// SPDX-License-Identifier: GPL-2.0-only

  /*
   *  linux/fs/pnode.c
   *
   * (C) Copyright IBM Corporation 2005.

   *	Author : Ram Pai (linuxram@us.ibm.com)

   */

  #include <linux/mnt_namespace.h>

  #include <linux/mount.h>
  #include <linux/fs.h>

  #include <linux/nsproxy.h>

  #include <uapi/linux/mount.h>

  #include "internal.h"

  #include "pnode.h"

  /* return the next shared peer mount of @p */

  static inline struct mount *next_peer(struct mount *p)

  {

  	return list_entry(p->mnt_share.next, struct mount, mnt_share);

  }

  static inline struct mount *first_slave(struct mount *p)

  {

  	return list_entry(p->mnt_slave_list.next, struct mount, mnt_slave);

  }

  static inline struct mount *last_slave(struct mount *p)
  {
  	return list_entry(p->mnt_slave_list.prev, struct mount, mnt_slave);
  }

  static inline struct mount *next_slave(struct mount *p)

  {

  	return list_entry(p->mnt_slave.next, struct mount, mnt_slave);

  }

  static struct mount *get_peer_under_root(struct mount *mnt,
  					 struct mnt_namespace *ns,
  					 const struct path *root)

  {

  	struct mount *m = mnt;

  
  	do {
  		/* Check the namespace first for optimization */

  		if (m->mnt_ns == ns && is_path_reachable(m, m->mnt.mnt_root, root))

  			return m;

  		m = next_peer(m);

  	} while (m != mnt);

  
  	return NULL;
  }
  
  /*
   * Get ID of closest dominating peer group having a representative
   * under the given root.
   *
   * Caller must hold namespace_sem
   */

  int get_dominating_id(struct mount *mnt, const struct path *root)

  {

  	struct mount *m;

  	for (m = mnt->mnt_master; m != NULL; m = m->mnt_master) {

  		struct mount *d = get_peer_under_root(m, mnt->mnt_ns, root);

  		if (d)

  			return d->mnt_group_id;

  	}
  
  	return 0;
  }

  static int do_make_slave(struct mount *mnt)

  {

  	struct mount *master, *slave_mnt;

  	if (list_empty(&mnt->mnt_share)) {
  		if (IS_MNT_SHARED(mnt)) {
  			mnt_release_group_id(mnt);
  			CLEAR_MNT_SHARED(mnt);
  		}
  		master = mnt->mnt_master;
  		if (!master) {
  			struct list_head *p = &mnt->mnt_slave_list;
  			while (!list_empty(p)) {
  				slave_mnt = list_first_entry(p,
  						struct mount, mnt_slave);
  				list_del_init(&slave_mnt->mnt_slave);
  				slave_mnt->mnt_master = NULL;
  			}
  			return 0;
  		}

  	} else {

  		struct mount *m;
  		/*
  		 * slave 'mnt' to a peer mount that has the
  		 * same root dentry. If none is available then
  		 * slave it to anything that is available.
  		 */
  		for (m = master = next_peer(mnt); m != mnt; m = next_peer(m)) {
  			if (m->mnt.mnt_root == mnt->mnt.mnt_root) {
  				master = m;
  				break;
  			}

  		}

  		list_del_init(&mnt->mnt_share);
  		mnt->mnt_group_id = 0;
  		CLEAR_MNT_SHARED(mnt);

  	}

  	list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave)
  		slave_mnt->mnt_master = master;
  	list_move(&mnt->mnt_slave, &master->mnt_slave_list);
  	list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev);
  	INIT_LIST_HEAD(&mnt->mnt_slave_list);

  	mnt->mnt_master = master;

  	return 0;
  }

  /*
   * vfsmount lock must be held for write
   */

  void change_mnt_propagation(struct mount *mnt, int type)

  {

  	if (type == MS_SHARED) {

  		set_mnt_shared(mnt);

  		return;
  	}

  	do_make_slave(mnt);

  	if (type != MS_SLAVE) {

  		list_del_init(&mnt->mnt_slave);

  		mnt->mnt_master = NULL;

  		if (type == MS_UNBINDABLE)

  			mnt->mnt.mnt_flags |= MNT_UNBINDABLE;

  		else

  			mnt->mnt.mnt_flags &= ~MNT_UNBINDABLE;

  	}

  }

  
  /*
   * get the next mount in the propagation tree.
   * @m: the mount seen last
   * @origin: the original mount from where the tree walk initiated

   *
   * Note that peer groups form contiguous segments of slave lists.
   * We rely on that in get_source() to be able to find out if
   * vfsmount found while iterating with propagation_next() is
   * a peer of one we'd found earlier.

