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attach_recursive_mnt(): do not lock the covering tree when sliding something under it

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If we are propagating across the userns boundary, we need to lock the
mounts added there.  However, in case when something has already
been mounted there and we end up sliding a new tree under that,
the stuff that had been there before should not get locked.

IOW, lock_mnt_tree() should be called before we reparent the
preexisting tree on top of what we are adding.

Fixes: 3bd045cc9c ("separate copying and locking mount tree on cross-userns copies")
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro
2025-06-22 18:03:29 -04:00
parent 7484e15dbb
commit ce7df19686
1 changed files with 4 additions and 4 deletions
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8
fs/namespace.c
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@@ -2768,14 +2768,14 @@ static int attach_recursive_mnt(struct mount *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;
q = __lookup_mnt(&child->mnt_parent->mnt,
child->mnt_mountpoint);
if (q)
mnt_change_mountpoint(child, smp, q);
commit_tree(child);
}
put_mountpoint(smp);