child mount list and to @mount_hashtable.
+ *
+ * If @beneath is true, remove @mnt from its current parent and
+ * mountpoint and mount it on @mp on @parent, and mount @parent on the
+ * old parent and old mountpoint of @mnt. Finally, attach @parent to
+ * @mnt_hashtable and @parent->mnt_parent->mnt_mounts.
+ *
+ * Note, when __attach_mnt() is called @mnt->mnt_parent already points
+ * to the correct parent.
+ *
+ * Context: This function expects namespace_lock() and lock_mount_hash()
+ *          to have been acquired in that order.
+ */
+static void attach_mnt(struct mount *mnt, struct mount *parent,
+		       struct mountpoint *mp, bool beneath)
+{
+	if (beneath)
+		mnt_set_mountpoint_beneath(mnt, parent, mp);
+	else
+		mnt_set_mountpoint(parent, mp, mnt);
+	/*
+	 * Note, @mnt->mnt_parent has to be used. If @mnt was mounted
+	 * beneath @parent then @mnt will need to be attached to
+	 * @parent's old parent, not @parent. IOW, @mnt->mnt_parent
+	 * isn't the same mount as @parent.
+	 */
+	__attach_mnt(mnt, mnt->mnt_parent);
+}
+
+void mnt_change_mountpoint(struct mount *parent, struct mountpoint *mp, struct mount *mnt)
+{
+	struct mountpoint *old_mp = mnt->mnt_mp;
+	struct mount *old_parent = mnt->mnt_parent;
+
+	list_del_init(&mnt->mnt_child);
+	hlist_del_init(&mnt->mnt_mp_list);
+	hlist_del_init_rcu(&mnt->mnt_hash);
+
+	attach_mnt(mnt, parent, mp, false);
+
+	put_mountpoint(old_mp);
+	mnt_add_count(old_parent, -1);
+}
+
+/*
+ * vfsmount lock must be held for write
+ */
+static void commit_tree(struct mount *mnt)
+{
+	struct mount *parent = mnt->mnt_parent;
+	struct mount *m;
+	LIST_HEAD(head);
+	struct mnt_namespace *n = parent->mnt_ns;
+
+	BUG_ON(parent == mnt);
+
+	list_add_tail(&head, &mnt->mnt_list);
+	list_for_each_entry(m, &head, mnt_list)
+		m->mnt_ns = n;
+
+	list_splice(&head, n->list.prev);
+
+	n->mounts += n->pending_mounts;
+	n->pending_mounts = 0;
+
+	__attach_mnt(mnt, parent);
+	touch_mnt_namespace(n);
+}
+
+static struct mount *next_mnt(struct mount *p, struct mount *root)
+{
+	struct list_head *next = p->mnt_mounts.next;
+	if (next == &p->mnt_mounts) {
+		while (1) {
+			if (p == root)
+				return NULL;
+			next = p->mnt_child.next;
+			if (next != &p->mnt_parent->mnt_mounts)
+				break;
+			p = p->mnt_parent;
+		}
+	}
+	return list_entry(next, struct mount, mnt_child);
+}
+
+static struct mount *skip_mnt_tree(struct mount *p)
+{
+	struct list_head *prev = p->mnt_mounts.prev;
+	while (prev != &p->mnt_mounts) {
+		p = list_entry(prev, struct mount, mnt_child);
+		prev = p->mnt_mounts.prev;
+	}
+	return p;
+}
+
+/**
+ * vfs_create_mount - Create a mount for a configured superblock
+ * @fc: The configuration context with the superblock attached
+ *
+ * Create a mount to an already configured superblock.  If necessary, the
+ * caller should invoke vfs_get_tree() before calling this.
+ *
+ * Note that this does not attach the mount to anything.
+ */
+struct vfsmount *vfs_create_mount(struct fs_context *fc)
+{
+	struct mount *mnt;
+
+	if (!fc->root)
+		return ERR_PTR(-EINVAL);
+
+	mnt = alloc_vfsmnt(fc->source ?: "none");
+	if (!mnt)
+		return ERR_PTR(-ENOMEM);
+
+	if (fc->sb_flags & SB_KERNMOUNT)
+		mnt->mnt.mnt_flags = MNT_INTERNAL;
+
+	atomic_inc(&fc->root->d_sb->s_active);
+	mnt->mnt.mnt_sb		= fc->root->d_sb;
+	mnt->mnt.mnt_root	= dget(fc->root);
+	mnt->mnt_mountpoint	= mnt->mnt.mnt_root;
+	mnt->mnt_parent		= mnt;
+
+	lock_mount_hash();
+	list_add_tail(&mnt->mnt_instance, &mnt->mnt.mnt_sb->s_mounts);
+	unlock_mount_hash();
+	return &mnt->mnt;
+}
+EXPORT_SYMBOL(vfs_create_mount);
+
+struct vfsmount *fc_mount(struct fs_context *fc)
+{
+	int err = vfs_get_tree(fc);
+	if (!err) {
+		up_write(&fc->root->d_sb->s_umount);
+		return vfs_create_mount(fc);
+	}
+	return ERR_PTR(err);
+}
+EXPORT_SYMBOL(fc_mount);
+
+struct vfsmount *vfs_kern_mount(struct file_system_type *type,
+				int flags, const char *name,
+				void *data)
+{
+	struct fs_context *fc;
+	struct vfsmount *mnt;
+	int ret = 0;
+
+	if (!type)
+		return ERR_PTR(-EINVAL);
+
+	fc = fs_context_for_mount(type, flags);
+	if (IS_ERR(fc))
+		return ERR_CAST(fc);
+
+	if (name)
+		ret = vfs_parse_fs_string(fc, "source",
+					  name, strlen(name));
+	if (!ret)
+		ret = parse_monolithic_mount_data(fc, data);
+	if (!ret)
+		mnt = fc_mount(fc);
+	else
+		mnt = ERR_PTR(ret);
+
+	put_fs_context(fc);
+	return mnt;
+}
+EXPORT_SYMBOL_GPL(vfs_kern_mount);
+
+struct vfsmount *
+vfs_submount(const struct dentry *mountpoint, struct file_system_type *type,
+	     const char *name, void *data)
+{
+	/* Until it is worked out how to pass the user namespace
+	 * through from the parent mount to the submount don't support
+	 * unprivileged mounts with submounts.
+	 */
+	if (mountpoint->d_sb->s_user_ns != &init_user_ns)
+		return ERR_PTR(-EPERM);
+
+	return vfs_kern_mount(type, SB_SUBMOUNT, name, data);
+}
+EXPORT_SYMBOL_GPL(vfs_submount);
+
+static struct mount *clone_mnt(struct mount *old, struct dentry *root,
+					int flag)
+{
+	struct super_block *sb = old->mnt.mnt_sb;
+	struct mount *mnt;
+	int err;
+
+	mnt = alloc_vfsmnt(old->mnt_devname);
+	if (!mnt)
+		return ERR_PTR(-ENOMEM);
+
+	if (flag & (CL_SLAVE | CL_PRIVATE | CL_SHARED_TO_SLAVE))
+		mnt->mnt_group_id = 0; /* not a peer of original */
+	else
+		mnt->mnt_group_id = old->mnt_group_id;
+
+	if ((flag & CL_MAKE_SHARED) && !mnt->mnt_group_id) {
+		err = mnt_alloc_group_id(mnt);
+		if (err)
+			goto out_free;
+	}
+
+	mnt->mnt.mnt_flags = old->mnt.mnt_flags;
+	mnt->mnt.mnt_flags &= ~(MNT_WRITE_HOLD|MNT_MARKED|MNT_INTERNAL);
+
+	atomic_inc(&sb->s_active);
+	mnt->mnt.mnt_idmap = mnt_idmap_get(mnt_idmap(&old->mnt));
+
+	mnt->mnt.mnt_sb = sb;
+	mnt->mnt.mnt_root = dget(root);
+	mnt->mnt_mountpoint = mnt->mnt.mnt_root;
+	mnt->mnt_parent = mnt;
+	lock_mount_hash();
+	list_add_tail(&mnt->mnt_instance, &sb->s_mounts);
+	unlock_mount_hash();
+
+	if ((flag & CL_SLAVE) ||
+	    ((flag & CL_SHARED_TO_SLAVE) && IS_MNT_SHARED(old))) {
+		list_add(&mnt->mnt_slave, &old->mnt_slave_list);
+		mnt->mnt_master = old;
+		CLEAR_MNT_SHARED(mnt);
+	} else if (!(flag & CL_PRIVATE)) {
+		if ((flag & CL_MAKE_SHARED) || IS_MNT_SHARED(old))
+			list_add(&mnt->mnt_share, &old->mnt_share);
+		if (IS_MNT_SLAVE(old))
+			list_add(&mnt->mnt_slave, &old->mnt_slave);
+		mnt->mnt_master = old->mnt_master;
+	} else {
+		CLEAR_MNT_SHARED(mnt);
+	}
+	if (flag & CL_MAKE_SHARED)
+		set_mnt_shared(mnt);
+
+	/* stick the duplicate mount on the same expiry list
+	 * as the original if that was on one */
+	if (flag & CL_EXPIRE) {
+		if (!list_empty(&old->mnt_expire))
+			list_add(&mnt->mnt_expire, &old->mnt_expire);
+	}
+
+	return mnt;
+
+ out_free:
+	mnt_free_id(mnt);
+	free_vfsmnt(mnt);
+	return ERR_PTR(err);
+}
+
+static void cleanup_mnt(struct mount *mnt)
+{
+	struct hlist_node *p;
+	struct mount *m;
+	/*
+	 * The warning here probably indicates that somebody messed
+	 * up a mnt_want/drop_write() pair.  If this happens, the
+	 * filesystem was probably unable to make r/w->r/o transitions.
+	 * The locking used to deal with mnt_count decrement provides barriers,
+	 * so mnt_get_writers() below is safe.
+	 */
+	WARN_ON(mnt_get_writers(mnt));
+	if (unlikely(mnt->mnt_pins.first))
+		mnt_pin_kill(mnt);
+	hlist_for_each_entry_safe(m, p, &mnt->mnt_stuck_children, mnt_umount) {
+		hlist_del(&m->mnt_umount);
+		mntput(&m->mnt);
+	}
+	fsnotify_vfsmount_delete(&mnt->mnt);
+	dput(mnt->mnt.mnt_root);
+	deactivate_super(mnt->mnt.mnt_sb);
+	mnt_free_id(mnt);
+	call_rcu(&mnt->mnt_rcu, delayed_free_vfsmnt);
+}
+
+static void __cleanup_mnt(struct rcu_head *head)
+{
+	cleanup_mnt(container_of(head, struct mount, mnt_rcu));
+}
+
+static LLIST_HEAD(delayed_mntput_list);
+static void delayed_mntput(struct work_struct *unused)
+{
+	struct llist_node *node = llist_del_all(&delayed_mntput_list);
+	struct mount *m, *t;
+
+	llist_for_each_entry_safe(m, t, node, mnt_llist)
+		cleanup_mnt(m);
+}
+static DECLARE_DELAYED_WORK(delayed_mntput_work, delayed_mntput);
+
+static void mntput_no_expire(struct mount *mnt)
+{
+	LIST_HEAD(list);
+	int count;
+
+	rcu_read_lock();
+	if (likely(READ_ONCE(mnt->mnt_ns))) {
+		/*
+		 * Since we don't do lock_mount_hash() here,
+		 * ->mnt_ns can change under us.  However, if it's
+		 * non-NULL, then there's a reference that won't
+		 * be dropped until after an RCU delay done after
+		 * turning ->mnt_ns NULL.  So if we observe it
+		 * non-NULL under rcu_read_lock(), the reference
+		 * we are dropping is not the final one.
+		 */
+		mnt_add_count(mnt, -1);
+		rcu_read_unlock();
+		return;
+	}
+	lock_mount_hash();
+	/*
+	 * make sure that if __legitimize_mnt() has not seen us grab
+	 * mount_lock, we'll see their refcount increment here.
+	 */
+	smp_mb();
+	mnt_add_count(mnt, -1);
+	count = mnt_get_count(mnt);
+	if (count != 0) {
+		WARN_ON(count < 0);
+		rcu_read_unlock();
+		unlock_mount_hash();
+		return;
+	}
+	if (unlikely(mnt->mnt.mnt_flags & MNT_DOOMED)) {
+		rcu_read_unlock();
+		unlock_mount_hash();
+		return;
+	}
+	mnt->mnt.mnt_flags |= MNT_DOOMED;
+	rcu_read_unlock();
+
+	list_del(&mnt->mnt_instance);
+
+	if (unlikely(!list_empty(&mnt->mnt_mounts))) {
+		struct mount *p, *tmp;
+		list_for_each_entry_safe(p, tmp, &mnt->mnt_mounts,  mnt_child) {
+			__put_mountpoint(unhash_mnt(p), &list);
+			hlist_add_head(&p->mnt_umount, &mnt->mnt_stuck_children);
+		}
+	}
+	unlock_mount_hash();
+	shrink_dentry_list(&list);
+
+	if (likely(!(mnt->mnt.mnt_flags & MNT_INTERNAL))) {
+		struct task_struct *task = current;
+		if (likely(!(task->flags & PF_KTHREAD))) {
+			init_task_work(&mnt->mnt_rcu, __cleanup_mnt);
+			if (!task_work_add(task, &mnt->mnt_rcu, TWA_RESUME))
+				return;
+		}
+		if (llist_add(&mnt->mnt_llist, &delayed_mntput_list))
+			schedule_delayed_work(&delayed_mntput_work, 1);
+		return;
+	}
+	cleanup_mnt(mnt);
+}
+
+void mntput(struct vfsmount *mnt)
+{
+	if (mnt) {
+		struct mount *m = real_mount(mnt);
+		/* avoid cacheline pingpong, hope gcc doesn't get "smart" */
+		if (unlikely(m->mnt_expiry_mark))
+			m->mnt_expiry_mark = 0;
+		mntput_no_expire(m);
+	}
+}
+EXPORT_SYMBOL(mntput);
+
+struct vfsmount *mntget(struct vfsmount *mnt)
+{
+	if (mnt)
+		mnt_add_count(real_mount(mnt), 1);
+	return mnt;
+}
+EXPORT_SYMBOL(mntget);
+
+/*
+ * Make a mount point inaccessible to new lookups.
+ * Because there may still be current users, the caller MUST WAIT
+ * for an RCU grace period before destroying the mount point.
+ */
+void mnt_make_shortterm(struct vfsmount *mnt)
+{
+	if (mnt)
+		real_mount(mnt)->mnt_ns = NULL;
+}
+
+/**
+ * path_is_mountpoint() - Check if path is a mount in the current namespace.
+ * @path: path to check
+ *
+ *  d_mountpoint() can only be used reliably to establish if a dentry is
+ *  not mounted in any namespace and that common case is handled inline.
+ *  d_mountpoint() isn't aware of the possibility there may be multiple
+ *  mounts using a given dentry in a different namespace. This function
+ *  checks if the passed in path is a mountpoint rather than the dentry
+ *  alone.
+ */
+bool path_is_mountpoint(const struct path *path)
+{
+	unsigned seq;
+	bool res;
+
+	if (!d_mountpoint(path->dentry))
+		return false;
+
+	rcu_read_lock();
+	do {
+		seq = read_seqbegin(&mount_lock);
+		res = __path_is_mountpoint(path);
+	} while (read_seqretry(&mount_lock, seq));
+	rcu_read_unlock();
+
+	return res;
+}
+EXPORT_SYMBOL(path_is_mountpoint);
+
+struct vfsmount *mnt_clone_internal(const struct path *path)
+{
+	struct mount *p;
+	p = clone_mnt(real_mount(path->mnt), path->dentry, CL_PRIVATE);
+	if (IS_ERR(p))
+		return ERR_CAST(p);
+	p->mnt.mnt_flags |= MNT_INTERNAL;
+	return &p->mnt;
+}
+
+#ifdef CONFIG_PROC_FS
+static struct mount *mnt_list_next(struct mnt_namespace *ns,
+				   struct list_head *p)
+{
+	struct mount *mnt, *ret = NULL;
+
+	lock_ns_list(ns);
+	list_for_each_continue(p, &ns->list) {
+		mnt = list_entry(p, typeof(*mnt), mnt_list);
+		if (!mnt_is_cursor(mnt)) {
+			ret = mnt;
+			break;
+		}
+	}
+	unlock_ns_list(ns);
+
+	return ret;
+}
+
+/* iterator; we want it to have access to namespace_sem, thus here... */
+static void *m_start(struct seq_file *m, loff_t *pos)
+{
+	struct proc_mounts *p = m->private;
+	struct list_head *prev;
+
+	down_read(&namespace_sem);
+	if (!*pos) {
+		prev = &p->ns->list;
+	} else {
+		prev = &p->cursor.mnt_list;
+
+		/* Read after we'd reached the end? */
+		if (list_empty(prev))
+			return NULL;
+	}
+
+	return mnt_list_next(p->ns, prev);
+}
+
+static void *m_next(struct seq_file *m, void *v, loff_t *pos)
+{
+	struct proc_mounts *p = m->private;
+	struct mount *mnt = v;
+
+	++*pos;
+	return mnt_list_next(p->ns, &mnt->mnt_list);
+}
+
+static void m_stop(struct seq_file *m, void *v)
+{
+	struct proc_mounts *p = m->private;
+	struct mount *mnt = v;
+
+	lock_ns_list(p->ns);
+	if (mnt)
+		list_move_tail(&p->cursor.mnt_list, &mnt->mnt_list);
+	else
+		list_del_init(&p->cursor.mnt_list);
+	unlock_ns_list(p->ns);
+	up_read(&namespace_sem);
+}
+
+static int m_show(struct seq_file *m, void *v)
+{
+	struct proc_mounts *p = m->private;
+	struct mount *r = v;
+	return p->show(m, &r->mnt);
+}
+
+const struct seq_operations mounts_op = {
+	.start	= m_start,
+	.next	= m_next,
+	.stop	= m_stop,
+	.show	= m_show,
+};
+
+void mnt_cursor_del(struct mnt_namespace *ns, struct mount *cursor)
+{
+	down_read(&namespace_sem);
+	lock_ns_list(ns);
+	list_del(&cursor->mnt_list);
+	unlock_ns_list(ns);
+	up_read(&namespace_sem);
+}
+#endif  /* CONFIG_PROC_FS */
+
+/**
+ * may_umount_tree - check if a mount tree is busy
+ * @m: root of mount tree
+ *
+ * This is called to check if a tree of mounts has any
+ * open files, pwds, chroots or sub mounts that are
+ * busy.
