linux/fs/pnode.c
Al Viro d1ddc6f1d9 fix IS_MNT_PROPAGATING uses
propagate_mnt() does not attach anything to mounts created during
propagate_mnt() itself.  What's more, anything on ->mnt_slave_list
of such new mount must also be new, so we don't need to even look
there.

When move_mount() had been introduced, we've got an additional
class of mounts to skip - if we are moving from anon namespace,
we do not want to propagate to mounts we are moving (i.e. all
mounts in that anon namespace).

Unfortunately, the part about "everything on their ->mnt_slave_list
will also be ignorable" is not true - if we have propagation graph
	A -> B -> C
and do OPEN_TREE_CLONE open_tree() of B, we get
	A -> [B <-> B'] -> C
as propagation graph, where B' is a clone of B in our detached tree.
Making B private will result in
	A -> B' -> C
C still gets propagation from A, as it would after making B private
if we hadn't done that open_tree(), but now the propagation goes
through B'.  Trying to move_mount() our detached tree on subdirectory
in A should have
	* moved B' on that subdirectory in A
	* skipped the corresponding subdirectory in B' itself
	* copied B' on the corresponding subdirectory in C.
As it is, the logics in propagation_next() and friends ends up
skipping propagation into C, since it doesn't consider anything
downstream of B'.

IOW, walking the propagation graph should only skip the ->mnt_slave_list
of new mounts; the only places where the check for "in that one
anon namespace" are applicable are propagate_one() (where we should
treat that as the same kind of thing as "mountpoint we are looking
at is not visible in the mount we are looking at") and
propagation_would_overmount().  The latter is better dealt with
in the caller (can_move_mount_beneath()); on the first call of
propagation_would_overmount() the test is always false, on the
second it is always true in "move from anon namespace" case and
always false in "move within our namespace" one, so it's easier
to just use check_mnt() before bothering with the second call and
be done with that.

Fixes: 064fe6e233 ("mount: handle mount propagation for detached mount trees")
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2025-05-09 18:06:27 -04:00

643 lines
16 KiB
C

// 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 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 visible in m */
if (!is_subdir(dest_mp->m_dentry, m->mnt.mnt_root))
return 0;
/* skip if m is in the anon_ns we are emptying */
if (m->mnt_ns->mntns_flags & MNTNS_PROPAGATING)
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 (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);
mnt_notify_add(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 across a partially unmounted
* mount in a 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;
}