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/prctl.h>
  10 #include <sys/stat.h>
  11 #include <sys/types.h>
  12 #include <unistd.h>
  13
  14 #include <limits>
  15
  16 #include "base/basictypes.h"
  17 #include "base/callback.h"
  18 #include "base/command_line.h"
  19 #include "base/compiler_specific.h"
  20 #include "base/files/scoped_file.h"
  21 #include "base/logging.h"
  22 #include "base/memory/scoped_ptr.h"
  23 #include "base/posix/eintr_wrapper.h"
  24 #include "build/build_config.h"
  25 #include "components/nacl/common/nacl_switches.h"
  26 #include "components/nacl/loader/nonsfi/nonsfi_sandbox.h"
  27 #include "components/nacl/loader/sandbox_linux/nacl_bpf_sandbox_linux.h"
  28 #include "content/public/common/content_switches.h"
  29 #include "sandbox/linux/seccomp-bpf/sandbox_bpf.h"
  30 #include "sandbox/linux/services/credentials.h"
  31 #include "sandbox/linux/services/namespace_sandbox.h"
  32 #include "sandbox/linux/services/proc_util.h"
  33 #include "sandbox/linux/services/resource_limits.h"
  34 #include "sandbox/linux/services/thread_helpers.h"
  35 #include "sandbox/linux/suid/client/setuid_sandbox_client.h"
  36
  37 namespace nacl {
  38
  39 namespace {
  40
  41 // This is a poor man's check on whether we are sandboxed.
  42 bool IsSandboxed() {
  43   int proc_fd = open("/proc/self/exe", O_RDONLY);
  44   if (proc_fd >= 0) {
  45     PCHECK(0 == IGNORE_EINTR(close(proc_fd)));
  46     return false;
  47   }
  48   return true;
  49 }
  50
  51 // Open a new file descriptor to /proc/self/task/ by using
  52 // |proc_fd|.
  53 base::ScopedFD GetProcSelfTask(int proc_fd) {
  54   base::ScopedFD proc_self_task(HANDLE_EINTR(
  55       openat(proc_fd, "self/task/", O_RDONLY | O_DIRECTORY | O_CLOEXEC)));
  56   PCHECK(proc_self_task.is_valid());
  57   return proc_self_task.Pass();
  58 }
  59
  60 bool MaybeSetProcessNonDumpable() {
  61   const base::CommandLine& command_line =
  62       *base::CommandLine::ForCurrentProcess();
  63   if (command_line.HasSwitch(switches::kAllowSandboxDebugging)) {
  64     return true;
  65   }
  66
  67   if (prctl(PR_SET_DUMPABLE, 0, 0, 0, 0) != 0) {
  68     PLOG(ERROR) << "Failed to set non-dumpable flag";
  69     return false;
  70   }
  71
  72   return prctl(PR_GET_DUMPABLE) == 0;
  73 }
  74
  75 void RestrictAddressSpaceUsage() {
  76 #if defined(ADDRESS_SANITIZER) || defined(MEMORY_SANITIZER) || \
  77     defined(THREAD_SANITIZER)
  78   // Sanitizers need to reserve huge chunks of the address space.
  79   return;
  80 #endif
  81
  82   // Add a limit to the brk() heap that would prevent allocations that can't be
  83   // indexed by an int. This helps working around typical security bugs.
  84   // This could almost certainly be set to zero. GLibc's allocator and others
  85   // would fall-back to mmap if brk() fails.
  86   const rlim_t kNewDataSegmentMaxSize = std::numeric_limits<int>::max();
  87   CHECK(sandbox::ResourceLimits::Lower(RLIMIT_DATA, kNewDataSegmentMaxSize));
  88
  89 #if defined(ARCH_CPU_64_BITS)
  90   // NaCl's x86-64 sandbox allocated 88GB address of space during startup:
  91   // - The main sandbox is 4GB
  92   // - There are two guard regions of 40GB each.
  93   // - 4GB are allocated extra to have a 4GB-aligned address.
  94   // See https://crbug.com/455839
  95   //
  96   // Set the limit to 128 GB and have some margin.
  97   const rlim_t kNewAddressSpaceLimit = 1UL << 37;
  98 #else
  99   // Some architectures such as X86 allow 32 bits processes to switch to 64
 100   // bits when running under 64 bits kernels. Set a limit in case this happens.
 101   const rlim_t kNewAddressSpaceLimit = std::numeric_limits<uint32_t>::max();
 102 #endif
 103   CHECK(sandbox::ResourceLimits::Lower(RLIMIT_AS, kNewAddressSpaceLimit));
 104 }
 105
 106 }  // namespace
 107
 108 NaClSandbox::NaClSandbox()
 109     : layer_one_enabled_(false),
 110       layer_one_sealed_(false),
 111       layer_two_enabled_(false),
 112       layer_two_is_nonsfi_(false),
 113       proc_fd_(-1),
 114       setuid_sandbox_client_(sandbox::SetuidSandboxClient::Create()) {
 115   proc_fd_.reset(
 116       HANDLE_EINTR(open("/proc", O_DIRECTORY | O_RDONLY | O_CLOEXEC)));
 117   PCHECK(proc_fd_.is_valid());
 118 }
 119
 120 NaClSandbox::~NaClSandbox() {
 121 }
 122
 123 bool NaClSandbox::IsSingleThreaded() {
 124   CHECK(proc_fd_.is_valid());
 125   base::ScopedFD proc_self_task(GetProcSelfTask(proc_fd_.get()));
 126   return sandbox::ThreadHelpers::IsSingleThreaded(proc_self_task.get());
 127 }
 128
 129 bool NaClSandbox::HasOpenDirectory() {
 130   CHECK(proc_fd_.is_valid());
 131   return sandbox::ProcUtil::HasOpenDirectory(proc_fd_.get());
 132 }
 133
 134 void NaClSandbox::InitializeLayerOneSandbox() {
 135   // Check that IsSandboxed() works. We should not be sandboxed at this point.
