text: /*
   *  linux/fs/namespace.c
   *
   * (C) Copyright Al Viro 2000, 2001
   *	Released under GPL v2.
   *
   * 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/uaccess.h>
  #include <linux/proc_ns.h>
  #include <linux/magic.h>
  #include <linux/memblock.h>
  #include <linux/task_work.h>
  #include <linux/sched/task.h>
  #include <uapi/linux/mount.h>
  #include <linux/fs_context.h>
  
  #include "pnode.h"
  #include "internal.h"
  
  /* Maximum number of mounts in a mount namespace */
  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);
  
  /* /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 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
   */
  unsigned int mnt_get_count(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_count;
  	}
  
  	return count;
  #else
  	return mnt->mnt_count;
  #endif
  }
  
  static void drop_mountpoint(struct fs_pin *p)
  {
  	struct mount *m = container_of(p, struct mount, mnt_umount);
  	dput(m->mnt_ex_mountpoint);
  	pin_remove(p);
  	mntput(&m->mnt);
  }
  
  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);
  			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_fs_pin(&mnt->mnt_umount, drop_mountpoint);
  	}
  	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 (mnt->mnt_sb->s_readonly_remount)
  		return 1;
  	/* Order wrt setting s_flags/s_readonly_remount in do_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();
  	while (READ_ONCE(mnt->mnt.mnt_flags) & MNT_WRITE_HOLD)
  		cpu_relax();
  	/*
  	 * After the slowpath clears MNT_WRITE_HOLD, mnt_is_readonly will
  	 * be set to match its requirements. So we must not load that until
  	 * MNT_WRITE_HOLD is cleared.
  	 */
  	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_clone_write - get write access to a mount
   * @mnt: the mount on which to take a write
   *
   * This is effectively like mnt_want_write, except
   * it must only be used to take an extra write reference
   * on a mountpoint that we already know has a write reference
   * on it. This allows some optimisation.
   *
   * After finished, mnt_drop_write must be called as usual to
   * drop the reference.
   */
  int mnt_clone_write(struct vfsmount *mnt)
  {
  	/* superblock may be r/o */
  	if (__mnt_is_readonly(mnt))
  		return -EROFS;
  	preempt_disable();
  	mnt_inc_writers(real_mount(mnt));
  	preempt_enable();
  	return 0;
  }
  EXPORT_SYMBOL_GPL(mnt_clone_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 it takes a file and can
   * do some optimisations if the file is open for write already
   */
  int __mnt_want_write_file(struct file *file)
  {
  	if (!(file->f_mode & FMODE_WRITER))
  		return __mnt_want_write(file->f_path.mnt);
  	else
  		return mnt_clone_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 it takes a file and can
   * do some optimisations if the file is open for write already
   */
  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)
  {
  	__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);
  
  static int mnt_make_readonly(struct mount *mnt)
  {
  	int ret = 0;
  
  	lock_mount_hash();
  	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)
  		ret = -EBUSY;
  	else
  		mnt->mnt.mnt_flags |= MNT_READONLY;
  	/*
  	 * 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;
  	unlock_mount_hash();
  	return ret;
  }
  
  static int __mnt_unmake_readonly(struct mount *mnt)
  {
  	lock_mount_hash();
  	mnt->mnt.mnt_flags &= ~MNT_READONLY;
  	unlock_mount_hash();
  	return 0;
  }
  
  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)) {
  			mnt->mnt.mnt_flags |= MNT_WRITE_HOLD;
  			smp_mb();
  			if (mnt_get_writers(mnt) > 0) {
  				err = -EBUSY;
  				break;
  			}
  		}
  	}
  	if (!err && atomic_long_read(&sb->s_remove_count))
  		err = -EBUSY;
  
  	if (!err) {
  		sb->s_readonly_remount = 1;
  		smp_wmb();
  	}
  	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)
  {
  	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 */
  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;
  }
  
  /*
   * find the first mount at @dentry on vfsmount @mnt.
   * call under rcu_read_lock()
   */
  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;
  }
  
