Add an whitelist for calling GN's exec_script.

tools/gn/function_exec_script.cc

 // Copyright (c) 2013 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 "base/command_line.h"
 #include "base/files/file_util.h"
 #include "base/logging.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/time/time.h"
 #include "build/build_config.h"
 #include "tools/gn/err.h"
 #include "tools/gn/exec_process.h"
 #include "tools/gn/filesystem_utils.h"
 #include "tools/gn/functions.h"
 #include "tools/gn/input_conversion.h"
 #include "tools/gn/input_file.h"
 #include "tools/gn/parse_tree.h"
 #include "tools/gn/scheduler.h"
 #include "tools/gn/trace.h"
 #include "tools/gn/value.h"
 
 namespace functions {
 
+namespace {
+
+bool CheckExecScriptPermissions(const BuildSettings* build_settings,
+                                const FunctionCallNode* function,
+                                Err* err) {
+  const std::set<SourceFile>* whitelist =
+      build_settings->exec_script_whitelist();
+  if (!whitelist)
+    return true;  // No whitelist specified, don't check.
+
+  LocationRange function_range = function->GetRange();
+  if (!function_range.begin().file())
+    return true;  // No file, might be some internal thing, implicitly pass.
+
+  if (whitelist->find(function_range.begin().file()->name()) !=
+      whitelist->end())
+    return true;  // Whitelisted, this is OK.
+
+  // Disallowed case.
+  *err = Err(function, "Disallowed exec_script call.",
+      "The use of exec_script use is restricted in this build. exec_script\n"
+      "is discouraged because it can slow down the GN run and is easily\n"
+      "abused.\n"
+      "\n"
+      "Generally nontrivial work should be done as build steps rather than\n"
+      "when GN is run. For example, if you need to compute a nontrivial\n"
+      "preprocessor define, it will be better to have an action target\n"
+      "generate a header containing the define rather than blocking the GN\n"
+      "run to compute the value.\n"
+      "\n"
+      "The allowed callers of exec_script is maintained in the \"//.gn\" file\n"
+      "if you need to modify the whitelist.");
+  return false;
+}
+
+}  // namespace
+
 const char kExecScript[] = "exec_script";
 const char kExecScript_HelpShort[] =
     "exec_script: Synchronously run a script and return the output.";
 const char kExecScript_Help[] =
     "exec_script: Synchronously run a script and return the output.\n"
     "\n"
     "  exec_script(filename,\n"
     "              arguments = [],\n"
     "              input_conversion = \"\",\n"
     "              file_dependencies = [])\n"
@@ skipping 50 matching lines @@
   if (args.size() < 1 || args.size() > 4) {
     *err = Err(function->function(), "Wrong number of arguments to exec_script",
                "I expected between one and four arguments.");
     return Value();
   }
 
   const Settings* settings = scope->settings();
   const BuildSettings* build_settings = settings->build_settings();
   const SourceDir& cur_dir = scope->GetSourceDir();
 
+  if (!CheckExecScriptPermissions(build_settings, function, err))
+    return Value();
+
   // Find the python script to run.
   if (!args[0].VerifyTypeIs(Value::STRING, err))
     return Value();
   SourceFile script_source =
       cur_dir.ResolveRelativeFile(args[0].string_value(),
           scope->settings()->build_settings()->root_path_utf8());
   base::FilePath script_path = build_settings->GetFullPath(script_source);
   if (!build_settings->secondary_source_path().empty() &&
       !base::PathExists(script_path)) {
     // Fall back to secondary source root when the file doesn't exist.
@@ skipping 95 matching lines @@
                msg);
     return Value();
   }
 
   // Default to None value for the input conversion if unspecified.
   return ConvertInputToValue(scope->settings(), output, function,
                              args.size() >= 3 ? args[2] : Value(), err);
 }
 
 }  // namespace functions