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Code Issues Projects Releases Wiki Activity

Reintroduce monitor changes.

Browse Source 
Signal handling in Monitor::MainLoop was fixed.

PiperOrigin-RevId: 248331692
Change-Id: I0f85d319802258632d2074742c53597bb922555a
This commit is contained in:
Wiktor Garbacz 2019-05-15 07:46:26 -07:00 committed by Copybara-Service
parent d8f7d861d2
commit 6588aa2a68
6 changed files with 333 additions and 474 deletions
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655
sandboxed_api/sandbox2/monitor.cc
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@ -84,6 +84,26 @@ std::string ReadProcMaps(pid_t pid) {
return contents.str();
}
void InterruptProcess(pid_t pid) {
if (ptrace(PTRACE_INTERRUPT, pid, 0, 0) == -1) {
PLOG(WARNING) << "ptrace(PTRACE_INTERRUPT, pid=" << pid << ")";
}
}
void ContinueProcess(pid_t pid, int signo) {
if (ptrace(PTRACE_CONT, pid, 0, signo) == -1) {
PLOG(ERROR) << "ptrace(PTRACE_CONT, pid=" << pid << ", sig=" << signo
<< ")";
}
}
void StopProcess(pid_t pid, int signo) {
if (ptrace(PTRACE_LISTEN, pid, 0, signo) == -1) {
PLOG(ERROR) << "ptrace(PTRACE_LISTEN, pid=" << pid << ", sig=" << signo
<< ")";
}
}
} // namespace
Monitor::Monitor(Executor* executor, Policy* policy, Notify* notify)
@ -92,11 +112,12 @@ Monitor::Monitor(Executor* executor, Policy* policy, Notify* notify)
policy_(policy),
comms_(executor_->ipc()->comms()),
ipc_(executor_->ipc()),
setup_counter_(new absl::BlockingCounter(1)),
done_(false),
setup_counter_(1),
wait_for_execve_(executor->enable_sandboxing_pre_execve_) {
std::string path =
absl::GetFlag(FLAGS_sandbox2_danger_danger_permit_all_and_log);
external_kill_request_flag_.test_and_set(std::memory_order_relaxed);
dump_stack_request_flag_.test_and_set(std::memory_order_relaxed);
if (!path.empty()) {
log_file_ = std::fopen(path.c_str(), "a+");
PCHECK(log_file_ != nullptr) << "Failed to open log file '" << path << "'";
@ -104,7 +125,6 @@ Monitor::Monitor(Executor* executor, Policy* policy, Notify* notify)
}
Monitor::~Monitor() {
CleanUpTimer();
if (log_file_) {
std::fclose(log_file_);
}
@ -122,9 +142,9 @@ void LogContainer(const std::vector<std::string>& container) {
void Monitor::Run() {
using DecrementCounter = decltype(setup_counter_);
std::unique_ptr<DecrementCounter, std::function<void(DecrementCounter*)>>
std::unique_ptr<DecrementCounter, void (*)(DecrementCounter*)>
decrement_count{&setup_counter_, [](DecrementCounter* counter) {
(*counter)->DecrementCount();
counter->DecrementCount();
}};
struct MonitorCleanup {
@ -138,16 +158,17 @@ void Monitor::Run() {
Monitor* capture;
} monitor_cleanup{this};
if (!InitSetupTimer()) {
result_.SetExitStatusCode(Result::SETUP_ERROR, Result::FAILED_TIMERS);
return;
if (executor_->limits()->wall_time_limit() != absl::ZeroDuration()) {
auto deadline = absl::Now() + executor_->limits()->wall_time_limit();
deadline_millis_.store(absl::ToUnixMillis(deadline),
std::memory_order_relaxed);
}
// It'd be costly to initialize the sigset_t for each sigtimedwait()
// invocation, so do it once per Monitor.
sigset_t sigtimedwait_sset;
if (!InitSetupSignals(&sigtimedwait_sset)) {
result_.SetExitStatusCode(Result::SETUP_ERROR, Result::FAILED_SIGNALS);
SetExitStatusCode(Result::SETUP_ERROR, Result::FAILED_SIGNALS);
return;
}
@ -180,43 +201,43 @@ void Monitor::Run() {
}
if (pid_ < 0) {
result_.SetExitStatusCode(Result::SETUP_ERROR, Result::FAILED_SUBPROCESS);
SetExitStatusCode(Result::SETUP_ERROR, Result::FAILED_SUBPROCESS);
return;
}
if (!notify_->EventStarted(pid_, comms_)) {
result_.SetExitStatusCode(Result::SETUP_ERROR, Result::FAILED_NOTIFY);
SetExitStatusCode(Result::SETUP_ERROR, Result::FAILED_NOTIFY);
return;
}
if (!InitAcceptConnection()) {
result_.SetExitStatusCode(Result::SETUP_ERROR, Result::FAILED_CONNECTION);
SetExitStatusCode(Result::SETUP_ERROR, Result::FAILED_CONNECTION);
return;
}
if (!InitSendIPC()) {
result_.SetExitStatusCode(Result::SETUP_ERROR, Result::FAILED_IPC);
SetExitStatusCode(Result::SETUP_ERROR, Result::FAILED_IPC);
return;
}
if (!InitSendCwd()) {
result_.SetExitStatusCode(Result::SETUP_ERROR, Result::FAILED_CWD);
SetExitStatusCode(Result::SETUP_ERROR, Result::FAILED_CWD);
return;
}
if (!InitSendPolicy()) {
result_.SetExitStatusCode(Result::SETUP_ERROR, Result::FAILED_POLICY);
SetExitStatusCode(Result::SETUP_ERROR, Result::FAILED_POLICY);
return;
}
if (!WaitForSandboxReady()) {
result_.SetExitStatusCode(Result::SETUP_ERROR, Result::FAILED_WAIT);
SetExitStatusCode(Result::SETUP_ERROR, Result::FAILED_WAIT);
return;
}
if (!InitApplyLimits()) {
result_.SetExitStatusCode(Result::SETUP_ERROR, Result::FAILED_LIMITS);
SetExitStatusCode(Result::SETUP_ERROR, Result::FAILED_LIMITS);
return;
}
// This call should be the last in the init sequence, because it can cause the
// sandboxee to enter ptrace-stopped state, in which it will not be able to
// send any messages over the Comms channel.
if (!InitPtraceAttach()) {
result_.SetExitStatusCode(Result::SETUP_ERROR, Result::FAILED_PTRACE);
SetExitStatusCode(Result::SETUP_ERROR, Result::FAILED_PTRACE);
return;
}
@ -225,11 +246,6 @@ void Monitor::Run() {
decrement_count.reset();
MainLoop(&sigtimedwait_sset);
// Disarm the timer: it will be deleted in ~Monitor, but the Monitor object
// lifetime is controlled by owner of Sandbox2, and we don't want to leave any
// timers behind (esp. armed ones) in the meantime.
