openmw/components/crashcatcher/crashcatcher.cpp

#include <algorithm>
#include <cstring>
#include <filesystem>
#include <fstream>
#include <span>

#include <errno.h>
#include <limits.h>
#include <pthread.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/param.h>
#include <sys/ptrace.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/utsname.h>
#include <sys/wait.h>
#include <unistd.h>

#include <components/debug/debuglog.hpp>

#include <SDL_messagebox.h>

#ifdef __linux__
#include <sys/prctl.h>
#include <sys/ucontext.h>
#ifndef PR_SET_PTRACER
#define PR_SET_PTRACER 0x59616d61
#endif
#elif defined(__APPLE__) || defined(__FreeBSD__) || defined(__OpenBSD__)
#include <signal.h>
#endif

#if defined(__APPLE__)
#include <cassert>
#include <libproc.h>
#include <sys/sysctl.h>
#endif

#if defined(__FreeBSD__)
#include <sys/sysctl.h>
#include <sys/user.h>
#endif

#include "crashcatcher.hpp"

static const char fatal_err[] = "\n\n*** Fatal Error ***\n";
static const char pipe_err[] = "!!! Failed to create pipe\n";
static const char fork_err[] = "!!! Failed to fork debug process\n";
static const char exec_err[] = "!!! Failed to exec debug process\n";

#ifndef PATH_MAX /* Not all platforms (GNU Hurd) have this. */
#define PATH_MAX 256
#endif

static char argv0[PATH_MAX];

static struct
{
    int signum;
    pid_t pid;
    int has_siginfo;
    siginfo_t siginfo;
    char buf[1024];
} crash_info;

namespace
{
    struct SignalInfo
    {
        int mCode;
        const char* mDescription;
    };

    constexpr SignalInfo signals[] = {
        { SIGSEGV, "Segmentation fault" },
        { SIGILL, "Illegal instruction" },
        { SIGFPE, "FPU exception" },
        { SIGBUS, "System BUS error" },
    };

    constexpr SignalInfo sigIllCodes[] = {
#if !defined(__FreeBSD__) && !defined(__FreeBSD_kernel__)
        { ILL_ILLOPC, "Illegal opcode" },
        { ILL_ILLOPN, "Illegal operand" },
        { ILL_ILLADR, "Illegal addressing mode" },
        { ILL_ILLTRP, "Illegal trap" },
        { ILL_PRVOPC, "Privileged opcode" },
        { ILL_PRVREG, "Privileged register" },
        { ILL_COPROC, "Coprocessor error" },
        { ILL_BADSTK, "Internal stack error" },
#endif
    };

    constexpr SignalInfo sigFpeCodes[] = {
        { FPE_INTDIV, "Integer divide by zero" },
        { FPE_INTOVF, "Integer overflow" },
        { FPE_FLTDIV, "Floating point divide by zero" },
        { FPE_FLTOVF, "Floating point overflow" },
        { FPE_FLTUND, "Floating point underflow" },
        { FPE_FLTRES, "Floating point inexact result" },
        { FPE_FLTINV, "Floating point invalid operation" },
        { FPE_FLTSUB, "Subscript out of range" },
    };

    constexpr SignalInfo sigSegvCodes[] = {
#ifndef __FreeBSD__
        { SEGV_MAPERR, "Address not mapped to object" },
        { SEGV_ACCERR, "Invalid permissions for mapped object" },
#endif
    };

    constexpr SignalInfo sigBusCodes[] = {
#ifndef __FreeBSD__
        { BUS_ADRALN, "Invalid address alignment" },
        { BUS_ADRERR, "Non-existent physical address" },
        { BUS_OBJERR, "Object specific hardware error" },
#endif
    };

    const char* findSignalDescription(std::span<const SignalInfo> info, int code)
    {
        const auto it = std::find_if(info.begin(), info.end(), [&](const SignalInfo& v) { return v.mCode == code; });
        return it == info.end() ? "" : it->mDescription;
    }
}

static int (*cc_user_info)(char*, char*);

static void gdb_info(pid_t pid)
{
    char respfile[64];
    FILE* f;
    int fd;

