uuns.c

/*
 * Copyright (c) 2017 Steven McDonald <steven@steven-mcdonald.id.au>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#define _GNU_SOURCE

#include <err.h>
#include <sched.h>
#include <stdlib.h>
#include <unistd.h>

#define DEFAULT_SHELL "/bin/sh"

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

	if (unshare(CLONE_NEWUSER) == -1)
		err(1, "unshare");

	if (argc > 1) {
		execvp(argv[1], &argv[1]);
		err(1, "%s", argv[1]);
	}

	if ((shell = getenv("SHELL")) == NULL || shell[0] == '\0')
		shell = DEFAULT_SHELL;

	execlp(shell, shell, "-i", NULL);
	err(1, "%s", shell);
}