netfilter: nf_tables: add last expression

Add a new optional expression that tells you when last matching on a
given rule / set element element has happened.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/net/netfilter/nf_tables_core.h

@@ -16,6 +16,7 @@ extern struct nft_expr_type nft_range_type;
 extern struct nft_expr_type nft_meta_type;
 extern struct nft_expr_type nft_rt_type;
 extern struct nft_expr_type nft_exthdr_type;
+extern struct nft_expr_type nft_last_type;
 
 #ifdef CONFIG_NETWORK_SECMARK
 extern struct nft_object_type nft_secmark_obj_type;

include/uapi/linux/netfilter/nf_tables.h

@@ -1195,6 +1195,21 @@ enum nft_counter_attributes {
 };
 #define NFTA_COUNTER_MAX	(__NFTA_COUNTER_MAX - 1)
 
+/**
+ * enum nft_last_attributes - nf_tables last expression netlink attributes
+ *
+ * @NFTA_LAST_SET: last update has been set, zero means never updated (NLA_U32)
+ * @NFTA_LAST_MSECS: milliseconds since last update (NLA_U64)
+ */
+enum nft_last_attributes {
+	NFTA_LAST_UNSPEC,
+	NFTA_LAST_SET,
+	NFTA_LAST_MSECS,
+	NFTA_LAST_PAD,
+	__NFTA_LAST_MAX
+};
+#define NFTA_LAST_MAX	(__NFTA_LAST_MAX - 1)
+
 /**
  * enum nft_log_attributes - nf_tables log expression netlink attributes
  *

net/netfilter/Makefile

@@ -74,7 +74,7 @@ obj-$(CONFIG_NF_DUP_NETDEV)	+= nf_dup_netdev.o
 nf_tables-objs := nf_tables_core.o nf_tables_api.o nft_chain_filter.o \
 		  nf_tables_trace.o nft_immediate.o nft_cmp.o nft_range.o \
 		  nft_bitwise.o nft_byteorder.o nft_payload.o nft_lookup.o \
-		  nft_dynset.o nft_meta.o nft_rt.o nft_exthdr.o \
+		  nft_dynset.o nft_meta.o nft_rt.o nft_exthdr.o nft_last.o \
 		  nft_chain_route.o nf_tables_offload.o \
 		  nft_set_hash.o nft_set_bitmap.o nft_set_rbtree.o \
 		  nft_set_pipapo.o

net/netfilter/nf_tables_core.c

@@ -268,6 +268,7 @@ static struct nft_expr_type *nft_basic_types[] = {
 	&nft_meta_type,
 	&nft_rt_type,
 	&nft_exthdr_type,
+	&nft_last_type,
 };
 
 static struct nft_object_type *nft_basic_objects[] = {

net/netfilter/nft_last.c

+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/netlink.h>
+#include <linux/netfilter.h>
+#include <linux/netfilter/nf_tables.h>
+#include <net/netfilter/nf_tables_core.h>
+#include <net/netfilter/nf_tables.h>
+
+struct nft_last_priv {
+	unsigned long	last_jiffies;
+	unsigned int	last_set;
+};
+
+static const struct nla_policy nft_last_policy[NFTA_LAST_MAX + 1] = {
+	[NFTA_LAST_SET] = { .type = NLA_U32 },
+	[NFTA_LAST_MSECS] = { .type = NLA_U64 },
+};
+
+static int nft_last_init(const struct nft_ctx *ctx, const struct nft_expr *expr,
+			 const struct nlattr * const tb[])
+{
+	struct nft_last_priv *priv = nft_expr_priv(expr);
+	u64 last_jiffies;
+	int err;
+
+	if (tb[NFTA_LAST_MSECS]) {
+		err = nf_msecs_to_jiffies64(tb[NFTA_LAST_MSECS], &last_jiffies);
+		if (err < 0)
+			return err;
+
+		priv->last_jiffies = jiffies + (unsigned long)last_jiffies;
+		priv->last_set = 1;
+	}
+
+	return 0;
+}
+
+static void nft_last_eval(const struct nft_expr *expr,
+			  struct nft_regs *regs, const struct nft_pktinfo *pkt)
+{
+	struct nft_last_priv *priv = nft_expr_priv(expr);
+
+	priv->last_jiffies = jiffies;
+	priv->last_set = 1;
+}
+
+static int nft_last_dump(struct sk_buff *skb, const struct nft_expr *expr)
+{
+	struct nft_last_priv *priv = nft_expr_priv(expr);
+	__be64 msecs;
+
+	if (time_before(jiffies, priv->last_jiffies))
+		priv->last_set = 0;
+
+	if (priv->last_set)
+		msecs = nf_jiffies64_to_msecs(jiffies - priv->last_jiffies);
+	else
+		msecs = 0;
+
+	if (nla_put_be32(skb, NFTA_LAST_SET, htonl(priv->last_set)) ||
+	    nla_put_be64(skb, NFTA_LAST_MSECS, msecs, NFTA_LAST_PAD))
+		goto nla_put_failure;
+
+	return 0;
+
+nla_put_failure:
+	return -1;
+}
+
+static const struct nft_expr_ops nft_last_ops = {
+	.type		= &nft_last_type,
+	.size		= NFT_EXPR_SIZE(sizeof(struct nft_last_priv)),
+	.eval		= nft_last_eval,
+	.init		= nft_last_init,
+	.dump		= nft_last_dump,
+};
+
+struct nft_expr_type nft_last_type __read_mostly = {
+	.name		= "last",
+	.ops		= &nft_last_ops,
+	.policy		= nft_last_policy,
+	.maxattr	= NFTA_LAST_MAX,
+	.flags		= NFT_EXPR_STATEFUL,
+	.owner		= THIS_MODULE,
+};