netfilter: nft_set_pipapo: allocate pcpu scratch maps on clone

This is needed in case a new transaction is made that doesn't insert any
new elements into an already existing set.

Else, after second 'nft -f ruleset.txt', lookups in such a set will fail
because ->lookup() encounters raw_cpu_ptr(m->scratch) == NULL.

For the initial rule load, insertion of elements takes care of the
allocation, but for rule reloads this isn't guaranteed: we might not
have additions to the set.

Fixes: 3c4287f62044a90e ("nf_tables: Add set type for arbitrary concatenation of ranges")
Reported-by: etkaar <[e-mail]>
Signed-off-by: Florian Westphal <[e-mail]>
Reviewed-by: Stefano Brivio <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

net/netfilter/nft_set_pipapo.c

···
 	if (!new->scratch_aligned)
 		goto out_scratch;
 #endif
+	for_each_possible_cpu(i)
+		*per_cpu_ptr(new->scratch, i) = NULL;
+
+	if (pipapo_realloc_scratch(new, old->bsize_max))
+		goto out_scratch_realloc;
 
 	rcu_head_init(&new->rcu);
 
···
 		kvfree(dst->lt);
 		dst--;
 	}
+out_scratch_realloc:
+	for_each_possible_cpu(i)
+		kfree(*per_cpu_ptr(new->scratch, i));
 #ifdef NFT_PIPAPO_ALIGN
 	free_percpu(new->scratch_aligned);
 #endif