+ */
+int may_umount_tree(struct vfsmount *m)
+{
+	struct mount *mnt = real_mount(m);
+	int actual_refs = 0;
+	int minimum_refs = 0;
+	struct mount *p;
+	BUG_ON(!m);
+
+	/* write lock needed for mnt_get_count */
+	lock_mount_hash();
+	for (p = mnt; p; p = next_mnt(p, mnt)) {
+		actual_refs += mnt_get_count(p);
+		minimum_refs += 2;
+	}
+	unlock_mount_hash();
+
+	if (actual_refs > minimum_refs)
+		return 0;
+
+	return 1;
+}
+
+EXPORT_SYMBOL(may_umount_tree);
+
+/**
+ * may_umount - check if a mount point is busy
+ * @mnt: root of mount
+ *
+ * This is called to check if a mount point has any
+ * open files, pwds, chroots or sub mounts. If the
+ * mount has sub mounts this will return busy
+ * regardless of whether the sub mounts are busy.
+ *
+ * Doesn't take quota and stuff into account. IOW, in some cases it will
+ * give false negatives. The main reason why it's here is that we need
+ * a non-destructive way to look for easily umountable filesystems.
+ */
+int may_umount(struct vfsmount *mnt)
+{
+	int ret = 1;
+	down_read(&namespace_sem);
+	lock_mount_hash();
+	if (propagate_mount_busy(real_mount(mnt), 2))
+		ret = 0;
+	unlock_mount_hash();
+	up_read(&namespace_sem);
+	return ret;
+}
+
+EXPORT_SYMBOL(may_umount);
+
+static void namespace_unlock(void)
+{
+	struct hlist_head head;
+	struct hlist_node *p;
+	struct mount *m;
+	LIST_HEAD(list);
+
+	hlist_move_list(&unmounted, &head);
+	list_splice_init(&ex_mountpoints, &list);
+
+	up_write(&namespace_sem);
+
+	shrink_dentry_list(&list);
+
+	if (likely(hlist_empty(&head)))
+		return;
+
+	synchronize_rcu_expedited();
+
+	hlist_for_each_entry_safe(m, p, &head, mnt_umount) {
+		hlist_del(&m->mnt_umount);
+		mntput(&m->mnt);
+	}
+}
+
+static inline void namespace_lock(void)
+{
+	down_write(&namespace_sem);
+}
+
+enum umount_tree_flags {
+	UMOUNT_SYNC = 1,
+	UMOUNT_PROPAGATE = 2,
+	UMOUNT_CONNECTED = 4,
+};
+
+static bool disconnect_mount(struct mount *mnt, enum umount_tree_flags how)
+{
+	/* Leaving mounts connected is only valid for lazy umounts */
+	if (how & UMOUNT_SYNC)
+		return true;
+
+	/* A mount without a parent has nothing to be connected to */
+	if (!mnt_has_parent(mnt))
+		return true;
+
+	/* Because the reference counting rules change when mounts are
+	 * unmounted and connected, umounted mounts may not be
+	 * connected to mounted mounts.
+	 */
+	if (!(mnt->mnt_parent->mnt.mnt_flags & MNT_UMOUNT))
+		return true;
+
+	/* Has it been requested that the mount remain connected? */
+	if (how & UMOUNT_CONNECTED)
+		return false;
+
+	/* Is the mount locked such that it needs to remain connected? */
+	if (IS_MNT_LOCKED(mnt))
+		return false;
+
+	/* By default disconnect the mount */
+	return true;
+}
+
+/*
+ * mount_lock must be held
+ * namespace_sem must be held for write
+ */
+static void umount_tree(struct mount *mnt, enum umount_tree_flags how)
+{
+	LIST_HEAD(tmp_list);
+	struct mount *p;
+
+	if (how & UMOUNT_PROPAGATE)
+		propagate_mount_unlock(mnt);
+
+	/* Gather the mounts to umount */
+	for (p = mnt; p; p = next_mnt(p, mnt)) {
+		p->mnt.mnt_flags |= MNT_UMOUNT;
+		list_move(&p->mnt_list, &tmp_list);
+	}
+
+	/* Hide the mounts from mnt_mounts */
+	list_for_each_entry(p, &tmp_list, mnt_list) {
+		list_del_init(&p->mnt_child);
+	}
+
+	/* Add propogated mounts to the tmp_list */
+	if (how & UMOUNT_PROPAGATE)
+		propagate_umount(&tmp_list);
+
+	while (!list_empty(&tmp_list)) {
+		struct mnt_namespace *ns;
+		bool disconnect;
+		p = list_first_entry(&tmp_list, struct mount, mnt_list);
+		list_del_init(&p->mnt_expire);
+		list_del_init(&p->mnt_list);
+		ns = p->mnt_ns;
+		if (ns) {
+			ns->mounts--;
+			__touch_mnt_namespace(ns);
+		}
+		p->mnt_ns = NULL;
+		if (how & UMOUNT_SYNC)
+			p->mnt.mnt_flags |= MNT_SYNC_UMOUNT;
+
+		disconnect = disconnect_mount(p, how);
+		if (mnt_has_parent(p)) {
+			mnt_add_count(p->mnt_parent, -1);
+			if (!disconnect) {
+				/* Don't forget about p */
+				list_add_tail(&p->mnt_child, &p->mnt_parent->mnt_mounts);
+			} else {
+				umount_mnt(p);
+			}
+		}
+		change_mnt_propagation(p, MS_PRIVATE);
+		if (disconnect)
+			hlist_add_head(&p->mnt_umount, &unmounted);
+	}
+}
+
+static void shrink_submounts(struct mount *mnt);
+
+static int do_umount_root(struct super_block *sb)
+{
+	int ret = 0;
+
+	down_write(&sb->s_umount);
+	if (!sb_rdonly(sb)) {
+		struct fs_context *fc;
+
+		fc = fs_context_for_reconfigure(sb->s_root, SB_RDONLY,
+						SB_RDONLY);
+		if (IS_ERR(fc)) {
+			ret = PTR_ERR(fc);
+		} else {
+			ret = parse_monolithic_mount_data(fc, NULL);
+			if (!ret)
+				ret = reconfigure_super(fc);
+			put_fs_context(fc);
+		}
+	}
+	up_write(&sb->s_umount);
+	return ret;
+}
+
+static int do_umount(struct mount *mnt, int flags)
+{
+	struct super_block *sb = mnt->mnt.mnt_sb;
+	int retval;
+
+	retval = security_sb_umount(&mnt->mnt, flags);
+	if (retval)
+		return retval;
+
+	/*
+	 * Allow userspace to request a mountpoint be expired rather than
+	 * unmounting unconditionally. Unmount only happens if:
+	 *  (1) the mark is already set (the mark is cleared by mntput())
+	 *  (2) the usage count == 1 [parent vfsmount] + 1 [sys_umount]
+	 */
+	if (flags & MNT_EXPIRE) {
+		if (&mnt->mnt == current->fs->root.mnt ||
+		    flags & (MNT_FORCE | MNT_DETACH))
+			return -EINVAL;
+
+		/*
+		 * probably don't strictly need the lock here if we examined
+		 * all race cases, but it's a slowpath.
+		 */
+		lock_mount_hash();
+		if (mnt_get_count(mnt) != 2) {
+			unlock_mount_hash();
+			return -EBUSY;
+		}
+		unlock_mount_hash();
+
+		if (!xchg(&mnt->mnt_expiry_mark, 1))
+			return -EAGAIN;
+	}
+
+	/*
+	 * If we may have to abort operations to get out of this
+	 * mount, and they will themselves hold resources we must
+	 * allow the fs to do things. In the Unix tradition of
+	 * 'Gee thats tricky lets do it in userspace' the umount_begin
+	 * might fail to complete on the first run through as other tasks
+	 * must return, and the like. Thats for the mount program to worry
+	 * about for the moment.
+	 */
+
+	if (flags & MNT_FORCE && sb->s_op->umount_begin) {
+		sb->s_op->umount_begin(sb);
+	}
+
+	/*
+	 * No sense to grab the lock for this test, but test itself looks
+	 * somewhat bogus. Suggestions for better replacement?
+	 * Ho-hum... In principle, we might treat that as umount + switch
+	 * to rootfs. GC would eventually take care of the old vfsmount.
+	 * Actually it makes sense, especially if rootfs would contain a
+	 * /reboot - static binary that would close all descriptors and
+	 * call reboot(9). Then init(8) could umount root and exec /reboot.
+	 */
+	if (&mnt->mnt == current->fs->root.mnt && !(flags & MNT_DETACH)) {
+		/*
+		 * Special case for "unmounting" root ...
+		 * we just try to remount it readonly.
+		 */
+		if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN))
+			return -EPERM;
+		return do_umount_root(sb);
+	}
+
+	namespace_lock();
+	lock_mount_hash();
+
+	/* Recheck MNT_LOCKED with the locks held */
+	retval = -EINVAL;
+	if (mnt->mnt.mnt_flags & MNT_LOCKED)
+		goto out;
+
+	event++;
+	if (flags & MNT_DETACH) {
+		if (!list_empty(&mnt->mnt_list))
+			umount_tree(mnt, UMOUNT_PROPAGATE);
+		retval = 0;
+	} else {
+		shrink_submounts(mnt);
+		retval = -EBUSY;
+		if (!propagate_mount_busy(mnt, 2)) {
+			if (!list_empty(&mnt->mnt_list))
+				umount_tree(mnt, UMOUNT_PROPAGATE|UMOUNT_SYNC);
+			retval = 0;
+		}
+	}
+out:
+	unlock_mount_hash();
+	namespace_unlock();
+	return retval;
+}
+
+/*
+ * __detach_mounts - lazily unmount all mounts on the specified dentry
+ *
+ * During unlink, rmdir, and d_drop it is possible to loose the path
+ * to an existing mountpoint, and wind up leaking the mount.
+ * detach_mounts allows lazily unmounting those mounts instead of
+ * leaking them.
+ *
+ * The caller may hold dentry->d_inode->i_mutex.
+ */
+void __detach_mounts(struct dentry *dentry)
+{
+	struct mountpoint *mp;
+	struct mount *mnt;
+
+	namespace_lock();
+	lock_mount_hash();
+	mp = lookup_mountpoint(dentry);
+	if (!mp)
+		goto out_unlock;
+
+	event++;
+	while (!hlist_empty(&mp->m_list)) {
+		mnt = hlist_entry(mp->m_list.first, struct mount, mnt_mp_list);
+		if (mnt->mnt.mnt_flags & MNT_UMOUNT) {
+			umount_mnt(mnt);
+			hlist_add_head(&mnt->mnt_umount, &unmounted);
+		}
+		else umount_tree(mnt, UMOUNT_CONNECTED);
+	}
+	put_mountpoint(mp);
+out_unlock:
+	unlock_mount_hash();
+	namespace_unlock();
+}
+
+/*
+ * Is the caller allowed to modify his namespace?
+ */
+bool may_mount(void)
+{
+	return ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN);
+}
+
+/**
+ * path_mounted - check whether path is mounted
+ * @path: path to check
+ *
+ * Determine whether @path refers to the root of a mount.
+ *
+ * Return: true if @path is the root of a mount, false if not.
+ */
+static inline bool path_mounted(const struct path *path)
+{
+	return path->mnt->mnt_root == path->dentry;
+}
+
+static void warn_mandlock(void)
+{
+	pr_warn_once("=======================================================\n"
+		     "WARNING: The mand mount option has been deprecated and\n"
+		     "         and is ignored by this kernel. Remove the mand\n"
+		     "         option from the mount to silence this warning.\n"
+		     "=======================================================\n");
+}
+
+static int can_umount(const struct path *path, int flags)
+{
+	struct mount *mnt = real_mount(path->mnt);
+
+	if (!may_mount())
+		return -EPERM;
+	if (!path_mounted(path))
+		return -EINVAL;
+	if (!check_mnt(mnt))
+		return -EINVAL;
+	if (mnt->mnt.mnt_flags & MNT_LOCKED) /* Check optimistically */
+		return -EINVAL;
+	if (flags & MNT_FORCE && !capable(CAP_SYS_ADMIN))
+		return -EPERM;
+	return 0;
+}
+
+// caller is responsible for flags being sane
+int path_umount(struct path *path, int flags)
+{
+	struct mount *mnt = real_mount(path->mnt);
+	int ret;
+
+	ret = can_umount(path, flags);
+	if (!ret)
+		ret = do_umount(mnt, flags);
+
+	/* we mustn't call path_put() as that would clear mnt_expiry_mark */
+	dput(path->dentry);
+	mntput_no_expire(mnt);
+	return ret;
+}
+
+static int ksys_umount(char __user *name, int flags)
+{
+	int lookup_flags = LOOKUP_MOUNTPOINT;
+	struct path path;
+	int ret;
+
+	// basic validity checks done first
+	if (flags & ~(MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW))
+		return -EINVAL;
+
+	if (!(flags & UMOUNT_NOFOLLOW))
+		lookup_flags |= LOOKUP_FOLLOW;
+	ret = user_path_at(AT_FDCWD, name, lookup_flags, &path);
+	if (ret)
+		return ret;
+	return path_umount(&path, flags);
+}
+
+SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
+{
+	return ksys_umount(name, flags);
+}
+
+#ifdef __ARCH_WANT_SYS_OLDUMOUNT
+
+/*
+ *	The 2.0 compatible umount. No flags.
+ */
+SYSCALL_DEFINE1(oldumount, char __user *, name)
+{
+	return ksys_umount(name, 0);
+}
+
+#endif
+
+static bool is_mnt_ns_file(struct dentry *dentry)
+{
+	/* Is this a proxy for a mount namespace? */
+	return dentry->d_op == &ns_dentry_operations &&
+	       dentry->d_fsdata == &mntns_operations;
+}
+
+static struct mnt_namespace *to_mnt_ns(struct ns_common *ns)
+{
+	return container_of(ns, struct mnt_namespace, ns);
+}
+
+struct ns_common *from_mnt_ns(struct mnt_namespace *mnt)
+{
+	return &mnt->ns;
+}
+
+static bool mnt_ns_loop(struct dentry *dentry)
+{
+	/* Could bind mounting the mount namespace inode cause a
+	 * mount namespace loop?
