ovl: check for bad and whiteout index on lookup

Index should always be of the same file type as origin, except for
the case of a whiteout index.  A whiteout index should only exist
if all lower aliases have been unlinked, which means that finding
a lower origin on lookup whose index is a whiteout should be treated
as a lookup error.
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/namei.c

@@ -513,6 +513,7 @@ static struct dentry *ovl_lookup_index(struct dentry *dentry,
 		goto out;
 	}
 
+	inode = d_inode(index);
 	if (d_is_negative(index)) {
 		if (upper && d_inode(origin)->i_nlink > 1) {
 			pr_warn_ratelimited("overlayfs: hard link with origin but no index (ino=%lu).\n",
@@ -522,11 +523,22 @@ static struct dentry *ovl_lookup_index(struct dentry *dentry,
 
 		dput(index);
 		index = NULL;
-	} else if (upper && d_inode(index) != d_inode(upper)) {
-		inode = d_inode(index);
-		pr_warn_ratelimited("overlayfs: wrong index found (index ino: %lu, upper ino: %lu).\n",
-				    d_inode(index)->i_ino,
-				    d_inode(upper)->i_ino);
+	} else if (upper && d_inode(upper) != inode) {
+		pr_warn_ratelimited("overlayfs: wrong index found (index=%pd2, ino=%lu, upper ino=%lu).\n",
+				    index, inode->i_ino, d_inode(upper)->i_ino);
+		goto fail;
+	} else if (ovl_dentry_weird(index) || ovl_is_whiteout(index) ||
+		   ((inode->i_mode ^ d_inode(origin)->i_mode) & S_IFMT)) {
+		/*
+		 * Index should always be of the same file type as origin
+		 * except for the case of a whiteout index. A whiteout
+		 * index should only exist if all lower aliases have been
+		 * unlinked, which means that finding a lower origin on lookup
+		 * whose index is a whiteout should be treated as an error.
+		 */
+		pr_warn_ratelimited("overlayfs: bad index found (index=%pd2, ftype=%x, origin ftype=%x).\n",
+				    index, d_inode(index)->i_mode & S_IFMT,
+				    d_inode(origin)->i_mode & S_IFMT);
 		goto fail;
 	}