sandboxed-api/sandboxed_api/sandbox.cc

// Copyright 2019 Google LLC
//
// 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 "sandboxed_api/sandbox.h"

#include <sys/ioctl.h>
#include <sys/resource.h>
#include <sys/uio.h>

#include <algorithm>
#include <cstdarg>
#include <cstdio>

#include <glog/logging.h>
#include "absl/base/casts.h"
#include "absl/base/macros.h"
#include "absl/memory/memory.h"
#include "absl/status/status.h"
#include "absl/status/statusor.h"
#include "absl/strings/str_cat.h"
#include "absl/strings/str_format.h"
#include "absl/time/time.h"
#include "sandboxed_api/config.h"
#include "sandboxed_api/embed_file.h"
#include "sandboxed_api/rpcchannel.h"
#include "sandboxed_api/sandbox2/executor.h"
#include "sandboxed_api/sandbox2/policy.h"
#include "sandboxed_api/sandbox2/policybuilder.h"
#include "sandboxed_api/sandbox2/sandbox2.h"
#include "sandboxed_api/sandbox2/util/bpf_helper.h"
#include "sandboxed_api/util/fileops.h"
#include "sandboxed_api/util/path.h"
#include "sandboxed_api/util/runfiles.h"
#include "sandboxed_api/util/status_macros.h"

namespace sapi {

Sandbox::~Sandbox() {
  Terminate();
  // The forkserver will die automatically when the executor goes out of scope
  // and closes the comms object.
}

// A generic policy which should work with majority of typical libraries, which
// are single-threaded and require ~30 basic syscalls.
void InitDefaultPolicyBuilder(sandbox2::PolicyBuilder* builder) {
  (*builder)
      .AllowRead()
      .AllowWrite()
      .AllowExit()
      .AllowGetRlimit()
      .AllowGetIDs()
      .AllowTCGETS()
      .AllowTime()
      .AllowOpen()
      .AllowStat()
      .AllowHandleSignals()
      .AllowSystemMalloc()
      .AllowSafeFcntl()
      .AllowSyscalls({
          __NR_recvmsg,
          __NR_sendmsg,
          __NR_futex,
          __NR_close,
          __NR_lseek,
          __NR_getpid,
          __NR_getppid,
          __NR_gettid,
          __NR_clock_nanosleep,
          __NR_nanosleep,
          __NR_uname,
          __NR_getrandom,
          __NR_kill,
          __NR_tgkill,
          __NR_tkill,
#ifdef __NR_readlink
          __NR_readlink,
#endif
#ifdef __NR_arch_prctl  // x86-64 only
          __NR_arch_prctl,
#endif
      })
      .AddFile("/etc/localtime")
      .AddTmpfs("/tmp", 1ULL << 30 /* 1GiB tmpfs (max size) */);
  if constexpr (sanitizers::IsAny()) {
    LOG(WARNING) << "Allowing additional calls to support the LLVM "
                 << "(ASAN/MSAN/TSAN) sanitizer";
    builder->AllowLlvmSanitizers();
  }
}

void Sandbox::Terminate(bool attempt_graceful_exit) {
  if (!is_active()) {
    return;
  }

  if (attempt_graceful_exit) {
    // Gracefully ask it to exit (with 1 second limit) first, then kill it.
    Exit();
  } else {
    // Kill it straight away
    s2_->Kill();
  }

  const auto& result = AwaitResult();
  if (result.final_status() == sandbox2::Result::OK &&
      result.reason_code() == 0) {
    VLOG(2) << "Sandbox2 finished with: " << result.ToString();
  } else {
    LOG(WARNING) << "Sandbox2 finished with: " << result.ToString();
  }
}

static std::string PathToSAPILib(const std::string& lib_path) {
  return file::IsAbsolutePath(lib_path) ? lib_path
                                        : GetDataDependencyFilePath(lib_path);
}

absl::Status Sandbox::Init() {
  // It's already initialized
  if (is_active()) {
    return absl::OkStatus();
  }

