judge runner implementation

* The runner requires Linux kernel version 3.10 or later.

* To measure memory and CPU time usage.

* To set limits and use other security measurement.

Code is hosted on Github

 https://github.com/IndeedPlusPlus/docker-judge-runner

Preview (old)

#include <unistd.h>
#include <sys/types.h>
#include <sys/resource.h>
#include <sys/wait.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define RUNNER_UID 1000
#define RUNNER_GID 1000

void print_preformance(const struct rusage * ruse) {
    unsigned time = ruse->ru_utime.tv_sec * 1000 + ruse->ru_utime.tv_usec / 1000;
    time += ruse->ru_stime.tv_sec * 1000 + ruse->ru_stime.tv_usec / 1000;
    fprintf(stderr, "Total time: %u seconds and %u milliseconds. Memory: %ld\n", time / 1000 , time % 1000, ruse->ru_maxrss);

}

int main(int argc, char ** argv)
{
    pid_t pid = fork();
    if (pid) {
        // monitor
        int status;
        struct rusage ruse;
        wait4(pid, &status, 0, &ruse);
        if (WIFEXITED(status)) {
            // exited normally
            int exit_code = WEXITSTATUS(status);
            fprintf(stderr, "Exit code: %d\n", exit_code);
        } else if (WIFSIGNALED(status)) {
            // killed by signal
            int signal = WTERMSIG(status);
            fprintf(stderr, "Signal: %s\n", strsignal(signal));
        } else {
            // should never get there
        }
        print_preformance(&ruse);
    } else {
        // runner    
        if (argc <= 1)
            return 1;
        char ** args = malloc(argc * sizeof(char *));
        int i = 0;
        for (i = 1 ; i < argc ; ++i)
            args[i - 1] = argv[i];
        args[i - 1] = NULL;
        // optionally set uid & gid
        if (setgid(RUNNER_GID))
            perror("setgid");
        if (setuid(RUNNER_UID))
            perror("setuid");
        if (execvp(argv[1] , args))
        {
            perror("exec");
            return 2;
        }
    }
    return 0;
}