process_manager.cc

//
// Copyright (C) 2015 The Android Open Source Project
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//

#include "shill/process_manager.h"

#include <signal.h>
#include <stdlib.h>
#include <sys/prctl.h>

#include <memory>
#include <utility>

#include "shill/event_dispatcher.h"
#include "shill/logging.h"

using std::map;
using std::string;
using std::vector;

namespace shill {

namespace Logging {
static auto kModuleLogScope = ScopeLogger::kManager;
static string ObjectID(const ProcessManager* pm) { return "process_manager"; }
}

namespace {

base::LazyInstance<ProcessManager> g_process_manager =
    LAZY_INSTANCE_INITIALIZER;

static const int kTerminationTimeoutSeconds = 2;
static const int kWaitpidPollTimesForSIGTERM = 10;
static const int kWaitpidPollTimesForSIGKILL = 8;
static const unsigned int kWaitpidPollIntervalUpperBoundMilliseconds = 2000;
static const unsigned int kWaitpidPollInitialIntervalMilliseconds = 4;

bool SetupChild(const map<string, string>& env, bool terminate_with_parent) {
  // Setup environment variables.
  clearenv();
  for (const auto& key_value : env) {
    setenv(key_value.first.c_str(), key_value.second.c_str(), 0);
  }
  if (terminate_with_parent) {
    prctl(PR_SET_PDEATHSIG, SIGTERM);
  }
  return true;
}

}  // namespace

ProcessManager::ProcessManager() {}

ProcessManager::~ProcessManager() {}

// static
ProcessManager* ProcessManager::GetInstance() {
  return g_process_manager.Pointer();
}

void ProcessManager::Init(EventDispatcher* dispatcher) {
  SLOG(this, 2) << __func__;
  CHECK(!async_signal_handler_);
  async_signal_handler_.reset(new brillo::AsynchronousSignalHandler());
  async_signal_handler_->Init();
  process_reaper_.Register(async_signal_handler_.get());
  dispatcher_ = dispatcher;
  minijail_ = brillo::Minijail::GetInstance();
}

void ProcessManager::Stop() {
  SLOG(this, 2) << __func__;
  CHECK(async_signal_handler_);
  process_reaper_.Unregister();
  async_signal_handler_.reset();
}

pid_t ProcessManager::StartProcess(
    const tracked_objects::Location& spawn_source,
    const base::FilePath& program,
    const vector<string>& arguments,
    const map<string, string>& environment,
    bool terminate_with_parent,
    const base::Callback<void(int)>& exit_callback) {
  SLOG(this, 2) << __func__ << "(" << program.value() << ")";

  // Setup/create child process.
  std::unique_ptr<brillo::Process> process(new brillo::ProcessImpl());
  process->AddArg(program.value());
  for (const auto& option : arguments) {
    process->AddArg(option);
  }
  process->SetCloseUnusedFileDescriptors(true);
  process->SetPreExecCallback(
      base::Bind(&SetupChild, environment, terminate_with_parent));
  if (!process->Start()) {
    LOG(ERROR) << "Failed to start child process for " << program.value();
    return -1;
  }

  // Setup watcher for the child process.
  pid_t pid = process->pid();
  CHECK(process_reaper_.WatchForChild(
      spawn_source,
      pid,
      base::Bind(&ProcessManager::OnProcessExited,
                 weak_factory_.GetWeakPtr(),
                 pid)));

  // Release ownership of the child process from the |process| object, so that
  // child process will not get killed on destruction of |process| object.
  process->Release();

  watched_processes_.emplace(pid, exit_callback);
  return pid;
}

pid_t ProcessManager::StartProcessInMinijailWithPipes(
    const tracked_objects::Location& spawn_source,
    const base::FilePath& program,
    const std::vector<std::string>& arguments,
    const std::string& user,
    const std::string& group,
    uint64_t capmask,
    const base::Callback<void(int)>& exit_callback,
    int* stdin_fd,
    int* stdout_fd,
    int* stderr_fd) {
  SLOG(this, 2) << __func__ << "(" << program.value() << ")";

  vector<char*> args;
  args.push_back(const_cast<char*>(program.value().c_str()));
  for (const auto& arg : arguments) {
    args.push_back(const_cast<char*>(arg.c_str()));
  }
  args.push_back(nullptr);

  struct minijail* jail = minijail_->New();

  if (!minijail_->DropRoot(jail, user.c_str(), group.c_str())) {
    LOG(ERROR) << "Minijail failed to drop root privileges?";
    return -1;
  }

  minijail_->UseCapabilities(jail, capmask);
  minijail_->ResetSignalMask(jail);

  pid_t pid;
  if (!minijail_->RunPipesAndDestroy(
          jail, args, &pid, stdin_fd, stdout_fd, stderr_fd)) {
    LOG(ERROR) << "Unable to spawn " << program.value() << " in a jail.";
    return -1;
  }

  CHECK(process_reaper_.WatchForChild(
      spawn_source,
      pid,
      base::Bind(&ProcessManager::OnProcessExited,
                 weak_factory_.GetWeakPtr(),
                 pid)));

  watched_processes_.emplace(pid, exit_callback);
  return pid;
}

bool ProcessManager::StopProcess(pid_t pid) {
  SLOG(this, 2) << __func__ << "(" << pid << ")";

  if (pending_termination_processes_.find(pid) !=
      pending_termination_processes_.end()) {
    LOG(ERROR) << "Process " << pid << " already being stopped.";
    return false;
  }

  if (watched_processes_.find(pid) == watched_processes_.end()) {
    LOG(ERROR) << "Process " << pid << " not being watched";
    return false;
  }
  // Caller not interested in watching this process anymore, since the
  // process termination is initiated by the caller.
  watched_processes_.erase(pid);

  // Attempt to send SIGTERM signal first.
  return TerminateProcess(pid, false);
}

bool ProcessManager::StopProcessAndBlock(pid_t pid) {
  SLOG(this, 2) << __func__ << "(" << pid << ")";

  auto terminated_process = pending_termination_processes_.find(pid);

  if (terminated_process != pending_termination_processes_.end()) {
    LOG(INFO) << "Process " << pid << " already being stopped.";
    terminated_process->second->Cancel();
    pending_termination_processes_.erase(terminated_process);
  } else {
    if (watched_processes_.find(pid) == watched_processes_.end()) {
      LOG(ERROR) << "Process " << pid << " not being watched";
      return false;
    }
    // Caller not interested in watching this process anymore, since the
    // process termination is initiated by the caller.
    watched_processes_.erase(pid);
  }

  // We are no longer interested in tracking the exit of this process.
  // Also, we will hopefully reap this process ourselves, so remove any
  // record of this pid from process_reaper_.
  process_reaper_.ForgetChild(pid);

  // Try SIGTERM firstly.
  // Send SIGKILL signal if SIGTERM was not handled in a timely manner.
  if (KillProcessWithTimeout(pid, false) ||
      KillProcessWithTimeout(pid, true)) {
    return true;
  }

  // In case of killing failure.
  LOG(ERROR) << "Timeout waiting for process " << pid << " to be killed.";

  return false;
}

bool ProcessManager::KillProcessWithTimeout(pid_t pid, bool kill_signal) {
  SLOG(this, 2) << __func__ << "(pid: " << pid << ")";

  bool killed = false;
  if (KillProcess(pid, kill_signal ? SIGKILL : SIGTERM, &killed)) {
    if (killed) {
      return true;
    }

    int poll_times = kill_signal ? kWaitpidPollTimesForSIGKILL :
        kWaitpidPollTimesForSIGTERM;

    if (WaitpidWithTimeout(pid, kWaitpidPollInitialIntervalMilliseconds,
                           kWaitpidPollIntervalUpperBoundMilliseconds,
                           poll_times)) {
      return true;
    }
  }
  return false;
}

