Fix race condition and add test

app/models/alternative.js

@@ -5,6 +5,12 @@ const mongoose = require('mongoose');
 const Election = require('./election');
 const Vote = require('./vote');
 const errors = require('../errors');
+const env = require('../../env');
+
+const redisClient = require('redis').createClient(6379, env.REDIS_URL);
+const Redlock = require('redlock');
+
+const redlock = new Redlock([redisClient], {});
 
 const Schema = mongoose.Schema;
 
@@ -38,19 +44,30 @@ alternativeSchema.methods.addVote = async function(user) {
   if (user.admin) throw new errors.AdminVotingError();
   if (user.moderator) throw new errors.ModeratorVotingError();
 
+  const lock = await redlock.lock('vote:' + user.username, 2000);
   const election = await Election.findById(this.election).exec();
-  if (!election.active) throw new errors.InactiveElectionError();
+  if (!election.active) {
+    await lock.unlock();
+    throw new errors.InactiveElectionError();
+  }
   const votedUsers = election.hasVotedUsers.toObject();
   const hasVoted = _.find(votedUsers, { user: user._id });
-  if (hasVoted) throw new errors.AlreadyVotedError();
+  if (hasVoted) {
+    await lock.unlock();
+    throw new errors.AlreadyVotedError();
+  }
 
   // 24 character random string
   const voteHash = crypto.randomBytes(12).toString('hex');
   const vote = new Vote({ hash: voteHash, alternative: this.id });
 
   election.hasVotedUsers.push({ user: user._id });
   await election.save();
-  return vote.save();
+  const savedVote = await vote.save();
+
+  await lock.unlock();
+
+  return savedVote;
 };
 
 module.exports = mongoose.model('Alternative', alternativeSchema);

docker-compose.yml

@@ -5,3 +5,8 @@ services:
     image: mongo:3.6
     ports:
       - '127.0.0.1:27017:27017'
+  redis:
+    image: redis:latest
+    ports:
+      - '127.0.0.1:6379:6379'
+

env.js

@@ -10,5 +10,6 @@ module.exports = {
   HOST: process.env.HOST || 'localhost',
   // DSN url for reporting errors to sentry
   RAVEN_DSN: process.env.RAVEN_DSN,
-  MONGO_URL: process.env.MONGO_URL || 'mongodb://localhost:27017/vote'
+  MONGO_URL: process.env.MONGO_URL || 'mongodb://localhost:27017/vote',
+  REDIS_URL: process.env.REDIS_URL || 'localhost'
 };

package.json

@@ -14,7 +14,7 @@
     "lint:prettier": "prettier '**/*.js' --list-different --ignore-path .gitignore",
     "lint:yaml": "yarn yamllint .drone.yml docker-compose.yml usage.yml deployment/docker-compose.yml",
     "prettier": "prettier '**/*.js' --write",
-    "mocha": "NODE_ENV=test MONGO_URL=${MONGO_URL:-'mongodb://localhost:27017/vote-test'} nyc mocha test/**/*.test.js",
+    "mocha": "NODE_ENV=test MONGO_URL=${MONGO_URL:-'mongodb://localhost:27017/vote-test'} nyc mocha test/**/*.test.js --exit",
     "coverage": "nyc report --reporter=text-lcov | coveralls",
     "protractor": "webdriver-manager update --standalone false && NODE_ENV=protractor MONGO_URL=${MONGO_URL:-'mongodb://localhost:27017/vote-test'} protractor ./features/protractor-conf.js",
     "postinstall": "yarn build"
@@ -62,6 +62,8 @@
     "qr-scanner": "1.1.1",
     "qrcode": "1.3.3",
     "raven": "2.6.4",
+    "redis": "2.8.0",
+    "redlock": "3.1.2",
     "serve-favicon": "2.5.0",
     "socket.io": "2.2.0",
     "style-loader": "0.23.1",

test/api/vote.test.js

@@ -136,6 +136,27 @@ describe('Vote API', () => {
     votes.length.should.equal(1);
   });
 
+  it('should not be vulnerable to race conditions', async function() {
+    const create = () =>
+      request(app)
+        .post('/api/vote')
+        .send(votePayload(this.activeAlternative.id));
+    await Promise.all([
+      create(),
+      create(),
+      create(),
+      create(),
+      create(),
+      create(),
+      create(),
+      create(),
+      create(),
+      create()
+    ]);
+    const votes = await Vote.find({ alternative: this.activeAlternative.id });
+    votes.length.should.equal(1);
+  });
+
   it('should not be possible to vote without logging in', async function() {
     passportStub.logout();
     const { body: error } = await request(app)

yarn.lock

@@ -750,7 +750,7 @@ bluebird@3.5.1:
   resolved "https://registry.yarnpkg.com/bluebird/-/bluebird-3.5.1.tgz#d9551f9de98f1fcda1e683d17ee91a0602ee2eb9"
   integrity sha512-MKiLiV+I1AA596t9w1sQJ8jkiSr5+ZKi0WKrYGUn6d1Fx+Ij4tIj+m2WMQSGczs5jZVxV339chE8iwk6F64wjA==
 
