/* Fucking with namespaces because bored.

* "Pegasus Epsilon" <pegasus@pimpninjas.org>

* (C) Apr 19 2023 - Educational Purposes

*/

#define _GNU_SOURCE

#include <stdarg.h> // va_*

#include <stdio.h> // vfprintf(), putc(), perror(), vsnprintf()

#include <stdlib.h> // exit(), malloc(), free(), setenv(), unsetenv(), getenv()

#include <fcntl.h> // open()

#include <unistd.h> // write(), close(), unlink(), execve()

#include <stdbool.h> // bool, true, false

#include <sched.h> // unshare()

#include <pwd.h> // getpwuid()

static void vperrorf (const char *const fmt, va_list *args) {

vfprintf(stderr, fmt, *args);

putc(':', stderr);

putc(' ', stderr);

perror(NULL);

}

static void perrorf (const char *const fmt, ...) {

va_list args;

va_start(args, fmt);

vperrorf(fmt, &args);

va_end(args);

}

__attribute__((noreturn))

static void fail (const int errlvl, const char *const fmt, ...) {

va_list args;

va_start(args, fmt);

vperrorf(fmt, &args);

va_end(args);

exit(errlvl);

}

static bool writefile (const char *const file, const char *const fmt, ...) {

int fd = open(file, O_WRONLY | O_CLOEXEC | O_CREAT);

if (0 > fd) { perror("open error"); return false; }

va_list args, copy;

va_start(args, fmt);

va_copy(copy, args);

int len = 1 + vsnprintf(NULL, 0, fmt, copy);

va_end(copy);

char *buf = malloc(len);

vsnprintf(buf, len, fmt, args);

va_end(args);

int wrote = write(fd, buf, len);

free(buf);

if (wrote != len) perrorf("error writing %s", file);

close(fd);

if (wrote == len) return true;

if (wrote) unlink(file);

return false;

}

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

uid_t uid = getuid();

gid_t gid = getgid();

if (unshare(CLONE_NEWUSER)) fail(1, "unshare CLONE_NEWUSER");

if (unshare(CLONE_NEWNET)) fail(2, "unshare CLONE_NEWNET");

if (!writefile("/proc/self/setgroups", "deny")) return 3;

if (!writefile("/proc/self/uid_map", "0 %d 1\n", uid)) return 4;

if (!writefile("/proc/self/gid_map", "0 %d 1\n", gid)) return 5;

struct passwd *pwd = getpwuid(0);

setenv("HOME", pwd->pw_dir, true);

unsetenv("HISTFILE");

execve(getenv("SHELL"), argv, envp);

return 0;

}