ovl: fix inconsistent d_ino for legacy merge dir

For a merge dir that was copied up before v4.12 or that was hand crafted
offline (e.g. mkdir {upper/lower}/dir), upper dir does not contain the
'trusted.overlay.origin' xattr.  In that case, stat(2) on the merge dir
returns the lower dir st_ino, but getdents(2) returns the upper dir d_ino.

After this change, on merge dir lookup, missing origin xattr on upper
dir will be fixed and 'impure' xattr will be fixed on parent of the legacy
merge dir.

Suggested-by: zhangyi (F) <yi.zhang@huawei.com>
Reviewed-by: zhangyi (F) <yi.zhang@huawei.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/copy_up.c

@@ -288,8 +288,8 @@ out:
 	return fh;
 }
 
-static int ovl_set_origin(struct dentry *dentry, struct dentry *lower,
-			  struct dentry *upper)
+int ovl_set_origin(struct dentry *dentry, struct dentry *lower,
+		   struct dentry *upper)
 {
 	const struct ovl_fh *fh = NULL;
 	int err;

fs/overlayfs/namei.c

@@ -584,6 +584,27 @@ static int ovl_find_layer(struct ovl_fs *ofs, struct ovl_path *path)
 	return i;
 }
 
+/* Fix missing 'origin' xattr */
+static int ovl_fix_origin(struct dentry *dentry, struct dentry *lower,
+			  struct dentry *upper)
+{
+	int err;
+
+	if (ovl_check_origin_xattr(upper))
+		return 0;
+
+	err = ovl_want_write(dentry);
+	if (err)
+		return err;
+
+	err = ovl_set_origin(dentry, lower, upper);
+	if (!err)
+		err = ovl_set_impure(dentry->d_parent, upper->d_parent);
+
+	ovl_drop_write(dentry);
+	return err;
+}
+
 struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 			  unsigned int flags)
 {
@@ -674,6 +695,18 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 		if (!this)
 			continue;
 
+		/*
+		 * If no origin fh is stored in upper of a merge dir, store fh
+		 * of lower dir and set upper parent "impure".
+		 */
+		if (upperdentry && !ctr && !ofs->noxattr) {
+			err = ovl_fix_origin(dentry, this, upperdentry);
+			if (err) {
+				dput(this);
+				goto out_put;
+			}
+		}
+
 		stack[ctr].dentry = this;
 		stack[ctr].layer = lower.layer;
 		ctr++;

fs/overlayfs/overlayfs.h

@@ -322,3 +322,5 @@ int ovl_copy_up_flags(struct dentry *dentry, int flags);
 int ovl_copy_xattr(struct dentry *old, struct dentry *new);
 int ovl_set_attr(struct dentry *upper, struct kstat *stat);
 struct ovl_fh *ovl_encode_fh(struct dentry *lower, bool is_upper);
+int ovl_set_origin(struct dentry *dentry, struct dentry *lower,
+		   struct dentry *upper);