Name
chroot — change root directory
Synopsis
#include <unistd.h>
int
chroot( |
const char *path); |
![[Note]](../stylesheet/note.png) |
Note | ||||||
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DESCRIPTION
chroot() changes the root
directory of the calling process to that specified in
path. This directory
will be used for pathnames beginning with /. The root directory is inherited by all
children of the calling process.
Only a privileged process (Linux: one with the
CAP_SYS_CHROOT capability in
its user namespace) may call chroot().
This call changes an ingredient in the pathname resolution
process and does nothing else. In particular, it is not
intended to be used for any kind of security purpose, neither
to fully sandbox a process nor to restrict filesystem system
calls. In the past, chroot()
has been used by daemons to restrict themselves prior to
passing paths supplied by untrusted users to system calls
such as open(2). However, if a
folder is moved out of the chroot directory, an attacker can
exploit that to get out of the chroot directory as well. The
easiest way to do that is to chdir(2) to the to-be-moved
directory, wait for it to be moved out, then open a path like
../../../etc/passwd.
A slightly trickier variation also works under some circumstances if chdir(2) is not permitted. If a daemon allows a "chroot directory" to be specified, that usually means that if you want to prevent remote users from accessing files outside the chroot directory, you must ensure that folders are never moved out of it.
This call does not change the current working directory,
so that after the call '.' can
be outside the tree rooted at '/'. In particular, the superuser can escape
from a "chroot jail" by doing:
mkdir foo; chroot foo; cd ..
This call does not close open file descriptors, and such file descriptors may allow access to files outside the chroot tree.
RETURN VALUE
On success, zero is returned. On error, −1 is
returned, and errno is set to
indicate the error.
ERRORS
Depending on the filesystem, other errors can be returned. The more general errors are listed below:
- EACCES
-
Search permission is denied on a component of the path prefix. (See also path_resolution(7).)
- EFAULT
-
pathpoints outside your accessible address space. - EIO
-
An I/O error occurred.
- ELOOP
-
Too many symbolic links were encountered in resolving
path. - ENAMETOOLONG
-
pathis too long. - ENOENT
-
The file does not exist.
- ENOMEM
-
Insufficient kernel memory was available.
- ENOTDIR
-
A component of
pathis not a directory. - EPERM
-
The caller has insufficient privilege.
NOTES
A child process created via fork(2) inherits its parent's root directory. The root directory is left unchanged by execve(2).
The magic symbolic link, /proc/[pid]/root, can be used to discover a
process's root directory; see proc(5) for details.
FreeBSD has a stronger jail() system call.