netfilter: nfnetlink: Initialise extack before use in ACKs

Add missing extack initialisation when ACKing BATCH_BEGIN and BATCH_END.

Fixes: bf2ac490 ("netfilter: nfnetlink: Handle ACK flags for batch messages")
Signed-off-by: Donald Hunter <donald.hunter@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nfnetlink.c

@@ -427,8 +427,10 @@ static void nfnetlink_rcv_batch(struct sk_buff *skb, struct nlmsghdr *nlh,
 
 	nfnl_unlock(subsys_id);
 
-	if (nlh->nlmsg_flags & NLM_F_ACK)
+	if (nlh->nlmsg_flags & NLM_F_ACK) {
+		memset(&extack, 0, sizeof(extack));
 		nfnl_err_add(&err_list, nlh, 0, &extack);
+	}
 
 	while (skb->len >= nlmsg_total_size(0)) {
 		int msglen, type;
@@ -577,6 +579,7 @@ static void nfnetlink_rcv_batch(struct sk_buff *skb, struct nlmsghdr *nlh,
 			ss->abort(net, oskb, NFNL_ABORT_NONE);
 			netlink_ack(oskb, nlmsg_hdr(oskb), err, NULL);
 		} else if (nlh->nlmsg_flags & NLM_F_ACK) {
+			memset(&extack, 0, sizeof(extack));
 			nfnl_err_add(&err_list, nlh, 0, &extack);
 		}
 	} else {