  /*
   * __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;
  
  	if (!d_mountpoint(dentry))
  		goto out;
  
  	down_read(&namespace_sem);
  	list_for_each_entry(mnt, &ns->list, mnt_list) {
  		is_covered = (mnt->mnt_mountpoint == dentry);
  		if (is_covered)
  			break;
  	}
  	up_read(&namespace_sem);
  out:
  	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 = 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;
  }
  
  static void put_mountpoint(struct mountpoint *mp)
  {
  	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);
  		hlist_del(&mp->m_hash);
  		kfree(mp);
  	}
  }
  
  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 void unhash_mnt(struct mount *mnt)
  {
  	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);
  	put_mountpoint(mnt->mnt_mp);
  	mnt->mnt_mp = NULL;
  }
  
  /*
   * vfsmount lock must be held for write
   */
  static void detach_mnt(struct mount *mnt, struct path *old_path)
  {
  	old_path->dentry = mnt->mnt_mountpoint;
  	old_path->mnt = &mnt->mnt_parent->mnt;
  	unhash_mnt(mnt);
  }
  
  /*
   * vfsmount lock must be held for write
   */
  static void umount_mnt(struct mount *mnt)
  {
  	/* old mountpoint will be dropped when we can do that */
  	mnt->mnt_ex_mountpoint = mnt->mnt_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 = dget(mp->m_dentry);
  	child_mnt->mnt_parent = mnt;
  	child_mnt->mnt_mp = mp;
  	hlist_add_head(&child_mnt->mnt_mp_list, &mp->m_list);
  }
  
  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);
  }
  
  /*
   * vfsmount lock must be held for write
   */
  static void attach_mnt(struct mount *mnt,
  			struct mount *parent,
  			struct mountpoint *mp)
  {
  	mnt_set_mountpoint(parent, mp, mnt);
  	__attach_mnt(mnt, parent);
  }
  
  void mnt_change_mountpoint(struct mount *parent, struct mountpoint *mp, struct mount *mnt)
  {
  	struct mountpoint *old_mp = mnt->mnt_mp;
  	struct dentry *old_mountpoint = mnt->mnt_mountpoint;
  	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);
  
  	put_mountpoint(old_mp);
  
  	/*
  	 * Safely avoid even the suggestion this code might sleep or
  	 * lock the mount hash by taking advantage of the knowledge that
  	 * mnt_change_mountpoint will not release the final reference
  	 * to a mountpoint.
  	 *
  	 * During mounting, the mount passed in as the parent mount will
  	 * continue to use the old mountpoint and during unmounting, the
  	 * old mountpoint will continue to exist until namespace_unlock,
  	 * which happens well after mnt_change_mountpoint.
  	 */
  	spin_lock(&old_mountpoint->d_lock);
  	old_mountpoint->d_lockref.count--;
  	spin_unlock(&old_mountpoint->d_lock);
  
  	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_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)
  {
  	/*
  	 * This 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);
  	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)
  {
  	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);
  	if (mnt_get_count(mnt)) {
  		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) {
  			umount_mnt(p);
  		}
  	}
  	unlock_mount_hash();
  
  	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, true))
  				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);
  
  /* path_is_mountpoint() - Check if path is a mount in the current
   *                          namespace.
   *
   *  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
  /* 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;
  
  	down_read(&namespace_sem);
  	if (p->cached_event == p->ns->event) {
  		void *v = p->cached_mount;
  		if (*pos == p->cached_index)
  			return v;
  		if (*pos == p->cached_index + 1) {
  			v = seq_list_next(v, &p->ns->list, &p->cached_index);
  			return p->cached_mount = v;
  		}
  	}
  
  	p->cached_event = p->ns->event;
  	p->cached_mount = seq_list_start(&p->ns->list, *pos);
  	p->cached_index = *pos;
  	return p->cached_mount;
  }
  
  static void *m_next(struct seq_file *m, void *v, loff_t *pos)
  {
  	struct proc_mounts *p = m->private;
  
  	p->cached_mount = seq_list_next(v, &p->ns->list, pos);
  	p->cached_index = *pos;
  	return p->cached_mount;
  }
  
  static void m_stop(struct seq_file *m, void *v)
  {
  	up_read(&namespace_sem);
  }
  
  static int m_show(struct seq_file *m, void *v)
  {
  	struct proc_mounts *p = m->private;
  	struct mount *r = list_entry(v, struct mount, mnt_list);
  	return p->show(m, &r->mnt);
  }
  
  const struct seq_operations mounts_op = {
  	.start	= m_start,
  	.next	= m_next,
  	.stop	= m_stop,
  	.show	= m_show,
  };
  #endif  /* CONFIG_PROC_FS */
  
