Make string_util::WriteInto() DCHECK() that the supplied |length_with_null| > 1, meaning that the...

net/http/http_mac_signature.cc

 // Copyright (c) 2011 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/http/http_mac_signature.h"
 
 #include "base/base64.h"
 #include "base/rand_util.h"
 #include "base/string_number_conversions.h"
 #include "base/string_util.h"
@@ skipping 140 matching lines @@
   std::string request = GenerateNormalizedRequest(age, nonce);
 
   crypto::HMAC hmac(mac_algorithm_);
   if (!hmac.Init(mac_key_)) {
     NOTREACHED();
     return false;
   }
 
   std::string signature;
   size_t length = hmac.DigestLength();
-  char* buffer = WriteInto(&signature, length);
-  if (!hmac.Sign(request, reinterpret_cast<unsigned char*>(buffer),
-                 length)) {
+  DCHECK_GT(length, 0u);
+  if (!hmac.Sign(request,
+          // We need the + 1 here not because the call will write a trailing \0,
+          // but so that signature.length() is correctly set to |length|.
+          reinterpret_cast<unsigned char*>(WriteInto(&signature, length + 1)),
+          length)) {
     NOTREACHED();
     return false;
   }
 
   std::string encoded_signature;
   if (!base::Base64Encode(signature, &encoded_signature)) {
     NOTREACHED();
     return false;
   }
 
   mac->swap(encoded_signature);
   return true;
 }
 
 }  // namespace net