// SPDX-License-Identifier: GPL-2.0-only
/*
* linux/fs/pnode.c
*
* (C) Copyright IBM Corporation 2005.
* Author : Ram Pai ([email protected])
*/
#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 hlist_head *list;
static inline bool peers(const struct mount *m1, const struct mount *m2)
{
return m1->mnt_group_id == m2->mnt_group_id && m1->mnt_group_id;
}
static int propagate_one(struct mount *m, struct mountpoint *dest_mp)
{
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(dest_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 (peers(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, dest_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;
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, dest_mp);
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, dest_mp);
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;
}
/**
* propagation_would_overmount - check whether propagation from @from
* would overmount @to
* @from: shared mount
* @to: mount to check
* @mp: future mountpoint of @to on @from
*
* If @from propagates mounts to @to, @from and @to must either be peers
* or one of the masters in the hierarchy of masters of @to must be a
* peer of @from.
*
* If the root of the @to mount is equal to the future mountpoint @mp of
* the @to mount on @from then @to will be overmounted by whatever is
* propagated to it.
*
* Context: This function expects namespace_lock() to be held and that
* @mp is stable.
* Return: If @from overmounts @to, true is returned, false if not.
*/
bool propagation_would_overmount(const struct mount *from,
const struct mount *to,
const struct mountpoint *mp)
{
if (!IS_MNT_SHARED(from))
return false;
if (IS_MNT_NEW(to))
return false;
if (to->mnt.mnt_root != mp->m_dentry)
return false;
for (const struct mount *m = to; m; m = m->mnt_master) {
if (peers(from, m))
return true;
}
return false;
}
/*
* 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);
move_from_ns(mnt, 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;
}
Codebase Browser
linux