Commit 2b11d80e authored by Al Viro's avatar Al Viro Committed by Greg Kroah-Hartman

fix d_walk()/non-delayed __d_free() race

commit 3d56c25e upstream.

Ascend-to-parent logics in d_walk() depends on all encountered child
dentries not getting freed without an RCU delay.  Unfortunately, in
quite a few cases it is not true, with hard-to-hit oopsable race as
the result.

Fortunately, the fix is simiple; right now the rule is "if it ever
been hashed, freeing must be delayed" and changing it to "if it
ever had a parent, freeing must be delayed" closes that hole and
covers all cases the old rule used to cover.  Moreover, pipes and
sockets remain _not_ covered, so we do not introduce RCU delay in
the cases which are the reason for having that delay conditional
in the first place.
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent c08b1a59
......@@ -1618,7 +1618,7 @@ struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
struct dentry *dentry = __d_alloc(parent->d_sb, name);
if (!dentry)
return NULL;
dentry->d_flags |= DCACHE_RCUACCESS;
spin_lock(&parent->d_lock);
/*
* don't need child lock because it is not subject
......@@ -2413,7 +2413,6 @@ static void __d_rehash(struct dentry * entry, struct hlist_bl_head *b)
{
BUG_ON(!d_unhashed(entry));
hlist_bl_lock(b);
entry->d_flags |= DCACHE_RCUACCESS;
hlist_bl_add_head_rcu(&entry->d_hash, b);
hlist_bl_unlock(b);
}
......@@ -2632,6 +2631,7 @@ static void __d_move(struct dentry *dentry, struct dentry *target,
/* ... and switch them in the tree */
if (IS_ROOT(dentry)) {
/* splicing a tree */
dentry->d_flags |= DCACHE_RCUACCESS;
dentry->d_parent = target->d_parent;
target->d_parent = target;
list_del_init(&target->d_child);
......
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