From 708ac4cdf5cd0a658d62490a9f4d78d3e1ec6612 Mon Sep 17 00:00:00 2001
From: Douglas Christopher Wilson <doug@somethingdoug.com>
Date: Wed, 13 Apr 2022 23:29:25 -0400
Subject: [PATCH] Fix handling very large stacks of sync middleware

closes #4891
---
 History.md          |  1 +
 lib/router/index.js |  8 ++++++++
 lib/router/route.js |  9 +++++++++
 test/Route.js       | 22 ++++++++++++++++++++++
 test/Router.js      | 16 ++++++++++++++++
 5 files changed, 56 insertions(+)

diff --git a/History.md b/History.md
index 4f43ad9255..3f7851ba57 100644
--- a/History.md
+++ b/History.md
@@ -5,6 +5,7 @@ unreleased
   * Allow `options` without `filename` in `res.download`
   * Deprecate string and non-integer arguments to `res.status`
   * Fix behavior of `null`/`undefined` as `maxAge` in `res.cookie`
+  * Fix handling very large stacks of sync middleware
   * Ignore `Object.prototype` values in settings through `app.set`/`app.get`
   * Invoke `default` with same arguments as types in `res.format`
   * Support proper 205 responses using `res.send`
diff --git a/lib/router/index.js b/lib/router/index.js
index 791a600f86..f4c8c0a79e 100644
--- a/lib/router/index.js
+++ b/lib/router/index.js
@@ -142,6 +142,7 @@ proto.handle = function handle(req, res, out) {
   var protohost = getProtohost(req.url) || ''
   var removed = '';
   var slashAdded = false;
+  var sync = 0
   var paramcalled = {};
 
   // store options for OPTIONS request
@@ -203,6 +204,11 @@ proto.handle = function handle(req, res, out) {
       return;
     }
 
+    // max sync stack
+    if (++sync > 100) {
+      return setImmediate(next, err)
+    }
+
     // get pathname of request
     var path = getPathname(req);
 
@@ -321,6 +327,8 @@ proto.handle = function handle(req, res, out) {
     } else {
       layer.handle_request(req, res, next);
     }
+
+    sync = 0
   }
 };
 
diff --git a/lib/router/route.js b/lib/router/route.js
index 178df0d516..5adaa125e2 100644
--- a/lib/router/route.js
+++ b/lib/router/route.js
@@ -98,6 +98,8 @@ Route.prototype._options = function _options() {
 Route.prototype.dispatch = function dispatch(req, res, done) {
   var idx = 0;
   var stack = this.stack;
+  var sync = 0
+
   if (stack.length === 0) {
     return done();
   }
@@ -127,6 +129,11 @@ Route.prototype.dispatch = function dispatch(req, res, done) {
       return done(err);
     }
 
+    // max sync stack
+    if (++sync > 100) {
+      return setImmediate(next, err)
+    }
+
     if (layer.method && layer.method !== method) {
       return next(err);
     }
@@ -136,6 +143,8 @@ Route.prototype.dispatch = function dispatch(req, res, done) {
     } else {
       layer.handle_request(req, res, next);
     }
+
+    sync = 0
   }
 };
 
diff --git a/test/Route.js b/test/Route.js
index 8e7ddbdbcc..3bdc8d7df2 100644
--- a/test/Route.js
+++ b/test/Route.js
@@ -13,6 +13,28 @@ describe('Route', function(){
     route.dispatch(req, {}, done)
   })
 
+  it('should not stack overflow with a large sync stack', function (done) {
+    this.timeout(5000) // long-running test
+
+    var req = { method: 'GET', url: '/' }
+    var route = new Route('/foo')
+
+    for (var i = 0; i < 6000; i++) {
+      route.all(function (req, res, next) { next() })
+    }
+
+    route.get(function (req, res, next) {
+      req.called = true
+      next()
+    })
+
+    route.dispatch(req, {}, function (err) {
+      if (err) return done(err)
+      assert.ok(req.called)
+      done()
+    })
+  })
+
   describe('.all', function(){
     it('should add handler', function(done){
       var req = { method: 'GET', url: '/' };
diff --git a/test/Router.js b/test/Router.js
index 907b972636..8a0654bca3 100644
--- a/test/Router.js
+++ b/test/Router.js
@@ -76,6 +76,22 @@ describe('Router', function(){
     router.handle({ url: '/', method: 'GET' }, { end: done });
   });
 
+  it('should not stack overflow with a large sync stack', function (done) {
+    this.timeout(5000) // long-running test
+
+    var router = new Router()
+
+    for (var i = 0; i < 6000; i++) {
+      router.use(function (req, res, next) { next() })
+    }
+
+    router.use(function (req, res) {
+      res.end()
+    })
+
+    router.handle({ url: '/', method: 'GET' }, { end: done })
+  })
+
   describe('.handle', function(){
     it('should dispatch', function(done){
       var router = new Router();