Avoid std::string copying in GetFileNameInWhitelist.

sandbox/linux/services/broker_process.cc

Index: sandbox/linux/services/broker_process.cc
diff --git a/sandbox/linux/services/broker_process.cc b/sandbox/linux/services/broker_process.cc
index d2302ea098215c8188eb74b0d36da37506ff302a..7999e77fa34fcef4ad8575fa905d66f645df6986 100644
--- a/sandbox/linux/services/broker_process.cc
+++ b/sandbox/linux/services/broker_process.cc
@@ -53,7 +53,7 @@ static const int kCurrentProcessOpenFlagsMask = O_CLOEXEC;
 // async signal safe if |file_to_open| is NULL.
 // TODO(jln): assert signal safety.
 bool GetFileNameInWhitelist(const std::vector<std::string>& allowed_file_names,
-                            const std::string& requested_filename,
+                            const char* requested_filename,
                             const char** file_to_open) {
   if (file_to_open && *file_to_open) {
     // Make sure that callers never pass a non-empty string. In case callers
@@ -62,13 +62,17 @@ bool GetFileNameInWhitelist(const std::vector<std::string>& allowed_file_names,
     RAW_LOG(FATAL, "*file_to_open should be NULL");
     return false;
   }
+
+  // Look for |requested_filename| in |allowed_file_names|.
+  // We don't use ::find() because it takes a std::string and
+  // the conversion allocates memory.
   std::vector<std::string>::const_iterator it;
-  it = std::find(allowed_file_names.begin(), allowed_file_names.end(),
-                 requested_filename);
-  if (it < allowed_file_names.end()) {  // requested_filename was found?
-    if (file_to_open)
-      *file_to_open = it->c_str();
-    return true;
+  for (it = allowed_file_names.begin(); it != allowed_file_names.end(); it++) {
+    if (strcmp(requested_filename, it->c_str()) == 0) {
+      if (file_to_open)
+        *file_to_open = it->c_str();
+      return true;
+    }
   }
   return false;
 }
@@ -393,6 +397,7 @@ void BrokerProcess::AccessFileForIPC(const std::string& requested_filename,
   const char* file_to_access = NULL;
   const bool safe_to_access_file = GetFileNameIfAllowedToAccess(
       requested_filename.c_str(), mode, &file_to_access);
+
   if (safe_to_access_file) {
     CHECK(file_to_access);
     int access_ret = access(file_to_access, mode);