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

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Message-ID: <4235.1219915184@redhat.com>
Date:	Thu, 28 Aug 2008 10:19:44 +0100
From:	David Howells <dhowells@...hat.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	dhowells@...hat.com, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org
Subject: Re: [PATCH 00/59] Introduce credentials

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.

David
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