/*
 * Medal of Honor: Allied Assault Linux dedicated server run helper
 * Part of dedtools
 * Adds these features to mohaa_lnxded:
 *   chroot (especially useful with chroot restrictions in kernel)
 *   setuid/setgid
 *   going to background and setting up logfile
 *   pidfile (pidfile deleting is currently commented out)
 *   enabling core dumps
 * Code by Tomas Janousek <tomi@nomi.cz>
 * This is GPL code.
 *
 * Refer to README.chroot about setting up chroot environment
 */
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#include <dlfcn.h>
#include <stdio.h>
#include <sys/time.h>
#include <errno.h>
#include <pwd.h>
#include <fcntl.h>
#include <signal.h>
#include <sys/resource.h>
#include <sys/prctl.h>
#include <string.h>

static void (*old_f)(FILE *stream, char *buf) = 0;
static sighandler_t (*old_signal)(int signum, sighandler_t handler) = 0;

static const char *pidfile = 0;

/* -- We do not want it now
static void (*old__exit)(int status) = 0;

// hook _exit for deleting pidfile
void _exit(int status)
{
    if (!old__exit) {
	old__exit = dlsym(RTLD_NEXT,"_exit");
	if (!old__exit)
	    exit(-1);
    }

    if (pidfile)
	unlink(pidfile);

    _exit(status);
}
*/

// create pidfile
static void setup_pidfile()
{
    pidfile = getenv("MOHAA_PIDFILE");
    if (!pidfile)
	return;

    FILE *f = fopen(pidfile,"w");
    if (f) {
	fprintf(f,"%i",(int)getpid());
	fprintf(stderr, "Writing pidfile\n");
	fclose(f);
    }

}

// chroot and chdir to /
static void chroot_it()
{
    if (chroot(".")) {
	fprintf(stderr, "Could not chroot (%s)\n", strerror(errno));
	exit(-1);
    }

    if (chdir("/")) {
	fprintf(stderr, "Could not chdir (%s)\n", strerror(errno));
	exit(-1);
    }

    fprintf(stderr, "Chrooted successfully\n");
}

static struct passwd *userent = 0;

// prepare uid and gid for dropping privileges
// (we can't read passwd after chroot)
static void droppriv_prep()
{
    const char *user = getenv("MOHAA_USER");
    if (user) {
	userent = getpwnam(user);
	if (!userent) {
	    fprintf(stderr, "Specified user does not exist (%s)\n", strerror(errno));
	    exit(-1);
	}
    }
}

// drop privileges
static void droppriv()
{
    if (userent) {
	if (setgid(userent->pw_gid)) {
	    fprintf(stderr, "Could not setgid (%s)\n", strerror(errno));
	    exit(-1);
	}

	if (setuid(userent->pw_uid)) {
	    fprintf(stderr, "Could not setuid (%s)\n", strerror(errno));
	    exit(-1);
	}

	fprintf(stderr, "Privileges dropped successfully\n");
    } else
	fprintf(stderr, "Will not setuid!\n");
}

// fork into background and setup logfile
static void background()
{
    if (daemon(1, 0)) {
	fprintf(stderr, "Could not daemon (%s)\n", strerror(errno));
	exit(-1);
    }

    const char *log = getenv("MOHAA_LOG");
    if (log) {
	int fd = open(log, O_WRONLY | O_APPEND | O_CREAT, 0666);
	if (fd < 0) {
	    fprintf(stderr, "Could not open log (%s)\n", strerror(errno));
	    exit(-1);
	}

	dup2(fd, 1);
	dup2(fd, 2);
	close(fd);

	fprintf(stderr, "Logfile opened\n");
    }
}

sighandler_t signal(int signum, sighandler_t handler)
{
    if (!old_signal) {
	old_signal = dlsym(RTLD_NEXT,"signal");
	if (!old_signal)
	    exit(-1);
    }

    if (signum == SIGSEGV)
	return old_signal(signum, SIG_DFL);
    if (signum == SIGABRT)
	return old_signal(signum, SIG_DFL);
    return old_signal(signum, handler);
}

void setup_coredump()
{
    setrlimit(RLIMIT_CORE, &((const struct rlimit){RLIM_INFINITY, RLIM_INFINITY}));
    prctl(PR_SET_DUMPABLE, 1);
}

// the first function called by mohaa_lnxded
void setbuf(FILE *stream, char *buf)
{
    if (!old_f) {
	old_f = dlsym(RTLD_NEXT,"setbuf");
	if (!old_f)
	    exit(-1);
    }

    static int done = 0;
    if (!done) {
	fprintf(stderr, "mohaa_chroot hooked!\n");
	droppriv_prep();
	chroot_it();
	droppriv();
	background();
	setup_pidfile();
	setup_coredump();
	done = 1;
    }

    return old_f(stream, buf);
}