On Mon, Oct 23, 2000 at 12:26:07PM -0400, Jon Lindgren wrote:
> I finally have a spare sparc to use as a true firewall.  I'm planning to
> burn a CD for this sucker to boot from.  I don't want it to have local 
> mass storage (besides the cd...).
> 
> I've been looking around at regular processes which run and require
> temporary files, such as the daily security items, etc...  I figure I can
> knock syslog stuff to a remote machine, I'll be disabling mail and other
> audit scripts (hmmm....), but what about items such as /var/log/wtmp and
> such?
> 
> So the 1e6 dollar question is: does anyone have any ideas what other
> subsystems may be affected by having a r/o local filesystem when running
> multiuser?  I've been able to experiment for a few hours or so, but I've
> not run the thing for months yet...
> 
> Any ideas, tips, etc... are well appreciated.

If you intend to let users to log in, then you'll need a writeable /dev
too.
Here's what I've done for my sparc machines I use as telnet/ssh gateway:
/, /usr, /netroot and /tripwire are on a R/O filesystem (in my case a scsi
disk which have the appropriate jumper, but this shouldn't matter).
/netroot/home, /netroot/dev and /netroot/var are mounted R/W, noexec for all
and nodev for /netroot/home & /netroot/var (/netroot/dev is writable by
root ony anyway, and you can play with chflags to limit what can be done).
As you guessed, inetd & ssh are chrooted to /netroot.
/netroot has only a limited set of binaries (not mount, for example),
/netroot/dev a limited set of devices (tty/pty, zero, null, ... no disks of
course).

inside /var there are symlinks to /netroot/var for appropriate directories
(log, acct, run). /netroot/etc is a symlink to /netroot/var/netetc, so that
passwd, skey & all are writable.

BTW a local disk is usefull anyway, for logs & accounting.

--
Manuel Bouyer <bouyer@antioche.eu.org>
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