netdev - Re: ip_set_hash

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Date:   Thu, 27 Oct 2022 03:06:55 -0600
From:   Daniel Xu <dxu@...uu.xyz>
To:     Jozsef Kadlecsik <kadlec@...filter.org>
Cc:     Pablo Neira Ayuso <pablo@...filter.org>,
        Florian Westphal <fw@...len.de>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        ppenkov@...atrix.com
Subject: Re: ip_set_hash_netiface

Hi Jozsef,

On Wed, Oct 26, 2022 at 02:26:08PM +0200, Jozsef Kadlecsik wrote:
> Hi Daniel,
> 
> On Tue, 25 Oct 2022, Daniel Xu wrote:
> 
> > I'm following up with our hallway chat yesterday about how ipset 
> > hash:net,iface can easily OOM.
> > 
> > Here's a quick reproducer (stolen from
> > https://bugzilla.kernel.org/show_bug.cgi?id=199107):
> > 
> >         $ ipset create ACL.IN.ALL_PERMIT hash:net,iface hashsize 1048576 timeout 0
> >         $ for i in $(seq 0 100); do /sbin/ipset add ACL.IN.ALL_PERMIT 0.0.0.0/0,kaf_$i timeout 0 -exist; done
> > 
> > This used to cause a NULL ptr deref panic before
> > https://github.com/torvalds/linux/commit/2b33d6ffa9e38f344418976b06 .
> > 
> > Now it'll either allocate a huge amount of memory or fail a
> > vmalloc():
> > 
> >         [Tue Oct 25 00:13:08 2022] ipset: vmalloc error: size 1073741848, exceeds total pages
> >         <...>
> >         [Tue Oct 25 00:13:08 2022] Call Trace:
> >         [Tue Oct 25 00:13:08 2022]  <TASK>
> >         [Tue Oct 25 00:13:08 2022]  dump_stack_lvl+0x48/0x60
> >         [Tue Oct 25 00:13:08 2022]  warn_alloc+0x155/0x180
> >         [Tue Oct 25 00:13:08 2022]  __vmalloc_node_range+0x72a/0x760
> >         [Tue Oct 25 00:13:08 2022]  ? hash_netiface4_add+0x7c0/0xb20
> >         [Tue Oct 25 00:13:08 2022]  ? __kmalloc_large_node+0x4a/0x90
> >         [Tue Oct 25 00:13:08 2022]  kvmalloc_node+0xa6/0xd0
> >         [Tue Oct 25 00:13:08 2022]  ? hash_netiface4_resize+0x99/0x710
> >         <...>
> > 
> > Note that this behavior is somewhat documented
> > (https://ipset.netfilter.org/ipset.man.html):
> > 
> > >  The internal restriction of the hash:net,iface set type is that the same
> > >  network prefix cannot be stored with more than 64 different interfaces
> > >  in a single set.
> > 
> > I'm not sure how hard it would be to enforce a limit, but I think it would
> > be a bit better to error than allocate many GBs of memory.
> 
> That's a bug, actually the limit is not enforced in spite of the 
> documentation. The next patch fixes it and I'm going to submit to Pablo:
> 
> diff --git a/net/netfilter/ipset/ip_set_hash_gen.h b/net/netfilter/ipset/ip_set_hash_gen.h
> index 6e391308431d..3f8853ed32e9 100644
> --- a/net/netfilter/ipset/ip_set_hash_gen.h
> +++ b/net/netfilter/ipset/ip_set_hash_gen.h
> @@ -61,10 +61,6 @@ tune_bucketsize(u8 curr, u32 multi)
>  	 */
>  	return n > curr && n <= AHASH_MAX_TUNED ? n : curr;
>  }
> -#define TUNE_BUCKETSIZE(h, multi)	\
> -	((h)->bucketsize = tune_bucketsize((h)->bucketsize, multi))
> -#else
> -#define TUNE_BUCKETSIZE(h, multi)
>  #endif
>  
>  /* A hash bucket */
> @@ -936,7 +932,11 @@ mtype_add(struct ip_set *set, void *value, const struct ip_set_ext *ext,
>  		goto set_full;
>  	/* Create a new slot */
>  	if (n->pos >= n->size) {
> -		TUNE_BUCKETSIZE(h, multi);
> +#ifdef IP_SET_HASH_WITH_MULTI
> +		if (h->bucketsize >= AHASH_MAX_TUNED)
> +			goto set_full;
> +		h->bucketsize = tune_bucketsize(h->bucketsize, multi);
> +#endif
>  		if (n->size >= AHASH_MAX(h)) {
>  			/* Trigger rehashing */
>  			mtype_data_next(&h->next, d);
> 
> Best regards,
> Jozsef
> -
> E-mail  : kadlec@...ckhole.kfki.hu, kadlecsik.jozsef@...ner.hu
> PGP key : https://wigner.hu/~kadlec/pgp_public_key.txt
> Address : Wigner Research Centre for Physics
>           H-1525 Budapest 114, POB. 49, Hungary

Thank you!

Daniel