    /*
     * Create a temp file to put gdb commands into.
     * Note: POSIX.1-2008 declares that the file should be already created with mode 0600 by default.
     * Modern systems implement it and suggest to do not touch masks in multithreaded applications.
     * So CoverityScan warning is valid only for ancient versions of stdlib.
     */
    strcpy(respfile, "/tmp/gdb-respfile-XXXXXX");
#ifdef __COVERITY__
    umask(0600);
#endif
    if ((fd = mkstemp(respfile)) >= 0 && (f = fdopen(fd, "w")) != nullptr)
    {
        fprintf(f,
            "attach %d\n"
            "shell echo \"\"\n"
            "shell echo \"* Loaded Libraries\"\n"
            "info sharedlibrary\n"
            "shell echo \"\"\n"
            "shell echo \"* Threads\"\n"
            "info threads\n"
            "shell echo \"\"\n"
            "shell echo \"* FPU Status\"\n"
            "info float\n"
            "shell echo \"\"\n"
            "shell echo \"* Registers\"\n"
            "info registers\n"
            "shell echo \"\"\n"
            "shell echo \"* Backtrace\"\n"
            "thread apply all backtrace full 1000\n"
            "detach\n"
            "quit\n",
            pid);
        fclose(f);

        /* Run gdb and print process info. */
        char cmd_buf[128];
        snprintf(cmd_buf, sizeof(cmd_buf), "gdb --quiet --batch --command=%s", respfile);
        printf("Executing: %s\n", cmd_buf);
        fflush(stdout);

        int ret = system(cmd_buf);

        if (ret != 0)
            printf(
                "\nFailed to create a crash report. Please make sure that 'gdb' is installed and present in PATH then "
                "crash again."
                "\nCurrent PATH: %s\n",
                getenv("PATH"));
        fflush(stdout);

        /* Clean up */
        if (remove(respfile) != 0)
            Log(Debug::Warning) << "Warning: can not remove file '" << respfile
                                << "': " << std::generic_category().message(errno);
    }
    else
    {
        /* Error creating temp file */
        if (fd >= 0)
        {
            if (close(fd) != 0)
                Log(Debug::Warning) << "Warning: can not close file '" << respfile
                                    << "': " << std::generic_category().message(errno);
            else if (remove(respfile) != 0)
                Log(Debug::Warning) << "Warning: can not remove file '" << respfile
                                    << "': " << std::generic_category().message(errno);
        }
        printf("!!! Could not create gdb command file\n");
    }
    fflush(stdout);
}

static void sys_info(void)
{
#ifdef __unix__
    struct utsname info;
    if (uname(&info))
        printf("!!! Failed to get system information\n");
    else
        printf("System: %s %s %s %s %s\n", info.sysname, info.nodename, info.release, info.version, info.machine);

    fflush(stdout);
#endif
}

static size_t safe_write(int fd, const void* buf, size_t len)
{
    size_t ret = 0;
    while (ret < len)
    {
        ssize_t rem;
        if ((rem = write(fd, (const char*)buf + ret, len - ret)) == -1)
        {
            if (errno == EINTR)
                continue;
            break;
        }
        ret += rem;
    }
    return ret;
}

static void crash_catcher(int signum, siginfo_t* siginfo, void* context)
{
    // ucontext_t *ucontext = (ucontext_t*)context;
    pid_t dbg_pid;
    int fd[2];

    /* Make sure the effective uid is the real uid */
    if (getuid() != geteuid())
    {
        raise(signum);
        return;
    }

    safe_write(STDERR_FILENO, fatal_err, sizeof(fatal_err) - 1);
    if (pipe(fd) == -1)
    {
        safe_write(STDERR_FILENO, pipe_err, sizeof(pipe_err) - 1);
        raise(signum);
        return;
    }

    crash_info.signum = signum;
    crash_info.pid = getpid();
    crash_info.has_siginfo = !!siginfo;
    if (siginfo)
        crash_info.siginfo = *siginfo;
    if (cc_user_info)
        cc_user_info(crash_info.buf, crash_info.buf + sizeof(crash_info.buf));