TimerArm(absl::ZeroDuration());
}
bool Monitor::IsActivelyMonitoring() {
@ -239,86 +255,110 @@ bool Monitor::IsActivelyMonitoring() {
void Monitor::SetActivelyMonitoring() { wait_for_execve_ = false; }
void Monitor::MainSignals(int signo, siginfo_t* si) {
VLOG(3) << "Signal '" << strsignal(signo) << "' (" << signo
<< ") received from PID: " << si->si_pid;
void Monitor::SetExitStatusCode(Result::StatusEnum final_status,
uintptr_t reason_code) {
CHECK(result_.final_status() == Result::UNSET);
result_.SetExitStatusCode(final_status, reason_code);
}
// SIGCHLD is received frequently due to ptrace() events being sent by child
// processes; return early to avoid costly syscalls.
if (signo == SIGCHLD) {
return;
bool Monitor::ShouldCollectStackTrace() {
// Only get the stacktrace if we are not in the libunwind sandbox (avoid
// recursion).
bool stacktrace_collection_possible =
policy_->GetNamespace() && executor_->libunwind_sbox_for_pid_ == 0;
if (!stacktrace_collection_possible) {
LOG(ERROR) << "Cannot collect stack trace. Unwind pid "
<< executor_->libunwind_sbox_for_pid_ << ", namespace "
<< policy_->GetNamespace();
return false;
}
// We should only receive signals from the same process (thread group). Other
// signals are suspicious (esp. if coming from a sandboxed process) Using
// syscall(__NR_getpid) here because getpid() is cached in glibc, and it
// might return previous pid if bare syscall(__NR_fork) was used instead of
// fork().
//
// The notable exception are signals caused by timer_settime which are sent
// by the kernel.
if (signo != Monitor::kTimerWallTimeSignal &&
si->si_pid != util::Syscall(__NR_getpid)) {
LOG(ERROR) << "Monitor received signal '" << strsignal(signo) << "' ("
<< signo << ") from PID " << si->si_pid
<< " which is not in the current thread group";
return;
}
switch (signo) {
case Monitor::kExternalKillSignal:
VLOG(1) << "Will kill the main pid";
ActionProcessKill(pid_, Result::EXTERNAL_KILL, 0);
break;
case Monitor::kTimerWallTimeSignal:
VLOG(1) << "Sandbox process hit timeout due to the walltime timer";
ActionProcessKill(pid_, Result::TIMEOUT, 0);
break;
case Monitor::kTimerSetSignal:
VLOG(1) << "Will set the walltime timer to " << si->si_value.sival_int
<< " seconds";
TimerArm(absl::Seconds(si->si_value.sival_int));
break;
case Monitor::kDumpStackSignal:
VLOG(1) << "Dump the main pid's stack";
should_dump_stack_ = true;
PidInterrupt(pid_);
break;
switch (result_.final_status()) {
case Result::EXTERNAL_KILL:
return policy_->collect_stacktrace_on_kill_;
case Result::TIMEOUT:
return policy_->collect_stacktrace_on_timeout_;
case Result::SIGNALED:
return policy_->collect_stacktrace_on_signal_;
case Result::VIOLATION:
return policy_->collect_stacktrace_on_violation_;
default:
LOG(ERROR) << "Unknown signal received: " << signo;
break;
return false;
}
}
void Monitor::SetAdditionalResultInfo(std::unique_ptr<Regs> regs) {
pid_t pid = regs->pid();
result_.SetRegs(std::move(regs));
result_.SetProgName(util::GetProgName(pid));
result_.SetProcMaps(ReadProcMaps(pid_));
if (ShouldCollectStackTrace()) {
result_.SetStackTrace(
GetStackTrace(result_.GetRegs(), policy_->GetNamespace()->mounts()));
LOG(ERROR) << "Stack trace: " << result_.GetStackTrace();
} else {
LOG(ERROR) << "Stack traces have been disabled";
}
}
void Monitor::KillSandboxee() {
VLOG(1) << "Sending SIGKILL to the PID: " << pid_;
if (kill(pid_, SIGKILL) != 0) {
LOG(ERROR) << "Could not send SIGKILL to PID " << pid_;
SetExitStatusCode(Result::INTERNAL_ERROR, Result::FAILED_KILL);
}
}
// Not defined in glibc.
#define __WPTRACEEVENT(x) ((x & 0xff0000) >> 16)
bool Monitor::MainWait() {
// All possible process status change event must be checked as SIGCHLD
// is reported once only for all events that arrived at the same time.
for (;;) {
int status;
void Monitor::MainLoop(sigset_t* sset) {
bool sandboxee_exited = false;
int status;
// All possible still running children of main process, will be killed due to
// PTRACE_O_EXITKILL ptrace() flag.
while (result_.final_status() == Result::UNSET) {
int64_t deadline = deadline_millis_.load(std::memory_order_relaxed);
if (deadline != 0 && absl::Now() >= absl::FromUnixMillis(deadline)) {
VLOG(1) << "Sandbox process hit timeout due to the walltime timer";
timed_out_ = true;
KillSandboxee();
}
if (!dump_stack_request_flag_.test_and_set(std::memory_order_relaxed)) {
should_dump_stack_ = true;
InterruptProcess(pid_);
}
if (!external_kill_request_flag_.test_and_set(std::memory_order_relaxed)) {
external_kill_ = true;
KillSandboxee();
}
// It should be a non-blocking operation (hence WNOHANG), so this function
// returns quickly if there are no events to be processed.
int ret = waitpid(-1, &status, __WNOTHREAD | __WALL | WUNTRACED | WNOHANG);
// No traced processes have changed their status yet.
