Move a couple of utility functions to a new namespace_utils class.

sandbox/linux/services/namespace_utils.cc

+// Copyright (c) 2014 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 "sandbox/linux/services/namespace_utils.h"
+
+#include <fcntl.h>
+#include <sched.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+#include <string>
+
+#include "base/files/file_path.h"
+#include "base/files/file_util.h"
+#include "base/files/scoped_file.h"
+#include "base/logging.h"
+#include "base/posix/eintr_wrapper.h"
+#include "base/strings/stringprintf.h"
+#include "base/third_party/valgrind/valgrind.h"
+
+namespace sandbox {
+
+namespace {
+bool IsRunningOnValgrind() {
+  return RUNNING_ON_VALGRIND;
+}
+}  // namespace

[jln (very slow on Chromium), 2015/01/14 00:46:38]

Nit: vertical space

[rickyz (no longer on Chrome), 2015/01/23 01:20:19]

Sorry, where should vertical space be added/removed here?

+
+// Write a uid or gid mapping from |id| to |id| in |map_file|.
+bool NamespaceUtils::WriteToIdMapFile(const char* map_file, generic_id_t id) {
+  base::ScopedFD fd(HANDLE_EINTR(open(map_file, O_WRONLY)));
+  if (!fd.is_valid()) {
+    return false;
+  }
+
+  const generic_id_t inside_id = id;
+  const generic_id_t outside_id = id;
+  const std::string mapping =
+      base::StringPrintf("%d %d 1\n", inside_id, outside_id);
+  const size_t len = mapping.size();
+  const ssize_t rc = HANDLE_EINTR(write(fd.get(), mapping.c_str(), len));
+  return rc == static_cast<ssize_t>(len);
+}
+
+bool NamespaceUtils::SupportsLinuxNamespace(int type) {

[jln (very slow on Chromium), 2015/01/14 00:46:38]

This implementation will have some false negatives. For instance, CLONE_NEWPID
was supported before /proc/self/ns/pid existed.

Could you track down which kernel added /proc/self/ns/pid to see if it's a
problem?

I think it was roughly added with unprivileged CLONE_NEWUSER. Let's document
that cleanly in the interface.

[rickyz (no longer on Chrome), 2015/01/23 00:23:38]

Darn, looks like this was added in 3.8. In view of this limitation, I think I'll
leave things as is in credentials.h and drop this CL for now and try to do this
a little more cleanly after the initial namespace sandbox stuff is in.

[jln (very slow on Chromium), 2015/01/23 00:27:09]

As you prefer, but it's also ok to keep as long as your rename the API
adequately.

Since we consider NEWUSER to be usefully supported only around 3.10 we can
consider this API to tell us what flags are compatible with NEWUSER. The current
name however seems to suggest kernel support for things like privileged
CLONE_NEWPID, which it doesn't do.

[rickyz (no longer on Chrome), 2015/01/23 01:20:19]

Yeah - on second thought, I prefer your suggestion, and having this makes the
namespace sandbox code easier - thanks!

+  // Valgrind will let clone(2) pass-through, but doesn't support unshare(),
+  // so always consider namespaces unsupported there.
+  if (IsRunningOnValgrind()) {
+    return false;
+  }
+
+  const char* path;
+  switch (type) {
+    case CLONE_NEWIPC:
+      path = "/proc/self/ns/ipc";
+      break;
+    case CLONE_NEWNET:
+      path = "/proc/self/ns/net";
+      break;
+    case CLONE_NEWNS:
+      path = "/proc/self/ns/mnt";
+      break;
+    case CLONE_NEWPID:
+      path = "/proc/self/ns/pid";
+      break;
+    case CLONE_NEWUSER:
+      path = "/proc/self/ns/user";
+      break;
+    case CLONE_NEWUTS:
+      path = "/proc/self/ns/uts";
+      break;
+    default:
+      NOTREACHED();
+      return false;
+  }
+
+  return base::PathExists(base::FilePath(path));
+}
+
+}  // namespace sandbox