Fix unprivileged user namespace regression

chrome/browser/ui/views/chrome_browser_main_extra_parts_views.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 "chrome/browser/ui/views/chrome_browser_main_extra_parts_views.h"
 
+#include <utility>
+
 #include "base/memory/ptr_util.h"
 #include "chrome/browser/ui/views/chrome_constrained_window_views_client.h"
 #include "chrome/browser/ui/views/chrome_views_delegate.h"
 #include "chrome/browser/ui/views/ime_driver/ime_driver_mus.h"
 #include "components/constrained_window/constrained_window_views.h"
 
 #if defined(USE_AURA)
 #include "base/run_loop.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/common/service_manager_connection.h"
 #include "services/service_manager/public/cpp/connector.h"
 #include "services/service_manager/runner/common/client_util.h"
 #include "services/ui/public/cpp/gpu/gpu.h"  // nogncheck
 #include "services/ui/public/cpp/input_devices/input_device_client.h"
 #include "services/ui/public/interfaces/constants.mojom.h"
 #include "services/ui/public/interfaces/input_devices/input_device_server.mojom.h"
 #include "ui/display/screen.h"
 #include "ui/views/mus/mus_client.h"
 #include "ui/views/widget/desktop_aura/desktop_screen.h"
 #include "ui/wm/core/wm_state.h"
 #endif  // defined(USE_AURA)
 
 #if defined(OS_LINUX) && !defined(OS_CHROMEOS)
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
 #include "base/command_line.h"
 #include "chrome/browser/ui/simple_message_box.h"
 #include "chrome/grit/chromium_strings.h"
 #include "chrome/grit/generated_resources.h"
 #include "content/public/common/content_switches.h"
 #include "ui/base/l10n/l10n_util.h"
 #endif  // defined(OS_LINUX) && !defined(OS_CHROMEOS)
 
 ChromeBrowserMainExtraPartsViews::ChromeBrowserMainExtraPartsViews() {
 }
@@ skipping 30 matching lines @@
     IMEDriver::Register();
 #endif
 
 #if defined(OS_LINUX) && !defined(OS_CHROMEOS)
   // On the Linux desktop, we want to prevent the user from logging in as root,
   // so that we don't destroy the profile. Now that we have some minimal ui
   // initialized, check to see if we're running as root and bail if we are.
   if (geteuid() != 0)
     return;
 
+  // Allow running inside an unprivileged user namespace. In that case, the
+  // root directory will be owned by an unmapped UID and GID.

[Jorge Lucangeli Obes, 2017/04/10 13:39:47]

This is not true all the time, is it? It's only true in the case where you enter
a user namespace without chrooting.

Maybe update the comment to make it clearer?

[Kevin Cernekee, 2017/04/10 21:40:21]

Done.

+  struct stat st;
+  if (stat("/", &st) == 0 && st.st_uid != 0)

[Jorge Lucangeli Obes, 2017/04/10 13:41:18]

Does this need to be HANDLE_EINTR?

[Kevin Cernekee, 2017/04/10 21:40:21]

I don't think it is strictly necessary, although I can add it.  stat(2) (Linux
and OSX) and signal(7) (Linux) do not say that stat() can be interrupted. 
However I do see a couple of HANDLE_EINTR(fstat(...)) invocations in existing
Chrome code.  And this isn't necessarily portable to other OSes, like Solaris:

http://docs.oracle.com/cd/E19253-01/816-5167/fstat-2/index.html

By contrast: other syscalls, such as open(2) and statfs(2), do explicitly list
EINTR as a possible error.

+    return;
+
   const base::CommandLine& command_line =
       *base::CommandLine::ForCurrentProcess();
   if (command_line.HasSwitch(switches::kNoSandbox))
     return;
 
   base::string16 title = l10n_util::GetStringFUTF16(
       IDS_REFUSE_TO_RUN_AS_ROOT, l10n_util::GetStringUTF16(IDS_PRODUCT_NAME));
   base::string16 message = l10n_util::GetStringFUTF16(
       IDS_REFUSE_TO_RUN_AS_ROOT_2, l10n_util::GetStringUTF16(IDS_PRODUCT_NAME));
 
@@ skipping 20 matching lines @@
     // WMState is owned as a member, so don't have MusClient create it.
     const bool create_wm_state = false;
     mus_client_ = base::MakeUnique<views::MusClient>(
         connection->GetConnector(), service_manager::Identity(),
         content::BrowserThread::GetTaskRunnerForThread(
             content::BrowserThread::IO),
         create_wm_state);
   }
 #endif  // defined(USE_AURA)
 }