path: root/src/mongo/util/signal_handlers_synchronous.cpp

/**
 *    Copyright (C) 2018-present MongoDB, Inc.
 *
 *    This program is free software: you can redistribute it and/or modify
 *    it under the terms of the Server Side Public License, version 1,
 *    as published by MongoDB, Inc.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    Server Side Public License for more details.
 *
 *    You should have received a copy of the Server Side Public License
 *    along with this program. If not, see
 *    <http://www.mongodb.com/licensing/server-side-public-license>.
 *
 *    As a special exception, the copyright holders give permission to link the
 *    code of portions of this program with the OpenSSL library under certain
 *    conditions as described in each individual source file and distribute
 *    linked combinations including the program with the OpenSSL library. You
 *    must comply with the Server Side Public License in all respects for
 *    all of the code used other than as permitted herein. If you modify file(s)
 *    with this exception, you may extend this exception to your version of the
 *    file(s), but you are not obligated to do so. If you do not wish to do so,
 *    delete this exception statement from your version. If you delete this
 *    exception statement from all source files in the program, then also delete
 *    it in the license file.
 */


#include "mongo/platform/basic.h"

#include "mongo/util/signal_handlers_synchronous.h"

#include <boost/exception/diagnostic_information.hpp>
#include <boost/exception/exception.hpp>
#include <csignal>
#include <exception>
#include <fmt/format.h>
#include <iostream>
#include <memory>
#include <streambuf>
#include <typeinfo>

#include "mongo/base/string_data.h"
#include "mongo/logv2/log.h"
#include "mongo/platform/compiler.h"
#include "mongo/stdx/exception.h"
#include "mongo/stdx/thread.h"
#include "mongo/util/assert_util.h"
#include "mongo/util/concurrency/thread_name.h"
#include "mongo/util/debug_util.h"
#include "mongo/util/debugger.h"
#include "mongo/util/dynamic_catch.h"
#include "mongo/util/exception_filter_win32.h"
#include "mongo/util/exit_code.h"
#include "mongo/util/quick_exit.h"
#include "mongo/util/signal_handlers.h"
#include "mongo/util/stacktrace.h"
#include "mongo/util/static_immortal.h"
#include "mongo/util/text.h"

#define MONGO_LOGV2_DEFAULT_COMPONENT ::mongo::logv2::LogComponent::kControl


namespace mongo {

namespace {

using namespace fmt::literals;

#if defined(_WIN32)
const char* strsignal(int signalNum) {
    // should only see SIGABRT on windows
    switch (signalNum) {
        case SIGABRT:
            return "SIGABRT";
        default:
            return "UNKNOWN";
    }
}

int sehExceptionFilter(unsigned int code, struct _EXCEPTION_POINTERS* excPointers) {
    exceptionFilter(excPointers);

    return EXCEPTION_EXECUTE_HANDLER;
}

// Follow SEH conventions by defining a status code per their conventions
// Bit 31-30: 11 = ERROR
// Bit 29:     1 = Client bit, i.e. a user-defined code
#define STATUS_EXIT_ABRUPT 0xE0000001

// Historically we relied on raising SEH exception and letting the unhandled exception handler then
// handle it to that we can dump the process. This works in all but one case.
// The C++ terminate handler runs the terminate handler in a SEH __try/__catch. Therefore, any SEH
// exceptions we raise become handled. Now, we setup our own SEH handler to quick catch the SEH
// exception and take the dump bypassing the unhandled exception handler.
//
void endProcessWithSignal(int signalNum) {

    __try {
        RaiseException(STATUS_EXIT_ABRUPT, EXCEPTION_NONCONTINUABLE, 0, nullptr);
    } __except (sehExceptionFilter(GetExceptionCode(), GetExceptionInformation())) {
        // The exception filter exits the process
        quickExit(ExitCode::abrupt);
    }
}

