ovl: cleanup temp index entries

A previous failed attempt to create or whiteout a directory index may
leave index entries named '#%x' in the index dir. Cleanup those temp
entries on mount instead of failing the mount.

In the future, we may drop 'work' dir and use 'index' dir instead.
This change is enough for cleaning up copy up leftovers 'from the future',
but it is not enough for cleaning up rmdir leftovers 'from the future'
(i.e. temp dir containing whiteouts).
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/namei.c

@@ -9,6 +9,7 @@
 
 #include <linux/fs.h>
 #include <linux/cred.h>
+#include <linux/ctype.h>
 #include <linux/namei.h>
 #include <linux/xattr.h>
 #include <linux/ratelimit.h>
@@ -467,6 +468,12 @@ static struct dentry *ovl_index_upper(struct ovl_fs *ofs, struct dentry *index)
 	return upper;
 }
 
+/* Is this a leftover from create/whiteout of directory index entry? */
+static bool ovl_is_temp_index(struct dentry *index)
+{
+	return index->d_name.name[0] == '#';
+}
+
 /*
  * Verify that an index entry name matches the origin file handle stored in
  * OVL_XATTR_ORIGIN and that origin file handle can be decoded to lower path.
@@ -484,6 +491,11 @@ int ovl_verify_index(struct ovl_fs *ofs, struct dentry *index)
 	if (!d_inode(index))
 		return 0;
 
+	/* Cleanup leftover from index create/cleanup attempt */
+	err = -ESTALE;
+	if (ovl_is_temp_index(index))
+		goto fail;
+
 	err = -EINVAL;
 	if (index->d_name.len < sizeof(struct ovl_fh)*2)
 		goto fail;