linux-kernel - Re: SMACK netfilter smacklabel socket match

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Date:	Wed, 01 Oct 2008 08:21:30 -0700
From:	Casey Schaufler <casey@...aufler-ca.com>
To:	Tilman Baumann <tilman.baumann@...lax.com>
CC:	Linux-Kernel <linux-kernel@...r.kernel.org>,
	linux-security-module@...r.kernel.org
Subject: Re: SMACK netfilter smacklabel socket match

Tilman Baumann wrote:
> Casey Schaufler wrote:
>>> Casey Schaufler wrote:
>> If you really want to be abusive you could replace the smack_access()
>> function in security/smack/smack_access.c (of all places) with a no-op
>> returning 0 in all cases.
>
> I thought of that too. :)
> But i would rather like to use the thing in it's intended function 
> sometime in the future.

Even better.

>>> What I then to is write iptables OUTPUT chain matches which match 
>>> for any of these labels and set some connection marks and firewall 
>>> marks.
>>> Which I then can use in routing rules to give different routing 
>>> rules to specific processes. (Like all proxy traffic over a second 
>>> DSL line)
>>>
>>> I know, it's totally crazy. But it seems to work. :)
>>> I just hope the security part of this all will not break anything. 
>>> But it does not look like it would right now.
>>
>> Smack will eventually bite you if you're not careful, but users of
>> MAC systems wouldn't be surprised by that.
> Speaking of the devil...
> This is exactly what happened to me right now. I have problems with 
> _some_ https connects. The problem lies somewhere in openssl.
> I did not yet find any clue with strace.
> Is there some straight forward way to audit/debug LSM interventions?

strace is probably your best bet, as it will tell you what syscalls
fail. Your current situation is most likely a case where your program
running with a label "Foo" is trying to communicate with a service on
a machine that doesn't talk CIPSO and hence Smack is treating all
packets to and from that host with the ambient (%cat /smack/ambient)
label, which is "_" unless you've changed it.

> I have probably missed something that a labeled process could not do 
> as a '_' process could. Have no idea right now, but it is probably 
> something stupidly simple.
>

A labeled system hoping to get services from an unlabeled server is the 
biggest
single pain in dealing with labeled systems. Per-host labeling is in the 
works,
and it will help in some cases. What I really need is a way to designate an
unlabeled host as safe to talk to at any label, but it will take some 
serious
work to come up with a scheme that makes that palatable for a labeled 
environment.
I know that SELinux allows for it, but the purist in me has serious doubts.

>> I don't think it's crazy,
>> I think it's a matter of using what's available in novel ways.
> I like that attitude. :)

It got me where I am today. Hmm, maybe you should be just a little bit 
careful.

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