(v6.x backport) crypto: warn on invalid authentication tag length

src/node_crypto.cc

@@ -3525,8 +3525,16 @@ void CipherBase::SetAuthTag(const FunctionCallbackInfo<Value>& args) {
 
   CipherBase* cipher;
   ASSIGN_OR_RETURN_UNWRAP(&cipher, args.Holder());
+  // Restrict GCM tag lengths according to NIST 800-38d, page 9.
+  unsigned int tag_len = Buffer::Length(buf);
+  if (tag_len > 16 || (tag_len < 12 && tag_len != 8 && tag_len != 4)) {
+    ProcessEmitWarning(cipher->env(),
+        "Permitting authentication tag lengths of %u bytes is deprecated. "
+        "Valid GCM tag lengths are 4, 8, 12, 13, 14, 15, 16.",
+        tag_len);
+  }
 
-  if (!cipher->SetAuthTag(Buffer::Data(buf), Buffer::Length(buf)))
+  if (!cipher->SetAuthTag(Buffer::Data(buf), tag_len))
     env->ThrowError("Attempting to set auth tag in unsupported state");
 }
 

test/parallel/test-crypto-authenticated.js

@@ -314,6 +314,14 @@ const errMessages = {
 
 const ciphers = crypto.getCiphers();
 
+common.expectWarning('Warning', (common.hasFipsCrypto ? [] : [
+  'Use Cipheriv for counter mode of aes-192-gcm'
+]).concat(
+  [0, 1, 2, 6, 9, 10, 11, 17]
+  .map((i) => `Permitting authentication tag lengths of ${i} bytes is ` +
+            'deprecated. Valid GCM tag lengths are 4, 8, 12, 13, 14, 15, 16.')
+));
+
 for (const i in TEST_CASES) {
   const test = TEST_CASES[i];
 
@@ -455,3 +463,14 @@ for (const i in TEST_CASES) {
   assert.throws(() => encrypt.setAAD(Buffer.from('123', 'ascii')),
                 errMessages.state);
 }
+
+// GCM only supports specific authentication tag lengths, invalid lengths should
+// produce warnings.
+{
+  for (const length of [0, 1, 2, 4, 6, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17]) {
+    const decrypt = crypto.createDecipheriv('aes-256-gcm',
+                                            'FxLKsqdmv0E9xrQhp0b1ZgI0K7JFZJM8',
+                                            'qkuZpJWCewa6Szih');
+    decrypt.setAuthTag(Buffer.from('1'.repeat(length)));
+  }
+}

test/parallel/test-crypto-cipher-decipher.js

@@ -141,7 +141,7 @@ testCipher2(Buffer.from('0123456789abcdef'));
 // setAutoPadding/setAuthTag/setAAD should return `this`
 {
   const key = '0123456789';
-  const tagbuf = Buffer.from('tagbuf');
+  const tagbuf = Buffer.from('auth_tag');
   const aadbuf = Buffer.from('aadbuf');
   const decipher = crypto.createDecipher('aes-256-gcm', key);
   assert.strictEqual(decipher.setAutoPadding(), decipher);