// Prioritize main pid to avoid resource starvation
pid_t ret =
waitpid(pid_, &status, __WNOTHREAD | __WALL | WUNTRACED | WNOHANG);
if (ret == 0) {
return false;
ret = waitpid(-1, &status, __WNOTHREAD | __WALL | WUNTRACED | WNOHANG);
}
if (ret == -1 && errno == ECHILD) {
LOG(ERROR) << "PANIC(). The main process has not exited yet, "
<< "yet we haven't seen its exit event";
// We'll simply exit which will kill all remaining processes (if
// there are any) because of the PTRACE_O_EXITKILL ptrace() flag.
return true;
}
if (ret == -1 && errno == EINTR) {
VLOG(3) << "waitpid() interruped with EINTR";
if (ret == 0) {
constexpr timespec ts = {kWakeUpPeriodSec, kWakeUpPeriodNSec};
int signo = sigtimedwait(sset, nullptr, &ts);
LOG_IF(ERROR, signo != -1 && signo != SIGCHLD)
<< "Unknown signal received: " << signo;
continue;
}
if (ret == -1) {
PLOG(ERROR) << "waitpid() failed";
if (errno == ECHILD) {
LOG(ERROR) << "PANIC(). The main process has not exited yet, "
<< "yet we haven't seen its exit event";
SetExitStatusCode(Result::INTERNAL_ERROR, Result::FAILED_CHILD);
} else {
PLOG(ERROR) << "waitpid() failed";
}
continue;
}
@ -332,32 +372,28 @@ bool Monitor::MainWait() {
// PTRACE_O_EXITKILL ptrace() flag.
if (ret == pid_) {
if (IsActivelyMonitoring()) {
result_.SetExitStatusCode(Result::OK, WEXITSTATUS(status));
SetExitStatusCode(Result::OK, WEXITSTATUS(status));
} else {
result_.SetExitStatusCode(Result::SETUP_ERROR,
Result::FAILED_MONITOR);
SetExitStatusCode(Result::SETUP_ERROR, Result::FAILED_MONITOR);
}
return true;
sandboxee_exited = true;
}
} else if (WIFSIGNALED(status)) {
// This usually does not happen, but might.
// Quote from the manual:
// A SIGKILL signal may still cause a PTRACE_EVENT_EXIT stop before
// actual signal death. This may be changed in the future;
VLOG(1) << "PID: " << ret << " terminated with signal: "
<< util::GetSignalName(WTERMSIG(status));
if (ret == pid_) {
// That's the main process, depending on the result of the process take
// the register content and/or the stack trace. The death of this
// process will cause all remaining processes to be killed (if there are
// any), see the PTRACE_O_EXITKILL ptrace() flag.
// When the process is killed from a signal from within the result
// status will be still unset, fix this.
// The other cases should either be already handled, or (in the case of
// Result::OK) should be impossible to reach.
if (result_.final_status() == Result::UNSET) {
result_.SetExitStatusCode(Result::SIGNALED, WTERMSIG(status));
} else if (result_.final_status() == Result::OK) {
LOG(ERROR) << "Unexpected codepath taken";
if (external_kill_) {
SetExitStatusCode(Result::EXTERNAL_KILL, 0);
} else if (timed_out_) {
SetExitStatusCode(Result::TIMEOUT, 0);
} else {
SetExitStatusCode(Result::SIGNALED, WTERMSIG(status));
}
return true;
sandboxee_exited = true;
}
} else if (WIFSTOPPED(status)) {
VLOG(2) << "PID: " << ret
@ -368,126 +404,63 @@ bool Monitor::MainWait() {
VLOG(2) << "PID: " << ret << " is being continued";
}
}
}
void Monitor::MainLoop(sigset_t* sset) {
for (;;) {
// Use a time-out, so we can check for missed waitpid() events. It should
// not happen during regular operations, so it's a defense-in-depth
// mechanism against SIGCHLD signals being lost by the kernel (since these
// are not-RT signals - i.e. not queued).
static const timespec ts = {kWakeUpPeriodSec, kWakeUpPeriodNSec};
// Wait for any kind of events, e.g. signals sent from the parent process,
// or SIGCHLD sent by kernel indicating that state of one of the traced
// processes has changed.
siginfo_t si;
int ret = sigtimedwait(sset, &si, &ts);
if (ret > 0) {
// Process signals which arrived.
MainSignals(ret, &si);
}
// If CheckWait reported no more traced processes, or that
// the main pid had exited, we should break this loop (i.e. our job is
// done here).
//
// MainWait() should use a not-blocking (e.g. WNOHANG with waitpid())
// syntax, so it returns quickly if there are not status changes in
// traced processes.
if (MainWait()) {
return;
// Try to make sure main pid is killed and reaped
if (!sandboxee_exited) {
kill(pid_, SIGKILL);
constexpr auto kGracefullExitTimeout = absl::Milliseconds(200);
auto deadline = absl::Now() + kGracefullExitTimeout;
for (;;) {
auto left = deadline - absl::Now();
if (absl::Now() >= deadline) {
LOG(INFO) << "Waiting for sandboxee exit timed out";
break;
}
pid_t ret =
waitpid(pid_, &status, __WNOTHREAD | __WALL | WUNTRACED | WNOHANG);
if (ret == 0) {
// Sometimes PTRACE_EVENT_EXIT needs to be handled for each child thread
// in order to observe main thread exit
ret = waitpid(-1, &status, __WNOTHREAD | __WALL | WUNTRACED | WNOHANG);
}
if (ret == -1) {
PLOG(ERROR) << "waitpid() failed";
break;
}
if (ret == pid_ && (WIFSIGNALED(status) || WIFEXITED(status))) {
break;
}
if (ret == 0) {
auto ts = absl::ToTimespec(left);
sigtimedwait(sset, nullptr, &ts);
} else if (WIFSTOPPED(status) &&
__WPTRACEEVENT(status) == PTRACE_EVENT_EXIT) {
VLOG(2) << "PID: " << ret << " PTRACE_EVENT_EXIT ";
ContinueProcess(ret, 0);
} else {
kill(pid_, SIGKILL);
}
}
}
}
bool Monitor::InitSetupTimer() {
walltime_timer_ = absl::make_unique<timer_t>();
// Set the wall-time timer.