 136   CHECK(!IsSandboxed()) << "Unexpectedly sandboxed!";
 137
 138   if (setuid_sandbox_client_->IsSuidSandboxChild()) {
 139     setuid_sandbox_client_->CloseDummyFile();
 140
 141     // Make sure that no directory file descriptor is open, as it would bypass
 142     // the setuid sandbox model.
 143     CHECK(!HasOpenDirectory());
 144
 145     // Get sandboxed.
 146     CHECK(setuid_sandbox_client_->ChrootMe());
 147     CHECK(MaybeSetProcessNonDumpable());
 148     CHECK(IsSandboxed());
 149     layer_one_enabled_ = true;
 150   } else if (sandbox::NamespaceSandbox::InNewUserNamespace()) {
 151     CHECK(sandbox::Credentials::MoveToNewUserNS());
 152     // This relies on SealLayerOneSandbox() to be called later.
 153     CHECK(!HasOpenDirectory());
 154     CHECK(sandbox::Credentials::DropFileSystemAccess());
 155     CHECK(IsSingleThreaded());
 156     CHECK(sandbox::Credentials::DropAllCapabilities());
 157     CHECK(IsSandboxed());
 158     layer_one_enabled_ = true;
 159   }
 160 }
 161
 162 void NaClSandbox::CheckForExpectedNumberOfOpenFds() {
 163   // We expect to have the following FDs open:
 164   //  1-3) stdin, stdout, stderr.
 165   //  4) The /dev/urandom FD used by base::GetUrandomFD().
 166   //  5) A dummy pipe FD used to overwrite kSandboxIPCChannel.
 167   //  6) The socket for the Chrome IPC channel that's connected to the
 168   //     browser process, kPrimaryIPCChannel.
 169   // We also have an fd for /proc (proc_fd_), but CountOpenFds excludes this.
 170   //
 171   // This sanity check ensures that dynamically loaded libraries don't
 172   // leave any FDs open before we enable the sandbox.
 173   int expected_num_fds = 6;
 174   if (setuid_sandbox_client_->IsSuidSandboxChild()) {
 175     // When using the setuid sandbox, there is one additional socket used for
 176     // ChrootMe(). After ChrootMe(), it is no longer connected to anything.
 177     ++expected_num_fds;
 178   }
 179
 180   CHECK_EQ(expected_num_fds, sandbox::ProcUtil::CountOpenFds(proc_fd_.get()));
 181 }
 182
 183 void NaClSandbox::InitializeLayerTwoSandbox(bool uses_nonsfi_mode) {
 184   // seccomp-bpf only applies to the current thread, so it's critical to only
 185   // have a single thread running here.
 186   DCHECK(!layer_one_sealed_);
 187   CHECK(IsSingleThreaded());
 188   CheckForExpectedNumberOfOpenFds();
 189
 190   RestrictAddressSpaceUsage();
 191
 192   base::ScopedFD proc_self_task(GetProcSelfTask(proc_fd_.get()));
 193
 194   if (uses_nonsfi_mode) {
 195     layer_two_enabled_ =
 196         nacl::nonsfi::InitializeBPFSandbox(proc_self_task.Pass());
 197     layer_two_is_nonsfi_ = true;
 198   } else {
 199     layer_two_enabled_ = nacl::InitializeBPFSandbox(proc_self_task.Pass());
 200   }
 201 }
 202
 203 void NaClSandbox::SealLayerOneSandbox() {
 204   if (!layer_two_enabled_) {
 205     // If nothing prevents us, check that there is no superfluous directory
 206     // open.
 207     CHECK(!HasOpenDirectory());
 208   }
 209   proc_fd_.reset();
 210   layer_one_sealed_ = true;
 211 }
 212
 213 void NaClSandbox::CheckSandboxingStateWithPolicy() {
 214   static const char kItIsDangerousMsg[] = " this is dangerous.";
 215   static const char kItIsNotAllowedMsg[] =
 216       " this is not allowed in this configuration.";
 217
 218   const bool no_sandbox_for_nonsfi_ok =
 219       base::CommandLine::ForCurrentProcess()->HasSwitch(
 220           switches::kNaClDangerousNoSandboxNonSfi);
 221   const bool can_be_no_sandbox =
 222       !layer_two_is_nonsfi_ || no_sandbox_for_nonsfi_ok;
 223
 224   if (!layer_one_enabled_ || !layer_one_sealed_) {
 225     static const char kNoSuidMsg[] =
 226         "The SUID sandbox is not engaged for NaCl:";
 227     if (can_be_no_sandbox)
 228       LOG(ERROR) << kNoSuidMsg << kItIsDangerousMsg;
 229     else
 230       LOG(FATAL) << kNoSuidMsg << kItIsNotAllowedMsg;
 231   }
 232
 233   if (!layer_two_enabled_) {
 234     static const char kNoBpfMsg[] =
 235         "The seccomp-bpf sandbox is not engaged for NaCl:";
 236     if (can_be_no_sandbox)
 237       LOG(ERROR) << kNoBpfMsg << kItIsDangerousMsg;
 238     else
 239       LOG(FATAL) << kNoBpfMsg << kItIsNotAllowedMsg;
 240   }
 241 }
 242
 243 }  // namespace nacl