freebsd-dev/share/examples/portal

$FreeBSD$

This contains a couple of examples for using the portal filing system.

The portal file system provides a way of obtaining a file descriptor
to a filesystem object (i.e. something that is accessed by open(2),
pipe(2), socket(2) or socketpair(2)) via the filesystem namespace.
At present the only file descriptor supported are TCP sockets and
files.

NOTE!!!! The portal file system is experimental in nature and should
not be considered secure, use with caution.

First off mount the filesystem using something like:

# mount_portalfs /usr/share/examples/portal/portal.conf /p

Then you should be able to do things like
# cat /p/tcp/localhost/daytime
Sun Nov 22 17:50:09 1998
(assuming inetd is running the daytime service, by default it is off)

Welcome to FreeBSD!

# mkdir -p /tmp/root
# cd /tmp/root
# mkdir bin p
# cp /bin/sh /bin/cat bin
# mount_portalfs /usr/share/examples/portal/portal.conf /tmp/root/p
# chroot /tmp/root
# pwd
/
# echo *
bin p
# cat /etc/motd
cat: /etc/motd: No such file or directory
# cat /p/fs/etc/motd
FreeBSD 2.2.6-RELEASE (COMPUTER) #0: Sat Aug 22 17:11:37 BST 1998

Welcome to FreeBSD!

Finally, a very simple example of the listening server is available,
fire up two xterms. In the first

xterm-1$ cat /p/tcplisten/ANY/6666
(the ANY is a wildcard just like using INADDR_ANY, any resolvable host
can be used).

In the second xterm
xterm-2$ echo "hello there" >/p/tcp/localhost/6666

You should see the "hello there" string appear on the first terminal.

Unprivilged users can't create servers on privalged ports.
xterm-1$ cat /p/tcplisten/ANY/666
cat: /p/tcplisten/ANY/666: Operation not permitted

but root can
xterm-1# cat /p/tcplisten/ANY/666

In the second
xterm-2$ echo "hello there" >/p/tcp/localhost/666
should produce the expected response.

You can also swap the client/server read and write commands etc.