netdev - Re: [PATCH] Security: Implement and document RLIMIT

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Date:	Wed, 7 Jan 2009 22:39:30 +0300
From:	Evgeniy Polyakov <zbr@...emap.net>
To:	"C. Scott Ananian" <cscott@...top.org>
Cc:	Michael Stone <michael@...top.org>, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH] Security: Implement and document RLIMIT_NETWORK.

On Wed, Jan 07, 2009 at 10:02:30PM +0300, Evgeniy Polyakov (zbr@...emap.net) wrote:
> > I haven't reviewed the patch to confirm this, but this is how I would
> > expect RLIMIT_NETWORK functions.  A trusted process like inetd (say)
> > would accept a network connection and create a file handle.  It would
> > then fork, drop the hard and soft RLIMIT_NETWORK to 0, and then exec
> > the untrusted client program.  This would allow the untrusted program
> > to use the 'trusted' network resource via the open file handle, but
> > prevent it from (say) leaking sensitive transaction data by making
> > further connections to some other network resource.  (There are better
> > use cases than inetd, of course.)
> 
> So effectively it requires higher-prio process to set the limit and then
> drop own priviledges. And by default network rlimit is turned off, so
> this does not work for usual processes?

More on this: patch operates with rlim_cur, which can be set and cleared
without checking the permissions at all, so process is allowed to set it
to 1, which means disabling all sendmsg calls except for unix sockets,
but then the same (or child) process is allowed to set rlim_cur to zero.

Setting rlim_max to be higher than it is requires CAP_SYS_RESOURCE
capabilities.

-- 
	Evgeniy Polyakov
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