Add an escape hatch for the ECDSA CBC cipher removal.

net/socket/ssl_client_socket_impl.cc

 // Copyright (c) 2012 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 "net/socket/ssl_client_socket_impl.h"
 
 #include <errno.h>
 #include <string.h>
 
 #include <utility>
 
 #include "base/bind.h"
 #include "base/callback_helpers.h"
+#include "base/feature_list.h"
 #include "base/lazy_instance.h"
 #include "base/macros.h"
 #include "base/memory/singleton.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/metrics/sparse_histogram.h"
 #include "base/profiler/scoped_tracker.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_piece.h"
 #include "base/synchronization/lock.h"
@@ skipping 185 matching lines @@
   if (base::StringToInt(base::FieldTrialList::FindFullName(field_trial),
                         &override_buffer_size)) {
     buffer_size = override_buffer_size;
     buffer_size = std::max(buffer_size, 1000);
     buffer_size = std::min(buffer_size, 2 * kDefaultOpenSSLBufferSize);
   }
 #endif  // !defined(OS_NACL)
   return buffer_size;
 }
 
+#if defined(OS_NACL)
+bool AreLegacyECDSACiphersEnabled() {
+  return false;
+}
+#else
+// TODO(davidben): Remove this after the ECDSA CBC removal sticks.
+// https:/crbug.com/666191.
+const base::Feature kLegacyECDSACiphersFeature{
+    "SSLLegacyECDSACiphers", base::FEATURE_DISABLED_BY_DEFAULT};
+
+bool AreLegacyECDSACiphersEnabled() {
+  return base::FeatureList::IsEnabled(kLegacyECDSACiphersFeature);
+}
+#endif
+
 }  // namespace
 
 class SSLClientSocketImpl::SSLContext {
  public:
   static SSLContext* GetInstance() {
     return base::Singleton<SSLContext>::get();
   }
   SSL_CTX* ssl_ctx() { return ssl_ctx_.get(); }
   SSLClientSessionCache* session_cache() { return &session_cache_; }
 
@@ skipping 707 matching lines @@
         "CECPQ1-RSA-CHACHA20-POLY1305-SHA256:"
         "CECPQ1-ECDSA-CHACHA20-POLY1305-SHA256:");
     if (!EVP_has_aes_hardware()) {
       command.append(
           "CECPQ1-RSA-AES256-GCM-SHA384:"
           "CECPQ1-ECDSA-AES256-GCM-SHA384:");
     }
   }
 
   // Use BoringSSL defaults, but disable HMAC-SHA256 and HMAC-SHA384 ciphers
-  // (note that SHA256 and SHA384 only select legacy CBC ciphers). Additionally
-  // disable HMAC-SHA1 ciphers in ECDSA. Also disable
+  // (note that SHA256 and SHA384 only select legacy CBC ciphers). Also disable
   // DHE_RSA_WITH_AES_256_GCM_SHA384. Historically, AES_256_GCM was not
-  // supported. As DHE is being deprecated, don't add a cipher only to remove it
-  // immediately.
+  // supported. As DHE is being deprecated, don't add a cipher only to remove
+  // it immediately.
   //
   // TODO(davidben): Remove the DHE_RSA_WITH_AES_256_GCM_SHA384 exclusion when
   // the DHEEnabled administrative policy expires.
-  command.append(
-      "ALL:!SHA256:!SHA384:!ECDSA+SHA1:!DHE-RSA-AES256-GCM-SHA384:!aPSK:!RC4");
+  command.append("ALL:!SHA256:!SHA384:!DHE-RSA-AES256-GCM-SHA384:!aPSK:!RC4");
 
   if (ssl_config_.require_ecdhe)
     command.append(":!kRSA:!kDHE");
 
   if (!ssl_config_.deprecated_cipher_suites_enabled) {
     // Only offer DHE on the second handshake. https://crbug.com/538690
     command.append(":!kDHE");
   }
 
+  // Additionally disable HMAC-SHA1 ciphers in ECDSA. These are the remaining
+  // CBC-mode ECDSA ciphers.
+  if (!AreLegacyECDSACiphersEnabled())
+    command.append("!ECDSA+SHA1");
+
   // Remove any disabled ciphers.
   for (uint16_t id : ssl_config_.disabled_cipher_suites) {
     const SSL_CIPHER* cipher = SSL_get_cipher_by_value(id);
     if (cipher) {
       command.append(":!");
       command.append(SSL_CIPHER_get_name(cipher));
     }
   }
 
   int rv = SSL_set_cipher_list(ssl_.get(), command.c_str());
@@ skipping 1025 matching lines @@
     if (ERR_GET_REASON(info->error_code) == SSL_R_TLSV1_ALERT_ACCESS_DENIED &&
         !certificate_requested_) {
       net_error = ERR_SSL_PROTOCOL_ERROR;
     }
   }
 
   return net_error;
 }
 
 }  // namespace net