sandboxed-api/sandboxed_api/sandbox2/global_forkclient.cc

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// 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.
// Implementation of the sandbox2::ForkServer class.
#include "sandboxed_api/sandbox2/global_forkclient.h"
#include <fcntl.h>
#include <sys/prctl.h>
#include <sys/socket.h>
#include <syscall.h>
#include <unistd.h>
#include <bitset>
#include <csignal>
#include <cstdlib>
#include <string>
#include <vector>
#include <glog/logging.h>
#include "sandboxed_api/util/flag.h"
#include "absl/memory/memory.h"
#include "absl/strings/ascii.h"
#include "absl/strings/str_cat.h"
#include "absl/strings/str_join.h"
#include "absl/strings/str_split.h"
#include "absl/strings/string_view.h"
#include "sandboxed_api/embed_file.h"
#include "sandboxed_api/sandbox2/comms.h"
#include "sandboxed_api/sandbox2/forkserver_bin_embed.h"
#include "sandboxed_api/sandbox2/util.h"
#include "sandboxed_api/sandbox2/util/fileops.h"
#include "sandboxed_api/sandbox2/util/strerror.h"
#include "sandboxed_api/util/raw_logging.h"
namespace sandbox2 {
namespace {
enum class GlobalForkserverStartMode {
kOnDemand,
// MUST be the last element
kNumGlobalForkserverStartModes,
};
class GlobalForkserverStartModeSet {
public:
static constexpr size_t kSize = static_cast<size_t>(
GlobalForkserverStartMode::kNumGlobalForkserverStartModes);
GlobalForkserverStartModeSet() {}
explicit GlobalForkserverStartModeSet(GlobalForkserverStartMode value) {
value_[static_cast<size_t>(value)] = true;
}
GlobalForkserverStartModeSet& operator|=(GlobalForkserverStartMode value) {
value_[static_cast<size_t>(value)] = true;
return *this;
}
GlobalForkserverStartModeSet operator|(
GlobalForkserverStartMode value) const {
GlobalForkserverStartModeSet rv(*this);
rv |= value;
return rv;
}
bool contains(GlobalForkserverStartMode value) const {
return value_[static_cast<size_t>(value)];
}
bool empty() { return value_.none(); }
private:
std::bitset<kSize> value_;
};
bool AbslParseFlag(absl::string_view text, GlobalForkserverStartModeSet* out,
std::string* error) {
*out = {};
if (text == "never") {
return true;
}
for (absl::string_view mode : absl::StrSplit(text, ',')) {
mode = absl::StripAsciiWhitespace(mode);
if (mode == "ondemand") {
*out |= GlobalForkserverStartMode::kOnDemand;
} else {
*error = absl::StrCat("Invalid forkserver start mode: ", mode);
return false;
}
}
return true;
}
std::string ToString(GlobalForkserverStartMode mode) {
switch (mode) {
case GlobalForkserverStartMode::kOnDemand:
return "ondemand";
default:
return "unknown";
}
}
std::string AbslUnparseFlag(GlobalForkserverStartModeSet in) {
std::vector<std::string> str_modes;
for (size_t i = 0; i < GlobalForkserverStartModeSet::kSize; ++i) {
auto mode = static_cast<GlobalForkserverStartMode>(i);
if (in.contains(mode)) {
str_modes.push_back(ToString(mode));
}
}
if (str_modes.empty()) {
return "never";
}
return absl::StrJoin(str_modes, ",");
}
bool ValidateStartMode(const char*, const std::string& flag) {
GlobalForkserverStartModeSet unused;
std::string error;
if (!AbslParseFlag(flag, &unused, &error)) {
SAPI_RAW_LOG(ERROR, "%s", error);
return false;
}
return true;
}
} // namespace
} // namespace sandbox2
ABSL_FLAG(string, sandbox2_forkserver_start_mode, "ondemand",