   */

  static struct mount *propagation_next(struct mount *m,
  					 struct mount *origin)

  {

  	/* are there any slaves of this mount? */

  	if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))

  		return first_slave(m);
  
  	while (1) {

  		struct mount *master = m->mnt_master;

  		if (master == origin->mnt_master) {

  			struct mount *next = next_peer(m);
  			return (next == origin) ? NULL : next;

  		} else if (m->mnt_slave.next != &master->mnt_slave_list)

  			return next_slave(m);
  
  		/* back at master */
  		m = master;
  	}
  }

  static struct mount *skip_propagation_subtree(struct mount *m,
  						struct mount *origin)
  {
  	/*
  	 * Advance m such that propagation_next will not return
  	 * the slaves of m.
  	 */
  	if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
  		m = last_slave(m);
  
  	return m;
  }

  static struct mount *next_group(struct mount *m, struct mount *origin)

  {

  	while (1) {
  		while (1) {
  			struct mount *next;
  			if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
  				return first_slave(m);
  			next = next_peer(m);
  			if (m->mnt_group_id == origin->mnt_group_id) {
  				if (next == origin)
  					return NULL;
  			} else if (m->mnt_slave.next != &next->mnt_slave)
  				break;
  			m = next;
  		}
  		/* m is the last peer */
  		while (1) {
  			struct mount *master = m->mnt_master;
  			if (m->mnt_slave.next != &master->mnt_slave_list)
  				return next_slave(m);
  			m = next_peer(master);
  			if (master->mnt_group_id == origin->mnt_group_id)
  				break;
  			if (master->mnt_slave.next == &m->mnt_slave)
  				break;
  			m = master;
  		}
  		if (m == origin)
  			return NULL;

  	}

  }

  /* all accesses are serialized by namespace_sem */

  static struct mount *last_dest, *first_source, *last_source, *dest_master;

  static struct mountpoint *mp;
  static struct hlist_head *list;

  static inline bool peers(struct mount *m1, struct mount *m2)
  {
  	return m1->mnt_group_id == m2->mnt_group_id && m1->mnt_group_id;
  }

  static int propagate_one(struct mount *m)
  {
  	struct mount *child;
  	int type;
  	/* skip ones added by this propagate_mnt() */
  	if (IS_MNT_NEW(m))
  		return 0;
  	/* skip if mountpoint isn't covered by it */
  	if (!is_subdir(mp->m_dentry, m->mnt.mnt_root))
  		return 0;

  	if (peers(m, last_dest)) {

  		type = CL_MAKE_SHARED;
  	} else {
  		struct mount *n, *p;

  		bool done;

  		for (n = m; ; n = p) {
  			p = n->mnt_master;

  			if (p == dest_master || IS_MNT_MARKED(p))

  				break;

  		}

  		do {
  			struct mount *parent = last_source->mnt_parent;
  			if (last_source == first_source)
  				break;
  			done = parent->mnt_master == p;
  			if (done && peers(n, parent))
  				break;
  			last_source = last_source->mnt_master;
  		} while (!done);

  		type = CL_SLAVE;
  		/* beginning of peer group among the slaves? */
  		if (IS_MNT_SHARED(m))
  			type |= CL_MAKE_SHARED;

  	}

  	child = copy_tree(last_source, last_source->mnt.mnt_root, type);
  	if (IS_ERR(child))
  		return PTR_ERR(child);

  	read_seqlock_excl(&mount_lock);

  	mnt_set_mountpoint(m, mp, child);

  	if (m->mnt_master != dest_master)
  		SET_MNT_MARK(m->mnt_master);
  	read_sequnlock_excl(&mount_lock);

  	last_dest = m;
  	last_source = child;

  	hlist_add_head(&child->mnt_hash, list);

  	return count_mounts(m->mnt_ns, child);

  }
  
  /*
   * mount 'source_mnt' under the destination 'dest_mnt' at
   * dentry 'dest_dentry'. And propagate that mount to
   * all the peer and slave mounts of 'dest_mnt'.
   * Link all the new mounts into a propagation tree headed at
   * source_mnt. Also link all the new mounts using ->mnt_list
   * headed at source_mnt's ->mnt_list
   *
   * @dest_mnt: destination mount.
   * @dest_dentry: destination dentry.
   * @source_mnt: source mount.
   * @tree_list : list of heads of trees to be attached.
   */

  int propagate_mnt(struct mount *dest_mnt, struct mountpoint *dest_mp,

  		    struct mount *source_mnt, struct hlist_head *tree_list)

  {

  	struct mount *m, *n;

  	int ret = 0;

  	/*
  	 * we don't want to bother passing tons of arguments to
  	 * propagate_one(); everything is serialized by namespace_sem,
  	 * so globals will do just fine.
  	 */

  	last_dest = dest_mnt;

  	first_source = source_mnt;

  	last_source = source_mnt;
  	mp = dest_mp;
  	list = tree_list;
  	dest_master = dest_mnt->mnt_master;
  
