Re: Securing my machine

[Alexander Economou <aecon@gnet.gr>]

Quoting Benjamin Walkenhorst <krylon@gmx.net>:

> Hello everybody,
> 
> I use Slackware 9.1 on my desktop-machine. I do so quite happily, it 
> took only a week for Slackware to become my new primary OS. =)
> 
> I connect to the internet through a small server/gateway running 
> NetBSD-1.6.1. The gateway connects to my ISP via ISDN-dial-up 
> connection.
> The NetBSD-machine runs ipf (NetBSD's packet filter, roughly equivalent 
> to iptables) and IPNAT. 
> 
> I run gtk-gnutella on my desktop-machine from time to time. Since I want 
> others to be able to connect to my machine (also, for getting 
> push-connections), I decided to forward the corresponding port to my 
> Linux-machine.
> This has even shown to work fine, thanks. =)
> 
> But I am getting a little concerned about letting others connect to my 
> machine. Since my desktop-machine is behind a firewall, also since I am 
> the only user on my home-network, I did not exactly take care to secure 
> my Linux-machine. 
> Now I am getting worried someone might break into my machine via 
> GNUtella. I don't think gtk-gnutella was written with security in 
> mind...
> 
> So I want to tighten the security on my Linux machine in a way that 
> includes minimal inconvenience. Of course, I am going to start with all 
> the usual stuff, like installing tripwire, shutting down unneeded 
> services (in fact, I do this by default after installation), taking 
> care of file-permissions, cleaning up unneeded suid/sgid-bits, and so 
> on.
> 
> But then I read, most of all network-attacks are done via 
> buffer-overflows, so this is what I am most concerned about. I hear, 
> there's basically two ways of handling this problem:
> - Using MAC/RBAC for controlling the ressources an application can
>   access - if it's getting compromised, it won't be able to harm the 
>   system (seLinux).
> - Preventing buffer-overflows in the first place. There's several
>   options how to achieve this, the most important are a) applying
>   patches to the kernel (PaX, grSecurity) or to the GNU C Compiler
>   (ProPolice)
> 
> In general, preventing buffer-overflows at all seems preferrable to me, 
> since it does not seem to require that much work. Also, this is they 
> way the OpenBSD-project has been going, and OpenBSD surely has a 
> reputation for first-class security.
> So I got several questions:
> - Has anyone worked with these system-add-ons? Got any experiences to
>   share with me?
> - ProPolice sounds nice. But using it would require lots of 
>   recompiling... What exactly do I have to recompile in order to benefit
>   from it? Just the application in question? The libraries, too? The 
>   kernel? The entire system?
>   I am going to evaluate CRUX and Gentoo on my desktop-machine, both of 
>   which offer the option of recompiling the entire system. If I choose 
>   to use one of these as my primary system, recompiling won't be a 
>   problem, any more. As of now, it is, if system libraries or even the 
>   base system are involved.
> - PaX/grSecurity sound really sweet. But I see on the homepages, there
>   are patches available only for linux-kernels 2.4.22. Is 2.6 going to 
>   be supported in the near future?
>   I am using 2.6.0-test8 right now, and I am rather happy with it, so I
>   would like to keep using 2.6, once the final version is out. 
>   On the other hand, I can switch back to 2.4.22 if PaX/grSecurity
>   offers serious protection. 
>   And a lot of grSec's features sound really neat. =) Right now, this
>   sounds like the best way to secure my machine, since it invloves only 
>   minimal setup, just patching and recompiling the kernel, while
>   increasing system-security drastically. If I got things right, that
>   is...
> - MAC/RBAC does not really sound like I need it. Then again, more
>   security never hurts.
>   But this also sounds like it is going to be a lot of learning plus a
>   lot of effort to get it working. Furthermore, the corresponding
>   kernel-patch is developed at the NSA, and I do not exactly trust the
>   NSA to contribute to my privacy.
>   In order for M/RB-AC to be really useful, I'm afraid, you have to take
>   a lot of time to set it up correctly. And, as I said, I do not know
>   terribly much about this topic. 
>   If I get things right, seLinux and grSecurity are not mutually
>   exclusive.
> 
> So, in general, any information will be appreciated. If there are 
> further promising ways of protecting my system against 
> buffer-overflows, I would like to know, as well.
> Of course, I like to read a lot, so any hints on where to look for 
> information will be appreciated as well (if there's something 
> useful/interesting to read, there). 
> I am aware of pageexec.virtualave.net (PaX's homepage) and 
> grsecurity.net, as well as the NSA's seLinux-page.
> Anything I missed? Anything I should know?
> 
> Thank you very much in advance,
> 
> Kind regards,
> 
> Benjamin Walkenhorst
> 
> -- 
> Benjamin Walkenhorst
> eMail: krylon@gmx.net
> http://www.krylon.de
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I would suggest you should try libsafe and Wolk. You can find libsafe @
freshmeat.net and wolk @ sf.net