udf: Skip parent dir link count update if corrupted

If the parent directory link count is too low (likely directory inode
corruption), just skip updating its link count as if it goes to 0 too
early it can cause unexpected issues.

Signed-off-by: Jan Kara <jack@suse.cz>

fs/udf/namei.c

@@ -517,7 +517,11 @@ static int udf_rmdir(struct inode *dir, struct dentry *dentry)
 			 inode->i_nlink);
 	clear_nlink(inode);
 	inode->i_size = 0;
-	inode_dec_link_count(dir);
+	if (dir->i_nlink >= 3)
+		inode_dec_link_count(dir);
+	else
+		udf_warn(inode->i_sb, "parent dir link count too low (%u)\n",
+			 dir->i_nlink);
 	udf_add_fid_counter(dir->i_sb, true, -1);
 	inode_set_mtime_to_ts(dir,
 			      inode_set_ctime_to_ts(dir, inode_set_ctime_current(inode)));