  	/* all peers of dest_mnt, except dest_mnt itself */
  	for (n = next_peer(dest_mnt); n != dest_mnt; n = next_peer(n)) {
  		ret = propagate_one(n);
  		if (ret)

  			goto out;

  	}

  	/* all slave groups */
  	for (m = next_group(dest_mnt, dest_mnt); m;
  			m = next_group(m, dest_mnt)) {
  		/* everything in that slave group */
  		n = m;
  		do {
  			ret = propagate_one(n);
  			if (ret)
  				goto out;
  			n = next_peer(n);
  		} while (n != m);

  	}
  out:

  	read_seqlock_excl(&mount_lock);
  	hlist_for_each_entry(n, tree_list, mnt_hash) {
  		m = n->mnt_parent;
  		if (m->mnt_master != dest_mnt->mnt_master)
  			CLEAR_MNT_MARK(m->mnt_master);

  	}

  	read_sequnlock_excl(&mount_lock);

  	return ret;
  }

  static struct mount *find_topper(struct mount *mnt)
  {
  	/* If there is exactly one mount covering mnt completely return it. */
  	struct mount *child;
  
  	if (!list_is_singular(&mnt->mnt_mounts))
  		return NULL;
  
  	child = list_first_entry(&mnt->mnt_mounts, struct mount, mnt_child);
  	if (child->mnt_mountpoint != mnt->mnt.mnt_root)
  		return NULL;
  
  	return child;
  }

  /*
   * return true if the refcount is greater than count
   */

  static inline int do_refcount_check(struct mount *mnt, int count)

  {

  	return mnt_get_count(mnt) > count;

  }
  
  /*
   * check if the mount 'mnt' can be unmounted successfully.
   * @mnt: the mount to be checked for unmount
   * NOTE: unmounting 'mnt' would naturally propagate to all
   * other mounts its parent propagates to.
   * Check if any of these mounts that **do not have submounts**
   * have more references than 'refcnt'. If so return busy.

   *

   * vfsmount lock must be held for write

   */

  int propagate_mount_busy(struct mount *mnt, int refcnt)

  {

  	struct mount *m, *child, *topper;

  	struct mount *parent = mnt->mnt_parent;

  	if (mnt == parent)

  		return do_refcount_check(mnt, refcnt);
  
  	/*
  	 * quickly check if the current mount can be unmounted.
  	 * If not, we don't have to go checking for all other
  	 * mounts
  	 */

  	if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))

  		return 1;

  	for (m = propagation_next(parent, parent); m;
  	     		m = propagation_next(m, parent)) {

  		int count = 1;
  		child = __lookup_mnt(&m->mnt, mnt->mnt_mountpoint);
  		if (!child)
  			continue;
  
  		/* Is there exactly one mount on the child that covers
  		 * it completely whose reference should be ignored?
  		 */
  		topper = find_topper(child);
  		if (topper)
  			count += 1;
  		else if (!list_empty(&child->mnt_mounts))
  			continue;
  
  		if (do_refcount_check(child, count))
  			return 1;

  	}

  	return 0;

  }
  
  /*

   * Clear MNT_LOCKED when it can be shown to be safe.
   *
   * mount_lock lock must be held for write
   */
  void propagate_mount_unlock(struct mount *mnt)
  {
  	struct mount *parent = mnt->mnt_parent;
  	struct mount *m, *child;
  
  	BUG_ON(parent == mnt);
  
  	for (m = propagation_next(parent, parent); m;
  			m = propagation_next(m, parent)) {

  		child = __lookup_mnt(&m->mnt, mnt->mnt_mountpoint);

  		if (child)
  			child->mnt.mnt_flags &= ~MNT_LOCKED;
  	}
  }

  static void umount_one(struct mount *mnt, struct list_head *to_umount)

  {

  	CLEAR_MNT_MARK(mnt);
  	mnt->mnt.mnt_flags |= MNT_UMOUNT;
  	list_del_init(&mnt->mnt_child);
  	list_del_init(&mnt->mnt_umounting);
  	list_move_tail(&mnt->mnt_list, to_umount);

  }
  
  /*

   * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
   * parent propagates to.
   */

  static bool __propagate_umount(struct mount *mnt,
  			       struct list_head *to_umount,
  			       struct list_head *to_restore)

  {

  	bool progress = false;
  	struct mount *child;

  	/*
  	 * The state of the parent won't change if this mount is
  	 * already unmounted or marked as without children.
  	 */
  	if (mnt->mnt.mnt_flags & (MNT_UMOUNT | MNT_MARKED))
  		goto out;

