netdev - Re: [PATCH] Enhance AF_PACKET implementation to not require high order contiguous memory allocation (v2)

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Message-ID: <20101109205716.GB9990@hmsreliant.think-freely.org>
Date:	Tue, 9 Nov 2010 15:57:16 -0500
From:	Neil Horman <nhorman@...driver.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net, zenczykowski@...il.com
Subject: Re: [PATCH] Enhance AF_PACKET implementation to not require high
 order contiguous memory allocation (v2)

On Tue, Nov 09, 2010 at 08:20:38PM +0100, Eric Dumazet wrote:
> Le mardi 09 novembre 2010 à 13:38 -0500, Neil Horman a écrit :
> > On Tue, Nov 09, 2010 at 07:02:32PM +0100, Eric Dumazet wrote:
> > > Le mardi 09 novembre 2010 à 12:46 -0500, nhorman@...driver.com a écrit :
> > ic char **alloc_pg_vec(struct tpacket_req *req, int order)
> > > > +static struct pgv *alloc_pg_vec(struct tpacket_req *req, int order)
> > > >  {
> > > >  	unsigned int block_nr = req->tp_block_nr;
> > > > -	char **pg_vec;
> > > > +	struct pgv *pg_vec;
> > > >  	int i;
> > > >  
> > > > -	pg_vec = kzalloc(block_nr * sizeof(char *), GFP_KERNEL);
> > > > +	pg_vec = kzalloc(block_nr * sizeof(struct pgv), GFP_KERNEL);
> > > 
> > > While we are at it, we could check block_nr being a sane value here ;)
> > > 
> > This is true.  What do you think a reasonable sane value is?  libpcap seems to
> > limit itself to 32 order 5 entries in the ring, but that seems a bit arbitrary.
> > Perhaps we could check and limit allocations to being no more than order 8
> > (1Mb), and a total allocation of no more than perhaps max(32Mb, 1% of all ram)?
> > Just throwing it out there, open to any suggestions here
> 
> I was refering to a malicious/buggy program giving a big tp_block_nr so
> that (block_nr * sizeof(struct pgv)) overflows the u32
> 
> One way to deal with that is to use
> 
> 	kcalloc(block_nr, sizeof(struct pgv), GFP_KERNEL);
> 
> I am not sure consistency checks done in packet_set_ring() are enough to
> properly detect such errors.
Ah, I get you, ok.  Yeah, I'll respin this with that taken into account.
Thanks!
Neil

> 
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