sigevent sevp;
sevp.sigev_value.sival_ptr = walltime_timer_.get();
sevp.sigev_signo = kTimerWallTimeSignal;
sevp.sigev_notify = SIGEV_THREAD_ID | SIGEV_SIGNAL;
sevp._sigev_un._tid = static_cast<pid_t>(util::Syscall(__NR_gettid));
// GLibc's implementation seem to mis-behave during timer_delete, as it's
// trying to find out whether POSIX TIMERs are available. So, we stick to
// syscalls for this class of calls.
if (util::Syscall(__NR_timer_create, CLOCK_REALTIME,
reinterpret_cast<uintptr_t>(&sevp),
reinterpret_cast<uintptr_t>(walltime_timer_.get())) == -1) {
walltime_timer_ = nullptr;
PLOG(ERROR) << "timer_create(CLOCK_REALTIME, walltime_timer_)";
return false;
}
return TimerArm(executor_->limits()->wall_time_limit());
}
// Can be used from a signal handler. Avoid non-reentrant functions.
bool Monitor::TimerArm(absl::Duration duration) {
VLOG(2) << (duration == absl::ZeroDuration() ? "Disarming" : "Arming")
<< " the walltime timer with " << absl::FormatDuration(duration);
itimerspec ts;
absl::Duration rem;
ts.it_value.tv_sec = absl::IDivDuration(duration, absl::Seconds(1), &rem);
ts.it_value.tv_nsec = absl::ToInt64Nanoseconds(rem);
ts.it_interval.tv_sec =
duration != absl::ZeroDuration() ? 1L : 0L; // Re-fire every 1 sec.
ts.it_interval.tv_nsec = 0UL;
itimerspec* null_ts = nullptr;
if (util::Syscall(__NR_timer_settime,
reinterpret_cast<uintptr_t>(*walltime_timer_), 0,
reinterpret_cast<uintptr_t>(&ts),
reinterpret_cast<uintptr_t>(null_ts)) == -1) {
PLOG(ERROR) << "timer_settime(): time: " << absl::FormatDuration(duration);
return false;
}
return true;
}
void Monitor::CleanUpTimer() {
if (walltime_timer_) {
if (util::Syscall(__NR_timer_delete,
reinterpret_cast<uintptr_t>(*walltime_timer_)) == -1) {
PLOG(ERROR) << "timer_delete()";
}
}
}
bool Monitor::InitSetupSig(int signo, sigset_t* sset) {
// sigtimedwait will react (wake-up) to arrival of this signal.
sigaddset(sset, signo);
// Block this specific signal, so only sigtimedwait reacts to it.
sigset_t block_set;
if (sigemptyset(&block_set) == -1) {
PLOG(ERROR) << "sigemptyset()";
return false;
}
if (sigaddset(&block_set, signo) == -1) {
PLOG(ERROR) << "sigaddset(" << signo << ")";
return false;
}
if (pthread_sigmask(SIG_BLOCK, &block_set, nullptr) == -1) {
PLOG(ERROR) << "pthread_sigmask(SIG_BLOCK, " << signo << ")";
return false;
}
return true;
}
bool Monitor::InitSetupSignals(sigset_t* sset) {
sigemptyset(sset);
if (sigemptyset(sset) == -1) {
PLOG(ERROR) << "sigemptyset()";
return false;
}
return Monitor::InitSetupSig(kExternalKillSignal, sset) &&
Monitor::InitSetupSig(kTimerWallTimeSignal, sset) &&
Monitor::InitSetupSig(kTimerSetSignal, sset) &&
Monitor::InitSetupSig(kDumpStackSignal, sset) &&
// SIGCHLD means that a new children process status change event
// has been delivered (e.g. due ptrace notification).
Monitor::InitSetupSig(SIGCHLD, sset);
// sigtimedwait will react (wake-up) to arrival of this signal.
if (sigaddset(sset, SIGCHLD) == -1) {
PLOG(ERROR) << "sigaddset(SIGCHLD)";
return false;
}
if (pthread_sigmask(SIG_BLOCK, sset, nullptr) == -1) {
PLOG(ERROR) << "pthread_sigmask(SIG_BLOCK, SIGCHLD)";
return false;
}
return true;
}
bool Monitor::InitSendPolicy() {
@ -728,20 +701,6 @@ bool Monitor::InitAcceptConnection() {
return true;
}
void Monitor::ActionProcessContinue(pid_t pid, int signo) {
if (ptrace(PTRACE_CONT, pid, 0, signo) == -1) {
PLOG(ERROR) << "ptrace(PTRACE_CONT, pid=" << pid << ", sig=" << signo
<< ")";
}
}
void Monitor::ActionProcessStop(pid_t pid, int signo) {
if (ptrace(PTRACE_LISTEN, pid, 0, signo) == -1) {
PLOG(ERROR) << "ptrace(PTRACE_LISTEN, pid=" << pid << ", sig=" << signo
<< ")";
}
}
void Monitor::ActionProcessSyscall(Regs* regs, const Syscall& syscall) {
// If the sandboxing is not enabled yet, allow the first __NR_execveat.
