Add checksums to enforce immutability (#250)

Co-authored-by: Ben Drucker <bvdrucker@gmail.com>
terraform-linters · Nov 7, 2024 · 8093687 · 8093687
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diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
@@ -88,6 +88,21 @@ jobs:
       if: matrix.tflint_version == 'latest'
       run: tflint -v
 
+  integration-checksum:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+      - name: Use Action
+        uses: ./
+        with:
+          tflint_version: 'v0.53.0'
+          # https://github.com/terraform-linters/tflint/releases/tag/v0.53.0
+          # checksums.txt
+          # tflint_linux_amd64
+          checksums: bb0a3a6043ea1bcd221fc95d49bac831bb511eb31946ca6a4050983e9e584578
+      - run: tflint -v
+
   integration-matchers:
     name: 'Integration test (tflint_version: ${{ matrix.tflint_version }})'
     runs-on: ubuntu-latest

diff --git a/README.md b/README.md
@@ -13,6 +13,15 @@ If version is `"latest"`, the action will get the latest version number using [O
 
 Default: `"latest"`
 
+### `checksums`
+
+**Optional** A newline-delimited list of valid checksums (SHA256 hashes) for the downloaded TFLint binary. When set, the action will verify that the binary matches one of these checksums before proceeding.
+
+This ensures that the downloaded binary for a given version is a known build. If your job runs in multiple operating systems or architectures, include appropriate checksums for all of them.
+
+**Note:** Checksums ensure _immutability_, but do not verify integrity. To prove that checksums come from a known build in TFLint's official repository, use [GitHub’s Artifact Attestations](https://github.com/terraform-linters/tflint?tab=readme-ov-file#github-cli-recommended) or [cosign](https://github.com/terraform-linters/tflint?tab=readme-ov-file#cosign).
+
+
 ### `github_token`
 
 Used to authenticate requests to the GitHub API to obtain release data from the TFLint repository. Authenticating will increase the [API rate limit](https://developer.github.com/v3/#rate-limiting). Any valid token is supported. No permissions are required.
@@ -32,7 +41,7 @@ Default: `"false"`
 The following outputs are available when the `tflint_wrapper` input is enabled:
 
 - `stdout` - The output (stdout) produced by the tflint command.
-- `stderr` - The error output (stdout) produced by the tflint command.
+- `stderr` - The error output (stderr) produced by the tflint command.
 - `exitcode` - The exit code produced by the tflint command.
 
 ## Usage
@@ -66,7 +75,6 @@ jobs:
       name: Setup TFLint
       with:
         tflint_version: v0.52.0
-
     - name: Show version
       run: tflint --version
 

diff --git a/action.yml b/action.yml
@@ -13,6 +13,9 @@ inputs:
     description: Installs a wrapper script to wrap subsequent calls to `tflint` and expose `stdout`, `stderr`, and `exitcode` outputs
     default: 'false'
     required: false
+  checksums:
+    description: Newline-delimited list of valid checksums (SHA256 hashes) for the downloaded TFLint binary. When set, the action will verify that the binary matches one of these checksums before proceeding.
+    required: false
 outputs:
   stdout:
     description: The output (stdout) produced by the tflint command. Only available if `tflint_wrapper` is set to `true`.

diff --git a/dist/index.js b/dist/index.js
@@ -9989,6 +9989,9 @@ function wrappy (fn, cb) {
 
 const os = __nccwpck_require__(2037);
 const path = __nccwpck_require__(1017);
+const crypto = __nccwpck_require__(6113);
+const fs = __nccwpck_require__(7147);
+const { pipeline } = __nccwpck_require__(4845)
 
 const core = __nccwpck_require__(2186);
 const io = __nccwpck_require__(7436);
@@ -10041,10 +10044,29 @@ async function getTFLintVersion(inputVersion) {
   return inputVersion;
 }
 
-async function downloadCLI(url) {
+async function fileSHA256(filePath) {
+  const hash = crypto.createHash('sha256');
+  const fileStream = fs.createReadStream(filePath);
+
+  await pipeline(fileStream, hash);
+  return hash.digest('hex');
+}
+
+async function downloadCLI(url, checksums) {
   core.debug(`Downloading tflint CLI from ${url}`);
   const pathToCLIZip = await tc.downloadTool(url);
 
