jail.2 revision 185435 

 ----------------------------------------------------------------------------
 "THE BEER-WARE LICENSE" (Revision 42):
 <phk@FreeBSD.ORG> wrote this file. As long as you retain this notice you
 can do whatever you want with this stuff. If we meet some day, and you think
 this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp
 ----------------------------------------------------------------------------

 $FreeBSD: head/lib/libc/sys/jail.2 185435 2008-11-29 14:32:14Z bz $

.Dd November 29, 2008
.Dt JAIL 2
.Os
.Sh NAME
.Nm jail , jail_attach
.Nd imprison current process and future descendants
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
n sys/param.h n sys/jail.h .Ft int
.Fn jail "struct jail *jail"
.Ft int
.Fn jail_attach "int jid"
.Sh DESCRIPTION
The
.Fn jail
system call sets up a jail and locks the current process in it.

p
The argument is a pointer to a structure describing the prison:
d -literal -offset indent struct jail {
 u_int32_t version;
 char *path;
 char *hostname;
 char *jailname;
 unsigned int ip4s;
 unsigned int ip6s;
 struct in_addr *ip4;
 struct in6_addr *ip6;
};
.Ed

p
.Dq Li version
defines the version of the API in use.
.Dv JAIL_API_VERSION
is defined for the current version.

p
The
.Dq Li path
pointer should be set to the directory which is to be the root of the
prison.

p
The
.Dq Li hostname
pointer can be set to the hostname of the prison.
This can be changed
from the inside of the prison.

p
The
.Dq Li jailname
pointer is an optional name that can be assigned to the jail
for example for managment purposes.

p
The
.Dq Li ip4s
and
.Dq Li ip6s
give the numbers of IPv4 and IPv6 addresses that will be passed
via their respective pointers.

p
The
.Dq Li ip4
and
.Dq Li ip6
pointers can be set to an arrays of IPv4 and IPv6 addresses to be assigned to
the prison, or NULL if none.
IPv4 addresses must be in network byte order.

p
The
.Fn jail_attach
system call attaches the current process to an existing jail,
identified by
.Fa jid .
.Sh RETURN VALUES
If successful,
.Fn jail
returns a non-negative integer, termed the jail identifier (JID).
It returns -1 on failure, and sets
.Va errno
to indicate the error.

p
.Rv -std jail_attach
.Sh PRISON?
Once a process has been put in a prison, it and its descendants cannot escape
the prison.

p
Inside the prison, the concept of
.Dq superuser
is very diluted.
In general,
it can be assumed that nothing can be mangled from inside a prison which
does not exist entirely inside that prison.
For instance the directory
tree below
.Dq Li path
can be manipulated all the ways a root can normally do it, including
.Dq Li "rm -rf /*"
but new device special nodes cannot be created because they reference
shared resources (the device drivers in the kernel).
The effective
.Dq securelevel
for a process is the greater of the global
.Dq securelevel
or, if present, the per-jail
.Dq securelevel .

p
All IP activity will be forced to happen to/from the IP number specified,
which should be an alias on one of the network interfaces.

p
It is possible to identify a process as jailed by examining
.Dq Li /proc/<pid>/status :
it will show a field near the end of the line, either as
a single hyphen for a process at large, or the hostname currently
set for the prison for jailed processes.
.Sh ERRORS
The
.Fn jail
system call
will fail if:
l -tag -width Er t Bq Er EINVAL The version number of the argument is not correct.
t Bq Er EAGAIN No free JID could be found.
.El

p
Further
.Fn jail
calls
.Xr chroot 2
internally, so it can fail for all the same reasons.
Please consult the
.Xr chroot 2
manual page for details.
.Sh SEE ALSO
.Xr chdir 2 ,
.Xr chroot 2
.Sh HISTORY
The
.Fn jail
system call appeared in
.Fx 4.0 .
The
.Fn jail_attach
system call appeared in
.Fx 5.1 .
.Sh AUTHORS
The jail feature was written by
.An Poul-Henning Kamp
for R&D Associates
.Dq Li http://www.rndassociates.com/
who contributed it to
.Fx .