sandbox/linux/services/namespace_sandbox.cc

   1 // Copyright 2015 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 "sandbox/linux/services/namespace_sandbox.h"
   6
   7 #include <sched.h>
   8 #include <signal.h>
   9 #include <stdlib.h>
  10 #include <sys/types.h>
  11 #include <unistd.h>
  12
  13 #include <string>
  14 #include <utility>
  15 #include <vector>
  16
  17 #include "base/command_line.h"
  18 #include "base/environment.h"
  19 #include "base/files/scoped_file.h"
  20 #include "base/logging.h"
  21 #include "base/macros.h"
  22 #include "base/posix/eintr_wrapper.h"
  23 #include "base/process/launch.h"
  24 #include "base/process/process.h"
  25 #include "sandbox/linux/services/credentials.h"
  26 #include "sandbox/linux/services/namespace_utils.h"
  27
  28 namespace sandbox {
  29
  30 namespace {
  31
  32 class WriteUidGidMapDelegate : public base::LaunchOptions::PreExecDelegate {
  33  public:
  34   WriteUidGidMapDelegate()
  35       : uid_(getuid()),
  36         gid_(getgid()),
  37         supports_deny_setgroups_(
  38             NamespaceUtils::KernelSupportsDenySetgroups()) {}
  39
  40   ~WriteUidGidMapDelegate() override {}
  41
  42   void RunAsyncSafe() override {
  43     if (supports_deny_setgroups_) {
  44       RAW_CHECK(NamespaceUtils::DenySetgroups());
  45     }
  46     RAW_CHECK(NamespaceUtils::WriteToIdMapFile("/proc/self/uid_map", uid_));
  47     RAW_CHECK(NamespaceUtils::WriteToIdMapFile("/proc/self/gid_map", gid_));
  48   }
  49
  50  private:
  51   const uid_t uid_;
  52   const gid_t gid_;
  53   const bool supports_deny_setgroups_;
  54   DISALLOW_COPY_AND_ASSIGN(WriteUidGidMapDelegate);
  55 };
  56
  57 void SetEnvironForNamespaceType(base::EnvironmentMap* environ,
  58                                 base::NativeEnvironmentString env_var,
  59                                 bool value) {
  60   // An empty string causes the env var to be unset in the child process.
  61   (*environ)[env_var] = value ? "1" : "";
  62 }
  63
  64 const char kSandboxUSERNSEnvironmentVarName[] = "SBX_USER_NS";
  65 const char kSandboxPIDNSEnvironmentVarName[] = "SBX_PID_NS";
  66 const char kSandboxNETNSEnvironmentVarName[] = "SBX_NET_NS";
  67
  68 // Linux supports up to 64 signals. This should be updated if that ever changes.
  69 int g_signal_exit_codes[64];
  70
  71 void TerminationSignalHandler(int sig) {
  72   // Return a special exit code so that the process is detected as terminated by
  73   // a signal.
  74   const size_t sig_idx = static_cast<size_t>(sig);
  75   if (sig_idx < arraysize(g_signal_exit_codes)) {
  76     _exit(g_signal_exit_codes[sig_idx]);
  77   }
  78
  79   _exit(NamespaceSandbox::kDefaultExitCode);
  80 }
  81
  82 }  // namespace
  83
  84 // static
  85 base::Process NamespaceSandbox::LaunchProcess(
  86     const base::CommandLine& cmdline,
  87     const base::LaunchOptions& options) {
  88   return LaunchProcess(cmdline.argv(), options);
  89 }
  90
  91 // static
  92 base::Process NamespaceSandbox::LaunchProcess(
  93     const std::vector<std::string>& argv,
  94     const base::LaunchOptions& options) {
  95   int clone_flags = 0;
  96   int ns_types[] = {CLONE_NEWUSER, CLONE_NEWPID, CLONE_NEWNET};
  97   for (const int ns_type : ns_types) {
  98     if (NamespaceUtils::KernelSupportsUnprivilegedNamespace(ns_type)) {
  99       clone_flags |= ns_type;
 100     }
 101   }
 102   CHECK(clone_flags & CLONE_NEWUSER);
 103
 104   // These fields may not be set by the caller.