if (syscall.nr() == __NR_execveat && !IsActivelyMonitoring()) {
@ -749,7 +708,7 @@ void Monitor::ActionProcessSyscall(Regs* regs, const Syscall& syscall) {
<< "SYSCALL ::: PID: " << regs->pid() << ", PROG: '"
<< util::GetProgName(regs->pid())
<< "' : " << syscall.GetDescription();
ActionProcessContinue(regs->pid(), 0);
ContinueProcess(regs->pid(), 0);
return;
}
@ -761,7 +720,7 @@ void Monitor::ActionProcessSyscall(Regs* regs, const Syscall& syscall) {
<< ", PROG: '" << util::GetProgName(regs->pid())
<< "' : " << syscall.GetDescription();
ActionProcessContinue(regs->pid(), 0);
ContinueProcess(regs->pid(), 0);
return;
}
@ -772,12 +731,12 @@ void Monitor::ActionProcessSyscall(Regs* regs, const Syscall& syscall) {
std::string syscall_description = syscall.GetDescription();
PCHECK(absl::FPrintF(log_file_, "PID: %d %s\n", regs->pid(),
syscall_description) >= 0);
ActionProcessContinue(regs->pid(), 0);
ContinueProcess(regs->pid(), 0);
return;
}
if (absl::GetFlag(FLAGS_sandbox2_danger_danger_permit_all)) {
ActionProcessContinue(regs->pid(), 0);
ContinueProcess(regs->pid(), 0);
return;
}
@ -786,40 +745,20 @@ void Monitor::ActionProcessSyscall(Regs* regs, const Syscall& syscall) {
void Monitor::ActionProcessSyscallViolation(Regs* regs, const Syscall& syscall,
ViolationType violation_type) {
pid_t pid = regs->pid();
LogAccessViolation(syscall);
LogSyscallViolation(syscall);
notify_->EventSyscallViolation(syscall, violation_type);
result_.SetExitStatusCode(Result::VIOLATION, syscall.nr());
SetExitStatusCode(Result::VIOLATION, syscall.nr());
result_.SetSyscall(absl::make_unique<Syscall>(syscall));
// Only get the stacktrace if we are not in the libunwind sandbox (avoid
// recursion).
if (executor_->libunwind_sbox_for_pid_ == 0 && policy_->GetNamespace()) {
if (policy_->collect_stacktrace_on_violation_) {
result_.SetStackTrace(
GetStackTrace(regs, policy_->GetNamespace()->mounts()));
LOG(ERROR) << "Stack trace: " << result_.GetStackTrace();
} else {
LOG(ERROR) << "Stack traces have been disabled";
}
}
// We make the result object create its own Reg instance. our regs is a
// pointer to a stack variable which might not live long enough.
result_.LoadRegs(pid);
result_.SetProgName(util::GetProgName(pid));
result_.SetProcMaps(ReadProcMaps(pid_));
// Rewrite the syscall argument to something invalid (-1). The process will
// be killed by ActionProcessKill(), so this is just a precaution.
SetAdditionalResultInfo(absl::make_unique<Regs>(*regs));
// Rewrite the syscall argument to something invalid (-1).
// The process will be killed anyway so this is just a precaution.
auto status = regs->SkipSyscallReturnValue(-ENOSYS);
if (!status.ok()) {
LOG(ERROR) << status;
}
ActionProcessKill(pid, Result::VIOLATION, syscall.nr());
}
void Monitor::LogAccessViolation(const Syscall& syscall) {
void Monitor::LogSyscallViolation(const Syscall& syscall) const {
// Do not unwind libunwind.
if (executor_->libunwind_sbox_for_pid_ != 0) {
LOG(ERROR) << "Sandbox violation during execution of libunwind: "
@ -827,58 +766,16 @@ void Monitor::LogAccessViolation(const Syscall& syscall) {
return;
}
uintptr_t syscall_nr = syscall.nr();
uintptr_t arg0 = syscall.args()[0];
// So, this is an invalid syscall. Will be killed by seccomp-bpf policies as
// well, but we should be on a safe side here as well.
LOG(ERROR) << "SANDBOX VIOLATION : PID: " << syscall.pid() << ", PROG: '"
<< util::GetProgName(syscall.pid())
<< "' : " << syscall.GetDescription();
// This follows policy in Policy::GetDefaultPolicy - keep it in sync.
if (syscall.arch() != Syscall::GetHostArch()) {
LOG(ERROR)
<< "This is a violation because the syscall was issued because the"
<< " sandboxee and executor architectures are different.";
return;
}
if (syscall_nr == __NR_ptrace) {
LOG(ERROR)
<< "This is a violation because the ptrace syscall would be unsafe in"
<< " sandbox2, so it has been blocked.";
return;
}
if (syscall_nr == __NR_bpf) {
LOG(ERROR)
<< "This is a violation because the bpf syscall would be risky in"
<< " a sandbox, so it has been blocked.";
return;
}
if (syscall_nr == __NR_clone && ((arg0 & CLONE_UNTRACED) != 0)) {
LOG(ERROR) << "This is a violation because calling clone with CLONE_UNTRACE"
<< " would be unsafe in sandbox2, so it has been blocked.";
return;
}
}
void Monitor::ActionProcessKill(pid_t pid, Result::StatusEnum status,
uintptr_t code) {
// Avoid overwriting result if we set it for instance after a violation.
if (result_.final_status() == Result::UNSET) {
result_.SetExitStatusCode(status, code);
}
VLOG(1) << "Sending SIGKILL to the PID: " << pid_;
if (kill(pid_, SIGKILL) != 0) {
LOG(FATAL) << "Could not send SIGKILL to PID " << pid_;
}
LogSyscallViolationExplanation(syscall);
}
void Monitor::EventPtraceSeccomp(pid_t pid, int event_msg) {
VLOG(1) << "PID: " << pid << " violation uncovered via the SECCOMP_EVENT";
// If the seccomp-policy is using RET_TRACE, we request that it returns the
// syscall architecture identifier in the SECCOMP_RET_DATA.
const auto syscall_arch = static_cast<Syscall::CpuArch>(event_msg);
@ -886,7 +783,7 @@ void Monitor::EventPtraceSeccomp(pid_t pid, int event_msg) {
auto status = regs.Fetch();
if (!status.ok()) {
LOG(ERROR) << status;
ActionProcessKill(pid, Result::INTERNAL_ERROR, Result::FAILED_FETCH);
SetExitStatusCode(Result::INTERNAL_ERROR, Result::FAILED_FETCH);
return;
}
@ -907,84 +804,50 @@ void Monitor::EventPtraceExec(pid_t pid, int event_msg) {
<< ". SANDBOX ENABLED!";
SetActivelyMonitoring();
}
ActionProcessContinue(pid, 0);
ContinueProcess(pid, 0);
}
void Monitor::EventPtraceExit(pid_t pid, int event_msg) {
// A regular exit, let it continue.
