linux-kernel - Re: [PATCH 00/59] Introduce credentials

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Date:	Thu, 28 Aug 2008 10:45:03 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	David Howells <dhowells@...hat.com>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	dhowells@...hat.com, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org
Subject: Re: [PATCH 00/59] Introduce credentials

On Thu, 28 Aug 2008 10:19:44 +0100
David Howells <dhowells@...hat.com> wrote:

> Alan Cox <alan@...rguk.ukuu.org.uk> wrote:
> 
> > > We get a number of things:
> > > 
> > >  (1) Multiple credential changes all happen simultaneously (setresuid() for
> > >      example).  The new set of credentials is committed with a single RCU
> > >      assignment.
> > 
> > Makes sense - except for the question of bounding memory utilisation.
> 
> Would it make sense to call synchronise_rcu() from commit_creds() or from
> setuid()/setresuid()/setgroups()/etc. to make sure that some user process
> doing:
> 
> 	while (1)
> 		alter_credentials();
> 
> doesn't run the system out of memory by having loads of frees waiting in RCU's
> queues because put_cred() uses call_rcu() to defer the destruction.

I suspect you to - or every "nth" event - building up a small queue as
would occur in normal usage probably isn't a problem.
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