components/nacl/loader/sandbox_linux/nacl_sandbox_linux.cc

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "components/nacl/loader/sandbox_linux/nacl_sandbox_linux.h"
   6
   7 #include <errno.h>
   8 #include <fcntl.h>
   9 #include <sys/stat.h>
  10 #include <sys/types.h>
  11 #include <unistd.h>
  12
  13 #include "base/basictypes.h"
  14 #include "base/callback.h"
  15 #include "base/command_line.h"
  16 #include "base/compiler_specific.h"
  17 #include "base/logging.h"
  18 #include "base/memory/scoped_ptr.h"
  19 #include "base/posix/eintr_wrapper.h"
  20 #include "build/build_config.h"
  21 #include "components/nacl/common/nacl_switches.h"
  22 #include "components/nacl/loader/nonsfi/nonsfi_sandbox.h"
  23 #include "components/nacl/loader/sandbox_linux/nacl_bpf_sandbox_linux.h"
  24 #include "sandbox/linux/services/credentials.h"
  25 #include "sandbox/linux/services/thread_helpers.h"
  26 #include "sandbox/linux/suid/client/setuid_sandbox_client.h"
  27
  28 namespace nacl {
  29
  30 namespace {
  31
  32 // This is a poor man's check on whether we are sandboxed.
  33 bool IsSandboxed() {
  34   int proc_fd = open("/proc/self/exe", O_RDONLY);
  35   if (proc_fd >= 0) {
  36     PCHECK(0 == IGNORE_EINTR(close(proc_fd)));
  37     return false;
  38   }
  39   return true;
  40 }
  41
  42 }  // namespace
  43
  44 NaClSandbox::NaClSandbox()
  45     : layer_one_enabled_(false),
  46       layer_one_sealed_(false),
  47       layer_two_enabled_(false),
  48       layer_two_is_nonsfi_(false),
  49       proc_fd_(-1),
  50       setuid_sandbox_client_(sandbox::SetuidSandboxClient::Create()) {
  51   proc_fd_.reset(
  52       HANDLE_EINTR(open("/proc", O_DIRECTORY | O_RDONLY | O_CLOEXEC)));
  53   PCHECK(proc_fd_.is_valid());
  54 }
  55
  56 NaClSandbox::~NaClSandbox() {
  57 }
  58
  59 bool NaClSandbox::IsSingleThreaded() {
  60   CHECK(proc_fd_.is_valid());
  61   base::ScopedFD proc_self_task(HANDLE_EINTR(openat(
  62       proc_fd_.get(), "self/task/", O_RDONLY | O_DIRECTORY | O_CLOEXEC)));
  63   PCHECK(proc_self_task.is_valid());
  64   return sandbox::ThreadHelpers::IsSingleThreaded(proc_self_task.get());
  65 }
  66
  67 bool NaClSandbox::HasOpenDirectory() {
  68   CHECK(proc_fd_.is_valid());
  69   sandbox::Credentials credentials;
  70   return credentials.HasOpenDirectory(proc_fd_.get());
  71 }
  72
  73 void NaClSandbox::InitializeLayerOneSandbox() {
  74   // Check that IsSandboxed() works. We should not be sandboxed at this point.
  75   CHECK(!IsSandboxed()) << "Unexpectedly sandboxed!";
  76
  77   if (setuid_sandbox_client_->IsSuidSandboxChild()) {
  78     setuid_sandbox_client_->CloseDummyFile();
  79
  80     // Make sure that no directory file descriptor is open, as it would bypass
  81     // the setuid sandbox model.
  82     CHECK(!HasOpenDirectory());
  83
  84     // Get sandboxed.
  85     CHECK(setuid_sandbox_client_->ChrootMe());
  86     CHECK(IsSandboxed());
  87     layer_one_enabled_ = true;
  88   }
  89 }
  90
  91 void NaClSandbox::CheckForExpectedNumberOfOpenFds() {
  92   if (setuid_sandbox_client_->IsSuidSandboxChild()) {
  93     // We expect to have the following FDs open:
  94     //  1-3) stdin, stdout, stderr.
  95     //  4) The /dev/urandom FD used by base::GetUrandomFD().
  96     //  5) A dummy pipe FD used to overwrite kSandboxIPCChannel.
  97     //  6) The socket created by the SUID sandbox helper, used by ChrootMe().
  98     //     After ChrootMe(), this is no longer connected to anything.
  99     //     (Only present when running under the SUID sandbox.)
 100     //  7) The socket for the Chrome IPC channel that's connected to the
 101     //     browser process, kPrimaryIPCChannel.
 102     //
 103     // This sanity check ensures that dynamically loaded libraries don't
 104     // leave any FDs open before we enable the sandbox.
 105     sandbox::Credentials credentials;
 106     CHECK_EQ(7, credentials.CountOpenFds(proc_fd_.get()));
 107   }
 108 }
 109
 110 void NaClSandbox::InitializeLayerTwoSandbox(bool uses_nonsfi_mode) {
 111   // seccomp-bpf only applies to the current thread, so it's critical to only
 112   // have a single thread running here.
 113   DCHECK(!layer_one_sealed_);
 114   CHECK(IsSingleThreaded());
 115   CheckForExpectedNumberOfOpenFds();
 116
 117   if (uses_nonsfi_mode) {
 118     layer_two_enabled_ = nacl::nonsfi::InitializeBPFSandbox();
 119     layer_two_is_nonsfi_ = true;
 120   } else {
 121     layer_two_enabled_ = nacl::InitializeBPFSandbox();
 122   }
 123 }
 124
 125 void NaClSandbox::SealLayerOneSandbox() {
 126   if (!layer_two_enabled_) {
 127     // If nothing prevents us, check that there is no superfluous directory
 128     // open.
 129     CHECK(!HasOpenDirectory());
 130   }
 131   proc_fd_.reset();
 132   layer_one_sealed_ = true;
 133 }
 134
 135 void NaClSandbox::CheckSandboxingStateWithPolicy() {
 136   static const char kItIsDangerousMsg[] = " this is dangerous.";
 137   static const char kItIsNotAllowedMsg[] =
 138       " this is not allowed in this configuration.";
 139
 140   const bool no_sandbox_for_nonsfi_ok =
 141       CommandLine::ForCurrentProcess()->HasSwitch(
 142           switches::kNaClDangerousNoSandboxNonSfi);
 143   const bool can_be_no_sandbox =
 144       !layer_two_is_nonsfi_ || no_sandbox_for_nonsfi_ok;
 145
 146   if (!layer_one_enabled_ || !layer_one_sealed_) {
 147     static const char kNoSuidMsg[] =
 148         "The SUID sandbox is not engaged for NaCl:";
 149     if (can_be_no_sandbox)
 150       LOG(ERROR) << kNoSuidMsg << kItIsDangerousMsg;
 151     else
 152       LOG(FATAL) << kNoSuidMsg << kItIsNotAllowedMsg;
 153   }
 154
 155   if (!layer_two_enabled_) {
 156     static const char kNoBpfMsg[] =
 157         "The seccomp-bpf sandbox is not engaged for NaCl:";
 158     if (can_be_no_sandbox)
 159       LOG(ERROR) << kNoBpfMsg << kItIsDangerousMsg;
 160     else
 161       LOG(FATAL) << kNoBpfMsg << kItIsNotAllowedMsg;
 162   }
 163 }
 164
 165 }  // namespace nacl