  /**
   * may_umount_tree - check if a mount tree is busy
   * @mnt: 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 HLIST_HEAD(unmounted);	/* protected by namespace_sem */
  
  static void namespace_unlock(void)
  {
  	struct hlist_head head;
  
  	hlist_move_list(&unmounted, &head);
  
  	up_write(&namespace_sem);
  
  	if (likely(hlist_empty(&head)))
  		return;
  
  	synchronize_rcu_expedited();
  
  	group_pin_kill(&head);
  }
  
  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);
  
  		pin_insert_group(&p->mnt_umount, &p->mnt_parent->mnt,
  				 disconnect ? &unmounted : NULL);
  		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);
  	}
  }
  
  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 (IS_ERR_OR_NULL(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) {
  			hlist_add_head(&mnt->mnt_umount.s_list, &unmounted);
  			umount_mnt(mnt);
  		}
  		else umount_tree(mnt, UMOUNT_CONNECTED);
  	}
  	put_mountpoint(mp);
  out_unlock:
  	unlock_mount_hash();
  	namespace_unlock();
  }
  
  /*
   * Is the caller allowed to modify his namespace?
   */
  static inline bool may_mount(void)
  {
  	return ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN);
  }
  
  static inline bool may_mandlock(void)
  {
  #ifndef	CONFIG_MANDATORY_FILE_LOCKING
  	return false;
  #endif
  	return capable(CAP_SYS_ADMIN);
  }
  
  /*
   * Now umount can handle mount points as well as block devices.
   * This is important for filesystems which use unnamed block devices.
   *
   * We now support a flag for forced unmount like the other 'big iron'
   * unixes. Our API is identical to OSF/1 to avoid making a mess of AMD
   */
  
  int ksys_umount(char __user *name, int flags)
  {
  	struct path path;
  	struct mount *mnt;
  	int retval;
  	int lookup_flags = 0;
  
  	if (flags & ~(MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW))
  		return -EINVAL;
  
  	if (!may_mount())
  		return -EPERM;
  
  	if (!(flags & UMOUNT_NOFOLLOW))
  		lookup_flags |= LOOKUP_FOLLOW;
  
  	lookup_flags |= LOOKUP_NO_EVAL;
  
  	retval = user_path_mountpoint_at(AT_FDCWD, name, lookup_flags, &path);
  	if (retval)
  		goto out;
  	mnt = real_mount(path.mnt);
  	retval = -EINVAL;
  	if (path.dentry != path.mnt->mnt_root)
  		goto dput_and_out;
  	if (!check_mnt(mnt))
  		goto dput_and_out;
  	if (mnt->mnt.mnt_flags & MNT_LOCKED) /* Check optimistically */
  		goto dput_and_out;
  	retval = -EPERM;
  	if (flags & MNT_FORCE && !capable(CAP_SYS_ADMIN))
  		goto dput_and_out;
  
  	retval = do_umount(mnt, flags);
  dput_and_out:
  	/* we mustn't call path_put() as that would clear mnt_expiry_mark */
  	dput(path.dentry);
  	mntput_no_expire(mnt);
  out:
  	return retval;
  }
  
  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;
  }
  
  struct mnt_namespace *to_mnt_ns(struct ns_common *ns)
  {
  	return container_of(ns, struct mnt_namespace, 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);
  			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;
  }
  
  void drop_collected_mounts(struct vfsmount *mnt)
  {
  	namespace_lock();
  	lock_mount_hash();
  	umount_tree(real_mount(mnt), 0);
  	unlock_mount_hash();
  	namespace_unlock();
  }
  
