netfilter: nft_set_hash: fix lookups with fixed size hash on big endian

Call jhash_1word() for the 4-bytes key case from the insertion and
deactivation path, otherwise big endian arch set lookups fail.

Fixes: 446a8268b7 ("netfilter: nft_set_hash: add lookup variant for fixed size hashtable")
Reported-by: Florian Westphal <fw@strlen.de>
Tested-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nft_set_hash.c

@@ -474,6 +474,23 @@ static bool nft_hash_lookup_fast(const struct net *net,
 	return false;
 }
 
+static u32 nft_jhash(const struct nft_set *set, const struct nft_hash *priv,
+		     const struct nft_set_ext *ext)
+{
+	const struct nft_data *key = nft_set_ext_key(ext);
+	u32 hash, k1;
+
+	if (set->klen == 4) {
+		k1 = *(u32 *)key;
+		hash = jhash_1word(k1, priv->seed);
+	} else {
+		hash = jhash(key, set->klen, priv->seed);
+	}
+	hash = reciprocal_scale(hash, priv->buckets);
+
+	return hash;
+}
+
 static int nft_hash_insert(const struct net *net, const struct nft_set *set,
 			   const struct nft_set_elem *elem,
 			   struct nft_set_ext **ext)
@@ -483,8 +500,7 @@ static int nft_hash_insert(const struct net *net, const struct nft_set *set,
 	u8 genmask = nft_genmask_next(net);
 	u32 hash;
 
-	hash = jhash(nft_set_ext_key(&this->ext), set->klen, priv->seed);
-	hash = reciprocal_scale(hash, priv->buckets);
+	hash = nft_jhash(set, priv, &this->ext);
 	hlist_for_each_entry(he, &priv->table[hash], node) {
 		if (!memcmp(nft_set_ext_key(&this->ext),
 			    nft_set_ext_key(&he->ext), set->klen) &&
@@ -523,8 +539,7 @@ static void *nft_hash_deactivate(const struct net *net,
 	u8 genmask = nft_genmask_next(net);
 	u32 hash;
 
-	hash = jhash(nft_set_ext_key(&this->ext), set->klen, priv->seed);
-	hash = reciprocal_scale(hash, priv->buckets);
+	hash = nft_jhash(set, priv, &this->ext);
 	hlist_for_each_entry(he, &priv->table[hash], node) {
 		if (!memcmp(nft_set_ext_key(&this->ext), &elem->key.val,
 			    set->klen) &&