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/* ischroot: detect if running in a chroot
*
* Debian ischroot program
* Copyright (C) 2011 Aurelien Jarno <aurel32@debian.org>
*
* This is free software; see the GNU General Public License version 2
* or later for copying conditions. There is NO warranty.
*/
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#ifdef HAVE_GETOPT_H
#include <getopt.h>
#endif /* HAVE_GETOPT_H */
void version()
{
fprintf(stderr, "Debian ischroot, version " PACKAGE_VERSION
"Copyright (C) 2011 Aurelien Jarno\n"
"This is free software; see the GNU General Public License version 2\n"
"or later for copying conditions. There is NO warranty.\n");
exit(0);
}
void usage()
{
fprintf(stderr, "Usage: ischroot [OPTION]\n"
" -f, --default-false return false if detection fails\n"
" -t, --default-true return true if detection fails\n"
" -V, --version output version information and exit.\n"
" -h, --help display this help and exit.\n");
exit(0);
}
/* return 1 if we are operating within a fakechroot environment,
return 0 otherwise */
int isfakechroot()
{
const char *fakechroot, *ldpreload;
return ((fakechroot = getenv("FAKECHROOT")) &&
(strcmp("true", fakechroot) == 0) &&
(NULL != getenv("FAKECHROOT_BASE")) &&
(ldpreload = getenv("LD_PRELOAD")) &&
(NULL != strstr(ldpreload, "libfakechroot.so")));
}
#if defined (__linux__)
/* On Linux we can detect chroots by checking if the
* devicenumber/inode pair of / are the same as that of
* /sbin/init's. This may fail if not running as root or if
* /proc is not mounted, in which case 2 is returned.
*
* If /proc/1/root exists but can not be stated as root,
* we're running in some limited environment (eg. vserver),
* which we consider as chroot here.
*/
static int ischroot()
{
struct stat st1, st2;
if (stat("/", &st1))
return 2;
if (stat("/proc/1/root", &st2)) {
/* Does /proc/1/root exist at all? */
if (lstat("/proc/1/root" , &st2))
return 2;
/* Are we root? */
if (geteuid() != 0)
return 2;
/* Root can not read /proc/1/root, assume vserver or similar */
return 0;
} else if ((st1.st_dev == st2.st_dev) && (st1.st_ino == st2.st_ino))
return 1;
else
return 0;
}
#elif defined (__FreeBSD_kernel__) || defined (__FreeBSD__)
#include <sys/sysctl.h>
#include <sys/user.h>
/* On FreeBSD we can detect chroot by looking for a specific
* file descriptor pointing to the location of the chroot. There
* is not need to be root, so it is unlikely to fail in normal
* cases, but return 2 if a memory failure or the like happens. */
static int ischroot()
{
int mib[4];
size_t kf_len = 0;
char *kf_buf, *kf_bufp;
mib[0] = CTL_KERN;
mib[1] = KERN_PROC;
mib[2] = KERN_PROC_FILEDESC;
mib[3] = getpid ();
if (sysctl (mib, 4, NULL, &kf_len, NULL, 0) != 0)
return 2;
kf_buf = kf_bufp = malloc (kf_len);
if (kf_buf == NULL)
return 2;
if (sysctl (mib, 4, kf_buf, &kf_len, NULL, 0) != 0)
{
free(kf_buf);
return 2;
}
while (kf_bufp < kf_buf + kf_len)
{
struct kinfo_file *kf = (struct kinfo_file *) (uintptr_t) kf_bufp;
if (kf->kf_fd == KF_FD_TYPE_JAIL)
{
free(kf_buf);
return 0;
}
kf_bufp += kf->kf_structsize;
}
free(kf_buf);
return 1;
}
#elif defined (__GNU__)
/* On Hurd we can detect chroot by looking at the device number
* containing /. The device number of the first mounted filesystem
* equals 3, and due to bug http://savannah.gnu.org/bugs/?23213
* chroots have to be created on a different filesystem. Return 2
* if it is not possible to probe this device. */
static int ischroot()
{
struct stat st;
if (stat("/", &st))
return 2;
else if (st.st_dev == 3)
return 1;
else
return 0;
}
#elif defined (__sun__)
/* Similar to Linux
* XXX: check zone?
* XXX: illumos kernel automatically mounts /proc on boot
*/
static int ischroot()
{
struct stat st1, st2;
if (stat("/", &st1))
return 2;
if (stat("/proc/1/root", &st2))
return 2;
if ((st1.st_dev == st2.st_dev) && (st1.st_ino == st2.st_ino))
return 1;
return 0;
}
#else
static int ischroot()
{
return 2;
}
#warning unknown system, chroot detection will always fail
#endif
/* Process options */
int main(int argc, char *argv[])
{
int default_false = 0;
int default_true = 0;
int exit_status;
for (;;) {
int c;
int option_index = 0;
static struct option long_options[] = {
{"default-false", 0, 0, 'f'},
{"default-true", 0, 0, 't'},
{"help", 0, 0, 'h'},
{"version", 0, 0, 'V'},
{0, 0, 0, 0}
};
c = getopt_long(argc, argv, "fthV", long_options, &option_index);
if (c == EOF)
break;
switch (c) {
case 'f':
default_false = 1;
break;
case 't':
default_true = 1;
break;
case 'h':
usage();
break;
case 'V':
version();
break;
default:
fprintf(stderr, "Try `ischroot --help' for more information.\n");
exit(1);
}
}
if (default_false && default_true) {
fprintf(stderr, "Can't default to both true and false!\n");
fprintf(stderr, "Try `ischroot --help' for more information.\n");
exit(1);
}
if (isfakechroot())
exit_status = 0;
else
exit_status = ischroot();
if (exit_status == 2) {
if (default_true)
exit_status = 0;
if (default_false)
exit_status = 1;
}
return exit_status;
}
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