[webcrypto] Reject AES-GCM tag lengths other than 32, 64, 96, 104, 112, 120, 128.

content/renderer/webcrypto/shared_crypto.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/renderer/webcrypto/shared_crypto.h"
 
 #include "base/logging.h"
 #include "content/renderer/webcrypto/crypto_data.h"
 #include "content/renderer/webcrypto/platform_crypto.h"
 #include "content/renderer/webcrypto/webcrypto_util.h"
@@ skipping 76 matching lines @@
                             blink::WebArrayBuffer* buffer) {
   platform::SymKey* sym_key;
   Status status = ToPlatformSymKey(key, &sym_key);
   if (status.IsError())
     return status;
 
   const blink::WebCryptoAesGcmParams* params = algorithm.aesGcmParams();
   if (!params)
     return Status::ErrorUnexpected();
 
-  // TODO(eroman): The spec doesn't define the default value. Assume 128 for now
-  // since that is the maximum tag length:
-  // http://www.w3.org/2012/webcrypto/track/issues/46
   unsigned int tag_length_bits = 128;
   if (params->hasTagLengthBits())
     tag_length_bits = params->optionalTagLengthBits();
-  if (tag_length_bits > 128)
+
+  if (tag_length_bits != 32 && tag_length_bits != 64 && tag_length_bits != 96 &&
+      tag_length_bits != 104 && tag_length_bits != 112 &&
+      tag_length_bits != 120 && tag_length_bits != 128)
     return Status::ErrorInvalidAesGcmTagLength();
 
   return platform::EncryptDecryptAesGcm(
       mode,
       sym_key,
       data,
       CryptoData(params->iv()),
       CryptoData(params->optionalAdditionalData()),
       tag_length_bits,
       buffer);
@@ skipping 364 matching lines @@
       return VerifyRsaSsaPkcs1v1_5(
           algorithm, key, signature, data, signature_match);
     default:
       return Status::ErrorUnsupported();
   }
 }
 
 }  // namespace webcrypto
 
 }  // namespace content