Fix unprivileged user namespace regression

chrome/browser/ui/views/chrome_browser_main_extra_parts_views.cc

Index: chrome/browser/ui/views/chrome_browser_main_extra_parts_views.cc
diff --git a/chrome/browser/ui/views/chrome_browser_main_extra_parts_views.cc b/chrome/browser/ui/views/chrome_browser_main_extra_parts_views.cc
index b7cc45a8b536650f06a1eaa3352356793256857f..accc3785c13ddb98a0a5fe67862475a6433341ed 100644
--- a/chrome/browser/ui/views/chrome_browser_main_extra_parts_views.cc
+++ b/chrome/browser/ui/views/chrome_browser_main_extra_parts_views.cc
@@ -4,6 +4,8 @@
 
 #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"
@@ -27,6 +29,10 @@
 #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"
@@ -77,6 +83,12 @@ void ChromeBrowserMainExtraPartsViews::PreProfileInit() {
   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))