// A regular exit, let it continue (fast-path).
if (WIFEXITED(event_msg)) {
ActionProcessContinue(pid, 0);
ContinueProcess(pid, 0);
return;
}
// Everything except the SECCOMP violation can continue.
if (!WIFSIGNALED(event_msg) || WTERMSIG(event_msg) != SIGSYS) {
// Process is dying because it received a signal.
// This can occur in three cases:
// 1) Process was killed from the sandbox, in this case the result status
// was already set to Result::EXTERNAL_KILL. We do not get the stack
// trace in this case.
// 2) Process was killed because it hit a timeout. The result status is
// also already set, however we are interested in the stack trace.
// 3) Regular signal. We need to obtain everything. The status will be set
// upon the process exit handler.
if (pid == pid_) {
result_.LoadRegs(pid_);
result_.SetProgName(util::GetProgName(pid_));
result_.SetProcMaps(ReadProcMaps(pid_));
bool stacktrace_collection_possible =
policy_->GetNamespace() && executor_->libunwind_sbox_for_pid_ == 0;
auto collect_stacktrace = [this]() {
result_.SetStackTrace(GetStackTrace(result_.GetRegs(),
policy_->GetNamespace()->mounts()));
};
switch (result_.final_status()) {
case Result::EXTERNAL_KILL:
if (stacktrace_collection_possible &&
policy_->collect_stacktrace_on_kill_) {
collect_stacktrace();
}
break;
case Result::TIMEOUT:
if (stacktrace_collection_possible &&
policy_->collect_stacktrace_on_timeout_) {
collect_stacktrace();
}
break;
case Result::VIOLATION:
break;
case Result::UNSET:
// Regular signal.
if (stacktrace_collection_possible &&
policy_->collect_stacktrace_on_signal_) {
collect_stacktrace();
}
break;
default:
LOG(ERROR) << "Unexpected codepath taken";
break;
}
}
ActionProcessContinue(pid, 0);
return;
}
VLOG(1) << "PID: " << pid << " violation uncovered via the EXIT_EVENT";
// We do not generate the stack trace in the SECCOMP case as it will be
// generated during ActionProcessSyscallViolation anyway.
Regs regs(pid);
auto status = regs.Fetch();
// Fetch the registers as we'll need them to fill the result in any case
auto regs = absl::make_unique<Regs>(pid);
auto status = regs->Fetch();
if (!status.ok()) {
LOG(ERROR) << status;
ActionProcessKill(pid, Result::INTERNAL_ERROR, Result::FAILED_FETCH);
LOG(ERROR) << "failed to fetch regs: " << status;
SetExitStatusCode(Result::INTERNAL_ERROR, Result::FAILED_FETCH);
return;
}
auto syscall = regs.ToSyscall(Syscall::GetHostArch());
// Process signaled due to seccomp violation.
if (WIFSIGNALED(event_msg) && WTERMSIG(event_msg) == SIGSYS) {
VLOG(1) << "PID: " << pid << " violation uncovered via the EXIT_EVENT";
ActionProcessSyscallViolation(
regs.get(), regs->ToSyscall(Syscall::GetHostArch()), kSyscallViolation);
return;
}
ActionProcessSyscallViolation(&regs, syscall, kSyscallViolation);
// This can be reached in three cases:
// 1) Process was killed from the sandbox.
// 2) Process was killed because it hit a timeout.
// 3) Regular signal/other exit cause.
if (pid == pid_) {
VLOG(1) << "PID: " << pid << " main special exit";
if (external_kill_) {
SetExitStatusCode(Result::EXTERNAL_KILL, 0);
} else if (timed_out_) {
SetExitStatusCode(Result::TIMEOUT, 0);
} else {
SetExitStatusCode(Result::SIGNALED, WTERMSIG(event_msg));
}
SetAdditionalResultInfo(std::move(regs));
}
VLOG(1) << "Continuing";
ContinueProcess(pid, 0);
}
void Monitor::EventPtraceStop(pid_t pid, int stopsig) {
@ -992,13 +855,13 @@ void Monitor::EventPtraceStop(pid_t pid, int stopsig) {
// flags to ptrace(PTRACE_SEIZE) might generate this event with SIGTRAP.
if (stopsig != SIGSTOP && stopsig != SIGTSTP && stopsig != SIGTTIN &&
stopsig != SIGTTOU) {
ActionProcessContinue(pid, 0);
ContinueProcess(pid, 0);
return;
}
// It's our PID stop signal. Stop it.
VLOG(2) << "PID: " << pid << " stopped due to "
<< util::GetSignalName(stopsig);
ActionProcessStop(pid, 0);
StopProcess(pid, 0);
}
void Monitor::StateProcessStopped(pid_t pid, int status) {
@ -1008,7 +871,7 @@ void Monitor::StateProcessStopped(pid_t pid, int status) {
VLOG(2) << "PID: " << pid
<< " received signal: " << util::GetSignalName(stopsig);
notify_->EventSignal(pid, stopsig);
ActionProcessContinue(pid, stopsig);
ContinueProcess(pid, stopsig);
return;
}
@ -1021,12 +884,13 @@ void Monitor::StateProcessStopped(pid_t pid, int status) {
return;
}
PLOG(ERROR) << "ptrace(PTRACE_GETEVENTMSG, " << pid << ")";
ActionProcessKill(pid, Result::INTERNAL_ERROR, Result::FAILED_GETEVENT);
SetExitStatusCode(Result::INTERNAL_ERROR, Result::FAILED_GETEVENT);
return;
}
if (pid == pid_ && should_dump_stack_ &&
executor_->libunwind_sbox_for_pid_ == 0 && policy_->GetNamespace()) {
if (ABSL_PREDICT_FALSE(pid == pid_ && should_dump_stack_ &&
executor_->libunwind_sbox_for_pid_ == 0 &&
policy_->GetNamespace())) {
Regs regs(pid);
auto status = regs.Fetch();
if (status.ok()) {
@ -1050,7 +914,7 @@ void Monitor::StateProcessStopped(pid_t pid, int status) {
case PTRACE_EVENT_CLONE:
/* fall through */
case PTRACE_EVENT_VFORK_DONE:
ActionProcessContinue(pid, 0);
ContinueProcess(pid, 0);
break;
case PTRACE_EVENT_EXEC:
VLOG(2) << "PID: " << pid << " PTRACE_EVENT_EXEC, PID: " << event_msg;
@ -1075,9 +939,34 @@ void Monitor::StateProcessStopped(pid_t pid, int status) {
}
}
void Monitor::PidInterrupt(pid_t pid) {
if (ptrace(PTRACE_INTERRUPT, pid, 0, 0) == -1) {
PLOG(WARNING) << "ptrace(PTRACE_INTERRUPT, pid=" << pid << ")";
void Monitor::LogSyscallViolationExplanation(const Syscall& syscall) const {
const uintptr_t syscall_nr = syscall.nr();
const uintptr_t arg0 = syscall.args()[0];
const uintptr_t arg3 = syscall.args()[3];
// This follows policy in Policy::GetDefaultPolicy - keep it in sync.