+  if (checksums.length > 0) {
+    core.debug('Verifying checksum of downloaded file');
+
+    const checksum = await fileSHA256(pathToCLIZip);
+
+    if (!checksums.includes(checksum)) {
+      throw new Error(`Mismatched checksum: expected one of ${checksums.join(', ')}, but got ${checksum}`);
+    }
+    core.debug('SHA256 hash verified successfully');
+  }
+
   core.debug('Extracting tflint CLI zip file');
   const pathToCLI = await tc.extractZip(pathToCLIZip);
   core.debug(`tflint CLI path is ${pathToCLI}.`);
@@ -10089,6 +10111,7 @@ async function installWrapper(pathToCLI) {
 async function run() {
   try {
     const inputVersion = core.getInput('tflint_version');
+    const checksums = core.getMultilineInput('checksums');
     const wrapper = core.getInput('tflint_wrapper') === 'true';
     const version = await getTFLintVersion(inputVersion);
     const platform = mapOS(os.platform());
@@ -10097,7 +10120,7 @@ async function run() {
     core.debug(`Getting download URL for tflint version ${version}: ${platform} ${arch}`);
     const url = `https://github.com/terraform-linters/tflint/releases/download/${version}/tflint_${platform}_${arch}.zip`;
 
-    const pathToCLI = await downloadCLI(url);
+    const pathToCLI = await downloadCLI(url, checksums);
 
     if (wrapper) {
       await installWrapper(pathToCLI);
@@ -10208,6 +10231,14 @@ module.exports = require("stream");
 
 /***/ }),
 
+/***/ 4845:
+/***/ ((module) => {
+
+"use strict";
+module.exports = require("stream/promises");
+
+/***/ }),
+
 /***/ 1576:
 /***/ ((module) => {
 

diff --git a/package-lock.json b/package-lock.json
diff --git a/package.json b/package.json
@@ -1,7 +1,7 @@
 {
   "name": "setup-tflint-action",
-  "version": "2.0.0",
-  "description": "Install and setup TFLint executable Action",
+  "version": "2.1.0",
+  "description": "Install and setup TFLint executable Action with SHA256 verification",
   "main": "index.js",
   "scripts": {
     "lint": "eslint --fix . src test",
@@ -24,7 +24,9 @@
     "GitHub",
     "Actions",
     "TFLint",
-    "Terraform"
+    "Terraform",
+    "SHA256",
+    "Verification"
   ],
   "license": "MIT",
   "bugs": {

diff --git a/src/setup-tflint.js b/src/setup-tflint.js
@@ -1,5 +1,8 @@
 const os = require('os');
 const path = require('path');
+const crypto = require('crypto');
+const fs = require('fs');
+const { pipeline } = require('stream/promises')
 
 const core = require('@actions/core');
 const io = require('@actions/io');
@@ -52,10 +55,29 @@ async function getTFLintVersion(inputVersion) {
   return inputVersion;
 }
 
-async function downloadCLI(url) {
+async function fileSHA256(filePath) {
+  const hash = crypto.createHash('sha256');
+  const fileStream = fs.createReadStream(filePath);
+
+  await pipeline(fileStream, hash);
+  return hash.digest('hex');
+}
+
+async function downloadCLI(url, checksums) {
   core.debug(`Downloading tflint CLI from ${url}`);
   const pathToCLIZip = await tc.downloadTool(url);
 
+  if (checksums.length > 0) {
+    core.debug('Verifying checksum of downloaded file');
+
+    const checksum = await fileSHA256(pathToCLIZip);
+
+    if (!checksums.includes(checksum)) {
+      throw new Error(`Mismatched checksum: expected one of ${checksums.join(', ')}, but got ${checksum}`);
+    }
+    core.debug('SHA256 hash verified successfully');
+  }
+
   core.debug('Extracting tflint CLI zip file');
   const pathToCLI = await tc.extractZip(pathToCLIZip);
   core.debug(`tflint CLI path is ${pathToCLI}.`);
@@ -100,6 +122,7 @@ async function installWrapper(pathToCLI) {
 async function run() {
   try {
     const inputVersion = core.getInput('tflint_version');
+    const checksums = core.getMultilineInput('checksums');
     const wrapper = core.getInput('tflint_wrapper') === 'true';
     const version = await getTFLintVersion(inputVersion);
     const platform = mapOS(os.platform());
@@ -108,7 +131,7 @@ async function run() {
     core.debug(`Getting download URL for tflint version ${version}: ${platform} ${arch}`);
     const url = `https://github.com/terraform-linters/tflint/releases/download/${version}/tflint_${platform}_${arch}.zip`;
 
-    const pathToCLI = await downloadCLI(url);
+    const pathToCLI = await downloadCLI(url, checksums);
 
     if (wrapper) {
       await installWrapper(pathToCLI);

diff --git a/test/index.test.js b/test/index.test.js
@@ -5,7 +5,6 @@ const tc = require('@actions/tool-cache');
 
 const setup = require('../src/setup-tflint');
 
-jest.mock('@actions/core');
 jest.mock('@actions/tool-cache');
 fs.chmodSync = jest.fn();
 
@@ -30,8 +29,8 @@ describe('Mock tests', () => {
   });
 
   test('add path should be called', async () => {
+    jest.spyOn(core, 'addPath');
     await setup();
-
     expect(core.addPath).toBeCalledTimes(1);
   });
 });