netfilter: nft_reject: add reject verdict support for netdev

Adds support for reject from ingress hook in netdev family.
Both stacks ipv4 and ipv6.  With reject packets supporting ICMP
and TCP RST.

This ability is required in devices that need to REJECT legitimate
clients which traffic is forwarded from the ingress hook.

Joint work with Laura Garcia.

Signed-off-by: Jose M. Guisado Gomez <guigom@riseup.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 189 insertions, 0 deletions

diff --git a/net/netfilter/nft_reject_netdev.c b/net/netfilter/nft_reject_netdev.c
new file mode 100644
index 000000000000..d89f68754f42
--- /dev/null
+++ b/net/netfilter/nft_reject_netdev.c
@@ -0,0 +1,189 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2020 Laura Garcia Liebana <nevola@gmail.com>
+ * Copyright (c) 2020 Jose M. Guisado <guigom@riseup.net>
+ */
+
+#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.h>
+#include <net/netfilter/nft_reject.h>
+#include <net/netfilter/ipv4/nf_reject.h>
+#include <net/netfilter/ipv6/nf_reject.h>
+
+static void nft_reject_queue_xmit(struct sk_buff *nskb, struct sk_buff *oldskb)
+{
+	dev_hard_header(nskb, nskb->dev, ntohs(oldskb->protocol),
+			eth_hdr(oldskb)->h_source, eth_hdr(oldskb)->h_dest,
+			nskb->len);
+	dev_queue_xmit(nskb);
+}
+
+static void nft_reject_netdev_send_v4_tcp_reset(struct net *net,
+						struct sk_buff *oldskb,
+						const struct net_device *dev,
+						int hook)
+{
+	struct sk_buff *nskb;
+
+	nskb = nf_reject_skb_v4_tcp_reset(net, oldskb, dev, hook);
+	if (!nskb)
+		return;
+
+	nft_reject_queue_xmit(nskb, oldskb);
+}
+
+static void nft_reject_netdev_send_v4_unreach(struct net *net,
+					      struct sk_buff *oldskb,
+					      const struct net_device *dev,
+					      int hook, u8 code)
+{
+	struct sk_buff *nskb;
+
+	nskb = nf_reject_skb_v4_unreach(net, oldskb, dev, hook, code);
+	if (!nskb)
+		return;
+
+	nft_reject_queue_xmit(nskb, oldskb);
+}
+
+static void nft_reject_netdev_send_v6_tcp_reset(struct net *net,
+						struct sk_buff *oldskb,
+						const struct net_device *dev,
+						int hook)
+{
+	struct sk_buff *nskb;
+
+	nskb = nf_reject_skb_v6_tcp_reset(net, oldskb, dev, hook);
+	if (!nskb)
+		return;
+
+	nft_reject_queue_xmit(nskb, oldskb);
+}
+
+
+static void nft_reject_netdev_send_v6_unreach(struct net *net,
+					      struct sk_buff *oldskb,
+					      const struct net_device *dev,
+					      int hook, u8 code)
+{
+	struct sk_buff *nskb;
+
+	nskb = nf_reject_skb_v6_unreach(net, oldskb, dev, hook, code);
+	if (!nskb)
+		return;
+
+	nft_reject_queue_xmit(nskb, oldskb);
+}
+
+static void nft_reject_netdev_eval(const struct nft_expr *expr,
+				   struct nft_regs *regs,
+				   const struct nft_pktinfo *pkt)
+{
+	struct ethhdr *eth = eth_hdr(pkt->skb);
+	struct nft_reject *priv = nft_expr_priv(expr);
+	const unsigned char *dest = eth->h_dest;
+
+	if (is_broadcast_ether_addr(dest) ||
+	    is_multicast_ether_addr(dest))
+		goto out;
+
+	switch (eth->h_proto) {
+	case htons(ETH_P_IP):
+		switch (priv->type) {
+		case NFT_REJECT_ICMP_UNREACH:
+			nft_reject_netdev_send_v4_unreach(nft_net(pkt), pkt->skb,
+							  nft_in(pkt),
+							  nft_hook(pkt),
+							  priv->icmp_code);
+			break;
+		case NFT_REJECT_TCP_RST:
+			nft_reject_netdev_send_v4_tcp_reset(nft_net(pkt), pkt->skb,
+							    nft_in(pkt),
+							    nft_hook(pkt));
+			break;
+		case NFT_REJECT_ICMPX_UNREACH:
+			nft_reject_netdev_send_v4_unreach(nft_net(pkt), pkt->skb,
+							  nft_in(pkt),
+							  nft_hook(pkt),
+							  nft_reject_icmp_code(priv->icmp_code));
+			break;
+		}
+		break;
+	case htons(ETH_P_IPV6):
+		switch (priv->type) {
+		case NFT_REJECT_ICMP_UNREACH:
+			nft_reject_netdev_send_v6_unreach(nft_net(pkt), pkt->skb,
+							  nft_in(pkt),
+							  nft_hook(pkt),
+							  priv->icmp_code);
+			break;
+		case NFT_REJECT_TCP_RST:
+			nft_reject_netdev_send_v6_tcp_reset(nft_net(pkt), pkt->skb,
+							    nft_in(pkt),
+							    nft_hook(pkt));
+			break;
+		case NFT_REJECT_ICMPX_UNREACH:
+			nft_reject_netdev_send_v6_unreach(nft_net(pkt), pkt->skb,
+							  nft_in(pkt),
+							  nft_hook(pkt),
+							  nft_reject_icmpv6_code(priv->icmp_code));
+			break;
+		}
+		break;
+	default:
+		/* No explicit way to reject this protocol, drop it. */
+		break;
+	}
+out:
+	regs->verdict.code = NF_DROP;
+}
+
+static int nft_reject_netdev_validate(const struct nft_ctx *ctx,
+				      const struct nft_expr *expr,
+				      const struct nft_data **data)
+{
+	return nft_chain_validate_hooks(ctx->chain, (1 << NF_NETDEV_INGRESS));
+}
+
+static struct nft_expr_type nft_reject_netdev_type;
+static const struct nft_expr_ops nft_reject_netdev_ops = {
+	.type		= &nft_reject_netdev_type,
+	.size		= NFT_EXPR_SIZE(sizeof(struct nft_reject)),
+	.eval		= nft_reject_netdev_eval,
+	.init		= nft_reject_init,
+	.dump		= nft_reject_dump,
+	.validate	= nft_reject_netdev_validate,
+};
+
+static struct nft_expr_type nft_reject_netdev_type __read_mostly = {
+	.family		= NFPROTO_NETDEV,
+	.name		= "reject",
+	.ops		= &nft_reject_netdev_ops,
+	.policy		= nft_reject_policy,
+	.maxattr	= NFTA_REJECT_MAX,
+	.owner		= THIS_MODULE,
+};
+
+static int __init nft_reject_netdev_module_init(void)
+{
+	return nft_register_expr(&nft_reject_netdev_type);
+}
+
+static void __exit nft_reject_netdev_module_exit(void)
+{
+	nft_unregister_expr(&nft_reject_netdev_type);
+}
+
+module_init(nft_reject_netdev_module_init);
+module_exit(nft_reject_netdev_module_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Laura Garcia Liebana <nevola@gmail.com>");
+MODULE_AUTHOR("Jose M. Guisado <guigom@riseup.net>");
+MODULE_DESCRIPTION("Reject packets from netdev via nftables");
+MODULE_ALIAS_NFT_AF_EXPR(5, "reject");