  // Initialize the forkserver if it is not already running.
  if (!fork_client_) {
    // If FileToc was specified, it will be used over any paths to the SAPI
    // library.
    std::string lib_path;
    int embed_lib_fd = -1;
    if (embed_lib_toc_) {
      embed_lib_fd = EmbedFile::GetEmbedFileSingleton()->GetDupFdForFileToc(
          embed_lib_toc_);
      if (embed_lib_fd == -1) {
        PLOG(ERROR) << "Cannot create executable FD for TOC:'"
                    << embed_lib_toc_->name << "'";
        return absl::UnavailableError("Could not create executable FD");
      }
      lib_path = embed_lib_toc_->name;
    } else {
      lib_path = PathToSAPILib(GetLibPath());
      if (lib_path.empty()) {
        LOG(ERROR) << "SAPI library path is empty";
        return absl::FailedPreconditionError("No SAPI library path given");
      }
    }

    std::vector<std::string> args = {lib_path};
    // Additional arguments, if needed.
    GetArgs(&args);
    std::vector<std::string> envs{};
    // Additional envvars, if needed.
    GetEnvs(&envs);

    forkserver_executor_ =
        (embed_lib_fd >= 0)
            ? absl::make_unique<sandbox2::Executor>(embed_lib_fd, args, envs)
            : absl::make_unique<sandbox2::Executor>(lib_path, args, envs);

    fork_client_ = forkserver_executor_->StartForkServer();

    if (!fork_client_) {
      LOG(ERROR) << "Could not start forkserver";
      return absl::UnavailableError("Could not start the forkserver");
    }
  }

    sandbox2::PolicyBuilder policy_builder;
    InitDefaultPolicyBuilder(&policy_builder);
  auto s2p = ModifyPolicy(&policy_builder);

  // Spawn new process from the forkserver.
  auto executor = absl::make_unique<sandbox2::Executor>(fork_client_.get());

  executor
      // The client.cc code is capable of enabling sandboxing on its own.
      ->set_enable_sandbox_before_exec(false)
      // By default, set cwd to "/", can be changed in ModifyExecutor().
      .set_cwd("/")
      .limits()
      // Disable time limits.
      ->set_walltime_limit(absl::ZeroDuration())
      .set_rlimit_cpu(RLIM64_INFINITY)
      // Needed by the Scudo Allocator, and by various *SAN options.
      .set_rlimit_as(RLIM64_INFINITY);

  // Modify the executor, e.g. by setting custom limits and IPC.
  ModifyExecutor(executor.get());

  s2_ = absl::make_unique<sandbox2::Sandbox2>(std::move(executor),
                                              std::move(s2p), CreateNotifier());
  auto res = s2_->RunAsync();

  comms_ = s2_->comms();
  pid_ = s2_->GetPid();

  rpc_channel_ = absl::make_unique<RPCChannel>(comms_);

  if (!res) {
    Terminate();
    return absl::UnavailableError("Could not start the sandbox");
  }
  return absl::OkStatus();
}

bool Sandbox::is_active() const { return s2_ && !s2_->IsTerminated(); }

absl::Status Sandbox::Allocate(v::Var* var, bool automatic_free) {
  if (!is_active()) {
    return absl::UnavailableError("Sandbox not active");
  }
  return var->Allocate(GetRpcChannel(), automatic_free);
}

absl::Status Sandbox::Free(v::Var* var) {
  if (!is_active()) {
    return absl::UnavailableError("Sandbox not active");
  }
  return var->Free(GetRpcChannel());
}

absl::Status Sandbox::SynchronizePtrBefore(v::Callable* ptr) {
  if (!is_active()) {
    return absl::UnavailableError("Sandbox not active");
  }
  if (ptr->GetType() != v::Type::kPointer) {
    return absl::OkStatus();
  }
  // Cast is safe, since type is v::Type::kPointer
  auto* p = static_cast<v::Ptr*>(ptr);
  if (p->GetSyncType() == v::Pointable::kSyncNone) {
    return absl::OkStatus();
  }

  if (p->GetPointedVar()->GetRemote() == nullptr) {
    // Allocate the memory, and make it automatically free-able, upon this
    // object's (p->GetPointedVar()) end of life-time.
    SAPI_RETURN_IF_ERROR(Allocate(p->GetPointedVar(), /*automatic_free=*/true));
  }

