Fix ->d_lock locking order in unlazy_walk()

Make sure that child is still a child of parent before nested locking
of child->d_lock in unlazy_walk(); otherwise we are risking a violation
of locking order and deadlocks.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/namei.c b/fs/namei.c
index 0223c41fb114..5c867dd1c0b3 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -433,6 +433,8 @@ static int unlazy_walk(struct nameidata *nd, struct dentry *dentry)
                         goto err_parent;
                 BUG_ON(nd->inode != parent->d_inode);
         } else {
+                if (dentry->d_parent != parent)
+                        goto err_parent;
                 spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
                 if (!__d_rcu_to_refcount(dentry, nd->seq))
                         goto err_child;