1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * Copyright (c) 2020 Laura Garcia Liebana <nevola@gmail.com>
4  * Copyright (c) 2020 Jose M. Guisado <guigom@riseup.net>
5  */
6 
7 #include <linux/etherdevice.h>
8 #include <linux/kernel.h>
9 #include <linux/init.h>
10 #include <linux/module.h>
11 #include <linux/netlink.h>
12 #include <linux/netfilter.h>
13 #include <linux/netfilter/nf_tables.h>
14 #include <net/netfilter/nf_tables.h>
15 #include <net/netfilter/nft_reject.h>
16 #include <net/netfilter/ipv4/nf_reject.h>
17 #include <net/netfilter/ipv6/nf_reject.h>
18 
nft_reject_queue_xmit(struct sk_buff * nskb,struct sk_buff * oldskb)19 static void nft_reject_queue_xmit(struct sk_buff *nskb, struct sk_buff *oldskb)
20 {
21 	dev_hard_header(nskb, nskb->dev, ntohs(oldskb->protocol),
22 			eth_hdr(oldskb)->h_source, eth_hdr(oldskb)->h_dest,
23 			nskb->len);
24 	dev_queue_xmit(nskb);
25 }
26 
nft_reject_netdev_send_v4_tcp_reset(struct net * net,struct sk_buff * oldskb,const struct net_device * dev,int hook)27 static void nft_reject_netdev_send_v4_tcp_reset(struct net *net,
28 						struct sk_buff *oldskb,
29 						const struct net_device *dev,
30 						int hook)
31 {
32 	struct sk_buff *nskb;
33 
34 	nskb = nf_reject_skb_v4_tcp_reset(net, oldskb, dev, hook);
35 	if (!nskb)
36 		return;
37 
38 	nft_reject_queue_xmit(nskb, oldskb);
39 }
40 
nft_reject_netdev_send_v4_unreach(struct net * net,struct sk_buff * oldskb,const struct net_device * dev,int hook,u8 code)41 static void nft_reject_netdev_send_v4_unreach(struct net *net,
42 					      struct sk_buff *oldskb,
43 					      const struct net_device *dev,
44 					      int hook, u8 code)
45 {
46 	struct sk_buff *nskb;
47 
48 	nskb = nf_reject_skb_v4_unreach(net, oldskb, dev, hook, code);
49 	if (!nskb)
50 		return;
51 
52 	nft_reject_queue_xmit(nskb, oldskb);
53 }
54 
nft_reject_netdev_send_v6_tcp_reset(struct net * net,struct sk_buff * oldskb,const struct net_device * dev,int hook)55 static void nft_reject_netdev_send_v6_tcp_reset(struct net *net,
56 						struct sk_buff *oldskb,
57 						const struct net_device *dev,
58 						int hook)
59 {
60 	struct sk_buff *nskb;
61 
62 	nskb = nf_reject_skb_v6_tcp_reset(net, oldskb, dev, hook);
63 	if (!nskb)
64 		return;
65 
66 	nft_reject_queue_xmit(nskb, oldskb);
67 }
68 
69 
nft_reject_netdev_send_v6_unreach(struct net * net,struct sk_buff * oldskb,const struct net_device * dev,int hook,u8 code)70 static void nft_reject_netdev_send_v6_unreach(struct net *net,
71 					      struct sk_buff *oldskb,
72 					      const struct net_device *dev,
73 					      int hook, u8 code)
74 {
75 	struct sk_buff *nskb;
76 
77 	nskb = nf_reject_skb_v6_unreach(net, oldskb, dev, hook, code);
78 	if (!nskb)
79 		return;
80 
81 	nft_reject_queue_xmit(nskb, oldskb);
82 }
83 
nft_reject_netdev_eval(const struct nft_expr * expr,struct nft_regs * regs,const struct nft_pktinfo * pkt)84 static void nft_reject_netdev_eval(const struct nft_expr *expr,
85 				   struct nft_regs *regs,
86 				   const struct nft_pktinfo *pkt)
87 {
88 	struct ethhdr *eth = eth_hdr(pkt->skb);
89 	struct nft_reject *priv = nft_expr_priv(expr);
90 	const unsigned char *dest = eth->h_dest;
91 
92 	if (is_broadcast_ether_addr(dest) ||
93 	    is_multicast_ether_addr(dest))