+	 */
+	struct mnt_namespace *mnt_ns;
+	if (!is_mnt_ns_file(dentry))
+		return false;
+
+	mnt_ns = to_mnt_ns(get_proc_ns(dentry->d_inode));
+	return current->nsproxy->mnt_ns->seq >= mnt_ns->seq;
+}
+
+struct mount *copy_tree(struct mount *mnt, struct dentry *dentry,
+					int flag)
+{
+	struct mount *res, *p, *q, *r, *parent;
+
+	if (!(flag & CL_COPY_UNBINDABLE) && IS_MNT_UNBINDABLE(mnt))
+		return ERR_PTR(-EINVAL);
+
+	if (!(flag & CL_COPY_MNT_NS_FILE) && is_mnt_ns_file(dentry))
+		return ERR_PTR(-EINVAL);
+
+	res = q = clone_mnt(mnt, dentry, flag);
+	if (IS_ERR(q))
+		return q;
+
+	q->mnt_mountpoint = mnt->mnt_mountpoint;
+
+	p = mnt;
+	list_for_each_entry(r, &mnt->mnt_mounts, mnt_child) {
+		struct mount *s;
+		if (!is_subdir(r->mnt_mountpoint, dentry))
+			continue;
+
+		for (s = r; s; s = next_mnt(s, r)) {
+			if (!(flag & CL_COPY_UNBINDABLE) &&
+			    IS_MNT_UNBINDABLE(s)) {
+				if (s->mnt.mnt_flags & MNT_LOCKED) {
+					/* Both unbindable and locked. */
+					q = ERR_PTR(-EPERM);
+					goto out;
+				} else {
+					s = skip_mnt_tree(s);
+					continue;
+				}
+			}
+			if (!(flag & CL_COPY_MNT_NS_FILE) &&
+			    is_mnt_ns_file(s->mnt.mnt_root)) {
+				s = skip_mnt_tree(s);
+				continue;
+			}
+			while (p != s->mnt_parent) {
+				p = p->mnt_parent;
+				q = q->mnt_parent;
+			}
+			p = s;
+			parent = q;
+			q = clone_mnt(p, p->mnt.mnt_root, flag);
+			if (IS_ERR(q))
+				goto out;
+			lock_mount_hash();
+			list_add_tail(&q->mnt_list, &res->mnt_list);
+			attach_mnt(q, parent, p->mnt_mp, false);
+			unlock_mount_hash();
+		}
+	}
+	return res;
+out:
+	if (res) {
+		lock_mount_hash();
+		umount_tree(res, UMOUNT_SYNC);
+		unlock_mount_hash();
+	}
+	return q;
+}
+
+/* Caller should check returned pointer for errors */
+
+struct vfsmount *collect_mounts(const struct path *path)
+{
+	struct mount *tree;
+	namespace_lock();
+	if (!check_mnt(real_mount(path->mnt)))
+		tree = ERR_PTR(-EINVAL);
+	else
+		tree = copy_tree(real_mount(path->mnt), path->dentry,
+				 CL_COPY_ALL | CL_PRIVATE);
+	namespace_unlock();
+	if (IS_ERR(tree))
+		return ERR_CAST(tree);
+	return &tree->mnt;
+}
+
+static void free_mnt_ns(struct mnt_namespace *);
+static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *, bool);
+
+void dissolve_on_fput(struct vfsmount *mnt)
+{
+	struct mnt_namespace *ns;
+	namespace_lock();
+	lock_mount_hash();
+	ns = real_mount(mnt)->mnt_ns;
+	if (ns) {
+		if (is_anon_ns(ns))
+			umount_tree(real_mount(mnt), UMOUNT_CONNECTED);
+		else
+			ns = NULL;
+	}
+	unlock_mount_hash();
+	namespace_unlock();
+	if (ns)
+		free_mnt_ns(ns);
+}
+
+void drop_collected_mounts(struct vfsmount *mnt)
+{
+	namespace_lock();
+	lock_mount_hash();
+	umount_tree(real_mount(mnt), 0);
+	unlock_mount_hash();
+	namespace_unlock();
+}
+
+static bool has_locked_children(struct mount *mnt, struct dentry *dentry)
+{
+	struct mount *child;
+
+	list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
+		if (!is_subdir(child->mnt_mountpoint, dentry))
+			continue;
+
+		if (child->mnt.mnt_flags & MNT_LOCKED)
+			return true;
+	}
+	return false;
+}
+
+/**
+ * clone_private_mount - create a private clone of a path
+ * @path: path to clone
+ *
+ * This creates a new vfsmount, which will be the clone of @path.  The new mount
+ * will not be attached anywhere in the namespace and will be private (i.e.
+ * changes to the originating mount won't be propagated into this).
+ *
+ * Release with mntput().
+ */
+struct vfsmount *clone_private_mount(const struct path *path)
+{
+	struct mount *old_mnt = real_mount(path->mnt);
+	struct mount *new_mnt;
+
+	down_read(&namespace_sem);
+	if (IS_MNT_UNBINDABLE(old_mnt))
+		goto invalid;
+
+	if (!check_mnt(old_mnt))
+		goto invalid;
+
+	if (has_locked_children(old_mnt, path->dentry))
+		goto invalid;
+
+	new_mnt = clone_mnt(old_mnt, path->dentry, CL_PRIVATE);
+	up_read(&namespace_sem);
+
+	if (IS_ERR(new_mnt))
+		return ERR_CAST(new_mnt);
+
+	/* Longterm mount to be removed by kern_unmount*() */
+	new_mnt->mnt_ns = MNT_NS_INTERNAL;
+
+	return &new_mnt->mnt;
+
+invalid:
+	up_read(&namespace_sem);
+	return ERR_PTR(-EINVAL);
+}
+EXPORT_SYMBOL_GPL(clone_private_mount);
+
+int iterate_mounts(int (*f)(struct vfsmount *, void *), void *arg,
+		   struct vfsmount *root)
+{
+	struct mount *mnt;
+	int res = f(root, arg);
+	if (res)
+		return res;
+	list_for_each_entry(mnt, &real_mount(root)->mnt_list, mnt_list) {
+		res = f(&mnt->mnt, arg);
+		if (res)
+			return res;
+	}
+	return 0;
+}
+
+static void lock_mnt_tree(struct mount *mnt)
+{
+	struct mount *p;
+
+	for (p = mnt; p; p = next_mnt(p, mnt)) {
+		int flags = p->mnt.mnt_flags;
+		/* Don't allow unprivileged users to change mount flags */
+		flags |= MNT_LOCK_ATIME;
+
+		if (flags & MNT_READONLY)
+			flags |= MNT_LOCK_READONLY;
+
+		if (flags & MNT_NODEV)
+			flags |= MNT_LOCK_NODEV;
+
+		if (flags & MNT_NOSUID)
+			flags |= MNT_LOCK_NOSUID;
+
+		if (flags & MNT_NOEXEC)
+			flags |= MNT_LOCK_NOEXEC;
+		/* Don't allow unprivileged users to reveal what is under a mount */
+		if (list_empty(&p->mnt_expire))
+			flags |= MNT_LOCKED;
+		p->mnt.mnt_flags = flags;
+	}
+}
+
+static void cleanup_group_ids(struct mount *mnt, struct mount *end)
+{
+	struct mount *p;
+
+	for (p = mnt; p != end; p = next_mnt(p, mnt)) {
+		if (p->mnt_group_id && !IS_MNT_SHARED(p))
+			mnt_release_group_id(p);
+	}
+}
+
+static int invent_group_ids(struct mount *mnt, bool recurse)
+{
+	struct mount *p;
+
+	for (p = mnt; p; p = recurse ? next_mnt(p, mnt) : NULL) {
+		if (!p->mnt_group_id && !IS_MNT_SHARED(p)) {
+			int err = mnt_alloc_group_id(p);
+			if (err) {
+				cleanup_group_ids(mnt, p);
+				return err;
+			}
+		}
+	}
+
+	return 0;
+}
+
+int count_mounts(struct mnt_namespace *ns, struct mount *mnt)
+{
+	unsigned int max = READ_ONCE(sysctl_mount_max);
+	unsigned int mounts = 0;
+	struct mount *p;
+
+	if (ns->mounts >= max)
+		return -ENOSPC;
+	max -= ns->mounts;
+	if (ns->pending_mounts >= max)
+		return -ENOSPC;
+	max -= ns->pending_mounts;
+
+	for (p = mnt; p; p = next_mnt(p, mnt))
+		mounts++;
+
+	if (mounts > max)
+		return -ENOSPC;
+
+	ns->pending_mounts += mounts;
+	return 0;
+}
+
+enum mnt_tree_flags_t {
+	MNT_TREE_MOVE = BIT(0),
+	MNT_TREE_BENEATH = BIT(1),
+};
+
+/**
+ * attach_recursive_mnt - attach a source mount tree
+ * @source_mnt: mount tree to be attached
+ * @top_mnt:    mount that @source_mnt will be mounted on or mounted beneath
+ * @dest_mp:    the mountpoint @source_mnt will be mounted at
+ * @flags:      modify how @source_mnt is supposed to be attached
+ *
+ *  NOTE: in the table below explains the semantics when a source mount
+ *  of a given type is attached to a destination mount of a given type.
+ * ---------------------------------------------------------------------------
+ * |         BIND MOUNT OPERATION                                            |
+ * |**************************************************************************
+ * | source-->| shared        |       private  |       slave    | unbindable |
+ * | dest     |               |                |                |            |
+ * |   |      |               |                |                |            |
+ * |   v      |               |                |                |            |
+ * |**************************************************************************
+ * |  shared  | shared (++)   |     shared (+) |     shared(+++)|  invalid   |
+ * |          |               |                |                |            |
+ * |non-shared| shared (+)    |      private   |      slave (*) |  invalid   |
+ * ***************************************************************************
+ * A bind operation clones the source mount and mounts the clone on the
+ * destination mount.
+ *
+ * (++)  the cloned mount is propagated to all the mounts in the propagation
+ * 	 tree of the destination mount and the cloned mount is added to
+ * 	 the peer group of the source mount.
+ * (+)   the cloned mount is created under the destination mount and is marked
+ *       as shared. The cloned mount is added to the peer group of the source
+ *       mount.
+ * (+++) the mount is propagated to all the mounts in the propagation tree
+ *       of the destination mount and the cloned mount is made slave
+ *       of the same master as that of the source mount. The cloned mount
+ *       is marked as 'shared and slave'.
+ * (*)   the cloned mount is made a slave of the same master as that of the
+ * 	 source mount.
+ *
+ * ---------------------------------------------------------------------------
+ * |         		MOVE MOUNT OPERATION                                 |
+ * |**************************************************************************
+ * | source-->| shared        |       private  |       slave    | unbindable |
+ * | dest     |               |                |                |            |
+ * |   |      |               |                |                |            |
+ * |   v      |               |                |                |            |
+ * |**************************************************************************
+ * |  shared  | shared (+)    |     shared (+) |    shared(+++) |  invalid   |
+ * |          |               |                |                |            |
+ * |non-shared| shared (+*)   |      private   |    slave (*)   | unbindable |
+ * ***************************************************************************
+ *
+ * (+)  the mount is moved to the destination. And is then propagated to
+ * 	all the mounts in the propagation tree of the destination mount.
+ * (+*)  the mount is moved to the destination.
+ * (+++)  the mount is moved to the destination and is then propagated to
+ * 	all the mounts belonging to the destination mount's propagation tree.
+ * 	the mount is marked as 'shared and slave'.
+ * (*)	the mount continues to be a slave at the new location.
+ *
+ * if the source mount is a tree, the operations explained above is
+ * applied to each mount in the tree.
+ * Must be called without spinlocks held, since this function can sleep
+ * in allocations.
+ *
+ * Context: The function expects namespace_lock() to be held.
+ * Return: If @source_mnt was successfully attached 0 is returned.
+ *         Otherwise a negative error code is returned.
+ */
+static int attach_recursive_mnt(struct mount *source_mnt,
+				struct mount *top_mnt,
+				struct mountpoint *dest_mp,
+				enum mnt_tree_flags_t flags)
+{
+	struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns;
+	HLIST_HEAD(tree_list);
+	struct mnt_namespace *ns = top_mnt->mnt_ns;
+	struct mountpoint *smp;
+	struct mount *child, *dest_mnt, *p;
+	struct hlist_node *n;
+	int err = 0;
+	bool moving = flags & MNT_TREE_MOVE, beneath = flags & MNT_TREE_BENEATH;
+
+	/*
+	 * Preallocate a mountpoint in case the new mounts need to be
+	 * mounted beneath mounts on the same mountpoint.
+	 */
+	smp = get_mountpoint(source_mnt->mnt.mnt_root);
+	if (IS_ERR(smp))
+		return PTR_ERR(smp);
+
+	/* Is there space to add these mounts to the mount namespace? */
+	if (!moving) {
+		err = count_mounts(ns, source_mnt);
+		if (err)
+			goto out;
+	}
+
+	if (beneath)
+		dest_mnt = top_mnt->mnt_parent;
+	else
+		dest_mnt = top_mnt;
+
+	if (IS_MNT_SHARED(dest_mnt)) {
+		err = invent_group_ids(source_mnt, true);
+		if (err)
+			goto out;
+		err = propagate_mnt(dest_mnt, dest_mp, source_mnt, &tree_list);
+	}
+	lock_mount_hash();
+	if (err)
+		goto out_cleanup_ids;
+
+	if (IS_MNT_SHARED(dest_mnt)) {
+		for (p = source_mnt; p; p = next_mnt(p, source_mnt))
+			set_mnt_shared(p);
+	}
+
+	if (moving) {
+		if (beneath)
+			dest_mp = smp;
+		unhash_mnt(source_mnt);
+		attach_mnt(source_mnt, top_mnt, dest_mp, beneath);
+		touch_mnt_namespace(source_mnt->mnt_ns);
+	} else {
+		if (source_mnt->mnt_ns) {
+			/* move from anon - the caller will destroy */
+			list_del_init(&source_mnt->mnt_ns->list);
+		}
+		if (beneath)
+			mnt_set_mountpoint_beneath(source_mnt, top_mnt, smp);
+		else
+			mnt_set_mountpoint(dest_mnt, dest_mp, source_mnt);
+		commit_tree(source_mnt);
+	}
+
+	hlist_for_each_entry_safe(child, n, &tree_list, mnt_hash) {
+		struct mount *q;
+		hlist_del_init(&child->mnt_hash);
+		q = __lookup_mnt(&child->mnt_parent->mnt,
+				 child->mnt_mountpoint);
+		if (q)
+			mnt_change_mountpoint(child, smp, q);
+		/* Notice when we are propagating across user namespaces */
+		if (child->mnt_parent->mnt_ns->user_ns != user_ns)
+			lock_mnt_tree(child);
+		child->mnt.mnt_flags &= ~MNT_LOCKED;
+		commit_tree(child);
+	}
+	put_mountpoint(smp);
+	unlock_mount_hash();
+
+	return 0;
+
+ out_cleanup_ids:
+	while (!hlist_empty(&tree_list)) {
+		child = hlist_entry(tree_list.first, struct mount, mnt_hash);
+		child->mnt_parent->mnt_ns->pending_mounts = 0;
+		umount_tree(child, UMOUNT_SYNC);
+	}
+	unlock_mount_hash();
+	cleanup_group_ids(source_mnt, NULL);
+ out:
+	ns->pending_mounts = 0;
+
+	read_seqlock_excl(&mount_lock);
+	put_mountpoint(smp);
+	read_sequnlock_excl(&mount_lock);
+
+	return err;
+}
+
+/**
+ * do_lock_mount - lock mount and mountpoint
+ * @path:    target path
+ * @beneath: whether the intention is to mount beneath @path
+ *
+ * Follow the mount stack on @path until the top mount @mnt is found. If
+ * the initial @path->{mnt,dentry} is a mountpoint lookup the first
+ * mount stacked on top of it. Then simply follow @{mnt,mnt->mnt_root}
+ * until nothing is stacked on top of it anymore.
+ *
+ * Acquire the inode_lock() on the top mount's ->mnt_root to protect
+ * against concurrent removal of the new mountpoint from another mount
+ * namespace.
+ *
+ * If @beneath is requested, acquire inode_lock() on @mnt's mountpoint
+ * @mp on @mnt->mnt_parent must be acquired. This protects against a
+ * concurrent unlink of @mp->mnt_dentry from another mount namespace
+ * where @mnt doesn't have a child mount mounted @mp. A concurrent
+ * removal of @mnt->mnt_root doesn't matter as nothing will be mounted
+ * on top of it for @beneath.
+ *
+ * In addition, @beneath needs to make sure that @mnt hasn't been
+ * unmounted or moved from its current mountpoint in between dropping
+ * @mount_lock and acquiring @namespace_sem. For the !@beneath case @mnt
+ * being unmounted would be detected later by e.g., calling
+ * check_mnt(mnt) in the function it's called from. For the @beneath
+ * case however, it's useful to detect it directly in do_lock_mount().
+ * If @mnt hasn't been unmounted then @mnt->mnt_mountpoint still points
+ * to @mnt->mnt_mp->m_dentry. But if @mnt has been unmounted it will
+ * point to @mnt->mnt_root and @mnt->mnt_mp will be NULL.
+ *
+ * Return: Either the target mountpoint on the top mount or the top
+ *         mount's mountpoint.
+ */
+static struct mountpoint *do_lock_mount(struct path *path, bool beneath)
+{
+	struct vfsmount *mnt = path->mnt;
+	struct dentry *dentry;
+	struct mountpoint *mp = ERR_PTR(-ENOENT);
+
+	for (;;) {
+		struct mount *m;
+
+		if (beneath) {
+			m = real_mount(mnt);
+			read_seqlock_excl(&mount_lock);
+			dentry = dget(m->mnt_mountpoint);
+			read_sequnlock_excl(&mount_lock);
+		} else {
+			dentry = path->dentry;
+		}
+
+		inode_lock(dentry->d_inode);
+		if (unlikely(cant_mount(dentry))) {
+			inode_unlock(dentry->d_inode);
+			goto out;
+		}
+
+		namespace_lock();
+
+		if (beneath && (!is_mounted(mnt) || m->mnt_mountpoint != dentry)) {
+			namespace_unlock();
+			inode_unlock(dentry->d_inode);
+			goto out;
+		}
+
+		mnt = lookup_mnt(path);
+		if (likely(!mnt))
+			break;
+
+		namespace_unlock();
+		inode_unlock(dentry->d_inode);
+		if (beneath)
+			dput(dentry);
+		path_put(path);
+		path->mnt = mnt;
+		path->dentry = dget(mnt->mnt_root);
+	}
+
+	mp = get_mountpoint(dentry);
+	if (IS_ERR(mp)) {
+		namespace_unlock();
+		inode_unlock(dentry->d_inode);
+	}
+
+out:
+	if (beneath)
+		dput(dentry);
+
+	return mp;
+}
+
+static inline struct mountpoint *lock_mount(struct path *path)
+{
+	return do_lock_mount(path, false);
+}
+
+static void unlock_mount(struct mountpoint *where)
+{
+	struct dentry *dentry = where->m_dentry;
+
+	read_seqlock_excl(&mount_lock);
+	put_mountpoint(where);
+	read_sequnlock_excl(&mount_lock);
+
+	namespace_unlock();
+	inode_unlock(dentry->d_inode);
+}
+
+static int graft_tree(struct mount *mnt, struct mount *p, struct mountpoint *mp)
+{
+	if (mnt->mnt.mnt_sb->s_flags & SB_NOUSER)
+		return -EINVAL;
+
+	if (d_is_dir(mp->m_dentry) !=
+	      d_is_dir(mnt->mnt.mnt_root))
+		return -ENOTDIR;
+
+	return attach_recursive_mnt(mnt, p, mp, 0);
+}
+
+/*
+ * Sanity check the flags to change_mnt_propagation.
