netfilter: nft_set_pipapo: fix null deref for empty set

commit 30c1d25 upstream.

Blamed commit broke the check for a null scratch map:
  -  if (unlikely(!m || !*raw_cpu_ptr(m->scratch)))
  +  if (unlikely(!raw_cpu_ptr(m->scratch)))

This should have been "if (!*raw_ ...)".
Use the pattern of the avx2 version which is more readable.

This can only be reproduced if avx2 support isn't available.

Fixes: d8d871a ("netfilter: nft_set_pipapo: merge pipapo_get/lookup")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Florian Westphal

net/netfilter/nft_set_pipapo.c

@@ -426,10 +426,9 @@ static struct nft_pipapo_elem *pipapo_get(const struct nft_pipapo_match *m,
 
 	local_bh_disable();
 
-	if (unlikely(!raw_cpu_ptr(m->scratch)))
-		goto out;
-
 	scratch = *raw_cpu_ptr(m->scratch);
+	if (unlikely(!scratch))
+		goto out;
 
 	map_index = scratch->map_index;