a40cf4175c
This builds on recently introduced NO_NEW_PRIVS flag to implement unprivileged chroot, enabled by `security.bsd.unprivileged_chroot`. It allows non-root processes to chroot(2), provided they have the NO_NEW_PRIVS flag set. The chroot(8) utility gets a new flag, -n, which sets NO_NEW_PRIVS before chrooting. Reviewed By: kib Sponsored By: EPSRC Relnotes: yes Differential Revision: https://reviews.freebsd.org/D30130
130 lines
3.6 KiB
Groff
130 lines
3.6 KiB
Groff
.\" Copyright (c) 1988, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)chroot.8 8.1 (Berkeley) 6/9/93
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.\" $FreeBSD$
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.\"
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.Dd July 20, 2021
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.Dt CHROOT 8
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.Os
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.Sh NAME
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.Nm chroot
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.Nd change root directory
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.Sh SYNOPSIS
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.Nm
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.Op Fl G Ar group Ns Op Cm \&, Ns Ar group ...
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.Op Fl g Ar group
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.Op Fl u Ar user
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.Op Fl n
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.Ar newroot
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.Op Ar command Op Ar arg ...
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.Sh DESCRIPTION
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The
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.Nm
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utility changes its current and root directories to the supplied directory
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.Ar newroot
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and then exec's
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.Ar command
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with provided arguments, if supplied,
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or an interactive copy of the user's login shell.
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.Pp
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The options are as follows:
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.Bl -tag -width "-G group[,group ...]"
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.It Fl G Ar group Ns Op Cm \&, Ns Ar group ...
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Run the command with the permissions of the specified groups.
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.It Fl g Ar group
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Run the command with the permissions of the specified
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.Ar group .
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.It Fl u Ar user
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Run the command as the
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.Ar user .
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.It Fl n
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Use the
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.Dv PROC_NO_NEW_PRIVS_CTL
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.Xr procctl 2
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command before chrooting, effectively disabling SUID/SGID bits
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for the calling process and its descendants.
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If
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.Dv security.bsd.unprivileged_chroot
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sysctl is set to 1, it will make it possible to chroot without
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superuser privileges.
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.El
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.Sh ENVIRONMENT
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The following environment variable is referenced by
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.Nm :
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.Bl -tag -width "SHELL"
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.It Ev SHELL
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If set,
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the string specified by
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.Ev SHELL
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is interpreted as the name of
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the shell to exec.
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If the variable
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.Ev SHELL
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is not set,
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.Pa /bin/sh
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is used.
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.El
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.Sh EXAMPLES
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.Bl -tag -width 0n
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.It Sy Example 1\&: No Chrooting into a New Root Directory
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.Pp
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The following command opens the
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.Xr csh 1
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shell after chrooting to the standard root directory.
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.Bd -literal -offset 2n
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.Li # Ic chroot / /bin/csh
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.Ed
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.It Sy Example 2\&: No Execution of a Command with a Changed Root Directory
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.Pp
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The following command changes a root directory with
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.Nm
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and then runs
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.Xr ls 1
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to list the contents of
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.Pa /sbin .
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.Bd -literal -offset 2n
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.Li # Ic chroot /tmp/testroot ls /sbin
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.Ed
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.El
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.Sh SEE ALSO
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.Xr chdir 2 ,
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.Xr chroot 2 ,
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.Xr setgid 2 ,
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.Xr setgroups 2 ,
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.Xr setuid 2 ,
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.Xr getgrnam 3 ,
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.Xr environ 7 ,
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.Xr jail 8
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.Sh HISTORY
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The
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.Nm
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utility first appeared in
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.At III
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and
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.Bx 4.3 Reno .
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