netfilter: nft_hash: get random bytes if seed is not specified

If the user doesn't specify a seed, generate one at configuration time.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nft_hash.c

@@ -57,7 +57,6 @@ static int nft_hash_init(const struct nft_ctx *ctx,
 	if (!tb[NFTA_HASH_SREG] ||
 	    !tb[NFTA_HASH_DREG] ||
 	    !tb[NFTA_HASH_LEN]  ||
-	    !tb[NFTA_HASH_SEED] ||
 	    !tb[NFTA_HASH_MODULUS])
 		return -EINVAL;
 
@@ -80,7 +79,10 @@ static int nft_hash_init(const struct nft_ctx *ctx,
 	if (priv->offset + priv->modulus - 1 < priv->offset)
 		return -EOVERFLOW;
 
-	priv->seed = ntohl(nla_get_be32(tb[NFTA_HASH_SEED]));
+	if (tb[NFTA_HASH_SEED])
+		priv->seed = ntohl(nla_get_be32(tb[NFTA_HASH_SEED]));
+	else
+		get_random_bytes(&priv->seed, sizeof(priv->seed));
 
 	return nft_validate_register_load(priv->sreg, len) &&
 	       nft_validate_register_store(ctx, priv->dreg, NULL,