added the description.

src/server/routes/tag.js

@@ -82,6 +82,10 @@ module.exports = function(crowi, app) {
    * @apiParam {String} q keyword
    */
   api.search = async function(req, res) {
+    // https://regex101.com/r/J1cN6O/1
+    // prevent from unexpecting attack doing regular expression on tag search (DoS attack)
+    // FOR EXAMPLE
+    // (((((((((((((((((((((((((((((((((((((((((((((((([a-z]*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*)*$
     const escapeRegExp = req.query.q.replace(/[\\^$/.*+?()[\]{}|]/g, '\\$&');
     let tags = await Tag.find({ name: new RegExp(`^${escapeRegExp}`) }).select('-_id name');
     tags = tags.map((tag) => { return tag.name });