netfilter: nft_set_pipapo: do not rely on ZERO_SIZE_PTR

pipapo relies on kmalloc(0) returning ZERO_SIZE_PTR (i.e., not NULL
but pointer is invalid).

Rework this to not call slab allocator when we'd request a 0-byte
allocation.
Reviewed-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: Florian Westphal <fw@strlen.de>

net/netfilter/nft_set_pipapo.c

@@ -525,6 +525,8 @@ static struct nft_pipapo_elem *pipapo_get(const struct net *net,
 	int i;
 
 	m = priv->clone;
+	if (m->bsize_max == 0)
+		return ret;
 
 	res_map = kmalloc_array(m->bsize_max, sizeof(*res_map), GFP_ATOMIC);
 	if (!res_map) {
@@ -1367,11 +1369,17 @@ static struct nft_pipapo_match *pipapo_clone(struct nft_pipapo_match *old)
 		       src->bsize * sizeof(*dst->lt) *
 		       src->groups * NFT_PIPAPO_BUCKETS(src->bb));
 
-		dst->mt = kvmalloc(src->rules * sizeof(*src->mt), GFP_KERNEL);
-		if (!dst->mt)
-			goto out_mt;
+		if (src->rules > 0) {
+			dst->mt = kvmalloc_array(src->rules, sizeof(*src->mt),
+						 GFP_KERNEL);
+			if (!dst->mt)
+				goto out_mt;
+
+			memcpy(dst->mt, src->mt, src->rules * sizeof(*src->mt));
+		} else {
+			dst->mt = NULL;
+		}
 
-		memcpy(dst->mt, src->mt, src->rules * sizeof(*src->mt));
 		src++;
 		dst++;
 	}