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  1/*
  2 *  linux/fs/pnode.c
  3 *
  4 * (C) Copyright IBM Corporation 2005.
  5 *	Released under GPL v2.
  6 *	Author : Ram Pai (linuxram@us.ibm.com)
  7 *
  8 */
  9#include <linux/mnt_namespace.h>
 10#include <linux/mount.h>
 11#include <linux/fs.h>
 12#include <linux/nsproxy.h>
 13#include "internal.h"
 14#include "pnode.h"
 15
 16/* return the next shared peer mount of @p */
 17static inline struct mount *next_peer(struct mount *p)
 18{
 19	return list_entry(p->mnt_share.next, struct mount, mnt_share);
 20}
 21
 22static inline struct mount *first_slave(struct mount *p)
 23{
 24	return list_entry(p->mnt_slave_list.next, struct mount, mnt_slave);
 25}
 26
 27static inline struct mount *next_slave(struct mount *p)
 28{
 29	return list_entry(p->mnt_slave.next, struct mount, mnt_slave);
 30}
 31
 32static struct mount *get_peer_under_root(struct mount *mnt,
 33					 struct mnt_namespace *ns,
 34					 const struct path *root)
 35{
 36	struct mount *m = mnt;
 37
 38	do {
 39		/* Check the namespace first for optimization */
 40		if (m->mnt_ns == ns && is_path_reachable(m, m->mnt.mnt_root, root))
 41			return m;
 42
 43		m = next_peer(m);
 44	} while (m != mnt);
 45
 46	return NULL;
 47}
 48
 49/*
 50 * Get ID of closest dominating peer group having a representative
 51 * under the given root.
 52 *
 53 * Caller must hold namespace_sem
 54 */
 55int get_dominating_id(struct mount *mnt, const struct path *root)
 56{
 57	struct mount *m;
 58
 59	for (m = mnt->mnt_master; m != NULL; m = m->mnt_master) {
 60		struct mount *d = get_peer_under_root(m, mnt->mnt_ns, root);
 61		if (d)
 62			return d->mnt_group_id;
 63	}
 64
 65	return 0;
 66}
 67
 68static int do_make_slave(struct mount *mnt)
 69{
 70	struct mount *peer_mnt = mnt, *master = mnt->mnt_master;
 71	struct mount *slave_mnt;
 72
 73	/*
 74	 * slave 'mnt' to a peer mount that has the
 75	 * same root dentry. If none is available then
 76	 * slave it to anything that is available.
 77	 */
 78	while ((peer_mnt = next_peer(peer_mnt)) != mnt &&
 79	       peer_mnt->mnt.mnt_root != mnt->mnt.mnt_root) ;
 80
 81	if (peer_mnt == mnt) {
 82		peer_mnt = next_peer(mnt);
 83		if (peer_mnt == mnt)
 84			peer_mnt = NULL;
 85	}
 86	if (mnt->mnt_group_id && IS_MNT_SHARED(mnt) &&
 87	    list_empty(&mnt->mnt_share))
 88		mnt_release_group_id(mnt);
 89
 90	list_del_init(&mnt->mnt_share);
 91	mnt->mnt_group_id = 0;
 92
 93	if (peer_mnt)
 94		master = peer_mnt;
 95
 96	if (master) {
 97		list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave)
 98			slave_mnt->mnt_master = master;
 99		list_move(&mnt->mnt_slave, &master->mnt_slave_list);
100		list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev);
101		INIT_LIST_HEAD(&mnt->mnt_slave_list);
102	} else {
103		struct list_head *p = &mnt->mnt_slave_list;
104		while (!list_empty(p)) {
105                        slave_mnt = list_first_entry(p,
106					struct mount, mnt_slave);
107			list_del_init(&slave_mnt->mnt_slave);
108			slave_mnt->mnt_master = NULL;
109		}
110	}
111	mnt->mnt_master = master;
112	CLEAR_MNT_SHARED(mnt);
113	return 0;
114}
115
116/*
117 * vfsmount lock must be held for write
118 */
119void change_mnt_propagation(struct mount *mnt, int type)
120{
121	if (type == MS_SHARED) {
122		set_mnt_shared(mnt);
123		return;
124	}
125	do_make_slave(mnt);
126	if (type != MS_SLAVE) {
127		list_del_init(&mnt->mnt_slave);
128		mnt->mnt_master = NULL;
129		if (type == MS_UNBINDABLE)
130			mnt->mnt.mnt_flags |= MNT_UNBINDABLE;
131		else
132			mnt->mnt.mnt_flags &= ~MNT_UNBINDABLE;
133	}
134}
135
136/*
137 * get the next mount in the propagation tree.
