Add namespace sandbox class.

sandbox/linux/services/namespace_sandbox.cc

+// Copyright 2015 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_sandbox.h"
+
+#include <sched.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include <string>
+
+#include "base/bind.h"
+#include "base/environment.h"
+#include "base/logging.h"
+#include "base/posix/eintr_wrapper.h"
+#include "base/strings/stringprintf.h"
+#include "sandbox/linux/services/namespace_utils.h"
+
+namespace sandbox {
+
+namespace {
+const char kPipeValue = '\xcc';
+
+void SetEnvironForNamespaceType(base::EnvironmentMap* environ,
+                                base::NativeEnvironmentString env_var,
+                                bool value) {
+  // An empty string causes the env var to be unset in the child process.
+  (*environ)[env_var] = value ? "1" : "";
+}
+
+const char kSandboxUSERNSEnvironmentVarName[] = "SBX_USER_NS";
+const char kSandboxPIDNSEnvironmentVarName[] = "SBX_PID_NS";
+const char kSandboxNETNSEnvironmentVarName[] = "SBX_NET_NS";
+
+}  // namespace
+
+NamespaceSandbox::NamespaceSandbox() {
+}
+
+NamespaceSandbox::~NamespaceSandbox() {
+}
+
+void NamespaceSandbox::SetupLaunchOptions(
+    base::LaunchOptions* options,
+    base::FileHandleMappingVector* fds_to_remap) {
+  int clone_flags = 0;
+  int ns_types[] = {CLONE_NEWUSER, CLONE_NEWPID, CLONE_NEWNET};
+  for (const int ns_type : ns_types) {
+    if (NamespaceUtils::KernelSupportsUnprivilegedNamespace(ns_type)) {
+      clone_flags |= ns_type;
+    }
+  }
+
+  CHECK(clone_flags & CLONE_NEWUSER);
+
+  base::EnvironmentMap* environ = &options->environ;

[jln (very slow on Chromium), 2015/01/28 02:34:39]

DCHECK environ?

[rickyz (no longer on Chrome), 2015/01/29 00:57:48]

Don't think this is needed since environ isn't a pointer (seems LaunchOptions is
a little inconsistent about using pointers or embedding classes).

+  SetEnvironForNamespaceType(environ, kSandboxUSERNSEnvironmentVarName,

[jln (very slow on Chromium), 2015/01/28 02:34:39]

For loop?

[rickyz (no longer on Chrome), 2015/01/29 00:57:48]

Done.

+                             clone_flags & CLONE_NEWUSER);
+  SetEnvironForNamespaceType(environ, kSandboxPIDNSEnvironmentVarName,
+                             clone_flags & CLONE_NEWPID);
+  SetEnvironForNamespaceType(environ, kSandboxNETNSEnvironmentVarName,
+                             clone_flags & CLONE_NEWNET);
+
+  int fds[2];
+  PCHECK(pipe(fds) == 0);
+  read_fd_.reset(fds[0]);
+  write_fd_.reset(fds[1]);
+  fds_to_remap->push_back(std::make_pair(read_fd_.get(), read_fd_.get()));
+  read_from_pipe_delegate_.set_fd(read_fd_.get());
+  options->pre_exec_delegate = &read_from_pipe_delegate_;
+  options->clone_flags = clone_flags;
+}
+
+void NamespaceSandbox::PrepareSandboxedProcess(base::ProcessId pid) {
+  read_fd_.reset();

[jln (very slow on Chromium), 2015/01/28 02:34:38]

This should destruct the ReadFromPipeDelegate instead, no?

[rickyz (no longer on Chrome), 2015/01/29 00:57:48]

See the other comment about read_fd_ ownership - the summary is that I didn't
want ReadFromPipeDelegate to own it because ReadFromPipeDelegate is only
meaningful in the child, and ReadFromPipeDelegate won't ever be destroyed in the
child.

+
+  const std::string uid_map_path = base::StringPrintf("/proc/%d/uid_map", pid);
+  const std::string gid_map_path = base::StringPrintf("/proc/%d/gid_map", pid);
+  NamespaceUtils::WriteToIdMapFile(uid_map_path.c_str(), getuid());
+  NamespaceUtils::WriteToIdMapFile(gid_map_path.c_str(), getgid());
+
+  PCHECK(HANDLE_EINTR(write(write_fd_.get(), &kPipeValue, 1)) == 1);
+  write_fd_.reset();
+}
+
+bool NamespaceSandbox::InNewUserNamespace() {
+  return getenv(kSandboxUSERNSEnvironmentVarName) != nullptr;
+}
+
+bool NamespaceSandbox::InNewPidNamespace() {
+  return getenv(kSandboxPIDNSEnvironmentVarName) != nullptr;
+}
+
+bool NamespaceSandbox::InNewNetNamespace() {
+  return getenv(kSandboxNETNSEnvironmentVarName) != nullptr;
+}
+
+NamespaceSandbox::ReadFromPipeDelegate::ReadFromPipeDelegate() : fd_(-1) {
+}
+
+NamespaceSandbox::ReadFromPipeDelegate::~ReadFromPipeDelegate() {
+}
+
+void NamespaceSandbox::ReadFromPipeDelegate::RunAsyncSafe() {
+  char c;
+  RAW_CHECK(HANDLE_EINTR(read(fd_, &c, 1)) == 1);
+  RAW_CHECK(IGNORE_EINTR(close(fd_)) == 0);
+  RAW_CHECK(c == kPipeValue);
+}
+
+void NamespaceSandbox::ReadFromPipeDelegate::set_fd(int fd) {
+  fd_ = fd;
+}
+
+}  // namespace sandbox