 105   CHECK(options.pre_exec_delegate == nullptr);
 106   CHECK_EQ(0, options.clone_flags);
 107
 108   WriteUidGidMapDelegate write_uid_gid_map_delegate;
 109
 110   base::LaunchOptions launch_options = options;
 111   launch_options.pre_exec_delegate = &write_uid_gid_map_delegate;
 112   launch_options.clone_flags = clone_flags;
 113
 114   const std::pair<int, const char*> clone_flag_environ[] = {
 115       std::make_pair(CLONE_NEWUSER, kSandboxUSERNSEnvironmentVarName),
 116       std::make_pair(CLONE_NEWPID, kSandboxPIDNSEnvironmentVarName),
 117       std::make_pair(CLONE_NEWNET, kSandboxNETNSEnvironmentVarName),
 118   };
 119
 120   base::EnvironmentMap* environ = &launch_options.environ;
 121   for (const auto& entry : clone_flag_environ) {
 122     const int flag = entry.first;
 123     const char* environ_name = entry.second;
 124     SetEnvironForNamespaceType(environ, environ_name, clone_flags & flag);
 125   }
 126
 127   return base::LaunchProcess(argv, launch_options);
 128 }
 129
 130 // static
 131 pid_t NamespaceSandbox::ForkInNewPidNamespace(bool drop_capabilities_in_child) {
 132   const pid_t pid =
 133       base::ForkWithFlags(CLONE_NEWPID | SIGCHLD, nullptr, nullptr);
 134   if (pid < 0) {
 135     return pid;
 136   }
 137
 138   if (pid == 0) {
 139     DCHECK_EQ(1, getpid());
 140     if (drop_capabilities_in_child) {
 141       // Since we just forked, we are single-threaded, so this should be safe.
 142       CHECK(Credentials::DropAllCapabilitiesOnCurrentThread());
 143     }
 144     return 0;
 145   }
 146
 147   return pid;
 148 }
 149
 150 // static
 151 void NamespaceSandbox::InstallDefaultTerminationSignalHandlers() {
 152   static const int kDefaultTermSignals[] = {
 153       SIGHUP, SIGINT, SIGABRT, SIGQUIT, SIGPIPE, SIGTERM, SIGUSR1, SIGUSR2,
 154   };
 155
 156   for (const int sig : kDefaultTermSignals) {
 157     InstallTerminationSignalHandler(sig, kDefaultExitCode);
 158   }
 159 }
 160
 161 // static
 162 bool NamespaceSandbox::InstallTerminationSignalHandler(
 163     int sig,
 164     int exit_code) {
 165   struct sigaction old_action;
 166   PCHECK(sigaction(sig, nullptr, &old_action) == 0);
 167
 168   if (old_action.sa_flags & SA_SIGINFO &&
 169       old_action.sa_sigaction != nullptr) {
 170     return false;
 171   } else if (old_action.sa_handler != SIG_DFL) {
 172     return false;
 173   }
 174
 175   const size_t sig_idx = static_cast<size_t>(sig);
 176   CHECK_LT(sig_idx, arraysize(g_signal_exit_codes));
 177
 178   DCHECK_GE(exit_code, 0);
 179   DCHECK_LT(exit_code, 256);
 180
 181   g_signal_exit_codes[sig_idx] = exit_code;
 182
 183   struct sigaction action = {};
 184   action.sa_handler = &TerminationSignalHandler;
 185   PCHECK(sigaction(sig, &action, nullptr) == 0);
 186   return true;
 187 }
 188
 189 // static
 190 bool NamespaceSandbox::InNewUserNamespace() {
 191   return getenv(kSandboxUSERNSEnvironmentVarName) != nullptr;
 192 }
 193
 194 // static
 195 bool NamespaceSandbox::InNewPidNamespace() {
 196   return getenv(kSandboxPIDNSEnvironmentVarName) != nullptr;
 197 }
 198
 199 // static
 200 bool NamespaceSandbox::InNewNetNamespace() {
 201   return getenv(kSandboxNETNSEnvironmentVarName) != nullptr;
 202 }
 203
 204 }  // namespace sandbox