138 * @m: the mount seen last
139 * @origin: the original mount from where the tree walk initiated
140 *
141 * Note that peer groups form contiguous segments of slave lists.
142 * We rely on that in get_source() to be able to find out if
143 * vfsmount found while iterating with propagation_next() is
144 * a peer of one we'd found earlier.
145 */
146static struct mount *propagation_next(struct mount *m,
147					 struct mount *origin)
148{
149	/* are there any slaves of this mount? */
150	if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
151		return first_slave(m);
152
153	while (1) {
154		struct mount *master = m->mnt_master;
155
156		if (master == origin->mnt_master) {
157			struct mount *next = next_peer(m);
158			return (next == origin) ? NULL : next;
159		} else if (m->mnt_slave.next != &master->mnt_slave_list)
160			return next_slave(m);
161
162		/* back at master */
163		m = master;
164	}
165}
166
167static struct mount *next_group(struct mount *m, struct mount *origin)
168{
169	while (1) {
170		while (1) {
171			struct mount *next;
172			if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
173				return first_slave(m);
174			next = next_peer(m);
175			if (m->mnt_group_id == origin->mnt_group_id) {
176				if (next == origin)
177					return NULL;
178			} else if (m->mnt_slave.next != &next->mnt_slave)
179				break;
180			m = next;
181		}
182		/* m is the last peer */
183		while (1) {
184			struct mount *master = m->mnt_master;
185			if (m->mnt_slave.next != &master->mnt_slave_list)
186				return next_slave(m);
187			m = next_peer(master);
188			if (master->mnt_group_id == origin->mnt_group_id)
189				break;
190			if (master->mnt_slave.next == &m->mnt_slave)
191				break;
192			m = master;
193		}
194		if (m == origin)
195			return NULL;
196	}
197}
198
199/* all accesses are serialized by namespace_sem */
200static struct user_namespace *user_ns;
201static struct mount *last_dest, *last_source, *dest_master;
202static struct mountpoint *mp;
203static struct hlist_head *list;
204
205static int propagate_one(struct mount *m)
206{
207	struct mount *child;
208	int type;
209	/* skip ones added by this propagate_mnt() */
210	if (IS_MNT_NEW(m))
211		return 0;
212	/* skip if mountpoint isn't covered by it */
213	if (!is_subdir(mp->m_dentry, m->mnt.mnt_root))
214		return 0;
215	if (m->mnt_group_id == last_dest->mnt_group_id) {
216		type = CL_MAKE_SHARED;
217	} else {
218		struct mount *n, *p;
219		for (n = m; ; n = p) {
220			p = n->mnt_master;
221			if (p == dest_master || IS_MNT_MARKED(p)) {
222				while (last_dest->mnt_master != p) {
223					last_source = last_source->mnt_master;
224					last_dest = last_source->mnt_parent;
225				}
226				if (n->mnt_group_id != last_dest->mnt_group_id) {
227					last_source = last_source->mnt_master;
228					last_dest = last_source->mnt_parent;
229				}
230				break;
231			}
232		}
233		type = CL_SLAVE;
234		/* beginning of peer group among the slaves? */
235		if (IS_MNT_SHARED(m))
236			type |= CL_MAKE_SHARED;
237	}
238		
239	/* Notice when we are propagating across user namespaces */
240	if (m->mnt_ns->user_ns != user_ns)
241		type |= CL_UNPRIVILEGED;
242	child = copy_tree(last_source, last_source->mnt.mnt_root, type);
243	if (IS_ERR(child))
244		return PTR_ERR(child);
245	mnt_set_mountpoint(m, mp, child);
246	last_dest = m;
247	last_source = child;
248	if (m->mnt_master != dest_master) {
249		read_seqlock_excl(&mount_lock);
250		SET_MNT_MARK(m->mnt_master);
251		read_sequnlock_excl(&mount_lock);
252	}
253	hlist_add_head(&child->mnt_hash, list);
254	return 0;
255}
256
257/*
258 * mount 'source_mnt' under the destination 'dest_mnt' at
259 * dentry 'dest_dentry'. And propagate that mount to
260 * all the peer and slave mounts of 'dest_mnt'.
261 * Link all the new mounts into a propagation tree headed at
262 * source_mnt. Also link all the new mounts using ->mnt_list
263 * headed at source_mnt's ->mnt_list
264 *
265 * @dest_mnt: destination mount.