+ */
+
+static int flags_to_propagation_type(int ms_flags)
+{
+	int type = ms_flags & ~(MS_REC | MS_SILENT);
+
+	/* Fail if any non-propagation flags are set */
+	if (type & ~(MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
+		return 0;
+	/* Only one propagation flag should be set */
+	if (!is_power_of_2(type))
+		return 0;
+	return type;
+}
+
+/*
+ * recursively change the type of the mountpoint.
+ */
+static int do_change_type(struct path *path, int ms_flags)
+{
+	struct mount *m;
+	struct mount *mnt = real_mount(path->mnt);
+	int recurse = ms_flags & MS_REC;
+	int type;
+	int err = 0;
+
+	if (!path_mounted(path))
+		return -EINVAL;
+
+	type = flags_to_propagation_type(ms_flags);
+	if (!type)
+		return -EINVAL;
+
+	namespace_lock();
+	if (type == MS_SHARED) {
+		err = invent_group_ids(mnt, recurse);
+		if (err)
+			goto out_unlock;
+	}
+
+	lock_mount_hash();
+	for (m = mnt; m; m = (recurse ? next_mnt(m, mnt) : NULL))
+		change_mnt_propagation(m, type);
+	unlock_mount_hash();
+
+ out_unlock:
+	namespace_unlock();
+	return err;
+}
+
+static struct mount *__do_loopback(struct path *old_path, int recurse)
+{
+	struct mount *mnt = ERR_PTR(-EINVAL), *old = real_mount(old_path->mnt);
+
+	if (IS_MNT_UNBINDABLE(old))
+		return mnt;
+
+	if (!check_mnt(old) && old_path->dentry->d_op != &ns_dentry_operations)
+		return mnt;
+
+	if (!recurse && has_locked_children(old, old_path->dentry))
+		return mnt;
+
+	if (recurse)
+		mnt = copy_tree(old, old_path->dentry, CL_COPY_MNT_NS_FILE);
+	else
+		mnt = clone_mnt(old, old_path->dentry, 0);
+
+	if (!IS_ERR(mnt))
+		mnt->mnt.mnt_flags &= ~MNT_LOCKED;
+
+	return mnt;
+}
+
+/*
+ * do loopback mount.
+ */
+static int do_loopback(struct path *path, const char *old_name,
+				int recurse)
+{
+	struct path old_path;
+	struct mount *mnt = NULL, *parent;
+	struct mountpoint *mp;
+	int err;
+	if (!old_name || !*old_name)
+		return -EINVAL;
+	err = kern_path(old_name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &old_path);
+	if (err)
+		return err;
+
+	err = -EINVAL;
+	if (mnt_ns_loop(old_path.dentry))
+		goto out;
+
+	mp = lock_mount(path);
+	if (IS_ERR(mp)) {
+		err = PTR_ERR(mp);
+		goto out;
+	}
+
+	parent = real_mount(path->mnt);
+	if (!check_mnt(parent))
+		goto out2;
+
+	mnt = __do_loopback(&old_path, recurse);
+	if (IS_ERR(mnt)) {
+		err = PTR_ERR(mnt);
+		goto out2;
+	}
+
+	err = graft_tree(mnt, parent, mp);
+	if (err) {
+		lock_mount_hash();
+		umount_tree(mnt, UMOUNT_SYNC);
+		unlock_mount_hash();
+	}
+out2:
+	unlock_mount(mp);
+out:
+	path_put(&old_path);
+	return err;
+}
+
+static struct file *open_detached_copy(struct path *path, bool recursive)
+{
+	struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns;
+	struct mnt_namespace *ns = alloc_mnt_ns(user_ns, true);
+	struct mount *mnt, *p;
+	struct file *file;
+
+	if (IS_ERR(ns))
+		return ERR_CAST(ns);
+
+	namespace_lock();
+	mnt = __do_loopback(path, recursive);
+	if (IS_ERR(mnt)) {
+		namespace_unlock();
+		free_mnt_ns(ns);
+		return ERR_CAST(mnt);
+	}
+
+	lock_mount_hash();
+	for (p = mnt; p; p = next_mnt(p, mnt)) {
+		p->mnt_ns = ns;
+		ns->mounts++;
+	}
+	ns->root = mnt;
+	list_add_tail(&ns->list, &mnt->mnt_list);
+	mntget(&mnt->mnt);
+	unlock_mount_hash();
+	namespace_unlock();
+
+	mntput(path->mnt);
+	path->mnt = &mnt->mnt;
+	file = dentry_open(path, O_PATH, current_cred());
+	if (IS_ERR(file))
+		dissolve_on_fput(path->mnt);
+	else
+		file->f_mode |= FMODE_NEED_UNMOUNT;
+	return file;
+}
+
+SYSCALL_DEFINE3(open_tree, int, dfd, const char __user *, filename, unsigned, flags)
+{
+	struct file *file;
+	struct path path;
+	int lookup_flags = LOOKUP_AUTOMOUNT | LOOKUP_FOLLOW;
+	bool detached = flags & OPEN_TREE_CLONE;
+	int error;
+	int fd;
+
+	BUILD_BUG_ON(OPEN_TREE_CLOEXEC != O_CLOEXEC);
+
+	if (flags & ~(AT_EMPTY_PATH | AT_NO_AUTOMOUNT | AT_RECURSIVE |
+		      AT_SYMLINK_NOFOLLOW | OPEN_TREE_CLONE |
+		      OPEN_TREE_CLOEXEC))
+		return -EINVAL;
+
+	if ((flags & (AT_RECURSIVE | OPEN_TREE_CLONE)) == AT_RECURSIVE)
+		return -EINVAL;
+
+	if (flags & AT_NO_AUTOMOUNT)
+		lookup_flags &= ~LOOKUP_AUTOMOUNT;
+	if (flags & AT_SYMLINK_NOFOLLOW)
+		lookup_flags &= ~LOOKUP_FOLLOW;
+	if (flags & AT_EMPTY_PATH)
+		lookup_flags |= LOOKUP_EMPTY;
+
+	if (detached && !may_mount())
+		return -EPERM;
+
+	fd = get_unused_fd_flags(flags & O_CLOEXEC);
+	if (fd < 0)
+		return fd;
+
+	error = user_path_at(dfd, filename, lookup_flags, &path);
+	if (unlikely(error)) {
+		file = ERR_PTR(error);
+	} else {
+		if (detached)
+			file = open_detached_copy(&path, flags & AT_RECURSIVE);
+		else
+			file = dentry_open(&path, O_PATH, current_cred());
+		path_put(&path);
+	}
+	if (IS_ERR(file)) {
+		put_unused_fd(fd);
+		return PTR_ERR(file);
+	}
+	fd_install(fd, file);
+	return fd;
+}
+
+/*
+ * Don't allow locked mount flags to be cleared.
+ *
+ * No locks need to be held here while testing the various MNT_LOCK
+ * flags because those flags can never be cleared once they are set.
+ */
+static bool can_change_locked_flags(struct mount *mnt, unsigned int mnt_flags)
+{
+	unsigned int fl = mnt->mnt.mnt_flags;
+
+	if ((fl & MNT_LOCK_READONLY) &&
+	    !(mnt_flags & MNT_READONLY))
+		return false;
+
+	if ((fl & MNT_LOCK_NODEV) &&
+	    !(mnt_flags & MNT_NODEV))
+		return false;
+
+	if ((fl & MNT_LOCK_NOSUID) &&
+	    !(mnt_flags & MNT_NOSUID))
+		return false;
+
+	if ((fl & MNT_LOCK_NOEXEC) &&
+	    !(mnt_flags & MNT_NOEXEC))
+		return false;
+
+	if ((fl & MNT_LOCK_ATIME) &&
+	    ((fl & MNT_ATIME_MASK) != (mnt_flags & MNT_ATIME_MASK)))
+		return false;
+
+	return true;
+}
+
+static int change_mount_ro_state(struct mount *mnt, unsigned int mnt_flags)
+{
+	bool readonly_request = (mnt_flags & MNT_READONLY);
+
+	if (readonly_request == __mnt_is_readonly(&mnt->mnt))
+		return 0;
+
+	if (readonly_request)
+		return mnt_make_readonly(mnt);
+
+	mnt->mnt.mnt_flags &= ~MNT_READONLY;
+	return 0;
+}
+
+static void set_mount_attributes(struct mount *mnt, unsigned int mnt_flags)
+{
+	mnt_flags |= mnt->mnt.mnt_flags & ~MNT_USER_SETTABLE_MASK;
+	mnt->mnt.mnt_flags = mnt_flags;
+	touch_mnt_namespace(mnt->mnt_ns);
+}
+
+static void mnt_warn_timestamp_expiry(struct path *mountpoint, struct vfsmount *mnt)
+{
+	struct super_block *sb = mnt->mnt_sb;
+
+	if (!__mnt_is_readonly(mnt) &&
+	   (!(sb->s_iflags & SB_I_TS_EXPIRY_WARNED)) &&
+	   (ktime_get_real_seconds() + TIME_UPTIME_SEC_MAX > sb->s_time_max)) {
+		char *buf = (char *)__get_free_page(GFP_KERNEL);
+		char *mntpath = buf ? d_path(mountpoint, buf, PAGE_SIZE) : ERR_PTR(-ENOMEM);
+
+		pr_warn("%s filesystem being %s at %s supports timestamps until %ptTd (0x%llx)\n",
+			sb->s_type->name,
+			is_mounted(mnt) ? "remounted" : "mounted",
+			mntpath, &sb->s_time_max,
+			(unsigned long long)sb->s_time_max);
+
+		free_page((unsigned long)buf);
+		sb->s_iflags |= SB_I_TS_EXPIRY_WARNED;
+	}
+}
+
+/*
+ * Handle reconfiguration of the mountpoint only without alteration of the
+ * superblock it refers to.  This is triggered by specifying MS_REMOUNT|MS_BIND
+ * to mount(2).
+ */
+static int do_reconfigure_mnt(struct path *path, unsigned int mnt_flags)
+{
+	struct super_block *sb = path->mnt->mnt_sb;
+	struct mount *mnt = real_mount(path->mnt);
+	int ret;
+
+	if (!check_mnt(mnt))
+		return -EINVAL;
+
+	if (!path_mounted(path))
+		return -EINVAL;
+
+	if (!can_change_locked_flags(mnt, mnt_flags))
+		return -EPERM;
+
+	/*
+	 * We're only checking whether the superblock is read-only not
+	 * changing it, so only take down_read(&sb->s_umount).
+	 */
+	down_read(&sb->s_umount);
+	lock_mount_hash();
+	ret = change_mount_ro_state(mnt, mnt_flags);
+	if (ret == 0)
+		set_mount_attributes(mnt, mnt_flags);
+	unlock_mount_hash();
+	up_read(&sb->s_umount);
+
+	mnt_warn_timestamp_expiry(path, &mnt->mnt);
+
+	return ret;
+}
+
+/*
+ * change filesystem flags. dir should be a physical root of filesystem.
+ * If you've mounted a non-root directory somewhere and want to do remount
+ * on it - tough luck.
+ */
+static int do_remount(struct path *path, int ms_flags, int sb_flags,
+		      int mnt_flags, void *data)
+{
+	int err;
+	struct super_block *sb = path->mnt->mnt_sb;
+	struct mount *mnt = real_mount(path->mnt);
+	struct fs_context *fc;
+
+	if (!check_mnt(mnt))
+		return -EINVAL;
+
+	if (!path_mounted(path))
+		return -EINVAL;
+
+	if (!can_change_locked_flags(mnt, mnt_flags))
+		return -EPERM;
+
+	fc = fs_context_for_reconfigure(path->dentry, sb_flags, MS_RMT_MASK);
+	if (IS_ERR(fc))
+		return PTR_ERR(fc);
+
+	/*
+	 * Indicate to the filesystem that the remount request is coming
+	 * from the legacy mount system call.
+	 */
+	fc->oldapi = true;
+
+	err = parse_monolithic_mount_data(fc, data);
+	if (!err) {
+		down_write(&sb->s_umount);
+		err = -EPERM;
+		if (ns_capable(sb->s_user_ns, CAP_SYS_ADMIN)) {
+			err = reconfigure_super(fc);
+			if (!err) {
+				lock_mount_hash();
+				set_mount_attributes(mnt, mnt_flags);
+				unlock_mount_hash();
+			}
+		}
+		up_write(&sb->s_umount);
+	}
+
+	mnt_warn_timestamp_expiry(path, &mnt->mnt);
+
+	put_fs_context(fc);
+	return err;
+}
+
+static inline int tree_contains_unbindable(struct mount *mnt)
+{
+	struct mount *p;
+	for (p = mnt; p; p = next_mnt(p, mnt)) {
+		if (IS_MNT_UNBINDABLE(p))
+			return 1;
+	}
+	return 0;
+}
+
+/*
+ * Check that there aren't references to earlier/same mount namespaces in the
+ * specified subtree.  Such references can act as pins for mount namespaces
+ * that aren't checked by the mount-cycle checking code, thereby allowing
+ * cycles to be made.
+ */
+static bool check_for_nsfs_mounts(struct mount *subtree)
+{
+	struct mount *p;
+	bool ret = false;
+
+	lock_mount_hash();
+	for (p = subtree; p; p = next_mnt(p, subtree))
+		if (mnt_ns_loop(p->mnt.mnt_root))
+			goto out;
+
+	ret = true;
+out:
+	unlock_mount_hash();
+	return ret;
+}
+
+static int do_set_group(struct path *from_path, struct path *to_path)
+{
+	struct mount *from, *to;
+	int err;
+
+	from = real_mount(from_path->mnt);
+	to = real_mount(to_path->mnt);
+
+	namespace_lock();
+
+	err = -EINVAL;
+	/* To and From must be mounted */
+	if (!is_mounted(&from->mnt))
+		goto out;
+	if (!is_mounted(&to->mnt))
+		goto out;
+
+	err = -EPERM;
+	/* We should be allowed to modify mount namespaces of both mounts */
+	if (!ns_capable(from->mnt_ns->user_ns, CAP_SYS_ADMIN))
+		goto out;
+	if (!ns_capable(to->mnt_ns->user_ns, CAP_SYS_ADMIN))
+		goto out;
+
+	err = -EINVAL;
+	/* To and From paths should be mount roots */
+	if (!path_mounted(from_path))
+		goto out;
+	if (!path_mounted(to_path))
+		goto out;
+
+	/* Setting sharing groups is only allowed across same superblock */
+	if (from->mnt.mnt_sb != to->mnt.mnt_sb)
+		goto out;
+
+	/* From mount root should be wider than To mount root */
+	if (!is_subdir(to->mnt.mnt_root, from->mnt.mnt_root))
+		goto out;
+
+	/* From mount should not have locked children in place of To's root */
+	if (has_locked_children(from, to->mnt.mnt_root))
+		goto out;
+
+	/* Setting sharing groups is only allowed on private mounts */
+	if (IS_MNT_SHARED(to) || IS_MNT_SLAVE(to))
+		goto out;
+
+	/* From should not be private */
+	if (!IS_MNT_SHARED(from) && !IS_MNT_SLAVE(from))
+		goto out;
+
+	if (IS_MNT_SLAVE(from)) {
+		struct mount *m = from->mnt_master;
+
+		list_add(&to->mnt_slave, &m->mnt_slave_list);
+		to->mnt_master = m;
+	}
+
+	if (IS_MNT_SHARED(from)) {
+		to->mnt_group_id = from->mnt_group_id;
+		list_add(&to->mnt_share, &from->mnt_share);
+		lock_mount_hash();
+		set_mnt_shared(to);
+		unlock_mount_hash();
+	}
+
+	err = 0;
+out:
+	namespace_unlock();
+	return err;
+}
+
+/**
+ * path_overmounted - check if path is overmounted
+ * @path: path to check
+ *
+ * Check if path is overmounted, i.e., if there's a mount on top of
+ * @path->mnt with @path->dentry as mountpoint.
+ *
+ * Context: This function expects namespace_lock() to be held.
+ * Return: If path is overmounted true is returned, false if not.
+ */
+static inline bool path_overmounted(const struct path *path)
+{
+	rcu_read_lock();
+	if (unlikely(__lookup_mnt(path->mnt, path->dentry))) {
+		rcu_read_unlock();
+		return true;
+	}
+	rcu_read_unlock();
+	return false;
+}
+
+/**
+ * can_move_mount_beneath - check that we can mount beneath the top mount
+ * @from: mount to mount beneath
+ * @to:   mount under which to mount
+ *
+ * - Make sure that @to->dentry is actually the root of a mount under
+ *   which we can mount another mount.