if (syscall.arch() != Syscall::GetHostArch()) {
LOG(ERROR)
<< "This is a violation because the syscall was issued because the"
<< " sandboxee and executor architectures are different.";
return;
}
if (syscall_nr == __NR_ptrace) {
LOG(ERROR)
<< "This is a violation because the ptrace syscall would be unsafe in"
<< " sandbox2, so it has been blocked.";
return;
}
if (syscall_nr == __NR_bpf) {
LOG(ERROR)
<< "This is a violation because the bpf syscall would be risky in"
<< " a sandbox, so it has been blocked.";
return;
}
if (syscall_nr == __NR_clone && ((arg0 & CLONE_UNTRACED) != 0)) {
LOG(ERROR) << "This is a violation because calling clone with CLONE_UNTRACE"
<< " would be unsafe in sandbox2, so it has been blocked.";
return;
}
}

97
sandboxed_api/sandbox2/monitor.h
View File

@ -52,23 +52,6 @@ class Monitor final {
private:
friend class Sandbox2;
// As per 'man 7 pthreads' pthreads uses first three RT signals, so we use
// something safe here (but still lower than __SIGRTMAX).
//
// A signal which makes wait() to exit due to interrupt, so the Monitor can
// check whether it should terminate.
static const int kExternalKillSignal = (__SIGRTMIN + 10);
// A signal which system timer delivers in case the wall-time timer limit was
// reached.
static const int kTimerWallTimeSignal = (__SIGRTMIN + 12);
// A signal which makes Monitor to arm its wall-time timer.
static const int kTimerSetSignal = (__SIGRTMIN + 13);
// Dump the main sandboxed process's stack trace to log.
static const int kDumpStackSignal = (__SIGRTMIN + 14);
#if ((__SIGRTMIN + 14) > __SIGRTMAX)
#error "sandbox2::Monitor exceeding > __SIGRTMAX)"
#endif
// Timeout used with sigtimedwait (0.5s).
static const int kWakeUpPeriodSec = 0L;
static const int kWakeUpPeriodNSec = (500L * 1000L * 1000L);
@ -83,16 +66,6 @@ class Monitor final {
bool IsActivelyMonitoring();
void SetActivelyMonitoring();
// Waits for events from monitored clients and signals from the main process.
void MainLoop(sigset_t* sset);
// Analyzes signals which Monitor might have already received.
void MainSignals(int signo, siginfo_t* si);
// Analyzes any possible children process status changes; returns 'true' if
// there are no more processes to track.
bool MainWait();
// Sends Policy to the Client.
// Returns success/failure status.
bool InitSendPolicy();
@ -112,9 +85,6 @@ class Monitor final {
// Sets up required signal masks/handlers; prepare mask for sigtimedwait().
bool InitSetupSignals(sigset_t* sset);
// Sets up a given signal; modify the sigmask used with sigtimedwait().
bool InitSetupSig(int signo, sigset_t* sset);
// Sends information about data exchange channels.
bool InitSendIPC();
@ -128,36 +98,37 @@ class Monitor final {
bool InitApplyLimit(pid_t pid, __rlimit_resource resource,
const rlimit64& rlim) const;
// Creates timers.
bool InitSetupTimer();
// Kills the main traced PID with PTRACE_KILL.
void KillSandboxee();
// Deletes timers.
void CleanUpTimer();
// Waits for events from monitored clients and signals from the main process.
void MainLoop(sigset_t* sset);
// Arms the walltime timer, absl::ZeroDuration() disarms the timer.
bool TimerArm(absl::Duration duration);
// Final action with regard to PID.
// Continues PID with an optional signal.
void ActionProcessContinue(pid_t pid, int signo);
// Stops the PID with an optional signal.
void ActionProcessStop(pid_t pid, int signo);
// Process with given PID changed state to a stopped state.
void StateProcessStopped(pid_t pid, int status);
// Logs the syscall violation and kills the process afterwards.
void ActionProcessSyscallViolation(Regs* regs, const Syscall& syscall,
ViolationType violation_type);
// Prints a SANDBOX VIOLATION message based on the registers.
// If the registers match something disallowed by Policy::GetDefaultPolicy,
// then it also prints a additional description of the reason.
void LogAccessViolation(const Syscall& syscall);
// PID called a syscall, or was killed due to syscall.
// PID called a traced syscall, or was killed due to syscall.
void ActionProcessSyscall(Regs* regs, const Syscall& syscall);
// Kills the PID with PTRACE_KILL.
void ActionProcessKill(pid_t pid, Result::StatusEnum status, uintptr_t code);
// Sets basic info status and reason code in the result object.
void SetExitStatusCode(Result::StatusEnum final_status,
uintptr_t reason_code);
// Whether a stack trace should be collected given the current status
bool ShouldCollectStackTrace();
// Sets additional information in the result object, such as program name,
// stack trace etc.
void SetAdditionalResultInfo(std::unique_ptr<Regs> regs);
// Logs a SANDBOX VIOLATION message based on the registers and additional
// explanation for the reason of the violation.
void LogSyscallViolation(const Syscall& syscall) const;
// Logs an additional explanation for the possible reason of the violation
// based on the registers.
void LogSyscallViolationExplanation(const Syscall& syscall) const;
// Ptrace events:
// Syscall violation processing path.
