utils-std

chroot.c (1370B)

// utils-std: Collection of commonly available Unix tools
// SPDX-FileCopyrightText: 2017 Haelwenn (lanodan) Monnier <contact+utils@hacktivis.me>
// SPDX-License-Identifier: MPL-2.0
#define _DEFAULT_SOURCE // chroot isn't POSIX
#include <assert.h>  // assert
#include <errno.h>   // errno
#include <limits.h>  // PATH_MAX
#include <stdbool.h> // false
#include <stdio.h>   // fprintf, perror
#include <stdlib.h>  // getenv
#include <string.h>  // strlen
#include <unistd.h>  // chroot, execl, execv
int
main(int argc, char *argv[])
{
	if(argc < 2)
	{
		fprintf(stderr, "chroot: Needs arguments\n");
		fprintf(stderr, "Usage: chroot <newroot> [command [args ...]]\n");
		return 125;
	}
	if(chroot(argv[1]) < 0)
	{
		perror("chroot");
		return 125;
	}
	if(chdir("/") < 0)
	{
		perror("chroot: chdir");
		return 125;
	}
	int ret = 0;
	errno = 0;
	if(argc == 2)
	{
		const char *shell = getenv("SHELL");
		if(shell == NULL) shell = "/bin/sh";
		if(strnlen(shell, PATH_MAX) >= PATH_MAX)
		{
			fprintf(stderr,
			        "chroot: Warning: $SHELL is longer than {PATH_MAX}(= %d), using '/bin/sh'\n",
			        PATH_MAX);
			shell = "/bin/sh";
		}
		ret = execlp(shell, shell, "-i", (char *)0);
	}
	else
	{
		argv += 2;
		ret = execvp(argv[0], argv);
	}
	if(ret != 0)
	{
		perror("chroot: exec");
		if(errno == ENOENT) return 127;
		return 126;
	}
	assert(false);
}