+ * - Make sure that nothing can be mounted beneath the caller's current
+ *   root or the rootfs of the namespace.
+ * - Make sure that the caller can unmount the topmost mount ensuring
+ *   that the caller could reveal the underlying mountpoint.
+ * - Ensure that nothing has been mounted on top of @from before we
+ *   grabbed @namespace_sem to avoid creating pointless shadow mounts.
+ * - Prevent mounting beneath a mount if the propagation relationship
+ *   between the source mount, parent mount, and top mount would lead to
+ *   nonsensical mount trees.
+ *
+ * Context: This function expects namespace_lock() to be held.
+ * Return: On success 0, and on error a negative error code is returned.
+ */
+static int can_move_mount_beneath(const struct path *from,
+				  const struct path *to,
+				  const struct mountpoint *mp)
+{
+	struct mount *mnt_from = real_mount(from->mnt),
+		     *mnt_to = real_mount(to->mnt),
+		     *parent_mnt_to = mnt_to->mnt_parent;
+
+	if (!mnt_has_parent(mnt_to))
+		return -EINVAL;
+
+	if (!path_mounted(to))
+		return -EINVAL;
+
+	if (IS_MNT_LOCKED(mnt_to))
+		return -EINVAL;
+
+	/* Avoid creating shadow mounts during mount propagation. */
+	if (path_overmounted(from))
+		return -EINVAL;
+
+	/*
+	 * Mounting beneath the rootfs only makes sense when the
+	 * semantics of pivot_root(".", ".") are used.
+	 */
+	if (&mnt_to->mnt == current->fs->root.mnt)
+		return -EINVAL;
+	if (parent_mnt_to == current->nsproxy->mnt_ns->root)
+		return -EINVAL;
+
+	for (struct mount *p = mnt_from; mnt_has_parent(p); p = p->mnt_parent)
+		if (p == mnt_to)
+			return -EINVAL;
+
+	/*
+	 * If the parent mount propagates to the child mount this would
+	 * mean mounting @mnt_from on @mnt_to->mnt_parent and then
+	 * propagating a copy @c of @mnt_from on top of @mnt_to. This
+	 * defeats the whole purpose of mounting beneath another mount.
+	 */
+	if (propagation_would_overmount(parent_mnt_to, mnt_to, mp))
+		return -EINVAL;
+
+	/*
+	 * If @mnt_to->mnt_parent propagates to @mnt_from this would
+	 * mean propagating a copy @c of @mnt_from on top of @mnt_from.
+	 * Afterwards @mnt_from would be mounted on top of
+	 * @mnt_to->mnt_parent and @mnt_to would be unmounted from
+	 * @mnt->mnt_parent and remounted on @mnt_from. But since @c is
+	 * already mounted on @mnt_from, @mnt_to would ultimately be
+	 * remounted on top of @c. Afterwards, @mnt_from would be
+	 * covered by a copy @c of @mnt_from and @c would be covered by
+	 * @mnt_from itself. This defeats the whole purpose of mounting
+	 * @mnt_from beneath @mnt_to.
+	 */
+	if (propagation_would_overmount(parent_mnt_to, mnt_from, mp))
+		return -EINVAL;
+
+	return 0;
+}
+
+static int do_move_mount(struct path *old_path, struct path *new_path,
+			 bool beneath)
+{
+	struct mnt_namespace *ns;
+	struct mount *p;
+	struct mount *old;
+	struct mount *parent;
+	struct mountpoint *mp, *old_mp;
+	int err;
+	bool attached;
+	enum mnt_tree_flags_t flags = 0;
+
+	mp = do_lock_mount(new_path, beneath);
+	if (IS_ERR(mp))
+		return PTR_ERR(mp);
+
+	old = real_mount(old_path->mnt);
+	p = real_mount(new_path->mnt);
+	parent = old->mnt_parent;
+	attached = mnt_has_parent(old);
+	if (attached)
+		flags |= MNT_TREE_MOVE;
+	old_mp = old->mnt_mp;
+	ns = old->mnt_ns;
+
+	err = -EINVAL;
+	/* The mountpoint must be in our namespace. */
+	if (!check_mnt(p))
+		goto out;
+
+	/* The thing moved must be mounted... */
+	if (!is_mounted(&old->mnt))
+		goto out;
+
+	/* ... and either ours or the root of anon namespace */
+	if (!(attached ? check_mnt(old) : is_anon_ns(ns)))
+		goto out;
+
+	if (old->mnt.mnt_flags & MNT_LOCKED)
+		goto out;
+
+	if (!path_mounted(old_path))
+		goto out;
+
+	if (d_is_dir(new_path->dentry) !=
+	    d_is_dir(old_path->dentry))
+		goto out;
+	/*
+	 * Don't move a mount residing in a shared parent.
+	 */
+	if (attached && IS_MNT_SHARED(parent))
+		goto out;
+
+	if (beneath) {
+		err = can_move_mount_beneath(old_path, new_path, mp);
+		if (err)
+			goto out;
+
+		err = -EINVAL;
+		p = p->mnt_parent;
+		flags |= MNT_TREE_BENEATH;
+	}
+
+	/*
+	 * Don't move a mount tree containing unbindable mounts to a destination
+	 * mount which is shared.
+	 */
+	if (IS_MNT_SHARED(p) && tree_contains_unbindable(old))
+		goto out;
+	err = -ELOOP;
+	if (!check_for_nsfs_mounts(old))
+		goto out;
+	for (; mnt_has_parent(p); p = p->mnt_parent)
+		if (p == old)
+			goto out;
+
+	err = attach_recursive_mnt(old, real_mount(new_path->mnt), mp, flags);
+	if (err)
+		goto out;
+
+	/* if the mount is moved, it should no longer be expire
+	 * automatically */
+	list_del_init(&old->mnt_expire);
+	if (attached)
+		put_mountpoint(old_mp);
+out:
+	unlock_mount(mp);
+	if (!err) {
+		if (attached)
+			mntput_no_expire(parent);
+		else
+			free_mnt_ns(ns);
+	}
+	return err;
+}
+
+static int do_move_mount_old(struct path *path, const char *old_name)
+{
+	struct path old_path;
+	int err;
+
+	if (!old_name || !*old_name)
+		return -EINVAL;
+
+	err = kern_path(old_name, LOOKUP_FOLLOW, &old_path);
+	if (err)
+		return err;
+
+	err = do_move_mount(&old_path, path, false);
+	path_put(&old_path);
+	return err;
+}
+
+/*
+ * add a mount into a namespace's mount tree
+ */
+static int do_add_mount(struct mount *newmnt, struct mountpoint *mp,
+			const struct path *path, int mnt_flags)
+{
+	struct mount *parent = real_mount(path->mnt);
+
+	mnt_flags &= ~MNT_INTERNAL_FLAGS;
+
+	if (unlikely(!check_mnt(parent))) {
+		/* that's acceptable only for automounts done in private ns */
+		if (!(mnt_flags & MNT_SHRINKABLE))
+			return -EINVAL;
+		/* ... and for those we'd better have mountpoint still alive */
+		if (!parent->mnt_ns)
+			return -EINVAL;
+	}
+
+	/* Refuse the same filesystem on the same mount point */
+	if (path->mnt->mnt_sb == newmnt->mnt.mnt_sb && path_mounted(path))
+		return -EBUSY;
+
+	if (d_is_symlink(newmnt->mnt.mnt_root))
+		return -EINVAL;
+
+	newmnt->mnt.mnt_flags = mnt_flags;
+	return graft_tree(newmnt, parent, mp);
+}
+
+static bool mount_too_revealing(const struct super_block *sb, int *new_mnt_flags);
+
+/*
+ * Create a new mount using a superblock configuration and request it
+ * be added to the namespace tree.
+ */
+static int do_new_mount_fc(struct fs_context *fc, struct path *mountpoint,
+			   unsigned int mnt_flags)
+{
+	struct vfsmount *mnt;
+	struct mountpoint *mp;
+	struct super_block *sb = fc->root->d_sb;
+	int error;
+
+	error = security_sb_kern_mount(sb);
+	if (!error && mount_too_revealing(sb, &mnt_flags))
+		error = -EPERM;
+
+	if (unlikely(error)) {
+		fc_drop_locked(fc);
+		return error;
+	}
+
+	up_write(&sb->s_umount);
+
+	mnt = vfs_create_mount(fc);
+	if (IS_ERR(mnt))
+		return PTR_ERR(mnt);
+
+	mnt_warn_timestamp_expiry(mountpoint, mnt);
+
+	mp = lock_mount(mountpoint);
+	if (IS_ERR(mp)) {
+		mntput(mnt);
+		return PTR_ERR(mp);
+	}
+	error = do_add_mount(real_mount(mnt), mp, mountpoint, mnt_flags);
+	unlock_mount(mp);
+	if (error < 0)
+		mntput(mnt);
+	return error;
+}
+
+/*
+ * create a new mount for userspace and request it to be added into the
+ * namespace's tree
+ */
+static int do_new_mount(struct path *path, const char *fstype, int sb_flags,
+			int mnt_flags, const char *name, void *data)
+{
+	struct file_system_type *type;
+	struct fs_context *fc;
+	const char *subtype = NULL;
+	int err = 0;
+
+	if (!fstype)
+		return -EINVAL;
+
+	type = get_fs_type(fstype);
+	if (!type)
+		return -ENODEV;
+
+	if (type->fs_flags & FS_HAS_SUBTYPE) {
+		subtype = strchr(fstype, '.');
+		if (subtype) {
+			subtype++;
+			if (!*subtype) {
+				put_filesystem(type);
+				return -EINVAL;
+			}
+		}
+	}
+
+	fc = fs_context_for_mount(type, sb_flags);
+	put_filesystem(type);
+	if (IS_ERR(fc))
+		return PTR_ERR(fc);
+
+	/*
+	 * Indicate to the filesystem that the mount request is coming
+	 * from the legacy mount system call.
+	 */
+	fc->oldapi = true;
+
+	if (subtype)
+		err = vfs_parse_fs_string(fc, "subtype",
+					  subtype, strlen(subtype));
+	if (!err && name)
+		err = vfs_parse_fs_string(fc, "source", name, strlen(name));
+	if (!err)
+		err = parse_monolithic_mount_data(fc, data);
+	if (!err && !mount_capable(fc))
+		err = -EPERM;
+	if (!err)
+		err = vfs_get_tree(fc);
+	if (!err)
+		err = do_new_mount_fc(fc, path, mnt_flags);
+
+	put_fs_context(fc);
+	return err;
+}
+
+int finish_automount(struct vfsmount *m, const struct path *path)
+{
+	struct dentry *dentry = path->dentry;
+	struct mountpoint *mp;
+	struct mount *mnt;
+	int err;
+
+	if (!m)
+		return 0;
+	if (IS_ERR(m))
+		return PTR_ERR(m);
+
+	mnt = real_mount(m);
+	/* The new mount record should have at least 2 refs to prevent it being
+	 * expired before we get a chance to add it
+	 */
+	BUG_ON(mnt_get_count(mnt) < 2);
+
+	if (m->mnt_sb == path->mnt->mnt_sb &&
+	    m->mnt_root == dentry) {
+		err = -ELOOP;
+		goto discard;
+	}
+
+	/*
+	 * we don't want to use lock_mount() - in this case finding something
+	 * that overmounts our mountpoint to be means "quitely drop what we've
+	 * got", not "try to mount it on top".
+	 */
+	inode_lock(dentry->d_inode);
+	namespace_lock();
+	if (unlikely(cant_mount(dentry))) {
+		err = -ENOENT;
+		goto discard_locked;
+	}
+	if (path_overmounted(path)) {
+		err = 0;
+		goto discard_locked;
+	}
+	mp = get_mountpoint(dentry);
+	if (IS_ERR(mp)) {
+		err = PTR_ERR(mp);
+		goto discard_locked;
+	}
+
+	err = do_add_mount(mnt, mp, path, path->mnt->mnt_flags | MNT_SHRINKABLE);
+	unlock_mount(mp);
+	if (unlikely(err))
+		goto discard;
+	mntput(m);
+	return 0;
+
+discard_locked:
+	namespace_unlock();
+	inode_unlock(dentry->d_inode);
+discard:
+	/* remove m from any expiration list it may be on */
+	if (!list_empty(&mnt->mnt_expire)) {
+		namespace_lock();
+		list_del_init(&mnt->mnt_expire);
+		namespace_unlock();
+	}
+	mntput(m);
+	mntput(m);
+	return err;
+}
+
+/**
+ * mnt_set_expiry - Put a mount on an expiration list
+ * @mnt: The mount to list.
+ * @expiry_list: The list to add the mount to.
+ */
+void mnt_set_expiry(struct vfsmount *mnt, struct list_head *expiry_list)
+{
+	namespace_lock();
+
+	list_add_tail(&real_mount(mnt)->mnt_expire, expiry_list);
+
+	namespace_unlock();
+}
+EXPORT_SYMBOL(mnt_set_expiry);
+
+/*
+ * process a list of expirable mountpoints with the intent of discarding any
+ * mountpoints that aren't in use and haven't been touched since last we came
+ * here
+ */
+void mark_mounts_for_expiry(struct list_head *mounts)
+{
+	struct mount *mnt, *next;
+	LIST_HEAD(graveyard);
+
+	if (list_empty(mounts))
+		return;
+
+	namespace_lock();
+	lock_mount_hash();
+
+	/* extract from the expiration list every vfsmount that matches the
+	 * following criteria:
+	 * - only referenced by its parent vfsmount
+	 * - still marked for expiry (marked on the last call here; marks are
+	 *   cleared by mntput())
+	 */
+	list_for_each_entry_safe(mnt, next, mounts, mnt_expire) {
+		if (!xchg(&mnt->mnt_expiry_mark, 1) ||
+			propagate_mount_busy(mnt, 1))
+			continue;
+		list_move(&mnt->mnt_expire, &graveyard);
+	}
+	while (!list_empty(&graveyard)) {
+		mnt = list_first_entry(&graveyard, struct mount, mnt_expire);
+		touch_mnt_namespace(mnt->mnt_ns);
+		umount_tree(mnt, UMOUNT_PROPAGATE|UMOUNT_SYNC);
+	}
+	unlock_mount_hash();
+	namespace_unlock();
+}
+
+EXPORT_SYMBOL_GPL(mark_mounts_for_expiry);
+
+/*
+ * Ripoff of 'select_parent()'
+ *
+ * search the list of submounts for a given mountpoint, and move any
+ * shrinkable submounts to the 'graveyard' list.
+ */
+static int select_submounts(struct mount *parent, struct list_head *graveyard)
+{
+	struct mount *this_parent = parent;
+	struct list_head *next;
+	int found = 0;
+
+repeat:
+	next = this_parent->mnt_mounts.next;
+resume:
+	while (next != &this_parent->mnt_mounts) {
+		struct list_head *tmp = next;
+		struct mount *mnt = list_entry(tmp, struct mount, mnt_child);
+
+		next = tmp->next;
+		if (!(mnt->mnt.mnt_flags & MNT_SHRINKABLE))
+			continue;
+		/*
+		 * Descend a level if the d_mounts list is non-empty.
+		 */
+		if (!list_empty(&mnt->mnt_mounts)) {
+			this_parent = mnt;
+			goto repeat;
+		}
+
+		if (!propagate_mount_busy(mnt, 1)) {
+			list_move_tail(&mnt->mnt_expire, graveyard);
+			found++;
+		}
+	}
+	/*
+	 * All done at this level ... ascend and resume the search
+	 */
+	if (this_parent != parent) {
+		next = this_parent->mnt_child.next;
+		this_parent = this_parent->mnt_parent;
+		goto resume;
+	}
+	return found;
+}
+
+/*
+ * process a list of expirable mountpoints with the intent of discarding any
+ * submounts of a specific parent mountpoint
+ *
+ * mount_lock must be held for write
+ */
+static void shrink_submounts(struct mount *mnt)
+{
+	LIST_HEAD(graveyard);
+	struct mount *m;
+
+	/* extract submounts of 'mountpoint' from the expiration list */
+	while (select_submounts(mnt, &graveyard)) {
+		while (!list_empty(&graveyard)) {
+			m = list_first_entry(&graveyard, struct mount,
+						mnt_expire);
+			touch_mnt_namespace(m->mnt_ns);
+			umount_tree(m, UMOUNT_PROPAGATE|UMOUNT_SYNC);
+		}
+	}
+}
+
+static void *copy_mount_options(const void __user * data)
+{
+	char *copy;
+	unsigned left, offset;
+
+	if (!data)
+		return NULL;
+
+	copy = kmalloc(PAGE_SIZE, GFP_KERNEL);
+	if (!copy)
+		return ERR_PTR(-ENOMEM);
+
+	left = copy_from_user(copy, data, PAGE_SIZE);
+
+	/*
+	 * Not all architectures have an exact copy_from_user(). Resort to
+	 * byte at a time.