@ -172,14 +143,6 @@ class Monitor final {
// Processes stop path.
void EventPtraceStop(pid_t pid, int stopsig);
// Changes the state of a given PID:
// Process is in a stopped state.
void StateProcessStopped(pid_t pid, int status);
// Helpers operating on PIDs.
// Interrupts the PID.
void PidInterrupt(pid_t pid);
// Internal objects, owned by the Sandbox2 object.
Executor* executor_;
Notify* notify_;
@ -193,17 +156,25 @@ class Monitor final {
// Parent (the Sandbox2 object) waits on it, until we either enable
// monitoring of a process (sandboxee) successfully, or the setup process
// fails.
std::unique_ptr<absl::BlockingCounter> setup_counter_;
// The Wall-Time timer for traced processes.
std::unique_ptr<timer_t> walltime_timer_;
absl::BlockingCounter setup_counter_;
// The main tracked PID.
pid_t pid_ = -1;
// The field indicates whether the sandboxing task has been completed (either
// successfully or with error).
std::atomic<bool> done_;
std::atomic<bool> done_{false};
absl::Mutex done_mutex_;
// False iff external kill is requested
std::atomic_flag external_kill_request_flag_;
// False iff dump stack is requested
std::atomic_flag dump_stack_request_flag_;
// Deadline in Unix millis
std::atomic<int64_t> deadline_millis_{0};
// Was external kill sent to the sandboxee
bool external_kill_ = false;
// Is the sandboxee timed out
bool timed_out_ = false;
// Should we dump the main sandboxed PID's stack?
bool should_dump_stack_ = false;

4
sandboxed_api/sandbox2/result.cc
View File

@ -177,6 +177,10 @@ std::string Result::ReasonCodeEnumToString(ReasonCodeEnum value) {
return "FAILED_GETEVENT";
case sandbox2::Result::FAILED_MONITOR:
return "FAILED_MONITOR";
case sandbox2::Result::FAILED_KILL:
return "FAILED_KILL";
case sandbox2::Result::FAILED_CHILD:
return "FAILED_CHILD";
case sandbox2::Result::VIOLATION_SYSCALL:
return "VIOLATION_SYSCALL";
case sandbox2::Result::VIOLATION_ARCH:

9
sandboxed_api/sandbox2/result.h
View File

@ -77,6 +77,8 @@ class Result {
FAILED_FETCH,
FAILED_GETEVENT,
FAILED_MONITOR,
FAILED_KILL,
FAILED_CHILD,
// TODO(wiktorg) not used currently (syscall number stored insted) - need to
// fix clients first
@ -111,13 +113,6 @@ class Result {
stack_trace_ = stack_trace;
}
void LoadRegs(pid_t pid) {
auto regs = absl::make_unique<Regs>(pid);
if (regs->Fetch().ok()) {
SetRegs(std::move(regs));
}
}
void SetRegs(std::unique_ptr<Regs> regs) { regs_ = std::move(regs); }
void SetSyscall(std::unique_ptr<Syscall> syscall) {

40
sandboxed_api/sandbox2/sandbox2.cc
View File

@ -75,26 +75,24 @@ bool Sandbox2::RunAsync() {
return true;
}
void Sandbox2::NotifyMonitor() {
if (monitor_thread_ != nullptr) {
pthread_kill(monitor_thread_->native_handle(), SIGCHLD);
}
}
void Sandbox2::Kill() {
CHECK(monitor_ != nullptr) << "Sandbox was not launched yet";
// The sandboxee (and its monitoring thread) are already gone. Ignore the
// request instead of panic'ing in such case.
if (monitor_thread_ == nullptr) {
return;
}
pthread_kill(monitor_thread_->native_handle(), Monitor::kExternalKillSignal);
monitor_->external_kill_request_flag_.clear(std::memory_order_relaxed);
NotifyMonitor();
}
void Sandbox2::DumpStackTrace() {
CHECK(monitor_ != nullptr) << "Sandbox was not launched yet";
if (monitor_thread_ == nullptr) {
return;
}
pthread_kill(monitor_thread_->native_handle(), Monitor::kDumpStackSignal);
monitor_->dump_stack_request_flag_.clear(std::memory_order_relaxed);
NotifyMonitor();
}
bool Sandbox2::IsTerminated() const {
@ -106,15 +104,15 @@ bool Sandbox2::IsTerminated() const {
void Sandbox2::SetWallTimeLimit(time_t limit) const {
CHECK(monitor_ != nullptr) << "Sandbox was not launched yet";
if (monitor_thread_ == nullptr) {
return;
if (limit == 0) {
VLOG(1) << "Disarming walltime timer to ";
monitor_->deadline_millis_.store(0, std::memory_order_relaxed);
} else {
VLOG(1) << "Will set the walltime timer to " << limit << " seconds";
auto deadline = absl::Now() + absl::Seconds(limit);
monitor_->deadline_millis_.store(absl::ToUnixMillis(deadline),
std::memory_order_relaxed);
}
union sigval v;
v.sival_int = static_cast<int>(limit);
pthread_sigqueue(monitor_thread_->native_handle(), Monitor::kTimerSetSignal,
v);
}
void Sandbox2::Launch() {
@ -126,7 +124,7 @@ void Sandbox2::Launch() {
// Wait for the Monitor to set-up the sandboxee correctly (or fail while
// doing that). From here on, it is safe to use the IPC object for
// non-sandbox-related data exchange.
monitor_->setup_counter_->Wait();
monitor_->setup_counter_.Wait();
}
} // namespace sandbox2

2
sandboxed_api/sandbox2/sandbox2.h
View File

@ -112,6 +112,8 @@ class Sandbox2 final {
private:
// Launches the Monitor.
void Launch();
// Notifies monitor about a state change
void NotifyMonitor();
// Executor set by user - owned by Sandbox2.
std::unique_ptr<Executor> executor_;