netfilter: nf_tables: Audit log dump reset after the fact

In theory, dumpreset may fail and invalidate the preceeding log message.
Fix this and use the occasion to prepare for object reset locking, which
benefits from a few unrelated changes:

* Add an early call to nfnetlink_unicast if not resetting which
  effectively skips the audit logging but also unindents it.
* Extract the table's name from the netlink attribute (which is verified
  via earlier table lookup) to not rely upon validity of the looked up
  table pointer.
* Do not use local variable family, it will vanish.

Fixes: 8e6cf365 ("audit: log nftables configuration change events")
Signed-off-by: Phil Sutter <phil@nwl.cc>
Reviewed-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_tables_api.c

@@ -8055,6 +8055,7 @@ static int nf_tables_dump_obj_done(struct netlink_callback *cb)
 static int nf_tables_getobj(struct sk_buff *skb, const struct nfnl_info *info,
 			    const struct nlattr * const nla[])
 {
+	const 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;
@@ -8064,6 +8065,7 @@ static int nf_tables_getobj(struct sk_buff *skb, const struct nfnl_info *info,
 	struct sk_buff *skb2;
 	bool reset = false;
 	u32 objtype;
+	char *buf;
 	int err;
 
 	if (info->nlh->nlmsg_flags & NLM_F_DUMP) {
@@ -8102,27 +8104,23 @@ static int nf_tables_getobj(struct sk_buff *skb, const struct nfnl_info *info,
 	if (NFNL_MSG_TYPE(info->nlh->nlmsg_type) == NFT_MSG_GETOBJ_RESET)
 		reset = true;
 
-	if (reset) {
-		const struct nftables_pernet *nft_net;
-		char *buf;
-
-		nft_net = nft_pernet(net);
-		buf = kasprintf(GFP_ATOMIC, "%s:%u", table->name, nft_net->base_seq);
-
-		audit_log_nfcfg(buf,
-				family,
-				1,
-				AUDIT_NFT_OP_OBJ_RESET,
-				GFP_ATOMIC);
-		kfree(buf);
-	}
-
 	err = nf_tables_fill_obj_info(skb2, net, NETLINK_CB(skb).portid,
 				      info->nlh->nlmsg_seq, NFT_MSG_NEWOBJ, 0,
 				      family, table, obj, reset);
 	if (err < 0)
 		goto err_fill_obj_info;
 
+	if (!reset)
+		return nfnetlink_unicast(skb2, net, NETLINK_CB(skb).portid);
+
+	buf = kasprintf(GFP_ATOMIC, "%.*s:%u",
+			nla_len(nla[NFTA_OBJ_TABLE]),
+			(char *)nla_data(nla[NFTA_OBJ_TABLE]),
+			nft_net->base_seq);
+	audit_log_nfcfg(buf, info->nfmsg->nfgen_family, 1,
+			AUDIT_NFT_OP_OBJ_RESET, GFP_ATOMIC);
+	kfree(buf);
+
 	return nfnetlink_unicast(skb2, net, NETLINK_CB(skb).portid);
 
 err_fill_obj_info: