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fix copy_tree() regression 

Since 3.14 we had copy_tree() get the shadowing wrong - if we had one
vfsmount shadowing another (i.e. if A is a slave of B, C is mounted
on A/foo, then D got mounted on B/foo creating D' on A/foo shadowed
by C), copy_tree() of A would make a copy of D' shadow the the copy of
C, not the other way around.

It's easy to fix, fortunately - just make sure that mount follows
the one that shadows it in mnt_child as well as in mnt_hash, and when
copy_tree() decides to attach a new mount, check if the last child
it has added to the same parent should be shadowing the new one.
And if it should, just use the same logics commit_tree() has - put the
new mount into the hash and children lists right after the one that
should shadow it.

Cc: stable@vger.kernel.org [3.14 and later]
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2014-08-10 03:44:55 -04:00
parent 60bb45297f
commit 12a5b5294c
1 changed files with 24 additions and 7 deletions
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31
fs/namespace.c
View File

@ -778,6 +778,20 @@ static void attach_mnt(struct mount *mnt,
list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
}
static void attach_shadowed(struct mount *mnt,
struct mount *parent,
struct mount *shadows)
{
if (shadows) {
hlist_add_after_rcu(&shadows->mnt_hash, &mnt->mnt_hash);
list_add(&mnt->mnt_child, &shadows->mnt_child);
} else {
hlist_add_head_rcu(&mnt->mnt_hash,
m_hash(&parent->mnt, mnt->mnt_mountpoint));
list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
}
}
/*
* vfsmount lock must be held for write
*/
@ -796,12 +810,7 @@ static void commit_tree(struct mount *mnt, struct mount *shadows)
list_splice(&head, n->list.prev);
if (shadows)
hlist_add_after_rcu(&shadows->mnt_hash, &mnt->mnt_hash);
else
hlist_add_head_rcu(&mnt->mnt_hash,
m_hash(&parent->mnt, mnt->mnt_mountpoint));
list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
attach_shadowed(mnt, parent, shadows);
touch_mnt_namespace(n);
}
@ -1474,6 +1483,7 @@ struct mount *copy_tree(struct mount *mnt, struct dentry *dentry,
continue;
for (s = r; s; s = next_mnt(s, r)) {
struct mount *t = NULL;
if (!(flag & CL_COPY_UNBINDABLE) &&
IS_MNT_UNBINDABLE(s)) {
s = skip_mnt_tree(s);
@ -1495,7 +1505,14 @@ struct mount *copy_tree(struct mount *mnt, struct dentry *dentry,
goto out;
lock_mount_hash();
list_add_tail(&q->mnt_list, &res->mnt_list);
attach_mnt(q, parent, p->mnt_mp);
mnt_set_mountpoint(parent, p->mnt_mp, q);
if (!list_empty(&parent->mnt_mounts)) {
t = list_last_entry(&parent->mnt_mounts,
struct mount, mnt_child);
if (t->mnt_mp != p->mnt_mp)
t = NULL;
}
attach_shadowed(q, parent, t);
unlock_mount_hash();
}
}