sandbox/linux/suid/client/setuid_sandbox_client.cc

// Copyright (c) 2012 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 <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>

#include "base/eintr_wrapper.h"
#include "base/environment.h"
#include "base/logging.h"
#include "base/memory/scoped_ptr.h"
#include "base/string_number_conversions.h"

#include "sandbox/linux/suid/common/sandbox.h"
#include "sandbox/linux/suid/common/suid_unsafe_environment_variables.h"
#include "setuid_sandbox_client.h"

namespace {

// Set an environment variable that reflects the API version we expect from the
// setuid sandbox. Old versions of the sandbox will ignore this.
void SetSandboxAPIEnvironmentVariable(base::Environment* env) {
  env->SetVar(sandbox::kSandboxEnvironmentApiRequest,
              base::IntToString(sandbox::kSUIDSandboxApiNumber));
}

// Wrapper around a shared C function.
// Returns the "saved" environment variable name corresponding to |envvar|
// in a new string or NULL.
std::string* CreateSavedVariableName(const char* env_var) {
  char* const saved_env_var = SandboxSavedEnvironmentVariable(env_var);
  if (!saved_env_var)
    return NULL;
  std::string* saved_env_var_copy = new std::string(saved_env_var);
  // SandboxSavedEnvironmentVariable is the C function that we wrap and uses
  // malloc() to allocate memory.
  free(saved_env_var);
  return saved_env_var_copy;
}

// The ELF loader will clear many environment variables so we save them to
// different names here so that the SUID sandbox can resolve them for the
// renderer.
void SaveSUIDUnsafeEnvironmentVariables(base::Environment* env) {
  for (unsigned i = 0; kSUIDUnsafeEnvironmentVariables[i]; ++i) {
    const char* env_var = kSUIDUnsafeEnvironmentVariables[i];
    // Get the saved environment variable corresponding to envvar.
    scoped_ptr<std::string> saved_env_var(CreateSavedVariableName(env_var));
    if (saved_env_var == NULL)
      continue;

    std::string value;
    if (env->GetVar(env_var, &value))
      env->SetVar(saved_env_var->c_str(), value);
    else
      env->UnSetVar(saved_env_var->c_str());
  }
}

int GetHelperApi(base::Environment* env) {
  std::string api_string;
  int api_number = 0;  // Assume API version 0 if no environment was found.
  if (env->GetVar(sandbox::kSandboxEnvironmentApiProvides, &api_string) &&
      !base::StringToInt(api_string, &api_number)) {
    // It's an error if we could not convert the API number.
    api_number = -1;
  }
  return api_number;
}

// Convert |var_name| from the environment |env| to an int.
// Return -1 if the variable does not exist or the value cannot be converted.
int EnvToInt(base::Environment* env, const char* var_name) {
  std::string var_string;
  int var_value = -1;
  if (env->GetVar(var_name, &var_string) &&
      !base::StringToInt(var_string, &var_value)) {
    var_value = -1;
  }
  return var_value;
}

pid_t GetHelperPID(base::Environment* env) {
  return EnvToInt(env, sandbox::kSandboxHelperPidEnvironmentVarName);
}

// Get the IPC file descriptor used to communicate with the setuid helper.
int GetIPCDescriptor(base::Environment* env) {
  return EnvToInt(env, sandbox::kSandboxDescriptorEnvironmentVarName);
}

}  // namespace

namespace sandbox {

SetuidSandboxClient* SetuidSandboxClient::Create() {
  base::Environment* environment(base::Environment::Create());
  SetuidSandboxClient* sandbox_client(new(SetuidSandboxClient));

  CHECK(environment);
  sandbox_client->env_ = environment;
  return sandbox_client;
}

SetuidSandboxClient::SetuidSandboxClient()
    : env_(NULL),
      sandboxed_(false) {
}

SetuidSandboxClient::~SetuidSandboxClient() {
  delete env_;
}

bool SetuidSandboxClient::ChrootMe() {
  int ipc_fd = GetIPCDescriptor(env_);

  if (ipc_fd < 0) {
    LOG(ERROR) << "Failed to obtain the sandbox IPC descriptor";
    return false;
  }

  if (HANDLE_EINTR(write(ipc_fd, &kMsgChrootMe, 1)) != 1) {
    PLOG(ERROR) << "Failed to write to chroot pipe";
    return false;
  }

  // We need to reap the chroot helper process in any event.
  pid_t helper_pid = GetHelperPID(env_);
  // If helper_pid is -1 we wait for any child.
  if (waitpid(helper_pid, NULL, 0) < 0) {
    PLOG(ERROR) << "Failed to wait for setuid helper to die";
    return false;
  }

  char reply;
  if (HANDLE_EINTR(read(ipc_fd, &reply, 1)) != 1) {
    PLOG(ERROR) << "Failed to read from chroot pipe";
    return false;
  }

  if (reply != kMsgChrootSuccessful) {
    LOG(ERROR) << "Error code reply from chroot helper";
    return false;
  }

  // We now consider ourselves "fully sandboxed" as far as the
  // setuid sandbox is concerned.
  sandboxed_ = true;
  return true;
}

bool SetuidSandboxClient::IsSuidSandboxUpToDate() const {
  return GetHelperApi(env_) == kSUIDSandboxApiNumber;
}

bool SetuidSandboxClient::IsSuidSandboxChild() const {
  return GetIPCDescriptor(env_) >= 0;
}

bool SetuidSandboxClient::IsInNewPIDNamespace() const {
  return env_->HasVar(kSandboxPIDNSEnvironmentVarName);
}

bool SetuidSandboxClient::IsInNewNETNamespace() const {
  return env_->HasVar(kSandboxNETNSEnvironmentVarName);
}

bool SetuidSandboxClient::IsSandboxed() const {
  return sandboxed_;
}

void SetuidSandboxClient::SetupLaunchEnvironment() {
  SaveSUIDUnsafeEnvironmentVariables(env_);
  SetSandboxAPIEnvironmentVariable(env_);
}

}  // namespace sandbox