netdev - RE: [PATCH 1/4] netfilter: ipset: fix timeout value overflow bug

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Date:	Tue, 15 May 2012 09:21:04 +0100
From:	"David Laight" <David.Laight@...LAB.COM>
To:	"Eric Dumazet" <eric.dumazet@...il.com>,
	"Pablo Neira Ayuso" <pablo@...filter.org>
Cc:	<netfilter-devel@...r.kernel.org>, <davem@...emloft.net>,
	<netdev@...r.kernel.org>,
	"Jozsef Kadlecsik" <kadlec@...ckhole.kfki.hu>
Subject: RE: [PATCH 1/4] netfilter: ipset: fix timeout value overflow bug

 

> -----Original Message-----
> From: Eric Dumazet [mailto:eric.dumazet@...il.com] 
> Sent: 14 May 2012 15:47
> To: Pablo Neira Ayuso
> Cc: David Laight; netfilter-devel@...r.kernel.org; 
> davem@...emloft.net; netdev@...r.kernel.org; Jozsef Kadlecsik
> Subject: Re: [PATCH 1/4] netfilter: ipset: fix timeout value 
> overflow bug
> 
> On Mon, 2012-05-14 at 16:36 +0200, Pablo Neira Ayuso wrote:
> > On Mon, May 14, 2012 at 03:19:49PM +0100, David Laight wrote:
> > >  
> > > > --- a/include/linux/netfilter/ipset/ip_set_timeout.h
> > > > +++ b/include/linux/netfilter/ipset/ip_set_timeout.h
> > > > @@ -30,6 +30,10 @@ ip_set_timeout_uget(struct nlattr *tb)
> > > >  {
> > > >  	unsigned int timeout = ip_set_get_h32(tb);
> > > >  
> > > > +	/* Normalize to fit into jiffies */
> > > > +	if (timeout > UINT_MAX/1000)
> > > > +		timeout = UINT_MAX/1000;
> > > > +
> > > 
> > > Doesn't that rather assume that HZ is 1000 ?
> > 
> > Indeed. I overlooked that. Thanks David.
> 
> I dont think so.
> 
> 1000 here is really MSEC_PER_SEC

I was just reading the comment above - which seemed to imply
the purpose of the code was to ensure the timeout wouldn't
exceeded 2^32 jiffies.

I tend to use variable names for timeouts/timestamps that
include the units - can make it more obvious when a divisor
is absent - and makes it more obvious what the literal
constants are converying beween.
After all, the number of milliseconds in a second isn't
subject to change :-)

	David


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