-bluebird@3.5.3, bluebird@^3.5.3:
+bluebird@3.5.3, bluebird@^3.3.3, bluebird@^3.5.3:
   version "3.5.3"
   resolved "https://registry.yarnpkg.com/bluebird/-/bluebird-3.5.3.tgz#7d01c6f9616c9a51ab0f8c549a79dfe6ec33efa7"
   integrity sha512-/qKPUQlaW1OyR51WeCPBvRnAlnZFUJkCSG5HzGnuIqhgyJtF+T94lFnn33eiazjRm2LAHVy2guNnaq48X9SJuw==
@@ -1781,6 +1781,11 @@ domain-browser@^1.1.1:
   resolved "https://registry.yarnpkg.com/domain-browser/-/domain-browser-1.2.0.tgz#3d31f50191a6749dd1375a7f522e823d42e54eda"
   integrity sha512-jnjyiM6eRyZl2H+W8Q/zLMA481hzi0eszAaBUzIVnmYVDBbnLxVNnfu1HgEBvCbL+71FrxMl3E6lpKH7Ge3OXA==
 
+double-ended-queue@^2.1.0-0:
+  version "2.1.0-0"
+  resolved "https://registry.yarnpkg.com/double-ended-queue/-/double-ended-queue-2.1.0-0.tgz#103d3527fd31528f40188130c841efdd78264e5c"
+  integrity sha1-ED01J/0xUo9AGIEwyEHv3XgmTlw=
+
 duplexify@^3.4.2, duplexify@^3.6.0:
   version "3.6.1"
   resolved "https://registry.yarnpkg.com/duplexify/-/duplexify-3.6.1.tgz#b1a7a29c4abfd639585efaecce80d666b1e34125"
@@ -5042,6 +5047,32 @@ readdirp@^2.0.0:
     micromatch "^3.1.10"
     readable-stream "^2.0.2"
 
+redis-commands@^1.2.0:
+  version "1.4.0"
+  resolved "https://registry.yarnpkg.com/redis-commands/-/redis-commands-1.4.0.tgz#52f9cf99153efcce56a8f86af986bd04e988602f"
+  integrity sha512-cu8EF+MtkwI4DLIT0x9P8qNTLFhQD4jLfxLR0cCNkeGzs87FN6879JOJwNQR/1zD7aSYNbU0hgsV9zGY71Itvw==
+
+redis-parser@^2.6.0:
+  version "2.6.0"
+  resolved "https://registry.yarnpkg.com/redis-parser/-/redis-parser-2.6.0.tgz#52ed09dacac108f1a631c07e9b69941e7a19504b"
+  integrity sha1-Uu0J2srBCPGmMcB+m2mUHnoZUEs=
+
+redis@2.8.0:
+  version "2.8.0"
+  resolved "https://registry.yarnpkg.com/redis/-/redis-2.8.0.tgz#202288e3f58c49f6079d97af7a10e1303ae14b02"
+  integrity sha512-M1OkonEQwtRmZv4tEWF2VgpG0JWJ8Fv1PhlgT5+B+uNq2cA3Rt1Yt/ryoR+vQNOQcIEgdCdfH0jr3bDpihAw1A==
+  dependencies:
+    double-ended-queue "^2.1.0-0"
+    redis-commands "^1.2.0"
+    redis-parser "^2.6.0"
+
+redlock@3.1.2:
+  version "3.1.2"
+  resolved "https://registry.yarnpkg.com/redlock/-/redlock-3.1.2.tgz#27c82534da8548027aa8d61084a08078ae74ed36"
+  integrity sha512-CKXhOvLd4In5QOfbcF0GIcSsa+pL9JPZd+eKeMk/Sydxh93NUNtwQMTIKFqwPu3PjEgDStwYFJTurVzNA33pZw==
+  dependencies:
+    bluebird "^3.3.3"
+
 regenerate@^1.2.1:
   version "1.4.0"
   resolved "https://registry.yarnpkg.com/regenerate/-/regenerate-1.4.0.tgz#4a856ec4b56e4077c557589cae85e7a4c8869a11"