  /**
   * clone_private_mount - create a private clone of a path
   *
   * This creates a new vfsmount, which will be the clone of @path.  The new 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;
  
  	if (IS_MNT_UNBINDABLE(old_mnt))
  		return ERR_PTR(-EINVAL);
  
  	new_mnt = clone_mnt(old_mnt, path->dentry, CL_PRIVATE);
  	if (IS_ERR(new_mnt))
  		return ERR_CAST(new_mnt);
  
  	return &new_mnt->mnt;
  }
  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, old, pending, sum;
  	struct mount *p;
  
  	for (p = mnt; p; p = next_mnt(p, mnt))
  		mounts++;
  
  	old = ns->mounts;
  	pending = ns->pending_mounts;
  	sum = old + pending;
  	if ((old > sum) ||
  	    (pending > sum) ||
  	    (max < sum) ||
  	    (mounts > (max - sum)))
  		return -ENOSPC;
  
  	ns->pending_mounts = pending + mounts;
  	return 0;
  }
  
  /*
   *  @source_mnt : mount tree to be attached
   *  @nd         : place the mount tree @source_mnt is attached
   *  @parent_nd  : if non-null, detach the source_mnt from its parent and
   *  		   store the parent mount and mountpoint dentry.
   *  		   (done when source_mnt is moved)
   *
   *  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.
   */
  static int attach_recursive_mnt(struct mount *source_mnt,
  			struct mount *dest_mnt,
  			struct mountpoint *dest_mp,
  			struct path *parent_path)
  {
  	struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns;
  	HLIST_HEAD(tree_list);
  	struct mnt_namespace *ns = dest_mnt->mnt_ns;
  	struct mountpoint *smp;
  	struct mount *child, *p;
  	struct hlist_node *n;
  	int err;
  
  	/* Preallocate a mountpoint in case the new mounts need
  	 * to be tucked under other mounts.
  	 */
  	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 (!parent_path) {
  		err = count_mounts(ns, source_mnt);
  		if (err)
  			goto out;
  	}
  
  	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;
  		for (p = source_mnt; p; p = next_mnt(p, source_mnt))
  			set_mnt_shared(p);
  	} else {
  		lock_mount_hash();
  	}
  	if (parent_path) {
  		detach_mnt(source_mnt, parent_path);
  		attach_mnt(source_mnt, dest_mnt, dest_mp);
  		touch_mnt_namespace(source_mnt->mnt_ns);
  	} 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;
  }
  
  static struct mountpoint *lock_mount(struct path *path)
  {
  	struct vfsmount *mnt;
  	struct dentry *dentry = path->dentry;
  retry:
  	inode_lock(dentry->d_inode);
  	if (unlikely(cant_mount(dentry))) {
  		inode_unlock(dentry->d_inode);
  		return ERR_PTR(-ENOENT);
  	}
  	namespace_lock();
  	mnt = lookup_mnt(path);
  	if (likely(!mnt)) {
  		struct mountpoint *mp = get_mountpoint(dentry);
  		if (IS_ERR(mp)) {
  			namespace_unlock();
  			inode_unlock(dentry->d_inode);
  			return mp;
  		}
  		return mp;
  	}
  	namespace_unlock();
  	inode_unlock(path->dentry->d_inode);
  	path_put(path);
  	path->mnt = mnt;
  	dentry = path->dentry = dget(mnt->mnt_root);
  	goto retry;
  }
  
  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, NULL);
  }
  
  /*
   * 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->dentry != path->mnt->mnt_root)
  		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 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;
  }
  
  /*
   * do loopback mount.
   */
  static int do_loopback(struct path *path, const char *old_name,
  				int recurse)
  {
  	struct path old_path;
  	struct mount *mnt = NULL, *old, *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);
  	err = PTR_ERR(mp);
  	if (IS_ERR(mp))
  		goto out;
  
  	old = real_mount(old_path.mnt);
  	parent = real_mount(path->mnt);
  
  	err = -EINVAL;
  	if (IS_MNT_UNBINDABLE(old))
  		goto out2;
  
  	if (!check_mnt(parent))
  		goto out2;
  
  	if (!check_mnt(old) && old_path.dentry->d_op != &ns_dentry_operations)
  		goto out2;
  
  	if (!recurse && has_locked_children(old, old_path.dentry))
  		goto out2;
  