266 * @dest_dentry: destination dentry.
267 * @source_mnt: source mount.
268 * @tree_list : list of heads of trees to be attached.
269 */
270int propagate_mnt(struct mount *dest_mnt, struct mountpoint *dest_mp,
271		    struct mount *source_mnt, struct hlist_head *tree_list)
272{
273	struct mount *m, *n;
274	int ret = 0;
275
276	/*
277	 * we don't want to bother passing tons of arguments to
278	 * propagate_one(); everything is serialized by namespace_sem,
279	 * so globals will do just fine.
280	 */
281	user_ns = current->nsproxy->mnt_ns->user_ns;
282	last_dest = dest_mnt;
283	last_source = source_mnt;
284	mp = dest_mp;
285	list = tree_list;
286	dest_master = dest_mnt->mnt_master;
287
288	/* all peers of dest_mnt, except dest_mnt itself */
289	for (n = next_peer(dest_mnt); n != dest_mnt; n = next_peer(n)) {
290		ret = propagate_one(n);
291		if (ret)
292			goto out;
293	}
294
295	/* all slave groups */
296	for (m = next_group(dest_mnt, dest_mnt); m;
297			m = next_group(m, dest_mnt)) {
298		/* everything in that slave group */
299		n = m;
300		do {
301			ret = propagate_one(n);
302			if (ret)
303				goto out;
304			n = next_peer(n);
305		} while (n != m);
306	}
307out:
308	read_seqlock_excl(&mount_lock);
309	hlist_for_each_entry(n, tree_list, mnt_hash) {
310		m = n->mnt_parent;
311		if (m->mnt_master != dest_mnt->mnt_master)
312			CLEAR_MNT_MARK(m->mnt_master);
313	}
314	read_sequnlock_excl(&mount_lock);
315	return ret;
316}
317
318/*
319 * return true if the refcount is greater than count
320 */
321static inline int do_refcount_check(struct mount *mnt, int count)
322{
323	return mnt_get_count(mnt) > count;
324}
325
326/*
327 * check if the mount 'mnt' can be unmounted successfully.
328 * @mnt: the mount to be checked for unmount
329 * NOTE: unmounting 'mnt' would naturally propagate to all
330 * other mounts its parent propagates to.
331 * Check if any of these mounts that **do not have submounts**
332 * have more references than 'refcnt'. If so return busy.
333 *
334 * vfsmount lock must be held for write
335 */
336int propagate_mount_busy(struct mount *mnt, int refcnt)
337{
338	struct mount *m, *child;
339	struct mount *parent = mnt->mnt_parent;
340	int ret = 0;
341
342	if (mnt == parent)
343		return do_refcount_check(mnt, refcnt);
344
345	/*
346	 * quickly check if the current mount can be unmounted.
347	 * If not, we don't have to go checking for all other
348	 * mounts
349	 */
350	if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
351		return 1;
352
353	for (m = propagation_next(parent, parent); m;
354	     		m = propagation_next(m, parent)) {
355		child = __lookup_mnt_last(&m->mnt, mnt->mnt_mountpoint);
356		if (child && list_empty(&child->mnt_mounts) &&
357		    (ret = do_refcount_check(child, 1)))
358			break;
359	}
360	return ret;
361}
362
363/*
364 * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
365 * parent propagates to.
366 */
367static void __propagate_umount(struct mount *mnt)
368{
369	struct mount *parent = mnt->mnt_parent;
370	struct mount *m;
371
372	BUG_ON(parent == mnt);
373
374	for (m = propagation_next(parent, parent); m;
375			m = propagation_next(m, parent)) {
376
377		struct mount *child = __lookup_mnt_last(&m->mnt,
378						mnt->mnt_mountpoint);
379		/*
380		 * umount the child only if the child has no
381		 * other children
382		 */
383		if (child && list_empty(&child->mnt_mounts)) {
384			hlist_del_init_rcu(&child->mnt_hash);
385			hlist_add_before_rcu(&child->mnt_hash, &mnt->mnt_hash);
386		}
387	}
388}
389
390/*
391 * collect all mounts that receive propagation from the mount in @list,
392 * and return these additional mounts in the same list.
393 * @list: the list of mounts to be unmounted.
394 *
395 * vfsmount lock must be held for write
396 */
397int propagate_umount(struct hlist_head *list)
398{
399	struct mount *mnt;
400
401	hlist_for_each_entry(mnt, list, mnt_hash)
402		__propagate_umount(mnt);
403	return 0;
404}