  // Allocation occurs during both before/after synchronization modes. But the
  // memory is transferred to the sandboxee only if v::Pointable::kSyncBefore
  // was requested.
  if ((p->GetSyncType() & v::Pointable::kSyncBefore) == 0) {
    return absl::OkStatus();
  }

  VLOG(3) << "Synchronization (TO), ptr " << p << ", Type: " << p->GetSyncType()
          << " for var: " << p->GetPointedVar()->ToString();

  return p->GetPointedVar()->TransferToSandboxee(GetRpcChannel(), pid());
}

absl::Status Sandbox::SynchronizePtrAfter(v::Callable* ptr) const {
  if (!is_active()) {
    return absl::UnavailableError("Sandbox not active");
  }
  if (ptr->GetType() != v::Type::kPointer) {
    return absl::OkStatus();
  }
  v::Ptr* p = reinterpret_cast<v::Ptr*>(ptr);
  if ((p->GetSyncType() & v::Pointable::kSyncAfter) == 0) {
    return absl::OkStatus();
  }

  VLOG(3) << "Synchronization (FROM), ptr " << p
          << ", Type: " << p->GetSyncType()
          << " for var: " << p->GetPointedVar()->ToString();

  if (p->GetPointedVar()->GetRemote() == nullptr) {
    LOG(ERROR) << "Trying to synchronize a variable which is not allocated in "
               << "the sandboxee p=" << p->ToString();
    return absl::FailedPreconditionError(absl::StrCat(
        "Trying to synchronize a variable which is not allocated in the "
        "sandboxee p=",
        p->ToString()));
  }

  return p->GetPointedVar()->TransferFromSandboxee(GetRpcChannel(), pid());
}

absl::Status Sandbox::Call(const std::string& func, v::Callable* ret,
                           std::initializer_list<v::Callable*> args) {
  if (!is_active()) {
    return absl::UnavailableError("Sandbox not active");
  }
  // Send data.
  FuncCall rfcall{};
  rfcall.argc = args.size();
  absl::SNPrintF(rfcall.func, ABSL_ARRAYSIZE(rfcall.func), "%s", func);

  VLOG(1) << "CALL ENTRY: '" << func << "' with " << args.size()
          << " argument(s)";

  // Copy all arguments into rfcall.
  int i = 0;
  for (auto* arg : args) {
    rfcall.arg_size[i] = arg->GetSize();
    rfcall.arg_type[i] = arg->GetType();

    // For pointers, set the auxiliary type and size.
    if (rfcall.arg_type[i] == v::Type::kPointer) {
      // Cast is safe, since type is v::Type::kPointer
      auto* p = static_cast<v::Ptr*>(arg);
      rfcall.aux_type[i] = p->GetPointedVar()->GetType();
      rfcall.aux_size[i] = p->GetPointedVar()->GetSize();
    }

    // Synchronize all pointers before the call if it's needed.
    SAPI_RETURN_IF_ERROR(SynchronizePtrBefore(arg));

    if (arg->GetType() == v::Type::kFloat) {
      arg->GetDataFromPtr(&rfcall.args[i].arg_float,
                          sizeof(rfcall.args[0].arg_float));
    } else {
      arg->GetDataFromPtr(&rfcall.args[i].arg_int,
                          sizeof(rfcall.args[0].arg_int));
    }

    if (rfcall.arg_type[i] == v::Type::kFd) {
      // Cast is safe, since type is v::Type::kFd
      auto* fd = static_cast<v::Fd*>(arg);
      if (fd->GetRemoteFd() < 0) {
        SAPI_RETURN_IF_ERROR(TransferToSandboxee(fd));
      }
      rfcall.args[i].arg_int = fd->GetRemoteFd();
    }

    VLOG(1) << "CALL ARG: (" << i << "), Type: " << arg->GetTypeString()
            << ", Size: " << arg->GetSize() << ", Val: " << arg->ToString();
    ++i;
  }
  rfcall.ret_type = ret->GetType();
  rfcall.ret_size = ret->GetSize();

