netfilter: nft_tunnel: ERSPAN_VERSION must not be null

Fixes: af308b94 ("netfilter: nf_tables: add tunnel support")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nft_tunnel.c

@@ -266,6 +266,9 @@ static int nft_tunnel_obj_erspan_init(const struct nlattr *attr,
 	if (err < 0)
 		return err;
 
+	if (!tb[NFTA_TUNNEL_KEY_ERSPAN_VERSION])
+		 return -EINVAL;
+
 	version = ntohl(nla_get_be32(tb[NFTA_TUNNEL_KEY_ERSPAN_VERSION]));
 	switch (version) {
 	case ERSPAN_VERSION: