germ/germ_zygote.cc

// Copyright 2015 The Chromium OS 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 "germ/germ_zygote.h"

#include <sched.h>
#include <signal.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/wait.h>

#include <string>
#include <vector>

#include <base/files/scoped_file.h>
#include <base/logging.h>
#include <base/memory/scoped_ptr.h>
#include <base/memory/scoped_vector.h>
#include <base/posix/eintr_wrapper.h>
#include <base/posix/unix_domain_socket_linux.h>
#include <base/pickle.h>
#include <base/process/launch.h>
#include <base/strings/string_piece.h>

#include "germ/germ_init.h"
#include "germ/proto_bindings/soma_container_spec.pb.h"

namespace germ {

namespace {
static const char kZygoteChildPingMessage[] = "CHILD_PING";
// TODO(rickyz) Is it reasonable to have a hard limit for the ContainerSpecs +
// pickle size?
static size_t kZygoteMaxMessageLength = 8192;
}  // namespace

GermZygote::GermZygote() : zygote_pid_(-1) {}
GermZygote::~GermZygote() {}

void GermZygote::Start() {
  int fds[2];
  PCHECK(socketpair(AF_UNIX, SOCK_SEQPACKET, 0, fds) == 0);

  client_fd_.reset(fds[0]);
  server_fd_.reset(fds[1]);

  zygote_pid_ = fork();
  PCHECK(zygote_pid_ != -1);

  if (zygote_pid_ == 0) {
    client_fd_.reset();
    HandleRequests();
    NOTREACHED();
  }

  server_fd_.reset();
}

void GermZygote::HandleRequests() {
  while (true) {
    // Yes, this is yet another hand-rolled protobuf RPC protocol :-( We're
    // doing this because we do not want to fork in the presence of binder.
    char buf[kZygoteMaxMessageLength];
    ScopedVector<base::ScopedFD> ipc_fds;
    ssize_t len =
        UnixDomainSocket::RecvMsg(server_fd_.get(), buf, sizeof(buf), &ipc_fds);

    if (len == 0 || (len == -1 && errno == ECONNRESET)) {
      _exit(0);
    }

    if (len == -1) {
      PLOG(ERROR) << "RecvMsg failed.";
      continue;
    }

    if (ipc_fds.size() != 1) {
      LOG(ERROR) << "Expected one IPC fd, received: " << ipc_fds.size();
      continue;
    }

    Pickle pickle(buf, len);
    PickleIterator iter(pickle);

    base::StringPiece serialized_spec;
    if (!iter.ReadStringPiece(&serialized_spec)) {
      LOG(ERROR) << "Failed to parse serialized spec from pickle.";
    }

    soma::ContainerSpec spec;
    if (!spec.ParseFromArray(serialized_spec.data(), serialized_spec.size())) {
      LOG(ERROR) << "Failed to parse spec.";
      continue;
    }

    const int ipc_fd = ipc_fds[0]->get();
    SpawnContainer(spec, ipc_fd);
  }

  NOTREACHED();
  _exit(1);
}

bool GermZygote::StartContainer(const soma::ContainerSpec& spec, pid_t* pid) {
  std::string serialized_spec;
  if (!spec.SerializeToString(&serialized_spec)) {
    LOG(ERROR) << "Failed to serialize spec.";
    return false;
  }

  Pickle pickle;
  if (!pickle.WriteString(serialized_spec)) {
    LOG(ERROR) << "Failed to pickle serialized spec.";
    return false;
  }

  int ipc_fds[2];
  if (socketpair(AF_UNIX, SOCK_SEQPACKET, 0, ipc_fds) != 0) {
    PLOG(ERROR) << "socketpair failed";
    return false;
  }

  // TODO(rickyz): These can CHECK fail.
  base::ScopedFD client_fd(ipc_fds[0]);
  base::ScopedFD server_fd(ipc_fds[1]);
  PCHECK(UnixDomainSocket::EnableReceiveProcessId(client_fd.get()));

  std::vector<int> fds = {server_fd.get()};
  if (!UnixDomainSocket::SendMsg(client_fd_.get(), pickle.data(), pickle.size(),
                                 fds)) {
    PLOG(ERROR) << "SendMsg failed (spec)";
    return false;
  }

  server_fd.reset();

  ScopedVector<base::ScopedFD> dummy_fds;
  char ping_message_buf[sizeof(kZygoteChildPingMessage)];
  if (!UnixDomainSocket::RecvMsgWithPid(client_fd.get(), ping_message_buf,
                                        sizeof(ping_message_buf), &dummy_fds,
                                        pid)) {
    PLOG(ERROR) << "RecvMsgWithPid failed (ping message)";
    return false;
  }

  if (memcmp(ping_message_buf, kZygoteChildPingMessage,
             sizeof(ping_message_buf)) != 0) {
    LOG(ERROR) << "Received invalid ping message: " << ping_message_buf;
    return false;
  }

  return true;
}

bool GermZygote::Kill(pid_t pid, int signal) {
  if (kill(pid, signal) != 0) {
    PLOG(ERROR) << "kill(" << pid << ", " << signal << ") failed";
    return false;
  }

  return true;
}

pid_t GermZygote::ForkContainer(const soma::ContainerSpec& spec) {
  unsigned long flags = SIGCHLD;  // NOLINT(runtime/int)
  for (const int ns_int : spec.namespaces()) {
    const soma::ContainerSpec::Namespace ns =
        static_cast<soma::ContainerSpec::Namespace>(ns_int);
    switch (ns) {
      case soma::ContainerSpec::NEWIPC:
        flags |= CLONE_NEWIPC;
        break;
      case soma::ContainerSpec::NEWNET:
        flags |= CLONE_NEWNET;
        break;
      case soma::ContainerSpec::NEWNS:
        flags |= CLONE_NEWNS;
        break;
      case soma::ContainerSpec::NEWPID:
        flags |= CLONE_NEWPID;
        break;
      case soma::ContainerSpec::NEWUSER:
        flags |= CLONE_NEWUSER;
        break;
      case soma::ContainerSpec::NEWUTS:
        flags |= CLONE_NEWUTS;
        break;
      default:
        LOG(FATAL) << "Invalid namespace type for: " << spec.name();
        break;
    }
  }

  if (!(flags & CLONE_NEWPID)) {
    LOG(WARNING)
        << "PID namespaces missing from ContainerSpec, enabling anyway: "
        << spec.name();
    flags |= CLONE_NEWPID;
  }

  PCHECK(setsid() != -1);
  return base::ForkWithFlags(flags, nullptr, nullptr);
}

void GermZygote::SpawnContainer(const soma::ContainerSpec& spec,
                                int client_fd) {
  const pid_t pid = fork();
  PCHECK(pid != -1);

  // Double-fork and exit in the parent. This gives up ownership of the
  // container init process.
  if (pid == 0) {
    server_fd_.reset();

    const pid_t init_pid = ForkContainer(spec);
    PCHECK(init_pid != -1);

    if (init_pid == 0) {
      // Send a ping back so that the requester can obtain our PID.
      CHECK(UnixDomainSocket::SendMsg(client_fd, kZygoteChildPingMessage,
                                      sizeof(kZygoteChildPingMessage),
                                      std::vector<int>()));
      PCHECK(IGNORE_EINTR(close(client_fd)) == 0);

      GermInit init(spec);
      _exit(init.Run());
    }

    _exit(0);
  }

  // TODO(rickyz): We may want to be more paranoid about not CHECK failing in
  // the Germ zygote, since it is a critical system process.
  int status;
  PCHECK(waitpid(pid, &status, 0) == pid);
  if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
    LOG(ERROR) << "Received unexpected exit status from first fork: " << status;
  }
}

}  // namespace germ