  // Call & receive data.
  FuncRet fret;
  SAPI_RETURN_IF_ERROR(
      GetRpcChannel()->Call(rfcall, comms::kMsgCall, &fret, rfcall.ret_type));

  if (fret.ret_type == v::Type::kFloat) {
    ret->SetDataFromPtr(&fret.float_val, sizeof(fret.float_val));
  } else {
    ret->SetDataFromPtr(&fret.int_val, sizeof(fret.int_val));
  }

  if (fret.ret_type == v::Type::kFd) {
    SAPI_RETURN_IF_ERROR(TransferFromSandboxee(reinterpret_cast<v::Fd*>(ret)));
  }

  // Synchronize all pointers after the call if it's needed.
  for (auto* arg : args) {
    SAPI_RETURN_IF_ERROR(SynchronizePtrAfter(arg));
  }

  VLOG(1) << "CALL EXIT: Type: " << ret->GetTypeString()
          << ", Size: " << ret->GetSize() << ", Val: " << ret->ToString();

  return absl::OkStatus();
}

absl::Status Sandbox::Symbol(const char* symname, void** addr) {
  if (!is_active()) {
    return absl::UnavailableError("Sandbox not active");
  }
  return rpc_channel_->Symbol(symname, addr);
}

absl::Status Sandbox::TransferToSandboxee(v::Var* var) {
  if (!is_active()) {
    return absl::UnavailableError("Sandbox not active");
  }
  return var->TransferToSandboxee(GetRpcChannel(), pid());
}

absl::Status Sandbox::TransferFromSandboxee(v::Var* var) {
  if (!is_active()) {
    return absl::UnavailableError("Sandbox not active");
  }
  return var->TransferFromSandboxee(GetRpcChannel(), pid());
}

absl::StatusOr<std::string> Sandbox::GetCString(const v::RemotePtr& str,
                                                size_t max_length) {
  if (!is_active()) {
    return absl::UnavailableError("Sandbox not active");
  }

  SAPI_ASSIGN_OR_RETURN(auto len, GetRpcChannel()->Strlen(str.GetValue()));
  if (len > max_length) {
    return absl::InvalidArgumentError(
        absl::StrCat("Target string too large: ", len, " > ", max_length));
  }
  std::string buffer(len, '\0');
  struct iovec local = {
      .iov_base = &buffer[0],
      .iov_len = len,
  };
  struct iovec remote = {
      .iov_base = str.GetValue(),
      .iov_len = len,
  };

  ssize_t ret = process_vm_readv(pid_, &local, 1, &remote, 1, 0);
  if (ret == -1) {
    PLOG(WARNING) << "reading c-string failed: process_vm_readv(pid: " << pid_
                  << " raddr: " << str.GetValue() << " size: " << len << ")";
    return absl::UnavailableError("process_vm_readv failed");
  }
  if (ret != len) {
    LOG(WARNING) << "partial read when reading c-string: process_vm_readv(pid: "
                 << pid_ << " raddr: " << str.GetValue() << " size: " << len
                 << ") transferred " << ret << " bytes";
    return absl::UnavailableError("process_vm_readv succeeded partially");
  }

  return buffer;
}

const sandbox2::Result& Sandbox::AwaitResult() {
  if (s2_) {
    result_ = s2_->AwaitResult();
    s2_.reset(nullptr);
  }
  return result_;
}

absl::Status Sandbox::SetWallTimeLimit(absl::Duration limit) const {
  if (!is_active()) {
    return absl::UnavailableError("Sandbox not active");
  }
  s2_->set_walltime_limit(limit);
  return absl::OkStatus();
}

absl::Status Sandbox::SetWallTimeLimit(time_t limit) const {
  return SetWallTimeLimit(absl::Seconds(limit));
}

void Sandbox::Exit() const {
  if (!is_active()) {
    return;
  }
  s2_->set_walltime_limit(absl::Seconds(1));
  if (!rpc_channel_->Exit().ok()) {
    LOG(WARNING) << "rpc_channel->Exit() failed, killing PID: " << pid();
    s2_->Kill();
  }
}

std::unique_ptr<sandbox2::Policy> Sandbox::ModifyPolicy(
    sandbox2::PolicyBuilder* builder) {
  return builder->BuildOrDie();
}

}  // namespace sapi