94 		goto out;
95 
96 	switch (eth->h_proto) {
97 	case htons(ETH_P_IP):
98 		switch (priv->type) {
99 		case NFT_REJECT_ICMP_UNREACH:
100 			nft_reject_netdev_send_v4_unreach(nft_net(pkt), pkt->skb,
101 							  nft_in(pkt),
102 							  nft_hook(pkt),
103 							  priv->icmp_code);
104 			break;
105 		case NFT_REJECT_TCP_RST:
106 			nft_reject_netdev_send_v4_tcp_reset(nft_net(pkt), pkt->skb,
107 							    nft_in(pkt),
108 							    nft_hook(pkt));
109 			break;
110 		case NFT_REJECT_ICMPX_UNREACH:
111 			nft_reject_netdev_send_v4_unreach(nft_net(pkt), pkt->skb,
112 							  nft_in(pkt),
113 							  nft_hook(pkt),
114 							  nft_reject_icmp_code(priv->icmp_code));
115 			break;
116 		}
117 		break;
118 	case htons(ETH_P_IPV6):
119 		switch (priv->type) {
120 		case NFT_REJECT_ICMP_UNREACH:
121 			nft_reject_netdev_send_v6_unreach(nft_net(pkt), pkt->skb,
122 							  nft_in(pkt),
123 							  nft_hook(pkt),
124 							  priv->icmp_code);
125 			break;
126 		case NFT_REJECT_TCP_RST:
127 			nft_reject_netdev_send_v6_tcp_reset(nft_net(pkt), pkt->skb,
128 							    nft_in(pkt),
129 							    nft_hook(pkt));
130 			break;
131 		case NFT_REJECT_ICMPX_UNREACH:
132 			nft_reject_netdev_send_v6_unreach(nft_net(pkt), pkt->skb,
133 							  nft_in(pkt),
134 							  nft_hook(pkt),
135 							  nft_reject_icmpv6_code(priv->icmp_code));
136 			break;
137 		}
138 		break;
139 	default:
140 		/* No explicit way to reject this protocol, drop it. */
141 		break;
142 	}
143 out:
144 	regs->verdict.code = NF_DROP;
145 }
146 
nft_reject_netdev_validate(const struct nft_ctx * ctx,const struct nft_expr * expr,const struct nft_data ** data)147 static int nft_reject_netdev_validate(const struct nft_ctx *ctx,
148 				      const struct nft_expr *expr,
149 				      const struct nft_data **data)
150 {
151 	return nft_chain_validate_hooks(ctx->chain, (1 << NF_NETDEV_INGRESS));
152 }
153 
154 static struct nft_expr_type nft_reject_netdev_type;
155 static const struct nft_expr_ops nft_reject_netdev_ops = {
156 	.type		= &nft_reject_netdev_type,
157 	.size		= NFT_EXPR_SIZE(sizeof(struct nft_reject)),
158 	.eval		= nft_reject_netdev_eval,
159 	.init		= nft_reject_init,
160 	.dump		= nft_reject_dump,
161 	.validate	= nft_reject_netdev_validate,
162 	.reduce		= NFT_REDUCE_READONLY,
163 };
164 
165 static struct nft_expr_type nft_reject_netdev_type __read_mostly = {
166 	.family		= NFPROTO_NETDEV,
167 	.name		= "reject",
168 	.ops		= &nft_reject_netdev_ops,
169 	.policy		= nft_reject_policy,
170 	.maxattr	= NFTA_REJECT_MAX,
171 	.owner		= THIS_MODULE,
172 };
173 
nft_reject_netdev_module_init(void)174 static int __init nft_reject_netdev_module_init(void)
175 {
176 	return nft_register_expr(&nft_reject_netdev_type);
177 }
178 
nft_reject_netdev_module_exit(void)179 static void __exit nft_reject_netdev_module_exit(void)
180 {
181 	nft_unregister_expr(&nft_reject_netdev_type);
182 }
183 
184 module_init(nft_reject_netdev_module_init);
185 module_exit(nft_reject_netdev_module_exit);
186 
187 MODULE_LICENSE("GPL");
188 MODULE_AUTHOR("Laura Garcia Liebana <nevola@gmail.com>");
189 MODULE_AUTHOR("Jose M. Guisado <guigom@riseup.net>");
190 MODULE_DESCRIPTION("Reject packets from netdev via nftables");
191 MODULE_ALIAS_NFT_AF_EXPR(5, "reject");
192