#else

void endProcessWithSignal(int signalNum) {
    // This works by restoring the system-default handler for the given signal and re-raising it, in
    // order to get the system default termination behavior (i.e., dumping core, or just exiting).
    struct sigaction defaultedSignals;
    memset(&defaultedSignals, 0, sizeof(defaultedSignals));
    defaultedSignals.sa_handler = SIG_DFL;
    sigemptyset(&defaultedSignals.sa_mask);
    invariant(sigaction(signalNum, &defaultedSignals, nullptr) == 0);
    raise(signalNum);
}

#endif

// This should only be used with MallocFreeOSteam
class MallocFreeStreambuf : public std::streambuf {
    MallocFreeStreambuf(const MallocFreeStreambuf&) = delete;
    MallocFreeStreambuf& operator=(const MallocFreeStreambuf&) = delete;

public:
    MallocFreeStreambuf() {
        setp(_buffer, _buffer + maxLogLineSize);
    }

    StringData str() const {
        return StringData(pbase(), pptr() - pbase());
    }
    void rewind() {
        setp(pbase(), epptr());
    }

private:
    static const size_t maxLogLineSize = 100 * 1000;
    char _buffer[maxLogLineSize];
};

class MallocFreeOStream : public std::ostream {
    MallocFreeOStream(const MallocFreeOStream&) = delete;
    MallocFreeOStream& operator=(const MallocFreeOStream&) = delete;

public:
    MallocFreeOStream() : std::ostream(&_buf) {}

    StringData str() const {
        return _buf.str();
    }
    void rewind() {
        _buf.rewind();
    }

private:
    MallocFreeStreambuf _buf;
};

MallocFreeOStream mallocFreeOStream;

/**
 * Instances of this type guard the mallocFreeOStream. While locking a mutex isn't guaranteed to
 * be signal-safe, this file does it anyway. The assumption is that the main safety risk to
 * locking a mutex is that you could deadlock with yourself. That risk is protected against by
 * only locking the mutex in fatal functions that log then exit. There is a remaining risk that
 * one of these functions recurses (possible if logging segfaults while handing a
 * segfault). This is currently acceptable because if things are that broken, there is little we
 * can do about it.
 *
 * If in the future, we decide to be more strict about posix signal safety, we could switch to
 * an atomic test-and-set loop, possibly with a mechanism for detecting signals raised while
 * handling other signals.
 */
class MallocFreeOStreamGuard {
public:
    explicit MallocFreeOStreamGuard() : _lk(_streamMutex, stdx::defer_lock) {
        if (terminateDepth++) {
            quickExit(ExitCode::abrupt);
        }
        _lk.lock();
    }

private:
    static stdx::mutex _streamMutex;  // NOLINT
    static thread_local int terminateDepth;
    stdx::unique_lock<stdx::mutex> _lk;
};

stdx::mutex MallocFreeOStreamGuard::_streamMutex;  // NOLINT
thread_local int MallocFreeOStreamGuard::terminateDepth = 0;

void logNoRecursion(StringData message) {
    // If we were within a log call when we hit a signal, don't call back into the logging
    // subsystem.
    if (logv2::loggingInProgress()) {
        logv2::signalSafeWriteToStderr(message);
    } else {
        LOGV2_FATAL_CONTINUE(6384300, "Writing fatal message", "message"_attr = message);
    }
}

// must hold MallocFreeOStreamGuard to call
void writeMallocFreeStreamToLog() {
    mallocFreeOStream << "\n";
    logNoRecursion(mallocFreeOStream.str());
    mallocFreeOStream.rewind();
}

// must hold MallocFreeOStreamGuard to call
void printStackTraceNoRecursion() {
    if (logv2::loggingInProgress()) {
        printStackTrace(mallocFreeOStream);
        writeMallocFreeStreamToLog();
    } else {
        printStackTrace();
    }
}

