1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * ebt_arpreply
4 *
5 * Authors:
6 * Grzegorz Borowiak <grzes@gnu.univ.gda.pl>
7 * Bart De Schuymer <bdschuym@pandora.be>
8 *
9 * August, 2003
10 *
11 */
12#include <linux/if_arp.h>
13#include <net/arp.h>
14#include <linux/module.h>
15#include <linux/netfilter/x_tables.h>
16#include <linux/netfilter_bridge/ebtables.h>
17#include <linux/netfilter_bridge/ebt_arpreply.h>
18
19static unsigned int
20ebt_arpreply_tg(struct sk_buff *skb, const struct xt_action_param *par)
21{
22 const struct ebt_arpreply_info *info = par->targinfo;
23 const __be32 *siptr, *diptr;
24 __be32 _sip, _dip;
25 const struct arphdr *ap;
26 struct arphdr _ah;
27 const unsigned char *shp;
28 unsigned char _sha[ETH_ALEN];
29
30 ap = skb_header_pointer(skb, offset: 0, len: sizeof(_ah), buffer: &_ah);
31 if (ap == NULL)
32 return EBT_DROP;
33
34 if (ap->ar_op != htons(ARPOP_REQUEST) ||
35 ap->ar_hln != ETH_ALEN ||
36 ap->ar_pro != htons(ETH_P_IP) ||
37 ap->ar_pln != 4)
38 return EBT_CONTINUE;
39
40 shp = skb_header_pointer(skb, offset: sizeof(_ah), ETH_ALEN, buffer: &_sha);
41 if (shp == NULL)
42 return EBT_DROP;
43
44 siptr = skb_header_pointer(skb, offset: sizeof(_ah) + ETH_ALEN,
45 len: sizeof(_sip), buffer: &_sip);
46 if (siptr == NULL)
47 return EBT_DROP;
48
49 diptr = skb_header_pointer(skb,
50 offset: sizeof(_ah) + 2 * ETH_ALEN + sizeof(_sip),
51 len: sizeof(_dip), buffer: &_dip);
52 if (diptr == NULL)
53 return EBT_DROP;
54
55 arp_send(ARPOP_REPLY, ETH_P_ARP, dest_ip: *siptr,
56 dev: (struct net_device *)xt_in(par),
57 src_ip: *diptr, dest_hw: shp, src_hw: info->mac, th: shp);
58
59 return info->target;
60}
61
62static int ebt_arpreply_tg_check(const struct xt_tgchk_param *par)
63{
64 const struct ebt_arpreply_info *info = par->targinfo;
65 const struct ebt_entry *e = par->entryinfo;
66
67 if (BASE_CHAIN && info->target == EBT_RETURN)
68 return -EINVAL;
69 if (e->ethproto != htons(ETH_P_ARP) ||
70 e->invflags & EBT_IPROTO)
71 return -EINVAL;
72 if (ebt_invalid_target(target: info->target))
73 return -EINVAL;
74
75 return 0;
76}
77
78static struct xt_target ebt_arpreply_tg_reg __read_mostly = {
79 .name = "arpreply",
80 .revision = 0,
81 .family = NFPROTO_BRIDGE,
82 .table = "nat",
83 .hooks = (1 << NF_BR_NUMHOOKS) | (1 << NF_BR_PRE_ROUTING),
84 .target = ebt_arpreply_tg,
85 .checkentry = ebt_arpreply_tg_check,
86 .targetsize = sizeof(struct ebt_arpreply_info),
87 .me = THIS_MODULE,
88};
89
90static int __init ebt_arpreply_init(void)
91{
92 return xt_register_target(target: &ebt_arpreply_tg_reg);
93}
94
95static void __exit ebt_arpreply_fini(void)
96{
97 xt_unregister_target(target: &ebt_arpreply_tg_reg);
98}
99
100module_init(ebt_arpreply_init);
101module_exit(ebt_arpreply_fini);
102MODULE_DESCRIPTION("Ebtables: ARP reply target");
103MODULE_LICENSE("GPL");
104

source code of linux/net/bridge/netfilter/ebt_arpreply.c