netfilter: nf_tables: add insert operation

This patch adds a new rule attribute NFTA_RULE_POSITION which is
used to store the position of a rule relatively to the others.
By providing the create command and specifying the position, the
rule is inserted after the rule with the handle equal to the
provided position.

Regarding notification, the position attribute specifies the
handle of the previous rule to make sure we don't point to any
stale rule in notifications coming from the commit path.

This patch includes the following fix from Pablo:

* nf_tables: fix rule deletion event reporting
Signed-off-by: Eric Leblond <eric@regit.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/uapi/linux/netfilter/nf_tables.h

@@ -153,6 +153,7 @@ enum nft_chain_attributes {
  * @NFTA_RULE_HANDLE: numeric handle of the rule (NLA_U64)
  * @NFTA_RULE_EXPRESSIONS: list of expressions (NLA_NESTED: nft_expr_attributes)
  * @NFTA_RULE_COMPAT: compatibility specifications of the rule (NLA_NESTED: nft_rule_compat_attributes)
+ * @NFTA_RULE_POSITION: numeric handle of the previous rule (NLA_U64)
  */
 enum nft_rule_attributes {
 	NFTA_RULE_UNSPEC,
@@ -161,6 +162,7 @@ enum nft_rule_attributes {
 	NFTA_RULE_HANDLE,
 	NFTA_RULE_EXPRESSIONS,
 	NFTA_RULE_COMPAT,
+	NFTA_RULE_POSITION,
 	__NFTA_RULE_MAX
 };
 #define NFTA_RULE_MAX		(__NFTA_RULE_MAX - 1)

net/netfilter/nf_tables_api.c

@@ -1273,6 +1273,7 @@ static const struct nla_policy nft_rule_policy[NFTA_RULE_MAX + 1] = {
 	[NFTA_RULE_HANDLE]	= { .type = NLA_U64 },
 	[NFTA_RULE_EXPRESSIONS]	= { .type = NLA_NESTED },
 	[NFTA_RULE_COMPAT]	= { .type = NLA_NESTED },
+	[NFTA_RULE_POSITION]	= { .type = NLA_U64 },
 };
 
 static int nf_tables_fill_rule_info(struct sk_buff *skb, u32 portid, u32 seq,
@@ -1285,9 +1286,10 @@ static int nf_tables_fill_rule_info(struct sk_buff *skb, u32 portid, u32 seq,
 	struct nfgenmsg *nfmsg;
 	const struct nft_expr *expr, *next;
 	struct nlattr *list;
+	const struct nft_rule *prule;
+	int type = event | NFNL_SUBSYS_NFTABLES << 8;
 
-	event |= NFNL_SUBSYS_NFTABLES << 8;
-	nlh = nlmsg_put(skb, portid, seq, event, sizeof(struct nfgenmsg),
+	nlh = nlmsg_put(skb, portid, seq, type, sizeof(struct nfgenmsg),
 			flags);
 	if (nlh == NULL)
 		goto nla_put_failure;
@@ -1304,6 +1306,13 @@ static int nf_tables_fill_rule_info(struct sk_buff *skb, u32 portid, u32 seq,
 	if (nla_put_be64(skb, NFTA_RULE_HANDLE, cpu_to_be64(rule->handle)))
 		goto nla_put_failure;
 
+	if ((event != NFT_MSG_DELRULE) && (rule->list.prev != &chain->rules)) {
+		prule = list_entry(rule->list.prev, struct nft_rule, list);
+		if (nla_put_be64(skb, NFTA_RULE_POSITION,
+				 cpu_to_be64(prule->handle)))
+			goto nla_put_failure;
+	}
+
 	list = nla_nest_start(skb, NFTA_RULE_EXPRESSIONS);
 	if (list == NULL)
 		goto nla_put_failure;
@@ -1499,7 +1508,7 @@ static int nf_tables_newrule(struct sock *nlsk, struct sk_buff *skb,
 	unsigned int size, i, n;
 	int err, rem;
 	bool create;
-	u64 handle;
+	u64 handle, pos_handle;
 
 	create = nlh->nlmsg_flags & NLM_F_CREATE ? true : false;
 
@@ -1533,6 +1542,16 @@ static int nf_tables_newrule(struct sock *nlsk, struct sk_buff *skb,
 		handle = nf_tables_alloc_handle(table);
 	}
 
+	if (nla[NFTA_RULE_POSITION]) {
+		if (!(nlh->nlmsg_flags & NLM_F_CREATE))
+			return -EOPNOTSUPP;
+
+		pos_handle = be64_to_cpu(nla_get_be64(nla[NFTA_RULE_POSITION]));
+		old_rule = __nf_tables_rule_lookup(chain, pos_handle);
+		if (IS_ERR(old_rule))
+			return PTR_ERR(old_rule);
+	}
+
 	nft_ctx_init(&ctx, skb, nlh, afi, table, chain, nla);
 
 	n = 0;
@@ -1573,9 +1592,16 @@ static int nf_tables_newrule(struct sock *nlsk, struct sk_buff *skb,
 		list_replace_rcu(&old_rule->list, &rule->list);
 		nf_tables_rule_destroy(old_rule);
 	} else if (nlh->nlmsg_flags & NLM_F_APPEND)
-		list_add_tail_rcu(&rule->list, &chain->rules);
-	else
-		list_add_rcu(&rule->list, &chain->rules);
+		if (old_rule)
+			list_add_rcu(&rule->list, &old_rule->list);
+		else
+			list_add_tail_rcu(&rule->list, &chain->rules);
+	else {
+		if (old_rule)
+			list_add_tail_rcu(&rule->list, &old_rule->list);
+		else
+			list_add_rcu(&rule->list, &chain->rules);
+	}
 
 	nf_tables_rule_notify(skb, nlh, table, chain, rule, NFT_MSG_NEWRULE,
 			      nlh->nlmsg_flags & (NLM_F_APPEND | NLM_F_REPLACE),