Re: ip_set_hash_netiface

From: Jozsef Kadlecsik
Date: Wed Oct 26 2022 - 08:35:58 EST


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
-
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