    /* Fork off to start a crash handler */
    switch ((dbg_pid = fork()))
    {
        /* Error */
        case -1:
            safe_write(STDERR_FILENO, fork_err, sizeof(fork_err) - 1);
            raise(signum);
            return;

        case 0:
            dup2(fd[0], STDIN_FILENO);
            close(fd[0]);
            close(fd[1]);

            execl(argv0, argv0, crash_switch, nullptr);

            safe_write(STDERR_FILENO, exec_err, sizeof(exec_err) - 1);
            _exit(1);

        default:
#ifdef __linux__
            prctl(PR_SET_PTRACER, dbg_pid, 0, 0, 0);
#endif
            safe_write(fd[1], &crash_info, sizeof(crash_info));
            close(fd[0]);
            close(fd[1]);

            /* Wait; we'll be killed when gdb is done */
            do
            {
                int status;
                if (waitpid(dbg_pid, &status, 0) == dbg_pid && (WIFEXITED(status) || WIFSIGNALED(status)))
                {
                    /* The debug process died before it could kill us */
                    raise(signum);
                    break;
                }
            } while (1);
    }
}

static void crash_handler(const char* logfile)
{
    if (fread(&crash_info, sizeof(crash_info), 1, stdin) != 1)
    {
        fprintf(stderr, "!!! Failed to retrieve info from crashed process\n");
        exit(1);
    }

    const char* sigdesc = findSignalDescription(signals, crash_info.signum);

    if (crash_info.has_siginfo)
    {
        switch (crash_info.signum)
        {
            case SIGSEGV:
                sigdesc = findSignalDescription(sigSegvCodes, crash_info.siginfo.si_code);
                break;

            case SIGFPE:
                sigdesc = findSignalDescription(sigFpeCodes, crash_info.siginfo.si_code);
                break;

            case SIGILL:
                sigdesc = findSignalDescription(sigIllCodes, crash_info.siginfo.si_code);
                break;

            case SIGBUS:
                sigdesc = findSignalDescription(sigBusCodes, crash_info.siginfo.si_code);
                break;
        }
    }
    fprintf(stderr, "%s (signal %i)\n", sigdesc, crash_info.signum);
    if (crash_info.has_siginfo)
        fprintf(stderr, "Address: %p\n", crash_info.siginfo.si_addr);
    fputc('\n', stderr);

    if (logfile)
    {
        /* Create crash log file and redirect shell output to it */
        if (freopen(logfile, "wa", stdout) != stdout)
        {
            fprintf(stderr, "!!! Could not create %s following signal\n", logfile);
            exit(1);
        }
        fprintf(stderr, "Generating %s and killing process %d, please wait... ", logfile, crash_info.pid);

        printf(
            "*** Fatal Error ***\n"
            "%s (signal %i)\n",
            sigdesc, crash_info.signum);
        if (crash_info.has_siginfo)
            printf("Address: %p\n", crash_info.siginfo.si_addr);
        fputc('\n', stdout);
        fflush(stdout);
    }

    sys_info();

    crash_info.buf[sizeof(crash_info.buf) - 1] = '\0';
    printf("%s\n", crash_info.buf);
    fflush(stdout);

    if (crash_info.pid > 0)
    {
        gdb_info(crash_info.pid);
        kill(crash_info.pid, SIGKILL);
    }

    // delay between killing of the crashed process and showing the message box to
    // work around occasional X server lock-up. this can only be a bug in X11 since
    // even faulty applications shouldn't be able to freeze the X server.
    usleep(100000);

    if (logfile)
    {
        std::string message = "OpenMW has encountered a fatal error.\nCrash log saved to '" + std::string(logfile)
            + "'.\n Please report this to https://gitlab.com/OpenMW/openmw/issues !";
        SDL_ShowSimpleMessageBox(0, "Fatal Error", message.c_str(), nullptr);
    }

    exit(0);
}

static void getExecPath(char** argv)
{
#if defined(__FreeBSD__)
    int mib[4] = { CTL_KERN, KERN_PROC, KERN_PROC_PATHNAME, -1 };
    size_t size = sizeof(argv0);

    if (sysctl(mib, 4, argv0, &size, nullptr, 0) == 0)
        return;
#endif

#if defined(__APPLE__)
    if (proc_pidpath(getpid(), argv0, sizeof(argv0)) > 0)
        return;
#endif
    int cwdlen;
    const char* statusPaths[] = { "/proc/self/exe", "/proc/self/file", "/proc/curproc/exe", "/proc/curproc/file" };
    memset(argv0, 0, sizeof(argv0));

