linux: add command-line flag to allow debugging of sandboxed processes

chrome/browser/zygote_main_linux.cc

 // Copyright (c) 2009 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 <unistd.h>
 #include <sys/epoll.h>
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <sys/signal.h>
 #include <sys/prctl.h>
 #include <sys/wait.h>
 
 #include "base/command_line.h"
 #include "base/eintr_wrapper.h"
 #include "base/global_descriptors_posix.h"
 #include "base/pickle.h"
 #include "base/rand_util.h"
 #include "base/unix_domain_socket_posix.h"
 
 #include "chrome/browser/zygote_host_linux.h"
 #include "chrome/common/chrome_descriptors.h"
+#include "chrome/common/chrome_switches.h"
 #include "chrome/common/main_function_params.h"
 #include "chrome/common/process_watcher.h"
 #include "chrome/common/sandbox_methods_linux.h"
 
 #include "skia/ext/SkFontHost_fontconfig_control.h"
 
 // http://code.google.com/p/chromium/wiki/LinuxZygote
 
 static const int kMagicSandboxIPCDescriptor = 5;
 
@@ skipping 298 matching lines @@
     // the SUID sandbox), they would nonetheless be in the /same/ PID
     // namespace. So they could ptrace each other unless they were non-dumpable.
     //
     // If the binary was readable, then there would be a window between process
     // startup and the point where we set the non-dumpable flag in which a
     // compromised renderer could ptrace attach.
     //
     // However, now that we have a zygote model, only the (trusted) zygote
     // exists at this point and we can set the non-dumpable flag which is
     // inherited by all our renderer children.
-    prctl(PR_SET_DUMPABLE, 0, 0, 0, 0);
-    if (prctl(PR_GET_DUMPABLE, 0, 0, 0, 0)) {
-      LOG(ERROR) << "Failed to set non-dumpable flag";
-      return false;
+    //
+    // Note: a non-dumpable process can't be debugged. To debug sandbox-related
+    // issues, one can specify --allow-sandbox-debugging to let the process be
+    // dumpable.
+    const CommandLine& command_line = *CommandLine::ForCurrentProcess();
+    if (!command_line.HasSwitch(switches::kAllowSandboxDebugging)) {
+      prctl(PR_SET_DUMPABLE, 0, 0, 0, 0);
+      if (prctl(PR_GET_DUMPABLE, 0, 0, 0, 0)) {
+        LOG(ERROR) << "Failed to set non-dumpable flag";
+        return false;
+      }
     }
   } else {
     SkiaFontConfigUseDirectImplementation();
   }
 
   return true;
 }
 
 bool ZygoteMain(const MainFunctionParams& params) {
   if (!MaybeEnterChroot()) {
     LOG(FATAL) << "Failed to enter sandbox. Fail safe abort. (errno: "
                << errno << ")";
     return false;
   }
 
   Zygote zygote;
   return zygote.ProcessRequests();
 }