ovl: whiteout orphan index entries on mount

Orphan index entries are non-dir index entries whose union nlink count
dropped to zero. With index=on, orphan index entries are removed on
mount. With NFS export feature enabled, orphan index entries are replaced
with white out index entries to block future open by handle from opening
the lower file.

When dir index has a stale 'upper' xattr, we assume that the upper dir
was removed and we treat the dir index as orphan entry that needs to be
whited out or removed.
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/namei.c

@@ -539,7 +539,15 @@ int ovl_verify_index(struct ovl_fs *ofs, struct dentry *index)
 	upper = ovl_index_upper(ofs, index);
 	if (IS_ERR_OR_NULL(upper)) {
 		err = PTR_ERR(upper);
-		if (!err)
+		/*
+		 * Directory index entries with no 'upper' xattr need to be
+		 * removed. When dir index entry has a stale 'upper' xattr,
+		 * we assume that upper dir was removed and we treat the dir
+		 * index as orphan entry that needs to be whited out.
+		 */
+		if (err == -ESTALE)
+			goto orphan;
+		else if (!err)
 			err = -ESTALE;
 		goto fail;
 	}
@@ -556,7 +564,7 @@ int ovl_verify_index(struct ovl_fs *ofs, struct dentry *index)
 			goto fail;
 
 		if (ovl_get_nlink(origin.dentry, index, 0) == 0)
-			err = -ENOENT;
+			goto orphan;
 	}
 
 out:
@@ -568,6 +576,13 @@ int ovl_verify_index(struct ovl_fs *ofs, struct dentry *index)
 	pr_warn_ratelimited("overlayfs: failed to verify index (%pd2, ftype=%x, err=%i)\n",
 			    index, d_inode(index)->i_mode & S_IFMT, err);
 	goto out;
+
+orphan:
+	pr_warn_ratelimited("overlayfs: orphan index entry (%pd2, ftype=%x, nlink=%u)\n",
+			    index, d_inode(index)->i_mode & S_IFMT,
+			    d_inode(index)->i_nlink);
+	err = -ENOENT;
+	goto out;
 }
 
 /*

fs/overlayfs/readdir.c

@@ -1067,12 +1067,33 @@ int ovl_indexdir_cleanup(struct ovl_fs *ofs)
 			break;
 		}
 		err = ovl_verify_index(ofs, index);
-		/* Cleanup stale and orphan index entries */
-		if (err && (err == -ESTALE || err == -ENOENT))
+		if (!err) {
+			goto next;
+		} else if (err == -ESTALE) {
+			/* Cleanup stale index entries */
+			err = ovl_cleanup(dir, index);
+		} else if (err != -ENOENT) {
+			/*
+			 * Abort mount to avoid corrupting the index if
+			 * an incompatible index entry was found or on out
+			 * of memory.
+			 */
+			break;
+		} else if (ofs->config.nfs_export) {
+			/*
+			 * Whiteout orphan index to block future open by
+			 * handle after overlay nlink dropped to zero.
+			 */
+			err = ovl_cleanup_and_whiteout(indexdir, dir, index);
+		} else {
+			/* Cleanup orphan index entries */
 			err = ovl_cleanup(dir, index);
+		}
+
 		if (err)
 			break;
 
+next:
 		dput(index);
 		index = NULL;
 	}