+	 */
+	offset = PAGE_SIZE - left;
+	while (left) {
+		char c;
+		if (get_user(c, (const char __user *)data + offset))
+			break;
+		copy[offset] = c;
+		left--;
+		offset++;
+	}
+
+	if (left == PAGE_SIZE) {
+		kfree(copy);
+		return ERR_PTR(-EFAULT);
+	}
+
+	return copy;
+}
+
+static char *copy_mount_string(const void __user *data)
+{
+	return data ? strndup_user(data, PATH_MAX) : NULL;
+}
+
+/*
+ * Flags is a 32-bit value that allows up to 31 non-fs dependent flags to
+ * be given to the mount() call (ie: read-only, no-dev, no-suid etc).
+ *
+ * data is a (void *) that can point to any structure up to
+ * PAGE_SIZE-1 bytes, which can contain arbitrary fs-dependent
+ * information (or be NULL).
+ *
+ * Pre-0.97 versions of mount() didn't have a flags word.
+ * When the flags word was introduced its top half was required
+ * to have the magic value 0xC0ED, and this remained so until 2.4.0-test9.
+ * Therefore, if this magic number is present, it carries no information
+ * and must be discarded.
+ */
+int path_mount(const char *dev_name, struct path *path,
+		const char *type_page, unsigned long flags, void *data_page)
+{
+	unsigned int mnt_flags = 0, sb_flags;
+	int ret;
+
+	/* Discard magic */
+	if ((flags & MS_MGC_MSK) == MS_MGC_VAL)
+		flags &= ~MS_MGC_MSK;
+
+	/* Basic sanity checks */
+	if (data_page)
+		((char *)data_page)[PAGE_SIZE - 1] = 0;
+
+	if (flags & MS_NOUSER)
+		return -EINVAL;
+
+	ret = security_sb_mount(dev_name, path, type_page, flags, data_page);
+	if (ret)
+		return ret;
+	if (!may_mount())
+		return -EPERM;
+	if (flags & SB_MANDLOCK)
+		warn_mandlock();
+
+	/* Default to relatime unless overriden */
+	if (!(flags & MS_NOATIME))
+		mnt_flags |= MNT_RELATIME;
+
+	/* Separate the per-mountpoint flags */
+	if (flags & MS_NOSUID)
+		mnt_flags |= MNT_NOSUID;
+	if (flags & MS_NODEV)
+		mnt_flags |= MNT_NODEV;
+	if (flags & MS_NOEXEC)
+		mnt_flags |= MNT_NOEXEC;
+	if (flags & MS_NOATIME)
+		mnt_flags |= MNT_NOATIME;
+	if (flags & MS_NODIRATIME)
+		mnt_flags |= MNT_NODIRATIME;
+	if (flags & MS_STRICTATIME)
+		mnt_flags &= ~(MNT_RELATIME | MNT_NOATIME);
+	if (flags & MS_RDONLY)
+		mnt_flags |= MNT_READONLY;
+	if (flags & MS_NOSYMFOLLOW)
+		mnt_flags |= MNT_NOSYMFOLLOW;
+
+	/* The default atime for remount is preservation */
+	if ((flags & MS_REMOUNT) &&
+	    ((flags & (MS_NOATIME | MS_NODIRATIME | MS_RELATIME |
+		       MS_STRICTATIME)) == 0)) {
+		mnt_flags &= ~MNT_ATIME_MASK;
+		mnt_flags |= path->mnt->mnt_flags & MNT_ATIME_MASK;
+	}
+
+	sb_flags = flags & (SB_RDONLY |
+			    SB_SYNCHRONOUS |
+			    SB_MANDLOCK |
+			    SB_DIRSYNC |
+			    SB_SILENT |
+			    SB_POSIXACL |
+			    SB_LAZYTIME |
+			    SB_I_VERSION);
+
+	if ((flags & (MS_REMOUNT | MS_BIND)) == (MS_REMOUNT | MS_BIND))
+		return do_reconfigure_mnt(path, mnt_flags);
+	if (flags & MS_REMOUNT)
+		return do_remount(path, flags, sb_flags, mnt_flags, data_page);
+	if (flags & MS_BIND)
+		return do_loopback(path, dev_name, flags & MS_REC);
+	if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
+		return do_change_type(path, flags);
+	if (flags & MS_MOVE)
+		return do_move_mount_old(path, dev_name);
+
+	return do_new_mount(path, type_page, sb_flags, mnt_flags, dev_name,
+			    data_page);
+}
+
+long do_mount(const char *dev_name, const char __user *dir_name,
+		const char *type_page, unsigned long flags, void *data_page)
+{
+	struct path path;
+	int ret;
+
+	ret = user_path_at(AT_FDCWD, dir_name, LOOKUP_FOLLOW, &path);
+	if (ret)
+		return ret;
+	ret = path_mount(dev_name, &path, type_page, flags, data_page);
+	path_put(&path);
+	return ret;
+}
+
+static struct ucounts *inc_mnt_namespaces(struct user_namespace *ns)
+{
+	return inc_ucount(ns, current_euid(), UCOUNT_MNT_NAMESPACES);
+}
+
+static void dec_mnt_namespaces(struct ucounts *ucounts)
+{
+	dec_ucount(ucounts, UCOUNT_MNT_NAMESPACES);
+}
+
+static void free_mnt_ns(struct mnt_namespace *ns)
+{
+	if (!is_anon_ns(ns))
+		ns_free_inum(&ns->ns);
+	dec_mnt_namespaces(ns->ucounts);
+	put_user_ns(ns->user_ns);
+	kfree(ns);
+}
+
+/*
+ * Assign a sequence number so we can detect when we attempt to bind
+ * mount a reference to an older mount namespace into the current
+ * mount namespace, preventing reference counting loops.  A 64bit
+ * number incrementing at 10Ghz will take 12,427 years to wrap which
+ * is effectively never, so we can ignore the possibility.
+ */
+static atomic64_t mnt_ns_seq = ATOMIC64_INIT(1);
+
+static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns, bool anon)
+{
+	struct mnt_namespace *new_ns;
+	struct ucounts *ucounts;
+	int ret;
+
+	ucounts = inc_mnt_namespaces(user_ns);
+	if (!ucounts)
+		return ERR_PTR(-ENOSPC);
+
+	new_ns = kzalloc(sizeof(struct mnt_namespace), GFP_KERNEL_ACCOUNT);
+	if (!new_ns) {
+		dec_mnt_namespaces(ucounts);
+		return ERR_PTR(-ENOMEM);
+	}
+	if (!anon) {
+		ret = ns_alloc_inum(&new_ns->ns);
+		if (ret) {
+			kfree(new_ns);
+			dec_mnt_namespaces(ucounts);
+			return ERR_PTR(ret);
+		}
+	}
+	new_ns->ns.ops = &mntns_operations;
+	if (!anon)
+		new_ns->seq = atomic64_add_return(1, &mnt_ns_seq);
+	refcount_set(&new_ns->ns.count, 1);
+	INIT_LIST_HEAD(&new_ns->list);
+	init_waitqueue_head(&new_ns->poll);
+	spin_lock_init(&new_ns->ns_lock);
+	new_ns->user_ns = get_user_ns(user_ns);
+	new_ns->ucounts = ucounts;
+	return new_ns;
+}
+
+__latent_entropy
+struct mnt_namespace *copy_mnt_ns(unsigned long flags, struct mnt_namespace *ns,
+		struct user_namespace *user_ns, struct fs_struct *new_fs)
+{
+	struct mnt_namespace *new_ns;
+	struct vfsmount *rootmnt = NULL, *pwdmnt = NULL;
+	struct mount *p, *q;
+	struct mount *old;
+	struct mount *new;
+	int copy_flags;
+
+	BUG_ON(!ns);
+
+	if (likely(!(flags & CLONE_NEWNS))) {
+		get_mnt_ns(ns);
+		return ns;
+	}
+
+	old = ns->root;
+
+	new_ns = alloc_mnt_ns(user_ns, false);
+	if (IS_ERR(new_ns))
+		return new_ns;
+
+	namespace_lock();
+	/* First pass: copy the tree topology */
+	copy_flags = CL_COPY_UNBINDABLE | CL_EXPIRE;
+	if (user_ns != ns->user_ns)
+		copy_flags |= CL_SHARED_TO_SLAVE;
+	new = copy_tree(old, old->mnt.mnt_root, copy_flags);
+	if (IS_ERR(new)) {
+		namespace_unlock();
+		free_mnt_ns(new_ns);
+		return ERR_CAST(new);
+	}
+	if (user_ns != ns->user_ns) {
+		lock_mount_hash();
+		lock_mnt_tree(new);
+		unlock_mount_hash();
+	}
+	new_ns->root = new;
+	list_add_tail(&new_ns->list, &new->mnt_list);
+
+	/*
+	 * Second pass: switch the tsk->fs->* elements and mark new vfsmounts
+	 * as belonging to new namespace.  We have already acquired a private
+	 * fs_struct, so tsk->fs->lock is not needed.
+	 */
+	p = old;
+	q = new;
+	while (p) {
+		q->mnt_ns = new_ns;
+		new_ns->mounts++;
+		if (new_fs) {
+			if (&p->mnt == new_fs->root.mnt) {
+				new_fs->root.mnt = mntget(&q->mnt);
+				rootmnt = &p->mnt;
+			}
+			if (&p->mnt == new_fs->pwd.mnt) {
+				new_fs->pwd.mnt = mntget(&q->mnt);
+				pwdmnt = &p->mnt;
+			}
+		}
+		p = next_mnt(p, old);
+		q = next_mnt(q, new);
+		if (!q)
+			break;
+		// an mntns binding we'd skipped?
+		while (p->mnt.mnt_root != q->mnt.mnt_root)
+			p = next_mnt(skip_mnt_tree(p), old);
+	}
+	namespace_unlock();
+
+	if (rootmnt)
+		mntput(rootmnt);
+	if (pwdmnt)
+		mntput(pwdmnt);
+
+	return new_ns;
+}
+
+struct dentry *mount_subtree(struct vfsmount *m, const char *name)
+{
+	struct mount *mnt = real_mount(m);
+	struct mnt_namespace *ns;
+	struct super_block *s;
+	struct path path;
+	int err;
+
+	ns = alloc_mnt_ns(&init_user_ns, true);
+	if (IS_ERR(ns)) {
+		mntput(m);
+		return ERR_CAST(ns);
+	}
+	mnt->mnt_ns = ns;
+	ns->root = mnt;
+	ns->mounts++;
+	list_add(&mnt->mnt_list, &ns->list);
+
+	err = vfs_path_lookup(m->mnt_root, m,
+			name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &path);
+
+	put_mnt_ns(ns);
+
+	if (err)
+		return ERR_PTR(err);
+
+	/* trade a vfsmount reference for active sb one */
+	s = path.mnt->mnt_sb;
+	atomic_inc(&s->s_active);
+	mntput(path.mnt);
+	/* lock the sucker */
+	down_write(&s->s_umount);
+	/* ... and return the root of (sub)tree on it */
+	return path.dentry;
+}
+EXPORT_SYMBOL(mount_subtree);
+
+SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
+		char __user *, type, unsigned long, flags, void __user *, data)
+{
+	int ret;
+	char *kernel_type;
+	char *kernel_dev;
+	void *options;
+
+	kernel_type = copy_mount_string(type);
+	ret = PTR_ERR(kernel_type);
+	if (IS_ERR(kernel_type))
+		goto out_type;
+
+	kernel_dev = copy_mount_string(dev_name);
+	ret = PTR_ERR(kernel_dev);
+	if (IS_ERR(kernel_dev))
+		goto out_dev;
+
+	options = copy_mount_options(data);
+	ret = PTR_ERR(options);
+	if (IS_ERR(options))
+		goto out_data;
+
+	ret = do_mount(kernel_dev, dir_name, kernel_type, flags, options);
+
+	kfree(options);
+out_data:
+	kfree(kernel_dev);
+out_dev:
+	kfree(kernel_type);
+out_type:
+	return ret;
+}
+
+#define FSMOUNT_VALID_FLAGS                                                    \
+	(MOUNT_ATTR_RDONLY | MOUNT_ATTR_NOSUID | MOUNT_ATTR_NODEV |            \
+	 MOUNT_ATTR_NOEXEC | MOUNT_ATTR__ATIME | MOUNT_ATTR_NODIRATIME |       \
+	 MOUNT_ATTR_NOSYMFOLLOW)
+
+#define MOUNT_SETATTR_VALID_FLAGS (FSMOUNT_VALID_FLAGS | MOUNT_ATTR_IDMAP)
+
+#define MOUNT_SETATTR_PROPAGATION_FLAGS \
+	(MS_UNBINDABLE | MS_PRIVATE | MS_SLAVE | MS_SHARED)
+
+static unsigned int attr_flags_to_mnt_flags(u64 attr_flags)
+{
+	unsigned int mnt_flags = 0;
+
+	if (attr_flags & MOUNT_ATTR_RDONLY)
+		mnt_flags |= MNT_READONLY;
+	if (attr_flags & MOUNT_ATTR_NOSUID)
+		mnt_flags |= MNT_NOSUID;
+	if (attr_flags & MOUNT_ATTR_NODEV)
+		mnt_flags |= MNT_NODEV;
+	if (attr_flags & MOUNT_ATTR_NOEXEC)
+		mnt_flags |= MNT_NOEXEC;
+	if (attr_flags & MOUNT_ATTR_NODIRATIME)
+		mnt_flags |= MNT_NODIRATIME;
+	if (attr_flags & MOUNT_ATTR_NOSYMFOLLOW)
+		mnt_flags |= MNT_NOSYMFOLLOW;
+
+	return mnt_flags;
+}
+
+/*
+ * Create a kernel mount representation for a new, prepared superblock
+ * (specified by fs_fd) and attach to an open_tree-like file descriptor.
+ */
+SYSCALL_DEFINE3(fsmount, int, fs_fd, unsigned int, flags,
+		unsigned int, attr_flags)
+{
+	struct mnt_namespace *ns;
+	struct fs_context *fc;
+	struct file *file;
+	struct path newmount;
+	struct mount *mnt;
+	struct fd f;
+	unsigned int mnt_flags = 0;
+	long ret;
+
+	if (!may_mount())
+		return -EPERM;
+
+	if ((flags & ~(FSMOUNT_CLOEXEC)) != 0)
+		return -EINVAL;
+
+	if (attr_flags & ~FSMOUNT_VALID_FLAGS)
+		return -EINVAL;
+
+	mnt_flags = attr_flags_to_mnt_flags(attr_flags);
+
+	switch (attr_flags & MOUNT_ATTR__ATIME) {
+	case MOUNT_ATTR_STRICTATIME:
+		break;
+	case MOUNT_ATTR_NOATIME:
+		mnt_flags |= MNT_NOATIME;
+		break;
+	case MOUNT_ATTR_RELATIME:
+		mnt_flags |= MNT_RELATIME;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	f = fdget(fs_fd);
+	if (!f.file)
+		return -EBADF;
+
+	ret = -EINVAL;
+	if (f.file->f_op != &fscontext_fops)
+		goto err_fsfd;
+
+	fc = f.file->private_data;
+
+	ret = mutex_lock_interruptible(&fc->uapi_mutex);
+	if (ret < 0)
+		goto err_fsfd;
+
+	/* There must be a valid superblock or we can't mount it */
+	ret = -EINVAL;
+	if (!fc->root)
+		goto err_unlock;
+
+	ret = -EPERM;
+	if (mount_too_revealing(fc->root->d_sb, &mnt_flags)) {
+		pr_warn("VFS: Mount too revealing\n");
+		goto err_unlock;
+	}
+
+	ret = -EBUSY;
+	if (fc->phase != FS_CONTEXT_AWAITING_MOUNT)
+		goto err_unlock;
+
+	if (fc->sb_flags & SB_MANDLOCK)
+		warn_mandlock();
+
+	newmount.mnt = vfs_create_mount(fc);
+	if (IS_ERR(newmount.mnt)) {
+		ret = PTR_ERR(newmount.mnt);
+		goto err_unlock;
+	}
+	newmount.dentry = dget(fc->root);
+	newmount.mnt->mnt_flags = mnt_flags;
+
+	/* We've done the mount bit - now move the file context into more or
+	 * less the same state as if we'd done an fspick().  We don't want to
+	 * do any memory allocation or anything like that at this point as we
+	 * don't want to have to handle any errors incurred.
+	 */
+	vfs_clean_context(fc);
+
+	ns = alloc_mnt_ns(current->nsproxy->mnt_ns->user_ns, true);
+	if (IS_ERR(ns)) {
+		ret = PTR_ERR(ns);
+		goto err_path;
+	}
+	mnt = real_mount(newmount.mnt);
+	mnt->mnt_ns = ns;
+	ns->root = mnt;
+	ns->mounts = 1;
+	list_add(&mnt->mnt_list, &ns->list);
+	mntget(newmount.mnt);
+
+	/* Attach to an apparent O_PATH fd with a note that we need to unmount
+	 * it, not just simply put it.