"When Sandbox2 Forkserver process should be started");
DEFINE_validator(sandbox2_forkserver_start_mode, &sandbox2::ValidateStartMode);
namespace sandbox2 {
namespace {
GlobalForkserverStartModeSet GetForkserverStartMode() {
GlobalForkserverStartModeSet rv;
std::string error;
CHECK(AbslParseFlag(absl::GetFlag(FLAGS_sandbox2_forkserver_start_mode), &rv,
&error));
return rv;
}
std::unique_ptr<GlobalForkClient> StartGlobalForkServer() {
if (getenv(kForkServerDisableEnv)) {
SAPI_RAW_VLOG(1,
"Start of the Global Fork-Server prevented by the '%s' "
"environment variable present",
kForkServerDisableEnv);
return {};
}
if (GetForkserverStartMode().empty()) {
SAPI_RAW_VLOG(
1, "Start of the Global Fork-Server prevented by commandline flag");
return {};
}
file_util::fileops::FDCloser exec_fd(
sapi::EmbedFile::GetEmbedFileSingleton()->GetFdForFileToc(
forkserver_bin_embed_create()));
SAPI_RAW_CHECK(exec_fd.get() >= 0, "Getting FD for init binary failed");
std::string proc_name = "S2-FORK-SERV";
int sv[2];
SAPI_RAW_CHECK(socketpair(AF_LOCAL, SOCK_STREAM | SOCK_CLOEXEC, 0, sv) != -1,
"creating socket pair");
// Fork the fork-server, and clean-up the resources (close remote sockets).
pid_t pid = util::ForkWithFlags(SIGCHLD);
SAPI_RAW_PCHECK(pid != -1, "during fork");
// Child.
if (pid == 0) {
// Move the comms FD to the proper, expected FD number.
// The new FD will not be CLOEXEC, which is what we want.
dup2(sv[0], Comms::kSandbox2ClientCommsFD);
char* const args[] = {proc_name.data(), nullptr};
char* const envp[] = {nullptr};
syscall(__NR_execveat, exec_fd.get(), "", args, envp, AT_EMPTY_PATH);
SAPI_RAW_PLOG(FATAL, "Could not launch forkserver binary");
abort();
}
close(sv[0]);
return absl::make_unique<GlobalForkClient>(sv[1], pid);
}
} // namespace
absl::Mutex GlobalForkClient::instance_mutex_(absl::kConstInit);
GlobalForkClient* GlobalForkClient::instance_ = nullptr;
void GlobalForkClient::EnsureStarted() {
absl::MutexLock lock(&GlobalForkClient::instance_mutex_);
EnsureStartedLocked(
GetForkserverStartMode().contains(GlobalForkserverStartMode::kOnDemand));
}
void GlobalForkClient::Shutdown() {
absl::MutexLock lock(&GlobalForkClient::instance_mutex_);
delete instance_;
instance_ = nullptr;
}
void GlobalForkClient::EnsureStartedLocked(bool start_if_needed) {
if (!instance_ && start_if_needed) {
instance_ = StartGlobalForkServer().release();
}
SAPI_RAW_CHECK(instance_ != nullptr, "global fork client not initialized");
}
pid_t GlobalForkClient::SendRequest(const ForkRequest& request, int exec_fd,
int comms_fd, int user_ns_fd,
pid_t* init_pid) {
absl::MutexLock lock(&GlobalForkClient::instance_mutex_);
EnsureStartedLocked(
GetForkserverStartMode().contains(GlobalForkserverStartMode::kOnDemand));
pid_t pid = instance_->fork_client_.SendRequest(request, exec_fd, comms_fd,
user_ns_fd, init_pid);
if (instance_->comms_.IsTerminated()) {
LOG(ERROR) << "Global forkserver connection terminated";
}
return pid;
}
pid_t GlobalForkClient::GetPid() {
absl::MutexLock lock(&instance_mutex_);
EnsureStartedLocked(
GetForkserverStartMode().contains(GlobalForkserverStartMode::kOnDemand));
SAPI_RAW_CHECK(instance_ != nullptr, "global fork client not initialized");
return instance_->fork_client_.pid();
}
} // namespace sandbox2