  	/* Verify topper is the only grandchild that has not been
  	 * speculatively unmounted.
  	 */
  	list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
  		if (child->mnt_mountpoint == mnt->mnt.mnt_root)

  			continue;

  		if (!list_empty(&child->mnt_umounting) && IS_MNT_MARKED(child))
  			continue;
  		/* Found a mounted child */
  		goto children;
  	}

  	/* Mark mounts that can be unmounted if not locked */
  	SET_MNT_MARK(mnt);
  	progress = true;

  	/* If a mount is without children and not locked umount it. */
  	if (!IS_MNT_LOCKED(mnt)) {
  		umount_one(mnt, to_umount);
  	} else {
  children:
  		list_move_tail(&mnt->mnt_umounting, to_restore);
  	}
  out:
  	return progress;
  }
  
  static void umount_list(struct list_head *to_umount,
  			struct list_head *to_restore)
  {
  	struct mount *mnt, *child, *tmp;
  	list_for_each_entry(mnt, to_umount, mnt_list) {
  		list_for_each_entry_safe(child, tmp, &mnt->mnt_mounts, mnt_child) {
  			/* topper? */
  			if (child->mnt_mountpoint == mnt->mnt.mnt_root)
  				list_move_tail(&child->mnt_umounting, to_restore);
  			else
  				umount_one(child, to_umount);

  		}

  	}
  }

  static void restore_mounts(struct list_head *to_restore)

  {

  	/* Restore mounts to a clean working state */
  	while (!list_empty(to_restore)) {

  		struct mount *mnt, *parent;
  		struct mountpoint *mp;

  		mnt = list_first_entry(to_restore, struct mount, mnt_umounting);
  		CLEAR_MNT_MARK(mnt);
  		list_del_init(&mnt->mnt_umounting);

  		/* Should this mount be reparented? */

  		mp = mnt->mnt_mp;
  		parent = mnt->mnt_parent;
  		while (parent->mnt.mnt_flags & MNT_UMOUNT) {
  			mp = parent->mnt_mp;
  			parent = parent->mnt_parent;
  		}

  		if (parent != mnt->mnt_parent)
  			mnt_change_mountpoint(parent, mp, mnt);

  	}
  }

  static void cleanup_umount_visitations(struct list_head *visited)
  {
  	while (!list_empty(visited)) {
  		struct mount *mnt =
  			list_first_entry(visited, struct mount, mnt_umounting);
  		list_del_init(&mnt->mnt_umounting);
  	}
  }

  /*
   * collect all mounts that receive propagation from the mount in @list,
   * and return these additional mounts in the same list.
   * @list: the list of mounts to be unmounted.

   *
   * vfsmount lock must be held for write

   */

  int propagate_umount(struct list_head *list)

  {

  	struct mount *mnt;

  	LIST_HEAD(to_restore);
  	LIST_HEAD(to_umount);

  	LIST_HEAD(visited);

  	/* Find candidates for unmounting */
  	list_for_each_entry_reverse(mnt, list, mnt_list) {

  		struct mount *parent = mnt->mnt_parent;
  		struct mount *m;

  		/*
  		 * If this mount has already been visited it is known that it's
  		 * entire peer group and all of their slaves in the propagation
  		 * tree for the mountpoint has already been visited and there is
  		 * no need to visit them again.
  		 */
  		if (!list_empty(&mnt->mnt_umounting))
  			continue;
  
  		list_add_tail(&mnt->mnt_umounting, &visited);

  		for (m = propagation_next(parent, parent); m;
  		     m = propagation_next(m, parent)) {
  			struct mount *child = __lookup_mnt(&m->mnt,
  							   mnt->mnt_mountpoint);
  			if (!child)
  				continue;

  			if (!list_empty(&child->mnt_umounting)) {
  				/*
  				 * If the child has already been visited it is
  				 * know that it's entire peer group and all of
  				 * their slaves in the propgation tree for the
  				 * mountpoint has already been visited and there
  				 * is no need to visit this subtree again.
  				 */
  				m = skip_propagation_subtree(m, parent);
  				continue;
  			} else if (child->mnt.mnt_flags & MNT_UMOUNT) {
  				/*
  				 * We have come accross an partially unmounted
  				 * mount in list that has not been visited yet.
  				 * Remember it has been visited and continue
  				 * about our merry way.
  				 */
  				list_add_tail(&child->mnt_umounting, &visited);
  				continue;
  			}

  			/* Check the child and parents while progress is made */
  			while (__propagate_umount(child,
  						  &to_umount, &to_restore)) {
  				/* Is the parent a umount candidate? */
  				child = child->mnt_parent;
  				if (list_empty(&child->mnt_umounting))
  					break;
  			}
  		}
  	}

  	umount_list(&to_umount, &to_restore);
  	restore_mounts(&to_restore);

  	cleanup_umount_visitations(&visited);

  	list_splice_tail(&to_umount, list);

  	return 0;
  }