bool ProcessManager::KillProcess(pid_t pid, int signal, bool* killed) {
  SLOG(this, 2) << __func__ << "(pid: " << pid << ")";

  if (kill(pid, signal) < 0) {
    if (errno == ESRCH) {
      SLOG(this, 2) << "Process " << pid << " has exited.";
      *killed = true;
      return true;
    }
    PLOG(ERROR) << "Failed to send " << signal <<"signal to process " << pid;
    return false;
  }
  return true;
}

bool ProcessManager::WaitpidWithTimeout(pid_t pid,
                                        unsigned int sleep_ms,
                                        unsigned int upper_bound_ms,
                                        int tries) {
  SLOG(this, 2) << __func__ << "(pid: " << pid << ")";

  while (tries-- > 0) {
    if (waitpid(pid, nullptr, WNOHANG) == pid) {
      return true;
    }
    usleep(sleep_ms * 1000);
    if (2 * sleep_ms < upper_bound_ms) {
      sleep_ms *= 2;
    }
  }
  return false;
}

bool ProcessManager::UpdateExitCallback(
    pid_t pid,
    const base::Callback<void(int)>& new_callback) {
  SLOG(this, 2) << __func__ << "(pid: " << pid << ")";

  const auto process_entry = watched_processes_.find(pid);
  if (process_entry == watched_processes_.end()) {
    LOG(ERROR) << "Process " << pid << " not being watched";
    return false;
  }

  process_entry->second = new_callback;
  return true;
}

void ProcessManager::OnProcessExited(pid_t pid, const siginfo_t& info) {
  SLOG(this, 2) << __func__ << "(pid: " << pid << ")";

  // Invoke the exit callback if the process is being watched.
  auto watched_process = watched_processes_.find(pid);
  if (watched_process != watched_processes_.end()) {
    base::Callback<void(int)> callback = watched_process->second;
    watched_processes_.erase(watched_process);
    callback.Run(info.si_status);
    return;
  }

  // Process terminated by us, cancel timeout handler.
  auto terminated_process = pending_termination_processes_.find(pid);
  if (terminated_process != pending_termination_processes_.end()) {
    terminated_process->second->Cancel();
    pending_termination_processes_.erase(terminated_process);
    return;
  }

  NOTREACHED() << "Unknown process " << pid << " status " << info.si_status;
}

void ProcessManager::ProcessTerminationTimeoutHandler(pid_t pid,
                                                      bool kill_signal) {
  SLOG(this, 2) << __func__ << "(pid: " << pid << ")";

  CHECK(pending_termination_processes_.find(pid) !=
        pending_termination_processes_.end());
  pending_termination_processes_.erase(pid);
  // Process still not killed after SIGKILL signal.
  if (kill_signal) {
    LOG(ERROR) << "Timeout waiting for process " << pid << " to be killed.";
    return;
  }

  // Retry using SIGKILL signal.
  TerminateProcess(pid, true);
}

bool ProcessManager::TerminateProcess(pid_t pid, bool kill_signal) {
  SLOG(this, 2) << __func__
                << "(pid: " << pid << ", "
                << "use_sigkill: " << kill_signal << ")";

  int signal = (kill_signal) ? SIGKILL : SIGTERM;
  bool killed = false;
  if (!KillProcess(pid, signal, &killed)) {
    return false;
  }
  if (killed) {
    return true;
  }
  auto termination_callback = std::make_unique<TerminationTimeoutCallback>(
      base::Bind(&ProcessManager::ProcessTerminationTimeoutHandler,
                 weak_factory_.GetWeakPtr(),
                 pid,
                 kill_signal));
  dispatcher_->PostDelayedTask(FROM_HERE, termination_callback->callback(),
                               kTerminationTimeoutSeconds * 1000);
  pending_termination_processes_.emplace(pid, std::move(termination_callback));
  return true;
}

}  // namespace shill