Re: ip_set_hash_netiface

From: Daniel Xu
Date: Thu Oct 27 2022 - 05:07:19 EST


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@xxxxxxxxxxxxxxxxx, kadlecsik.jozsef@xxxxxxxxx
> 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