// must hold MallocFreeOStreamGuard to call
void printSignalAndBacktrace(int signalNum) {
    mallocFreeOStream << "Got signal: " << signalNum << " (" << strsignal(signalNum) << ").";
    writeMallocFreeStreamToLog();
    printStackTraceNoRecursion();
}

void dumpScopedDebugInfo(std::ostream& os) {
    auto diagStack = scopedDebugInfoStack().getAll();
    if (diagStack.empty())
        return;
    os << "ScopedDebugInfo: [";
    StringData sep;
    for (const auto& s : diagStack) {
        os << sep << "(" << s << ")";
        sep = ", "_sd;
    }
    os << "]\n";
}

// this will be called in certain c++ error cases, for example if there are two active
// exceptions
void myTerminate() {
    MallocFreeOStreamGuard lk{};
    mallocFreeOStream << "terminate() called.";
    if (std::current_exception()) {
        mallocFreeOStream << " An exception is active; attempting to gather more information";
        writeMallocFreeStreamToLog();
        globalActiveExceptionWitness().describe(mallocFreeOStream);
    } else {
        mallocFreeOStream << " No exception is active";
    }
    writeMallocFreeStreamToLog();
    dumpScopedDebugInfo(mallocFreeOStream);
    writeMallocFreeStreamToLog();
    printStackTraceNoRecursion();
    breakpoint();
    endProcessWithSignal(SIGABRT);
}

extern "C" void abruptQuit(int signalNum) {
    MallocFreeOStreamGuard lk{};
    dumpScopedDebugInfo(mallocFreeOStream);
    writeMallocFreeStreamToLog();
    printSignalAndBacktrace(signalNum);
    breakpoint();
    endProcessWithSignal(signalNum);
}

#if defined(_WIN32)

void myInvalidParameterHandler(const wchar_t* expression,
                               const wchar_t* function,
                               const wchar_t* file,
                               unsigned int line,
                               uintptr_t pReserved) {

    logNoRecursion(
        "Invalid parameter detected in function {} in {} at line {} with expression '{}'\n"_format(
            toUtf8String(function), toUtf8String(file), line, toUtf8String(expression)));

    abruptQuit(SIGABRT);
}

void myPureCallHandler() {
    logNoRecursion("Pure call handler invoked. Immediate exit due to invalid pure call\n");
    abruptQuit(SIGABRT);
}

#else

extern "C" void abruptQuitAction(int signalNum, siginfo_t*, void*) {
    abruptQuit(signalNum);
};

extern "C" void abruptQuitWithAddrSignal(int signalNum, siginfo_t* siginfo, void* ucontext_erased) {
    // For convenient debugger access.
    [[maybe_unused]] auto ucontext = static_cast<const ucontext_t*>(ucontext_erased);

    MallocFreeOStreamGuard lk{};

    const char* action = (signalNum == SIGSEGV || signalNum == SIGBUS) ? "access" : "operation";
    mallocFreeOStream << "Invalid " << action << " at address: " << siginfo->si_addr;

    // Writing out message to log separate from the stack trace so at least that much gets
    // logged. This is important because we may get here by jumping to an invalid address which
    // could cause unwinding the stack to break.
    writeMallocFreeStreamToLog();

    printSignalAndBacktrace(signalNum);
    breakpoint();
    endProcessWithSignal(signalNum);
}

#endif

}  // namespace

#if !defined(_WIN32)
extern "C" typedef void(sigAction_t)(int signum, siginfo_t* info, void* context);
#endif

void setupSynchronousSignalHandlers() {
    stdx::set_terminate(myTerminate);
    std::set_new_handler(reportOutOfMemoryErrorAndExit);

