netfilter: conntrack: avoid integer overflow when resizing

Can overflow so we might allocate very small table when bucket count is
high on a 32bit platform.

Note: resize is only possible from init_netns.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_conntrack_core.c

@@ -1601,8 +1601,15 @@ void *nf_ct_alloc_hashtable(unsigned int *sizep, int nulls)
 	unsigned int nr_slots, i;
 	size_t sz;
 
+	if (*sizep > (UINT_MAX / sizeof(struct hlist_nulls_head)))
+		return NULL;
+
 	BUILD_BUG_ON(sizeof(struct hlist_nulls_head) != sizeof(struct hlist_head));
 	nr_slots = *sizep = roundup(*sizep, PAGE_SIZE / sizeof(struct hlist_nulls_head));
+
+	if (nr_slots > (UINT_MAX / sizeof(struct hlist_nulls_head)))
+		return NULL;
+
 	sz = nr_slots * sizeof(struct hlist_nulls_head);
 	hash = (void *)__get_free_pages(GFP_KERNEL | __GFP_NOWARN | __GFP_ZERO,
 					get_order(sz));