This Implements the mumbled about "Jail" feature.

This is a seriously beefed up chroot kind of thing.  The process
is jailed along the same lines as a chroot does it, but with
additional tough restrictions imposed on what the superuser can do.

For all I know, it is safe to hand over the root bit inside a
prison to the customer living in that prison, this is what
it was developed for in fact:  "real virtual servers".

Each prison has an ip number associated with it, which all IP
communications will be coerced to use and each prison has its own
hostname.

Needless to say, you need more RAM this way, but the advantage is
that each customer can run their own particular version of apache
and not stomp on the toes of their neighbors.

It generally does what one would expect, but setting up a jail
still takes a little knowledge.

A few notes:

   I have no scripts for setting up a jail, don't ask me for them.

   The IP number should be an alias on one of the interfaces.

   mount a /proc in each jail, it will make ps more useable.

   /proc/<pid>/status tells the hostname of the prison for
   jailed processes.

   Quotas are only sensible if you have a mountpoint per prison.

   There are no privisions for stopping resource-hogging.

   Some "#ifdef INET" and similar may be missing (send patches!)

If somebody wants to take it from here and develop it into
more of a "virtual machine" they should be most welcome!

Tools, comments, patches & documentation most welcome.

Have fun...

Sponsored by:   http://www.rndassociates.com/
Run for almost a year by:       http://www.servetheweb.com/

1 files changed, 87 insertions, 0 deletions

diff --git a/lib/libc/sys/jail.2 b/lib/libc/sys/jail.2
new file mode 100644
index 000000000000..0fe73989c163
--- /dev/null
+++ b/lib/libc/sys/jail.2
@@ -0,0 +1,87 @@
+.\"
+.\"----------------------------------------------------------------------------
+.\""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
+.\"----------------------------------------------------------------------------
+.\"
+.\"$Id: malloc.c,v 1.44 1999/03/28 14:16:05 phk Exp $
+.\"
+.\"
+.Dd April 28, 1999
+.Dt JAIL 2
+.Os FreeBSD 4.0
+.Sh NAME
+.Nm jail
+.Nd Imprison current process and future decendants.
+.Sh SYNOPSIS
+.Fd #include <sys/types.h>
+.Fd #include <sys/jail.h>
+.Ft int
+.Fn jail "struct *jail"
+.Sh DESCRIPTION
+The
+.Nm
+system call sets up a jail and locks the current process in it.
+.Pp
+The argument is a pointer to a structure describing the prison:
+.Bd -literal -offset indent
+struct jail {
+        char *path;
+        char *hostname;
+        u_int32_t ip_number;
+};
+.Ed
+.Pp
+The
+.Dq Li path
+pointer should be set to the directory which is to be the root of the
+prison.
+.Pp
+The
+.Dq Li hostname
+pointer can be set the hostname of the prison.  This can be changed
+from the inside of the prison.
+.Pp
+The
+.Dq Li ip_number
+can be set to the IP number assigned to the prison.
+.Sh PRISON ?
+Once a process has been put in a prison, it and its decendants cannot escape
+the prison.  It is not possible to add a process to a preexisting prison.
+.Pp
+Inside the prison, the concept of "superuser" is very diluted, in general
+it can be assumed that nothing can be mangled from inside a prison, that
+doesn't exist inside that prison (ie: the directory tree below
+.Dq Li path .
+.Pp
+All IP activity will be forced to happen to/from the IP number specified,
+which should be an alias on one of the systems interfaces.
+.Pp
+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
+.Fn Jail
+calls
+.Xr chroot 2
+internally, so the it can fail for all the same reasons.
+Please consult the
+.Xr chroot 2
+manual page for details.
+.Sh SEE ALSO
+.Xr chroot 2
+.Xr chdir 2
+.Sh HISTORY
+The
+.Fn jail
+function call appeared in
+.Fx 4.0 .
+.Pp
+The jail feature was written by Poul-Henning Kamp for
+R&D Associates
+.Dq Li http://www.rndassociates.com/
+who contributed it to FreeBSD.