+	 */
+	file = dentry_open(&newmount, O_PATH, fc->cred);
+	if (IS_ERR(file)) {
+		dissolve_on_fput(newmount.mnt);
+		ret = PTR_ERR(file);
+		goto err_path;
+	}
+	file->f_mode |= FMODE_NEED_UNMOUNT;
+
+	ret = get_unused_fd_flags((flags & FSMOUNT_CLOEXEC) ? O_CLOEXEC : 0);
+	if (ret >= 0)
+		fd_install(ret, file);
+	else
+		fput(file);
+
+err_path:
+	path_put(&newmount);
+err_unlock:
+	mutex_unlock(&fc->uapi_mutex);
+err_fsfd:
+	fdput(f);
+	return ret;
+}
+
+/*
+ * Move a mount from one place to another.  In combination with
+ * fsopen()/fsmount() this is used to install a new mount and in combination
+ * with open_tree(OPEN_TREE_CLONE [| AT_RECURSIVE]) it can be used to copy
+ * a mount subtree.
+ *
+ * Note the flags value is a combination of MOVE_MOUNT_* flags.
+ */
+SYSCALL_DEFINE5(move_mount,
+		int, from_dfd, const char __user *, from_pathname,
+		int, to_dfd, const char __user *, to_pathname,
+		unsigned int, flags)
+{
+	struct path from_path, to_path;
+	unsigned int lflags;
+	int ret = 0;
+
+	if (!may_mount())
+		return -EPERM;
+
+	if (flags & ~MOVE_MOUNT__MASK)
+		return -EINVAL;
+
+	if ((flags & (MOVE_MOUNT_BENEATH | MOVE_MOUNT_SET_GROUP)) ==
+	    (MOVE_MOUNT_BENEATH | MOVE_MOUNT_SET_GROUP))
+		return -EINVAL;
+
+	/* If someone gives a pathname, they aren't permitted to move
+	 * from an fd that requires unmount as we can't get at the flag
+	 * to clear it afterwards.
+	 */
+	lflags = 0;
+	if (flags & MOVE_MOUNT_F_SYMLINKS)	lflags |= LOOKUP_FOLLOW;
+	if (flags & MOVE_MOUNT_F_AUTOMOUNTS)	lflags |= LOOKUP_AUTOMOUNT;
+	if (flags & MOVE_MOUNT_F_EMPTY_PATH)	lflags |= LOOKUP_EMPTY;
+
+	ret = user_path_at(from_dfd, from_pathname, lflags, &from_path);
+	if (ret < 0)
+		return ret;
+
+	lflags = 0;
+	if (flags & MOVE_MOUNT_T_SYMLINKS)	lflags |= LOOKUP_FOLLOW;
+	if (flags & MOVE_MOUNT_T_AUTOMOUNTS)	lflags |= LOOKUP_AUTOMOUNT;
+	if (flags & MOVE_MOUNT_T_EMPTY_PATH)	lflags |= LOOKUP_EMPTY;
+
+	ret = user_path_at(to_dfd, to_pathname, lflags, &to_path);
+	if (ret < 0)
+		goto out_from;
+
+	ret = security_move_mount(&from_path, &to_path);
+	if (ret < 0)
+		goto out_to;
+
+	if (flags & MOVE_MOUNT_SET_GROUP)
+		ret = do_set_group(&from_path, &to_path);
+	else
+		ret = do_move_mount(&from_path, &to_path,
+				    (flags & MOVE_MOUNT_BENEATH));
+
+out_to:
+	path_put(&to_path);
+out_from:
+	path_put(&from_path);
+	return ret;
+}
+
+/*
+ * Return true if path is reachable from root
+ *
+ * namespace_sem or mount_lock is held
+ */
+bool is_path_reachable(struct mount *mnt, struct dentry *dentry,
+			 const struct path *root)
+{
+	while (&mnt->mnt != root->mnt && mnt_has_parent(mnt)) {
+		dentry = mnt->mnt_mountpoint;
+		mnt = mnt->mnt_parent;
+	}
+	return &mnt->mnt == root->mnt && is_subdir(dentry, root->dentry);
+}
+
+bool path_is_under(const struct path *path1, const struct path *path2)
+{
+	bool res;
+	read_seqlock_excl(&mount_lock);
+	res = is_path_reachable(real_mount(path1->mnt), path1->dentry, path2);
+	read_sequnlock_excl(&mount_lock);
+	return res;
+}
+EXPORT_SYMBOL(path_is_under);
+
+/*
+ * pivot_root Semantics:
+ * Moves the root file system of the current process to the directory put_old,
+ * makes new_root as the new root file system of the current process, and sets
+ * root/cwd of all processes which had them on the current root to new_root.
+ *
+ * Restrictions:
+ * The new_root and put_old must be directories, and  must not be on the
+ * same file  system as the current process root. The put_old  must  be
+ * underneath new_root,  i.e. adding a non-zero number of /.. to the string
+ * pointed to by put_old must yield the same directory as new_root. No other
+ * file system may be mounted on put_old. After all, new_root is a mountpoint.
+ *
+ * Also, the current root cannot be on the 'rootfs' (initial ramfs) filesystem.
+ * See Documentation/filesystems/ramfs-rootfs-initramfs.rst for alternatives
+ * in this situation.
+ *
+ * Notes:
+ *  - we don't move root/cwd if they are not at the root (reason: if something
+ *    cared enough to change them, it's probably wrong to force them elsewhere)
+ *  - it's okay to pick a root that isn't the root of a file system, e.g.
+ *    /nfs/my_root where /nfs is the mount point. It must be a mountpoint,
+ *    though, so you may need to say mount --bind /nfs/my_root /nfs/my_root
+ *    first.
+ */
+SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
+		const char __user *, put_old)
+{
+	struct path new, old, root;
+	struct mount *new_mnt, *root_mnt, *old_mnt, *root_parent, *ex_parent;
+	struct mountpoint *old_mp, *root_mp;
+	int error;
+
+	if (!may_mount())
+		return -EPERM;
+
+	error = user_path_at(AT_FDCWD, new_root,
+			     LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &new);
+	if (error)
+		goto out0;
+
+	error = user_path_at(AT_FDCWD, put_old,
+			     LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &old);
+	if (error)
+		goto out1;
+
+	error = security_sb_pivotroot(&old, &new);
+	if (error)
+		goto out2;
+
+	get_fs_root(current->fs, &root);
+	old_mp = lock_mount(&old);
+	error = PTR_ERR(old_mp);
+	if (IS_ERR(old_mp))
+		goto out3;
+
+	error = -EINVAL;
+	new_mnt = real_mount(new.mnt);
+	root_mnt = real_mount(root.mnt);
+	old_mnt = real_mount(old.mnt);
+	ex_parent = new_mnt->mnt_parent;
+	root_parent = root_mnt->mnt_parent;
+	if (IS_MNT_SHARED(old_mnt) ||
+		IS_MNT_SHARED(ex_parent) ||
+		IS_MNT_SHARED(root_parent))
+		goto out4;
+	if (!check_mnt(root_mnt) || !check_mnt(new_mnt))
+		goto out4;
+	if (new_mnt->mnt.mnt_flags & MNT_LOCKED)
+		goto out4;
+	error = -ENOENT;
+	if (d_unlinked(new.dentry))
+		goto out4;
+	error = -EBUSY;
+	if (new_mnt == root_mnt || old_mnt == root_mnt)
+		goto out4; /* loop, on the same file system  */
+	error = -EINVAL;
+	if (!path_mounted(&root))
+		goto out4; /* not a mountpoint */
+	if (!mnt_has_parent(root_mnt))
+		goto out4; /* not attached */
+	if (!path_mounted(&new))
+		goto out4; /* not a mountpoint */
+	if (!mnt_has_parent(new_mnt))
+		goto out4; /* not attached */
+	/* make sure we can reach put_old from new_root */
+	if (!is_path_reachable(old_mnt, old.dentry, &new))
+		goto out4;
+	/* make certain new is below the root */
+	if (!is_path_reachable(new_mnt, new.dentry, &root))
+		goto out4;
+	lock_mount_hash();
+	umount_mnt(new_mnt);
+	root_mp = unhash_mnt(root_mnt);  /* we'll need its mountpoint */
+	if (root_mnt->mnt.mnt_flags & MNT_LOCKED) {
+		new_mnt->mnt.mnt_flags |= MNT_LOCKED;
+		root_mnt->mnt.mnt_flags &= ~MNT_LOCKED;
+	}
+	/* mount old root on put_old */
+	attach_mnt(root_mnt, old_mnt, old_mp, false);
+	/* mount new_root on / */
+	attach_mnt(new_mnt, root_parent, root_mp, false);
+	mnt_add_count(root_parent, -1);
+	touch_mnt_namespace(current->nsproxy->mnt_ns);
+	/* A moved mount should not expire automatically */
+	list_del_init(&new_mnt->mnt_expire);
+	put_mountpoint(root_mp);
+	unlock_mount_hash();
+	chroot_fs_refs(&root, &new);
+	error = 0;
+out4:
+	unlock_mount(old_mp);
+	if (!error)
+		mntput_no_expire(ex_parent);
+out3:
+	path_put(&root);
+out2:
+	path_put(&old);
+out1:
+	path_put(&new);
+out0:
+	return error;
+}
+
+static unsigned int recalc_flags(struct mount_kattr *kattr, struct mount *mnt)
+{
+	unsigned int flags = mnt->mnt.mnt_flags;
+
+	/*  flags to clear */
+	flags &= ~kattr->attr_clr;
+	/* flags to raise */
+	flags |= kattr->attr_set;
+
+	return flags;
+}
+
+static int can_idmap_mount(const struct mount_kattr *kattr, struct mount *mnt)
+{
+	struct vfsmount *m = &mnt->mnt;
+	struct user_namespace *fs_userns = m->mnt_sb->s_user_ns;
+
+	if (!kattr->mnt_idmap)
+		return 0;
+
+	/*
+	 * Creating an idmapped mount with the filesystem wide idmapping
+	 * doesn't make sense so block that. We don't allow mushy semantics.
+	 */
+	if (!check_fsmapping(kattr->mnt_idmap, m->mnt_sb))
+		return -EINVAL;
+
+	/*
+	 * Once a mount has been idmapped we don't allow it to change its
+	 * mapping. It makes things simpler and callers can just create
+	 * another bind-mount they can idmap if they want to.
+	 */
+	if (is_idmapped_mnt(m))
+		return -EPERM;
+
+	/* The underlying filesystem doesn't support idmapped mounts yet. */
+	if (!(m->mnt_sb->s_type->fs_flags & FS_ALLOW_IDMAP))
+		return -EINVAL;
+
+	/* We're not controlling the superblock. */
+	if (!ns_capable(fs_userns, CAP_SYS_ADMIN))
+		return -EPERM;
+
+	/* Mount has already been visible in the filesystem hierarchy. */
+	if (!is_anon_ns(mnt->mnt_ns))
+		return -EINVAL;
+
+	return 0;
+}
+
+/**
+ * mnt_allow_writers() - check whether the attribute change allows writers
+ * @kattr: the new mount attributes
+ * @mnt: the mount to which @kattr will be applied
+ *
+ * Check whether thew new mount attributes in @kattr allow concurrent writers.
+ *
+ * Return: true if writers need to be held, false if not
+ */
+static inline bool mnt_allow_writers(const struct mount_kattr *kattr,
+				     const struct mount *mnt)
+{
+	return (!(kattr->attr_set & MNT_READONLY) ||
+		(mnt->mnt.mnt_flags & MNT_READONLY)) &&
+	       !kattr->mnt_idmap;
+}
+
+static int mount_setattr_prepare(struct mount_kattr *kattr, struct mount *mnt)
+{
+	struct mount *m;
+	int err;
+
+	for (m = mnt; m; m = next_mnt(m, mnt)) {
+		if (!can_change_locked_flags(m, recalc_flags(kattr, m))) {
+			err = -EPERM;
+			break;
+		}
+
+		err = can_idmap_mount(kattr, m);
+		if (err)
+			break;
+
+		if (!mnt_allow_writers(kattr, m)) {
+			err = mnt_hold_writers(m);
+			if (err)
+				break;
+		}
+
+		if (!kattr->recurse)
+			return 0;
+	}
+
+	if (err) {
+		struct mount *p;
+
+		/*
+		 * If we had to call mnt_hold_writers() MNT_WRITE_HOLD will
+		 * be set in @mnt_flags. The loop unsets MNT_WRITE_HOLD for all
+		 * mounts and needs to take care to include the first mount.
+		 */
+		for (p = mnt; p; p = next_mnt(p, mnt)) {
+			/* If we had to hold writers unblock them. */
+			if (p->mnt.mnt_flags & MNT_WRITE_HOLD)
+				mnt_unhold_writers(p);
+
+			/*
+			 * We're done once the first mount we changed got
+			 * MNT_WRITE_HOLD unset.
+			 */
+			if (p == m)
+				break;
+		}
+	}
+	return err;
+}
+
+static void do_idmap_mount(const struct mount_kattr *kattr, struct mount *mnt)
+{
+	if (!kattr->mnt_idmap)
+		return;
+
+	/*
+	 * Pairs with smp_load_acquire() in mnt_idmap().
+	 *
+	 * Since we only allow a mount to change the idmapping once and
+	 * verified this in can_idmap_mount() we know that the mount has
+	 * @nop_mnt_idmap attached to it. So there's no need to drop any
+	 * references.
+	 */
+	smp_store_release(&mnt->mnt.mnt_idmap, mnt_idmap_get(kattr->mnt_idmap));
+}
+
+static void mount_setattr_commit(struct mount_kattr *kattr, struct mount *mnt)
+{
+	struct mount *m;
+
+	for (m = mnt; m; m = next_mnt(m, mnt)) {
+		unsigned int flags;
+
+		do_idmap_mount(kattr, m);
+		flags = recalc_flags(kattr, m);
+		WRITE_ONCE(m->mnt.mnt_flags, flags);
+
+		/* If we had to hold writers unblock them. */
+		if (m->mnt.mnt_flags & MNT_WRITE_HOLD)
+			mnt_unhold_writers(m);
+
+		if (kattr->propagation)
+			change_mnt_propagation(m, kattr->propagation);
+		if (!kattr->recurse)
+			break;
+	}
+	touch_mnt_namespace(mnt->mnt_ns);
+}
+
+static int do_mount_setattr(struct path *path, struct mount_kattr *kattr)
+{
+	struct mount *mnt = real_mount(path->mnt);
+	int err = 0;
+
+	if (!path_mounted(path))
+		return -EINVAL;
+
+	if (kattr->mnt_userns) {
+		struct mnt_idmap *mnt_idmap;
+
+		mnt_idmap = alloc_mnt_idmap(kattr->mnt_userns);
+		if (IS_ERR(mnt_idmap))
+			return PTR_ERR(mnt_idmap);
+		kattr->mnt_idmap = mnt_idmap;
+	}
+
+	if (kattr->propagation) {
+		/*
+		 * Only take namespace_lock() if we're actually changing
+		 * propagation.
+		 */
+		namespace_lock();
+		if (kattr->propagation == MS_SHARED) {
+			err = invent_group_ids(mnt, kattr->recurse);
+			if (err) {
+				namespace_unlock();
+				return err;
+			}
+		}
+	}
+
+	err = -EINVAL;
+	lock_mount_hash();
+
+	/* Ensure that this isn't anything purely vfs internal. */
+	if (!is_mounted(&mnt->mnt))
+		goto out;
+
+	/*
+	 * If this is an attached mount make sure it's located in the callers
+	 * mount namespace. If it's not don't let the caller interact with it.
+	 * If this is a detached mount make sure it has an anonymous mount
+	 * namespace attached to it, i.e. we've created it via OPEN_TREE_CLONE.
+	 */
+	if (!(mnt_has_parent(mnt) ? check_mnt(mnt) : is_anon_ns(mnt->mnt_ns)))
+		goto out;
+
+	/*
+	 * First, we get the mount tree in a shape where we can change mount
+	 * properties without failure. If we succeeded to do so we commit all
+	 * changes and if we failed we clean up.
+	 */
+	err = mount_setattr_prepare(kattr, mnt);
+	if (!err)
+		mount_setattr_commit(kattr, mnt);
+
+out:
+	unlock_mount_hash();
+
+	if (kattr->propagation) {
+		if (err)
+			cleanup_group_ids(mnt, NULL);
+		namespace_unlock();
+	}
+
+	return err;
+}
+
+static int build_mount_idmapped(const struct mount_attr *attr, size_t usize,
+				struct mount_kattr *kattr, unsigned int flags)
+{
+	int err = 0;
+	struct ns_common *ns;
+	struct user_namespace *mnt_userns;
+	struct fd f;
+
+	if (!((attr->attr_set | attr->attr_clr) & MOUNT_ATTR_IDMAP))
+		return 0;
+
+	/*
+	 * We currently do not support clearing an idmapped mount. If this ever
+	 * is a use-case we can revisit this but for now let's keep it simple
+	 * and not allow it.
+	 */
+	if (attr->attr_clr & MOUNT_ATTR_IDMAP)
+		return -EINVAL;
+
+	if (attr->userns_fd > INT_MAX)
+		return -EINVAL;
+
+	f = fdget(attr->userns_fd);
+	if (!f.file)
+		return -EBADF;
+
+	if (!proc_ns_file(f.file)) {
+		err = -EINVAL;
+		goto out_fput;
+	}
+
+	ns = get_proc_ns(file_inode(f.file));
+	if (ns->ops->type != CLONE_NEWUSER) {
+		err = -EINVAL;
+		goto out_fput;
+	}
+
+	/*
+	 * The initial idmapping cannot be used to create an idmapped
+	 * mount. We use the initial idmapping as an indicator of a mount
+	 * that is not idmapped. It can simply be passed into helpers that
+	 * are aware of idmapped mounts as a convenient shortcut. A user
+	 * can just create a dedicated identity mapping to achieve the same
+	 * result.
