netfilter: nf_tables: allow to filter stateful object dumps by type

This patch adds the netlink code to filter out dump of stateful objects,
through the NFTA_OBJ_TYPE netlink attribute.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_tables_api.c

@@ -4183,12 +4183,18 @@ static int nf_tables_fill_obj_info(struct sk_buff *skb, struct net *net,
 	return -1;
 }
 
+struct nft_obj_filter {
+	char		table[NFT_OBJ_MAXNAMELEN];
+	u32		type;
+};
+
 static int nf_tables_dump_obj(struct sk_buff *skb, struct netlink_callback *cb)
 {
 	const struct nfgenmsg *nfmsg = nlmsg_data(cb->nlh);
 	const struct nft_af_info *afi;
 	const struct nft_table *table;
 	unsigned int idx = 0, s_idx = cb->args[0];
+	struct nft_obj_filter *filter = cb->data;
 	struct net *net = sock_net(skb->sk);
 	int family = nfmsg->nfgen_family;
 	struct nft_object *obj;
@@ -4213,6 +4219,13 @@ static int nf_tables_dump_obj(struct sk_buff *skb, struct netlink_callback *cb)
 				if (idx > s_idx)
 					memset(&cb->args[1], 0,
 					       sizeof(cb->args) - sizeof(cb->args[0]));
+				if (filter->table[0] &&
+				    strcmp(filter->table, table->name))
+					goto cont;
+				if (filter->type != NFT_OBJECT_UNSPEC &&
+				    obj->type->type != filter->type)
+					goto cont;
+
 				if (nf_tables_fill_obj_info(skb, net, NETLINK_CB(cb->skb).portid,
 							    cb->nlh->nlmsg_seq,
 							    NFT_MSG_NEWOBJ,
@@ -4233,6 +4246,31 @@ static int nf_tables_dump_obj(struct sk_buff *skb, struct netlink_callback *cb)
 	return skb->len;
 }
 
+static int nf_tables_dump_obj_done(struct netlink_callback *cb)
+{
+	kfree(cb->data);
+
+	return 0;
+}
+
+static struct nft_obj_filter *
+nft_obj_filter_alloc(const struct nlattr * const nla[])
+{
+	struct nft_obj_filter *filter;
+
+	filter = kzalloc(sizeof(*filter), GFP_KERNEL);
+	if (!filter)
+		return ERR_PTR(-ENOMEM);
+
+	if (nla[NFTA_OBJ_TABLE])
+		nla_strlcpy(filter->table, nla[NFTA_OBJ_TABLE],
+			    NFT_TABLE_MAXNAMELEN);
+	if (nla[NFTA_OBJ_TYPE])
+		filter->type = ntohl(nla_get_be32(nla[NFTA_OBJ_TYPE]));
+
+	return filter;
+}
+
 static int nf_tables_getobj(struct net *net, struct sock *nlsk,
 			    struct sk_buff *skb, const struct nlmsghdr *nlh,
 			    const struct nlattr * const nla[])
@@ -4251,7 +4289,19 @@ static int nf_tables_getobj(struct net *net, struct sock *nlsk,
 	if (nlh->nlmsg_flags & NLM_F_DUMP) {
 		struct netlink_dump_control c = {
 			.dump = nf_tables_dump_obj,
+			.done = nf_tables_dump_obj_done,
 		};
+
+		if (nla[NFTA_OBJ_TABLE] ||
+		    nla[NFTA_OBJ_TYPE]) {
+			struct nft_obj_filter *filter;
+
+			filter = nft_obj_filter_alloc(nla);
+			if (IS_ERR(filter))
+				return -ENOMEM;
+
+			c.data = filter;
+		}
 		return netlink_dump_start(nlsk, skb, nlh, &c);
 	}