#if defined(_WIN32)
    invariant(signal(SIGABRT, abruptQuit) != SIG_ERR);
    _set_purecall_handler(myPureCallHandler);
    _set_invalid_parameter_handler(myInvalidParameterHandler);
    setWindowsUnhandledExceptionFilter();
#else
    static constexpr struct {
        int signal;
        sigAction_t* function;  // signal ignored if nullptr
    } kSignalSpecs[] = {
        {SIGHUP, nullptr},
        {SIGUSR2, nullptr},
        {SIGPIPE, nullptr},
        {SIGQUIT, &abruptQuitAction},  // sent by '^\'. Log and hard quit, no cleanup.
        {SIGABRT, &abruptQuitAction},
        {SIGSEGV, &abruptQuitWithAddrSignal},
        {SIGBUS, &abruptQuitWithAddrSignal},
        {SIGILL, &abruptQuitWithAddrSignal},
        {SIGFPE, &abruptQuitWithAddrSignal},
    };
    for (const auto& spec : kSignalSpecs) {
        struct sigaction sa;
        memset(&sa, 0, sizeof(sa));
        sigemptyset(&sa.sa_mask);
        if (spec.function == nullptr) {
            sa.sa_handler = SIG_IGN;
        } else {
            sa.sa_sigaction = spec.function;
            sa.sa_flags = SA_SIGINFO | SA_ONSTACK;
        }
        if (sigaction(spec.signal, &sa, nullptr) != 0) {
            int savedErr = errno;
            LOGV2_FATAL(31334,
                        "Failed to install sigaction for signal {signal}: {error}",
                        "Failed to install sigaction for signal",
                        "signal"_attr = spec.signal,
                        "error"_attr = strerror(savedErr));
        }
    }
    setupSIGTRAPforDebugger();
#if defined(MONGO_STACKTRACE_CAN_DUMP_ALL_THREADS)
    setupStackTraceSignalAction(stackTraceSignal());
#endif
#endif
}

void reportOutOfMemoryErrorAndExit() {
    MallocFreeOStreamGuard lk{};
    mallocFreeOStream << "out of memory.";
    writeMallocFreeStreamToLog();
    printStackTraceNoRecursion();
    quickExit(ExitCode::abrupt);
}

void clearSignalMask() {
#ifndef _WIN32
    // We need to make sure that all signals are unmasked so signals are handled correctly
    sigset_t unblockSignalMask;
    invariant(sigemptyset(&unblockSignalMask) == 0);
    invariant(sigprocmask(SIG_SETMASK, &unblockSignalMask, nullptr) == 0);
#endif
}

#if defined(MONGO_STACKTRACE_HAS_SIGNAL)
int stackTraceSignal() {
    return SIGUSR2;
}
#endif

ActiveExceptionWitness::ActiveExceptionWitness() {
    // Later entries in the catch chain will become the innermost catch blocks, so
    // these are in order of increasing specificity. User-provided probes
    // will be appended, so they will be considered more specific than any of
    // these, which are essentially "fallback" handlers.
    addHandler<boost::exception>([](auto&& ex, std::ostream& os) {
        os << "boost::diagnostic_information(): " << boost::diagnostic_information(ex) << "\n";
    });
    addHandler<std::exception>([](auto&& ex, std::ostream& os) {
        os << "std::exception::what(): " << redact(ex.what()) << "\n";
    });
    addHandler<DBException>([](auto&& ex, std::ostream& os) {
        os << "DBException::toString(): " << redact(ex) << "\n";
    });
}

void ActiveExceptionWitness::describe(std::ostream& os) {
    CatchAndDescribe dc;
    for (const auto& config : _configurators)
        config(dc);
    try {
        dc.doCatch(os);
    } catch (...) {
        os << "A non-standard exception type was thrown\n";
    }
}

void ActiveExceptionWitness::_exceptionTypeBlurb(const std::type_info& ex, std::ostream& os) {
    os << "Actual exception type: " << demangleName(ex) << "\n";
}

ActiveExceptionWitness& globalActiveExceptionWitness() {
    static StaticImmortal<ActiveExceptionWitness> v;
    return *v;
}

}  // namespace mongo