mirror of https://github.com/mkerrisk/man-pages
186 lines
5.5 KiB
Groff
186 lines
5.5 KiB
Groff
.\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
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.\"
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.\" %%%LICENSE_START(VERBATIM)
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\" %%%LICENSE_END
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.\"
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.\" Modified by Michael Haardt <michael@moria.de>
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.\" Modified 1993-07-21 by Rik Faith <faith@cs.unc.edu>
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.\" Modified 1994-08-21 by Michael Chastain <mec@shell.portal.com>
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.\" Modified 1996-06-13 by aeb
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.\" Modified 1996-11-06 by Eric S. Raymond <esr@thyrsus.com>
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.\" Modified 1997-08-21 by Joseph S. Myers <jsm28@cam.ac.uk>
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.\" Modified 2004-06-23 by Michael Kerrisk <mtk.manpages@gmail.com>
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.\"
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.TH CHROOT 2 2019-03-06 "Linux" "Linux Programmer's Manual"
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.SH NAME
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chroot \- change root directory
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.SH SYNOPSIS
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.B #include <unistd.h>
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.PP
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.BI "int chroot(const char *" path );
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.PP
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.in -4n
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Feature Test Macro Requirements for glibc (see
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.BR feature_test_macros (7)):
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.in
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.PP
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.BR chroot ():
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.ad l
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.RS 4
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.PD 0
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.TP 4
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Since glibc 2.2.2:
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.nf
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_XOPEN_SOURCE && ! (_POSIX_C_SOURCE\ >=\ 200112L)
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|| /* Since glibc 2.20: */ _DEFAULT_SOURCE
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|| /* Glibc versions <= 2.19: */ _BSD_SOURCE
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.TP 4
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Before glibc 2.2.2: none
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.PD
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.RE
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.ad b
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.SH DESCRIPTION
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.BR chroot ()
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changes the root directory of the calling process to that specified in
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.IR path .
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This directory will be used for pathnames beginning with \fI/\fP.
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The root directory is inherited by all children of the calling process.
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.PP
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Only a privileged process (Linux: one with the
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.B CAP_SYS_CHROOT
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capability in its user namespace) may call
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.BR chroot ().
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.PP
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This call changes an ingredient in the pathname resolution process
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and does nothing else.
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In particular, it is not intended to be used
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for any kind of security purpose, neither to fully sandbox a process nor
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to restrict filesystem system calls.
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In the past,
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.BR chroot ()
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has been used by daemons to restrict themselves prior to passing paths
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supplied by untrusted users to system calls such as
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.BR open (2).
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However, if a folder is moved out of the chroot directory, an attacker
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can exploit that to get out of the chroot directory as well.
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The easiest way to do that is to
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.BR chdir (2)
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to the to-be-moved directory, wait for it to be moved out, then open a
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path like ../../../etc/passwd.
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.PP
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.\" This is how the "slightly trickier variation" works:
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.\" https://github.com/QubesOS/qubes-secpack/blob/master/QSBs/qsb-014-2015.txt#L142
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A slightly
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trickier variation also works under some circumstances if
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.BR chdir (2)
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is not permitted.
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If a daemon allows a "chroot directory" to be specified,
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that usually means that if you want to prevent remote users from accessing
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files outside the chroot directory, you must ensure that folders are never
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moved out of it.
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.PP
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This call does not change the current working directory,
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so that after the call \(aq\fI.\fP\(aq can
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be outside the tree rooted at \(aq\fI/\fP\(aq.
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In particular, the superuser can escape from a "chroot jail"
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by doing:
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.PP
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.in +4n
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.EX
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mkdir foo; chroot foo; cd ..
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.EE
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.in
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.PP
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This call does not close open file descriptors, and such file
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descriptors may allow access to files outside the chroot tree.
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.SH RETURN VALUE
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On success, zero is returned.
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On error, \-1 is returned, and
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.I errno
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is set appropriately.
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.SH ERRORS
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Depending on the filesystem, other errors can be returned.
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The more general errors are listed below:
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.TP
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.B EACCES
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Search permission is denied on a component of the path prefix.
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(See also
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.BR path_resolution (7).)
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.\" Also search permission is required on the final component,
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.\" maybe just to guarantee that it is a directory?
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.TP
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.B EFAULT
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.I path
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points outside your accessible address space.
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.TP
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.B EIO
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An I/O error occurred.
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.TP
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.B ELOOP
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Too many symbolic links were encountered in resolving
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.IR path .
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.TP
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.B ENAMETOOLONG
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.I path
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is too long.
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.TP
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.B ENOENT
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The file does not exist.
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.TP
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.B ENOMEM
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Insufficient kernel memory was available.
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.TP
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.B ENOTDIR
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A component of
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.I path
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is not a directory.
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.TP
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.B EPERM
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The caller has insufficient privilege.
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.SH CONFORMING TO
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SVr4, 4.4BSD, SUSv2 (marked LEGACY).
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This function is not part of POSIX.1-2001.
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.\" SVr4 documents additional EINTR, ENOLINK and EMULTIHOP error conditions.
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.\" X/OPEN does not document EIO, ENOMEM or EFAULT error conditions.
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.SH NOTES
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A child process created via
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.BR fork (2)
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inherits its parent's root directory.
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The root directory is left unchanged by
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.BR execve (2).
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.PP
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The magic symbolic link,
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.IR /proc/[pid]/root ,
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can be used to discover a process's root directory; see
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.BR proc (5)
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for details.
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.PP
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FreeBSD has a stronger
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.BR jail ()
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system call.
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.SH SEE ALSO
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.BR chroot (1),
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.BR chdir (2),
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.BR pivot_root (2),
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.BR path_resolution (7),
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.BR switch_root (8)
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