netfilter: ipset: enforce documented limit to prevent allocating huge memory

Daniel Xu reported that the hash:net,iface type of the ipset subsystem does
not limit adding the same network with different interfaces to a set, which
can lead to huge memory usage or allocation failure.

The quick reproducer is

$ 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

The backtrace when vmalloc fails:

        [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
        <...>

The fix is to enforce the limit documented in the ipset(8) manpage:

>  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.

Fixes: ccf0a4b7 ("netfilter: ipset: Add bucketsize parameter to all hash types")
Reported-by: Daniel Xu <dxu@dxuuu.xyz>
Signed-off-by: Jozsef Kadlecsik <kadlec@netfilter.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/ipset/ip_set_hash_gen.h

@@ -42,31 +42,8 @@
 #define AHASH_MAX_SIZE			(6 * AHASH_INIT_SIZE)
 /* Max muber of elements in the array block when tuned */
 #define AHASH_MAX_TUNED			64
-
 #define AHASH_MAX(h)			((h)->bucketsize)
 
-/* Max number of elements can be tuned */
-#ifdef IP_SET_HASH_WITH_MULTI
-static u8
-tune_bucketsize(u8 curr, u32 multi)
-{
-	u32 n;
-
-	if (multi < curr)
-		return curr;
-
-	n = curr + AHASH_INIT_SIZE;
-	/* Currently, at listing one hash bucket must fit into a message.
-	 * Therefore we have a hard limit here.
-	 */
-	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 */
 struct hbucket {
 	struct rcu_head rcu;	/* for call_rcu */
@@ -936,7 +913,12 @@ 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;
+		else if (h->bucketsize < multi)
+			h->bucketsize += AHASH_INIT_SIZE;
+#endif
 		if (n->size >= AHASH_MAX(h)) {
 			/* Trigger rehashing */
 			mtype_data_next(&h->next, d);