    for (const char* path : statusPaths)
    {
        if (readlink(path, argv0, sizeof(argv0)) != -1)
            return;
    }

    if (argv[0][0] == '/')
        snprintf(argv0, sizeof(argv0), "%s", argv[0]);
    else if (getcwd(argv0, sizeof(argv0)) != nullptr)
    {
        cwdlen = strlen(argv0);
        snprintf(argv0 + cwdlen, sizeof(argv0) - cwdlen, "/%s", argv[0]);
    }
}

int crashCatcherInstallHandlers(
    int argc, char** argv, int num_signals, int* signals, const char* logfile, int (*user_info)(char*, char*))
{
    struct sigaction sa;
    stack_t altss;
    int retval;

    if (argc == 2 && strcmp(argv[1], crash_switch) == 0)
        crash_handler(logfile);

    cc_user_info = user_info;

    getExecPath(argv);

    /* Set an alternate signal stack so SIGSEGVs caused by stack overflows
     * still run */
    static char* altstack = new char[SIGSTKSZ];
    altss.ss_sp = altstack;
    altss.ss_flags = 0;
    altss.ss_size = SIGSTKSZ;
    sigaltstack(&altss, nullptr);

    memset(&sa, 0, sizeof(sa));
    sa.sa_sigaction = crash_catcher;
    sa.sa_flags = SA_RESETHAND | SA_NODEFER | SA_SIGINFO | SA_ONSTACK;
    sigemptyset(&sa.sa_mask);

    retval = 0;
    while (num_signals--)
    {
        if ((*signals != SIGSEGV && *signals != SIGILL && *signals != SIGFPE && *signals != SIGABRT
                && *signals != SIGBUS)
            || sigaction(*signals, &sa, nullptr) == -1)
        {
            *signals = 0;
            retval = -1;
        }
        ++signals;
    }
    return retval;
}

static bool is_debugger_present()
{
#if defined(__linux__)
    std::filesystem::path procstatus = std::filesystem::path("/proc/self/status");
    if (std::filesystem::exists(procstatus))
    {
        std::ifstream file((procstatus));
        while (!file.eof())
        {
            std::string word;
            file >> word;
            if (word == "TracerPid:")
            {
                file >> word;
                return word != "0";
            }
        }
    }
    return false;
#elif defined(__APPLE__)
    int junk;
    int mib[4];
    struct kinfo_proc info;
    size_t size;

    // Initialize the flags so that, if sysctl fails for some bizarre
    // reason, we get a predictable result.

    info.kp_proc.p_flag = 0;

    // Initialize mib, which tells sysctl the info we want, in this case
    // we're looking for information about a specific process ID.

    mib[0] = CTL_KERN;
    mib[1] = KERN_PROC;
    mib[2] = KERN_PROC_PID;
    mib[3] = getpid();

    // Call sysctl.

    size = sizeof(info);
    junk = sysctl(mib, sizeof(mib) / sizeof(*mib), &info, &size, nullptr, 0);
    assert(junk == 0);

    // We're being debugged if the P_TRACED flag is set.

    return (info.kp_proc.p_flag & P_TRACED) != 0;
#elif defined(__FreeBSD__)
    struct kinfo_proc info;
    size_t size = sizeof(info);
    int mib[4] = { CTL_KERN, KERN_PROC, KERN_PROC_PID, getpid() };

    if (sysctl(mib, sizeof(mib) / sizeof(*mib), &info, &size, nullptr, 0) == 0)
        return (info.ki_flag & P_TRACED) != 0;
    else
        perror("Failed to retrieve process info");
    return false;
#else
    return false;
#endif
}

void crashCatcherInstall(int argc, char** argv, const std::filesystem::path& crashLogPath)
{
    if ((argc == 2 && strcmp(argv[1], crash_switch) == 0) || !is_debugger_present())
    {
        int s[5] = { SIGSEGV, SIGILL, SIGFPE, SIGBUS, SIGABRT };
        if (crashCatcherInstallHandlers(argc, argv, 5, s, crashLogPath.c_str(), nullptr) == -1)
        {
            Log(Debug::Warning) << "Installing crash handler failed";
        }
        else
            Log(Debug::Info) << "Crash handler installed";
    }
}