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

[Eric Dumazet <eric.dumazet@gmail.com>]

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@tuxdriver.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.