netfilter: nf_tables: take module reference when starting a batch

Signed-off-by: Florian Westphal <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

include/linux/netfilter/nfnetlink.h

···
 	__u8 subsys_id;			/* nfnetlink subsystem ID */
 	__u8 cb_count;			/* number of callbacks */
 	const struct nfnl_callback *cb;	/* callback for individual types */
+	struct module *owner;
 	int (*commit)(struct net *net, struct sk_buff *skb);
 	int (*abort)(struct net *net, struct sk_buff *skb);
 	void (*cleanup)(struct net *net);

net/netfilter/nf_tables_api.c

···
 	.abort		= nf_tables_abort,
 	.cleanup	= nf_tables_cleanup,
 	.valid_genid	= nf_tables_valid_genid,
+	.owner		= THIS_MODULE,
 };
 
 int nft_chain_validate_dependency(const struct nft_chain *chain,

net/netfilter/nfnetlink.c

···
 		return kfree_skb(skb);
 	}
 
+	if (!try_module_get(ss->owner)) {
+		nfnl_unlock(subsys_id);
+		netlink_ack(oskb, nlh, -EOPNOTSUPP, NULL);
+		return kfree_skb(skb);
+	}
+
 	if (!ss->valid_genid(net, genid)) {
+		module_put(ss->owner);
 		nfnl_unlock(subsys_id);
 		netlink_ack(oskb, nlh, -ERESTART, NULL);
 		return kfree_skb(skb);
···
 		nfnl_err_reset(&err_list);
 		nfnl_unlock(subsys_id);
 		kfree_skb(skb);
+		module_put(ss->owner);
 		goto replay;
 	} else if (status == NFNL_BATCH_DONE) {
 		err = ss->commit(net, oskb);
···
 	nfnl_err_deliver(&err_list, oskb);
 	nfnl_unlock(subsys_id);
 	kfree_skb(skb);
+	module_put(ss->owner);
 }
 
 static const struct nla_policy nfnl_batch_policy[NFNL_BATCH_MAX + 1] = {