  	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)) {
  		err = PTR_ERR(mnt);
  		goto out2;
  	}
  
  	mnt->mnt.mnt_flags &= ~MNT_LOCKED;
  
  	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;
  }
  
  /*
   * 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);
  
  	return __mnt_unmake_readonly(mnt);
  }
  
  /*
   * Update the user-settable attributes on a mount.  The caller must hold
   * sb->s_umount for writing.
   */
  static void set_mount_attributes(struct mount *mnt, unsigned int mnt_flags)
  {
  	lock_mount_hash();
  	mnt_flags |= mnt->mnt.mnt_flags & ~MNT_USER_SETTABLE_MASK;
  	mnt->mnt.mnt_flags = mnt_flags;
  	touch_mnt_namespace(mnt->mnt_ns);
  	unlock_mount_hash();
  }
  
  /*
   * 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->dentry != mnt->mnt.mnt_root)
  		return -EINVAL;
  
  	if (!can_change_locked_flags(mnt, mnt_flags))
  		return -EPERM;
  
  	down_write(&sb->s_umount);
  	ret = change_mount_ro_state(mnt, mnt_flags);
  	if (ret == 0)
  		set_mount_attributes(mnt, mnt_flags);
  	up_write(&sb->s_umount);
  	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->dentry != path->mnt->mnt_root)
  		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);
  
  	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)
  				set_mount_attributes(mnt, mnt_flags);
  		}
  		up_write(&sb->s_umount);
  	}
  	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;
  }
  
  static int do_move_mount(struct path *path, const char *old_name)
  {
  	struct path old_path, parent_path;
  	struct mount *p;
  	struct mount *old;
  	struct mountpoint *mp;
  	int err;
  	if (!old_name || !*old_name)
  		return -EINVAL;
  	err = kern_path(old_name, LOOKUP_FOLLOW, &old_path);
  	if (err)
  		return err;
  
  	mp = lock_mount(path);
  	err = PTR_ERR(mp);
  	if (IS_ERR(mp))
  		goto out;
  
  	old = real_mount(old_path.mnt);
  	p = real_mount(path->mnt);
  
  	err = -EINVAL;
  	if (!check_mnt(p) || !check_mnt(old))
  		goto out1;
  
  	if (old->mnt.mnt_flags & MNT_LOCKED)
  		goto out1;
  
  	err = -EINVAL;
  	if (old_path.dentry != old_path.mnt->mnt_root)
  		goto out1;
  
  	if (!mnt_has_parent(old))
  		goto out1;
  
  	if (d_is_dir(path->dentry) !=
  	      d_is_dir(old_path.dentry))
  		goto out1;
  	/*
  	 * Don't move a mount residing in a shared parent.
  	 */
  	if (IS_MNT_SHARED(old->mnt_parent))
  		goto out1;
  	/*
  	 * 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 out1;
  	err = -ELOOP;
  	for (; mnt_has_parent(p); p = p->mnt_parent)
  		if (p == old)
  			goto out1;
  
  	err = attach_recursive_mnt(old, real_mount(path->mnt), mp, &parent_path);
  	if (err)
  		goto out1;
  
  	/* if the mount is moved, it should no longer be expire
  	 * automatically */
  	list_del_init(&old->mnt_expire);
  out1:
  	unlock_mount(mp);
  out:
  	if (!err)
  		path_put(&parent_path);
  	path_put(&old_path);
  	return err;
  }
  
  /*
   * add a mount into a namespace's mount tree
   */
  static int do_add_mount(struct mount *newmnt, struct path *path, int mnt_flags)
  {
  	struct mountpoint *mp;
  	struct mount *parent;
  	int err;
  
  	mnt_flags &= ~MNT_INTERNAL_FLAGS;
  
  	mp = lock_mount(path);
  	if (IS_ERR(mp))
  		return PTR_ERR(mp);
  
  	parent = real_mount(path->mnt);
  	err = -EINVAL;
  	if (unlikely(!check_mnt(parent))) {
  		/* that's acceptable only for automounts done in private ns */
  		if (!(mnt_flags & MNT_SHRINKABLE))
  			goto unlock;
  		/* ... and for those we'd better have mountpoint still alive */
  		if (!parent->mnt_ns)
  			goto unlock;
  	}
  
  	/* Refuse the same filesystem on the same mount point */
  	err = -EBUSY;
  	if (path->mnt->mnt_sb == newmnt->mnt.mnt_sb &&
  	    path->mnt->mnt_root == path->dentry)
  		goto unlock;
  
  	err = -EINVAL;
  	if (d_is_symlink(newmnt->mnt.mnt_root))
  		goto unlock;
  
  	newmnt->mnt.mnt_flags = mnt_flags;
  	err = graft_tree(newmnt, parent, mp);
  
  unlock:
  	unlock_mount(mp);
  	return err;
  }
  
  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 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);
  
  	error = do_add_mount(real_mount(mnt), mountpoint, mnt_flags);
  	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;
  			}
  		} else {
  			subtype = "";
  		}
  	}
  
  	fc = fs_context_for_mount(type, sb_flags);
  	put_filesystem(type);
  	if (IS_ERR(fc))
  		return PTR_ERR(fc);
  
  	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)
  		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, struct path *path)
  {
  	struct mount *mnt = real_mount(m);
  	int err;
  	/* 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 == path->dentry) {
  		err = -ELOOP;
  		goto fail;
  	}
  
  	err = do_add_mount(mnt, path, path->mnt->mnt_flags | MNT_SHRINKABLE);
  	if (!err)
  		return 0;
  fail:
  	/* 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);
  		}
  	}
  }
  
  /*
   * Some copy_from_user() implementations do not return the exact number of
   * bytes remaining to copy on a fault.  But copy_mount_options() requires that.
   * Note that this function differs from copy_from_user() in that it will oops
   * on bad values of `to', rather than returning a short copy.
   */
  static long exact_copy_from_user(void *to, const void __user * from,
  				 unsigned long n)
  {
  	char *t = to;
  	const char __user *f = from;
  	char c;
  
  	if (!access_ok(from, n))
  		return n;
  
  	while (n) {
  		if (__get_user(c, f)) {
  			memset(t, 0, n);
  			break;
  		}
  		*t++ = c;
  		f++;
  		n--;
  	}
  	return n;
  }
  
  void *copy_mount_options(const void __user * data)
  {
  	int i;
  	unsigned long size;
  	char *copy;
  
  	if (!data)
  		return NULL;
  
  	copy = kmalloc(PAGE_SIZE, GFP_KERNEL);
  	if (!copy)
  		return ERR_PTR(-ENOMEM);
  
  	/* We only care that *some* data at the address the user
  	 * gave us is valid.  Just in case, we'll zero
  	 * the remainder of the page.
  	 */
  	/* copy_from_user cannot cross TASK_SIZE ! */
  	size = TASK_SIZE - (unsigned long)data;
  	if (size > PAGE_SIZE)
  		size = PAGE_SIZE;
  
  	i = size - exact_copy_from_user(copy, data, size);
  	if (!i) {
  		kfree(copy);
  		return ERR_PTR(-EFAULT);
  	}
  	if (i != PAGE_SIZE)
  		memset(copy + i, 0, PAGE_SIZE - i);
  	return copy;
  }
  
  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.
   */
  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;
  	unsigned int mnt_flags = 0, sb_flags;
  	int retval = 0;
  
  	/* 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;
  
  	/* ... and get the mountpoint */
  	retval = user_path(dir_name, &path);
  	if (retval)
  		return retval;
  
  	retval = security_sb_mount(dev_name, &path,
  				   type_page, flags, data_page);
  	if (!retval && !may_mount())
  		retval = -EPERM;
  	if (!retval && (flags & SB_MANDLOCK) && !may_mandlock())
  		retval = -EPERM;
  	if (retval)
  		goto dput_out;
  
  	/* 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;
  
