linux-kernel - Re: [PATCH 3/6] secmark: export binary yes/no rather than kernel internal secid

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Message-ID: <1285616748.4935.43.camel@sifl>
Date:	Mon, 27 Sep 2010 15:45:48 -0400
From:	Paul Moore <paul.moore@...com>
To:	Eric Paris <eparis@...hat.com>
Cc:	James Morris <jmorris@...ei.org>, linux-kernel@...r.kernel.org,
	selinux@...ho.nsa.gov, netfilter-devel@...r.kernel.org,
	sds@...ho.nsa.gov, jengelh@...ozas.de, casey@...aufler-ca.com,
	linux-security-module@...r.kernel.org, netfilter@...r.kernel.org,
	mr.dash.four@...glemail.com
Subject: Re: [PATCH 3/6] secmark: export binary yes/no rather than kernel
 internal secid

On Mon, 2010-09-27 at 15:25 -0400, Eric Paris wrote:
> On Mon, 2010-09-27 at 14:29 -0400, Paul Moore wrote:
> > On Mon, 2010-09-27 at 13:01 -0400, Eric Paris wrote:
> > > On Mon, 2010-09-27 at 10:50 +1000, James Morris wrote:
> > > > On Fri, 24 Sep 2010, Eric Paris wrote:
> > > 
> > > > For the reasons above, I think the secctx string needs to be exported in 
> > > > addition to this rather than instead of.
> > > 
> > > I won't argue, I don't agree with your reasoning, but I'm not opposed to
> > > this result.  We have 3 competing suggestions:
> > > 
> > > Jan suggested we:
> > > completely eliminate secmark from procfs+netlink and only export secctx
> > > in netlink.
> > > 
> > > Eric suggested we:
> > > completely eliminate secmark from procfs+netlink and then export secctx
> > > in procfs+netlink
> > > 
> > > sounds like James suggested we:
> > > continue to export meaningless and confusing secmark from procfs+netlink
> > > and then export secctx in procfs+netlink as well.
> > > 
> > > I'm going to implement James' idea and resend the patch series.  Any
> > > strong objections?
> > 
> > I apologize for not getting a chance to look at these patches sooner.
> > In general they look fine to me and my only real concern was addressed
> > by Pablo already (breaking userspace due to #define changes).
> > 
> > As far as exporting the 32bit secid/secmark to userspace, I think that
> > is a mistake.  James correctly points out that it does map to a LSM
> > specific value, e.g. SELinux and Smack security labels, but I don't
> > think he makes it clear that in the two LSMs that currently use secids
> > the mapping between the secid and the secctx is not constant; the secids
> > are transient values that will change with each boot in a manner that
> > userspace can not predict.  For this reason, I think exporting the
> > secids is only going to cause users/admins grief, whereas exporting the
> > associated secctx should be a much more stable value and is likely what
> > the user/admin is expecting anyway.
> 
> So it sounds to me like Paul agrees with me that exporting the SELinux
> sid as 'secmark=' was a bad idea.  It's the whole reason this thread
> started, someone wanted to be able to translate and use that field (and
> instantly realized it was useless.)
> 
> I see it as having 3 options.  lets assume was have a packet with
> selinux sid=121 and selinux context=packet_t.  We can
> 
> 1) secmark=121 secctx=packet_t
> 	This continues to send secmark like we do and people might continue to
> be baffled by the 121.
> 
> 2) secmark=1 secctx=packet_t
> 	This sends a secmark field to userspace so if an application which
> reads this exists (I doubt such an application actually exists in in the
> real world) it will still get all of the information it got before but
> noone will be baffled by what the number means.  1/0 is pretty obvious.
> 
> 3) secctx=packet_t
> 	Smallest easiest, what my patches actually do.  Could theoretically
> break some script that expected the field to be there, but any such
> script is already broken since that field can be easily compiled
> out......
> 
> James, if you are adamant about #1 I'll resend, otherwise I'm sticking
> with #3.....

James, if you do feel strongly about door #1, can you provide a good
example of how someone might use the secid to do something useful in
userspace?  I ask because I can't think of anything and it would be nice
to have the example on record for future work.

-- 
paul moore
linux @ hp


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