netfilter: nf_tables: Introduce nf_tables_getrule_single()

Outsource the reply skb preparation for non-dump getrule requests into a
distinct function. Prep work for rule reset locking.
Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_tables_api.c

@@ -3586,65 +3586,81 @@ static int nf_tables_dump_rules_done(struct netlink_callback *cb)
 }
 
 /* called with rcu_read_lock held */
-static int nf_tables_getrule(struct sk_buff *skb, const struct nfnl_info *info,
-			     const struct nlattr * const nla[])
+static struct sk_buff *
+nf_tables_getrule_single(u32 portid, const struct nfnl_info *info,
+			 const struct nlattr * const nla[], bool reset)
 {
-	struct nftables_pernet *nft_net = nft_pernet(info->net);
 	struct netlink_ext_ack *extack = info->extack;
 	u8 genmask = nft_genmask_cur(info->net);
 	u8 family = info->nfmsg->nfgen_family;
-	u32 portid = NETLINK_CB(skb).portid;
 	const struct nft_chain *chain;
 	const struct nft_rule *rule;
 	struct net *net = info->net;
 	struct nft_table *table;
 	struct sk_buff *skb2;
-	bool reset = false;
-	char *buf;
 	int err;
 
-	if (info->nlh->nlmsg_flags & NLM_F_DUMP) {
-		struct netlink_dump_control c = {
-			.start= nf_tables_dump_rules_start,
-			.dump = nf_tables_dump_rules,
-			.done = nf_tables_dump_rules_done,
-			.module = THIS_MODULE,
-			.data = (void *)nla,
-		};
-
-		return nft_netlink_dump_start_rcu(info->sk, skb, info->nlh, &c);
-	}
-
 	table = nft_table_lookup(net, nla[NFTA_RULE_TABLE], family, genmask, 0);
 	if (IS_ERR(table)) {
 		NL_SET_BAD_ATTR(extack, nla[NFTA_RULE_TABLE]);
-		return PTR_ERR(table);
+		return ERR_CAST(table);
 	}
 
 	chain = nft_chain_lookup(net, table, nla[NFTA_RULE_CHAIN], genmask);
 	if (IS_ERR(chain)) {
 		NL_SET_BAD_ATTR(extack, nla[NFTA_RULE_CHAIN]);
-		return PTR_ERR(chain);
+		return ERR_CAST(chain);
 	}
 
 	rule = nft_rule_lookup(chain, nla[NFTA_RULE_HANDLE]);
 	if (IS_ERR(rule)) {
 		NL_SET_BAD_ATTR(extack, nla[NFTA_RULE_HANDLE]);
-		return PTR_ERR(rule);
+		return ERR_CAST(rule);
 	}
 
 	skb2 = alloc_skb(NLMSG_GOODSIZE, GFP_ATOMIC);
 	if (!skb2)
-		return -ENOMEM;
-
-	if (NFNL_MSG_TYPE(info->nlh->nlmsg_type) == NFT_MSG_GETRULE_RESET)
-		reset = true;
+		return ERR_PTR(-ENOMEM);
 
 	err = nf_tables_fill_rule_info(skb2, net, portid,
 				       info->nlh->nlmsg_seq, NFT_MSG_NEWRULE, 0,
 				       family, table, chain, rule, 0, reset);
-	if (err < 0)
-		goto err_fill_rule_info;
+	if (err < 0) {
+		kfree_skb(skb2);
+		return ERR_PTR(err);
+	}
+
+	return skb2;
+}
+
+static int nf_tables_getrule(struct sk_buff *skb, const struct nfnl_info *info,
+			     const struct nlattr * const nla[])
+{
+	struct nftables_pernet *nft_net = nft_pernet(info->net);
+	u32 portid = NETLINK_CB(skb).portid;
+	struct net *net = info->net;
+	struct sk_buff *skb2;
+	bool reset = false;
+	char *buf;
+
+	if (info->nlh->nlmsg_flags & NLM_F_DUMP) {
+		struct netlink_dump_control c = {
+			.start= nf_tables_dump_rules_start,
+			.dump = nf_tables_dump_rules,
+			.done = nf_tables_dump_rules_done,
+			.module = THIS_MODULE,
+			.data = (void *)nla,
+		};
+
+		return nft_netlink_dump_start_rcu(info->sk, skb, info->nlh, &c);
+	}
+
+	if (NFNL_MSG_TYPE(info->nlh->nlmsg_type) == NFT_MSG_GETRULE_RESET)
+		reset = true;
+
+	skb2 = nf_tables_getrule_single(portid, info, nla, reset);
+	if (IS_ERR(skb2))
+		return PTR_ERR(skb2);
 
 	if (!reset)
 		return nfnetlink_unicast(skb2, net, portid);
@@ -3658,10 +3674,6 @@ static int nf_tables_getrule(struct sk_buff *skb, const struct nfnl_info *info,
 	kfree(buf);
 
 	return nfnetlink_unicast(skb2, net, portid);
-
-err_fill_rule_info:
-	kfree_skb(skb2);
-	return err;
 }
 
 void nf_tables_rule_destroy(const struct nft_ctx *ctx, struct nft_rule *rule)