  	/* 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))
  		retval = do_reconfigure_mnt(&path, mnt_flags);
  	else if (flags & MS_REMOUNT)
  		retval = do_remount(&path, flags, sb_flags, mnt_flags,
  				    data_page);
  	else if (flags & MS_BIND)
  		retval = do_loopback(&path, dev_name, flags & MS_REC);
  	else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
  		retval = do_change_type(&path, flags);
  	else if (flags & MS_MOVE)
  		retval = do_move_mount(&path, dev_name);
  	else
  		retval = do_new_mount(&path, type_page, sb_flags, mnt_flags,
  				      dev_name, data_page);
  dput_out:
  	path_put(&path);
  	return retval;
  }
  
  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);
  	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);
  	atomic_set(&new_ns->count, 1);
  	INIT_LIST_HEAD(&new_ns->list);
  	init_waitqueue_head(&new_ns->poll);
  	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;
  		while (p->mnt.mnt_root != q->mnt.mnt_root)
  			p = next_mnt(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);
  
  int ksys_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;
  }
  
  SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
  		char __user *, type, unsigned long, flags, void __user *, data)
  {
  	return ksys_mount(dev_name, dir_name, type, flags, data);
  }
  
  /*
   * 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.txt 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, parent_path, root_parent, root;
  	struct mount *new_mnt, *root_mnt, *old_mnt;
  	struct mountpoint *old_mp, *root_mp;
  	int error;
  
  	if (!may_mount())
  		return -EPERM;
  
  	error = user_path_dir(new_root, &new);
  	if (error)
  		goto out0;
  
  	error = user_path_dir(put_old, &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);
  	if (IS_MNT_SHARED(old_mnt) ||
  		IS_MNT_SHARED(new_mnt->mnt_parent) ||
  		IS_MNT_SHARED(root_mnt->mnt_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 (root.mnt->mnt_root != root.dentry)
  		goto out4; /* not a mountpoint */
  	if (!mnt_has_parent(root_mnt))
  		goto out4; /* not attached */
  	root_mp = root_mnt->mnt_mp;
  	if (new.mnt->mnt_root != new.dentry)
  		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;
  	root_mp->m_count++; /* pin it so it won't go away */
  	lock_mount_hash();
  	detach_mnt(new_mnt, &parent_path);
  	detach_mnt(root_mnt, &root_parent);
  	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);
  	/* mount new_root on / */
  	attach_mnt(new_mnt, real_mount(root_parent.mnt), root_mp);
  	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) {
  		path_put(&root_parent);
  		path_put(&parent_path);
  	}
  out3:
  	path_put(&root);
  out2:
  	path_put(&old);
  out1:
  	path_put(&new);
  out0:
  	return error;
  }
  
  static void __init init_mount_tree(void)
  {
  	struct vfsmount *mnt;
  	struct mount *m;
  	struct mnt_namespace *ns;
  	struct path root;
  	struct file_system_type *type;
  
  	type = get_fs_type("rootfs");
  	if (!type)
  		panic("Can't find rootfs type");
  	mnt = vfs_kern_mount(type, 0, "rootfs", NULL);
  	put_filesystem(type);
  	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, 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__);
  	init_rootfs();
  	init_mount_tree();
  }
  
  void put_mnt_ns(struct mnt_namespace *ns)
  {
  	if (!atomic_dec_and_test(&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_OR_NULL(mnt)) {
  		real_mount(mnt)->mnt_ns = NULL;
  		synchronize_rcu();	/* yecchhh... */
  		mntput(mnt);
  	}
  }
  EXPORT_SYMBOL(kern_unmount);
  
  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);
  	list_for_each_entry(mnt, &ns->list, mnt_list) {
  		struct mount *child;
  		int mnt_flags;
  
  		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:
  	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 nsproxy *nsproxy, struct ns_common *ns)
  {
  	struct fs_struct *fs = current->fs;
  	struct mnt_namespace *mnt_ns = to_mnt_ns(ns), *old_mnt_ns;
  	struct path root;
  	int err;
  
  	if (!ns_capable(mnt_ns->user_ns, CAP_SYS_ADMIN) ||
  	    !ns_capable(current_user_ns(), CAP_SYS_CHROOT) ||
  	    !ns_capable(current_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,
  };
  