+	 */
+	mnt_userns = container_of(ns, struct user_namespace, ns);
+	if (mnt_userns == &init_user_ns) {
+		err = -EPERM;
+		goto out_fput;
+	}
+
+	/* We're not controlling the target namespace. */
+	if (!ns_capable(mnt_userns, CAP_SYS_ADMIN)) {
+		err = -EPERM;
+		goto out_fput;
+	}
+
+	kattr->mnt_userns = get_user_ns(mnt_userns);
+
+out_fput:
+	fdput(f);
+	return err;
+}
+
+static int build_mount_kattr(const struct mount_attr *attr, size_t usize,
+			     struct mount_kattr *kattr, unsigned int flags)
+{
+	unsigned int lookup_flags = LOOKUP_AUTOMOUNT | LOOKUP_FOLLOW;
+
+	if (flags & AT_NO_AUTOMOUNT)
+		lookup_flags &= ~LOOKUP_AUTOMOUNT;
+	if (flags & AT_SYMLINK_NOFOLLOW)
+		lookup_flags &= ~LOOKUP_FOLLOW;
+	if (flags & AT_EMPTY_PATH)
+		lookup_flags |= LOOKUP_EMPTY;
+
+	*kattr = (struct mount_kattr) {
+		.lookup_flags	= lookup_flags,
+		.recurse	= !!(flags & AT_RECURSIVE),
+	};
+
+	if (attr->propagation & ~MOUNT_SETATTR_PROPAGATION_FLAGS)
+		return -EINVAL;
+	if (hweight32(attr->propagation & MOUNT_SETATTR_PROPAGATION_FLAGS) > 1)
+		return -EINVAL;
+	kattr->propagation = attr->propagation;
+
+	if ((attr->attr_set | attr->attr_clr) & ~MOUNT_SETATTR_VALID_FLAGS)
+		return -EINVAL;
+
+	kattr->attr_set = attr_flags_to_mnt_flags(attr->attr_set);
+	kattr->attr_clr = attr_flags_to_mnt_flags(attr->attr_clr);
+
+	/*
+	 * Since the MOUNT_ATTR_<atime> values are an enum, not a bitmap,
+	 * users wanting to transition to a different atime setting cannot
+	 * simply specify the atime setting in @attr_set, but must also
+	 * specify MOUNT_ATTR__ATIME in the @attr_clr field.
+	 * So ensure that MOUNT_ATTR__ATIME can't be partially set in
+	 * @attr_clr and that @attr_set can't have any atime bits set if
+	 * MOUNT_ATTR__ATIME isn't set in @attr_clr.
+	 */
+	if (attr->attr_clr & MOUNT_ATTR__ATIME) {
+		if ((attr->attr_clr & MOUNT_ATTR__ATIME) != MOUNT_ATTR__ATIME)
+			return -EINVAL;
+
+		/*
+		 * Clear all previous time settings as they are mutually
+		 * exclusive.
+		 */
+		kattr->attr_clr |= MNT_RELATIME | MNT_NOATIME;
+		switch (attr->attr_set & MOUNT_ATTR__ATIME) {
+		case MOUNT_ATTR_RELATIME:
+			kattr->attr_set |= MNT_RELATIME;
+			break;
+		case MOUNT_ATTR_NOATIME:
+			kattr->attr_set |= MNT_NOATIME;
+			break;
+		case MOUNT_ATTR_STRICTATIME:
+			break;
+		default:
+			return -EINVAL;
+		}
+	} else {
+		if (attr->attr_set & MOUNT_ATTR__ATIME)
+			return -EINVAL;
+	}
+
+	return build_mount_idmapped(attr, usize, kattr, flags);
+}
+
+static void finish_mount_kattr(struct mount_kattr *kattr)
+{
+	put_user_ns(kattr->mnt_userns);
+	kattr->mnt_userns = NULL;
+
+	if (kattr->mnt_idmap)
+		mnt_idmap_put(kattr->mnt_idmap);
+}
+
+SYSCALL_DEFINE5(mount_setattr, int, dfd, const char __user *, path,
+		unsigned int, flags, struct mount_attr __user *, uattr,
+		size_t, usize)
+{
+	int err;
+	struct path target;
+	struct mount_attr attr;
+	struct mount_kattr kattr;
+
+	BUILD_BUG_ON(sizeof(struct mount_attr) != MOUNT_ATTR_SIZE_VER0);
+
+	if (flags & ~(AT_EMPTY_PATH |
+		      AT_RECURSIVE |
+		      AT_SYMLINK_NOFOLLOW |
+		      AT_NO_AUTOMOUNT))
+		return -EINVAL;
+
+	if (unlikely(usize > PAGE_SIZE))
+		return -E2BIG;
+	if (unlikely(usize < MOUNT_ATTR_SIZE_VER0))
+		return -EINVAL;
+
+	if (!may_mount())
+		return -EPERM;
+
+	err = copy_struct_from_user(&attr, sizeof(attr), uattr, usize);
+	if (err)
+		return err;
+
+	/* Don't bother walking through the mounts if this is a nop. */
+	if (attr.attr_set == 0 &&
+	    attr.attr_clr == 0 &&
+	    attr.propagation == 0)
+		return 0;
+
+	err = build_mount_kattr(&attr, usize, &kattr, flags);
+	if (err)
+		return err;
+
+	err = user_path_at(dfd, path, kattr.lookup_flags, &target);
+	if (!err) {
+		err = do_mount_setattr(&target, &kattr);
+		path_put(&target);
+	}
+	finish_mount_kattr(&kattr);
+	return err;
+}
+
+static void __init init_mount_tree(void)
+{
+	struct vfsmount *mnt;
+	struct mount *m;
+	struct mnt_namespace *ns;
+	struct path root;
+
+	mnt = vfs_kern_mount(&rootfs_fs_type, 0, "rootfs", NULL);
+	if (IS_ERR(mnt))
+		panic("Can't create rootfs");
+
+	ns = alloc_mnt_ns(&init_user_ns, false);
+	if (IS_ERR(ns))
+		panic("Can't allocate initial namespace");
+	m = real_mount(mnt);
+	m->mnt_ns = ns;
+	ns->root = m;
+	ns->mounts = 1;
+	list_add(&m->mnt_list, &ns->list);
+	init_task.nsproxy->mnt_ns = ns;
+	get_mnt_ns(ns);
+
+	root.mnt = mnt;
+	root.dentry = mnt->mnt_root;
+	mnt->mnt_flags |= MNT_LOCKED;
+
+	set_fs_pwd(current->fs, &root);
+	set_fs_root(current->fs, &root);
+}
+
+void __init mnt_init(void)
+{
+	int err;
+
+	mnt_cache = kmem_cache_create("mnt_cache", sizeof(struct mount),
+			0, SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT, NULL);
+
+	mount_hashtable = alloc_large_system_hash("Mount-cache",
+				sizeof(struct hlist_head),
+				mhash_entries, 19,
+				HASH_ZERO,
+				&m_hash_shift, &m_hash_mask, 0, 0);
+	mountpoint_hashtable = alloc_large_system_hash("Mountpoint-cache",
+				sizeof(struct hlist_head),
+				mphash_entries, 19,
+				HASH_ZERO,
+				&mp_hash_shift, &mp_hash_mask, 0, 0);
+
+	if (!mount_hashtable || !mountpoint_hashtable)
+		panic("Failed to allocate mount hash table\n");
+
+	kernfs_init();
+
+	err = sysfs_init();
+	if (err)
+		printk(KERN_WARNING "%s: sysfs_init error: %d\n",
+			__func__, err);
+	fs_kobj = kobject_create_and_add("fs", NULL);
+	if (!fs_kobj)
+		printk(KERN_WARNING "%s: kobj create error\n", __func__);
+	shmem_init();
+	init_rootfs();
+	init_mount_tree();
+}
+
+void put_mnt_ns(struct mnt_namespace *ns)
+{
+	if (!refcount_dec_and_test(&ns->ns.count))
+		return;
+	drop_collected_mounts(&ns->root->mnt);
+	free_mnt_ns(ns);
+}
+
+struct vfsmount *kern_mount(struct file_system_type *type)
+{
+	struct vfsmount *mnt;
+	mnt = vfs_kern_mount(type, SB_KERNMOUNT, type->name, NULL);
+	if (!IS_ERR(mnt)) {
+		/*
+		 * it is a longterm mount, don't release mnt until
+		 * we unmount before file sys is unregistered
+		*/
+		real_mount(mnt)->mnt_ns = MNT_NS_INTERNAL;
+	}
+	return mnt;
+}
+EXPORT_SYMBOL_GPL(kern_mount);
+
+void kern_unmount(struct vfsmount *mnt)
+{
+	/* release long term mount so mount point can be released */
+	if (!IS_ERR(mnt)) {
+		mnt_make_shortterm(mnt);
+		synchronize_rcu();	/* yecchhh... */
+		mntput(mnt);
+	}
+}
+EXPORT_SYMBOL(kern_unmount);
+
+void kern_unmount_array(struct vfsmount *mnt[], unsigned int num)
+{
+	unsigned int i;
+
+	for (i = 0; i < num; i++)
+		mnt_make_shortterm(mnt[i]);
+	synchronize_rcu_expedited();
+	for (i = 0; i < num; i++)
+		mntput(mnt[i]);
+}
+EXPORT_SYMBOL(kern_unmount_array);
+
+bool our_mnt(struct vfsmount *mnt)
+{
+	return check_mnt(real_mount(mnt));
+}
+
+bool current_chrooted(void)
+{
+	/* Does the current process have a non-standard root */
+	struct path ns_root;
+	struct path fs_root;
+	bool chrooted;
+
+	/* Find the namespace root */
+	ns_root.mnt = &current->nsproxy->mnt_ns->root->mnt;
+	ns_root.dentry = ns_root.mnt->mnt_root;
+	path_get(&ns_root);
+	while (d_mountpoint(ns_root.dentry) && follow_down_one(&ns_root))
+		;
+
+	get_fs_root(current->fs, &fs_root);
+
+	chrooted = !path_equal(&fs_root, &ns_root);
+
+	path_put(&fs_root);
+	path_put(&ns_root);
+
+	return chrooted;
+}
+
+static bool mnt_already_visible(struct mnt_namespace *ns,
+				const struct super_block *sb,
+				int *new_mnt_flags)
+{
+	int new_flags = *new_mnt_flags;
+	struct mount *mnt;
+	bool visible = false;
+
+	down_read(&namespace_sem);
+	lock_ns_list(ns);
+	list_for_each_entry(mnt, &ns->list, mnt_list) {
+		struct mount *child;
+		int mnt_flags;
+
+		if (mnt_is_cursor(mnt))
+			continue;
+
+		if (mnt->mnt.mnt_sb->s_type != sb->s_type)
+			continue;
+
+		/* This mount is not fully visible if it's root directory
+		 * is not the root directory of the filesystem.
+		 */
+		if (mnt->mnt.mnt_root != mnt->mnt.mnt_sb->s_root)
+			continue;
+
+		/* A local view of the mount flags */
+		mnt_flags = mnt->mnt.mnt_flags;
+
+		/* Don't miss readonly hidden in the superblock flags */
+		if (sb_rdonly(mnt->mnt.mnt_sb))
+			mnt_flags |= MNT_LOCK_READONLY;
+
+		/* Verify the mount flags are equal to or more permissive
+		 * than the proposed new mount.
+		 */
+		if ((mnt_flags & MNT_LOCK_READONLY) &&
+		    !(new_flags & MNT_READONLY))
+			continue;
+		if ((mnt_flags & MNT_LOCK_ATIME) &&
+		    ((mnt_flags & MNT_ATIME_MASK) != (new_flags & MNT_ATIME_MASK)))
+			continue;
+
+		/* This mount is not fully visible if there are any
+		 * locked child mounts that cover anything except for
+		 * empty directories.
+		 */
+		list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
+			struct inode *inode = child->mnt_mountpoint->d_inode;
+			/* Only worry about locked mounts */
+			if (!(child->mnt.mnt_flags & MNT_LOCKED))
+				continue;
+			/* Is the directory permanetly empty? */
+			if (!is_empty_dir_inode(inode))
+				goto next;
+		}
+		/* Preserve the locked attributes */
+		*new_mnt_flags |= mnt_flags & (MNT_LOCK_READONLY | \
+					       MNT_LOCK_ATIME);
+		visible = true;
+		goto found;
+	next:	;
+	}
+found:
+	unlock_ns_list(ns);
+	up_read(&namespace_sem);
+	return visible;
+}
+
+static bool mount_too_revealing(const struct super_block *sb, int *new_mnt_flags)
+{
+	const unsigned long required_iflags = SB_I_NOEXEC | SB_I_NODEV;
+	struct mnt_namespace *ns = current->nsproxy->mnt_ns;
+	unsigned long s_iflags;
+
+	if (ns->user_ns == &init_user_ns)
+		return false;
+
+	/* Can this filesystem be too revealing? */
+	s_iflags = sb->s_iflags;
+	if (!(s_iflags & SB_I_USERNS_VISIBLE))
+		return false;
+
+	if ((s_iflags & required_iflags) != required_iflags) {
+		WARN_ONCE(1, "Expected s_iflags to contain 0x%lx\n",
+			  required_iflags);
+		return true;
+	}
+
+	return !mnt_already_visible(ns, sb, new_mnt_flags);
+}
+
+bool mnt_may_suid(struct vfsmount *mnt)
+{
+	/*
+	 * Foreign mounts (accessed via fchdir or through /proc
+	 * symlinks) are always treated as if they are nosuid.  This
+	 * prevents namespaces from trusting potentially unsafe
+	 * suid/sgid bits, file caps, or security labels that originate
+	 * in other namespaces.
+	 */
+	return !(mnt->mnt_flags & MNT_NOSUID) && check_mnt(real_mount(mnt)) &&
+	       current_in_userns(mnt->mnt_sb->s_user_ns);
+}
+
+static struct ns_common *mntns_get(struct task_struct *task)
+{
+	struct ns_common *ns = NULL;
+	struct nsproxy *nsproxy;
+
+	task_lock(task);
+	nsproxy = task->nsproxy;
+	if (nsproxy) {
+		ns = &nsproxy->mnt_ns->ns;
+		get_mnt_ns(to_mnt_ns(ns));
+	}
+	task_unlock(task);
+
+	return ns;
+}
+
+static void mntns_put(struct ns_common *ns)
+{
+	put_mnt_ns(to_mnt_ns(ns));
+}
+
+static int mntns_install(struct nsset *nsset, struct ns_common *ns)
+{
+	struct nsproxy *nsproxy = nsset->nsproxy;
+	struct fs_struct *fs = nsset->fs;
+	struct mnt_namespace *mnt_ns = to_mnt_ns(ns), *old_mnt_ns;
+	struct user_namespace *user_ns = nsset->cred->user_ns;
+	struct path root;
+	int err;
+
+	if (!ns_capable(mnt_ns->user_ns, CAP_SYS_ADMIN) ||
+	    !ns_capable(user_ns, CAP_SYS_CHROOT) ||
+	    !ns_capable(user_ns, CAP_SYS_ADMIN))
+		return -EPERM;
+
+	if (is_anon_ns(mnt_ns))
+		return -EINVAL;
+
+	if (fs->users != 1)
+		return -EINVAL;
+
+	get_mnt_ns(mnt_ns);
+	old_mnt_ns = nsproxy->mnt_ns;
+	nsproxy->mnt_ns = mnt_ns;
+
+	/* Find the root */
+	err = vfs_path_lookup(mnt_ns->root->mnt.mnt_root, &mnt_ns->root->mnt,
+				"/", LOOKUP_DOWN, &root);
+	if (err) {
+		/* revert to old namespace */
+		nsproxy->mnt_ns = old_mnt_ns;
+		put_mnt_ns(mnt_ns);
+		return err;
+	}
+
+	put_mnt_ns(old_mnt_ns);
+
+	/* Update the pwd and root */
+	set_fs_pwd(fs, &root);
+	set_fs_root(fs, &root);
+
+	path_put(&root);
+	return 0;
+}
+
+static struct user_namespace *mntns_owner(struct ns_common *ns)
+{
+	return to_mnt_ns(ns)->user_ns;
+}
+
+const struct proc_ns_operations mntns_operations = {
+	.name		= "mnt",
+	.type		= CLONE_NEWNS,
+	.get		= mntns_get,
+	.put		= mntns_put,
+	.install	= mntns_install,
+	.owner		= mntns_owner,
+};
+
+#ifdef CONFIG_SYSCTL
+static struct ctl_table fs_namespace_sysctls[] = {
+	{
+		.procname	= "mount-max",
+		.data		= &sysctl_mount_max,
+		.maxlen		= sizeof(unsigned int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= SYSCTL_ONE,
+	},
+	{ }
+};
+
+static int __init init_fs_namespace_sysctls(void)
+{
+	register_sysctl_init("fs", fs_namespace_sysctls);
+	return 0;
+}
+fs_initcall(init_fs_namespace_sysctls);
+
+#endif /* CONFIG_SYSCTL */