1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * ebt_snat
4 *
5 * Authors:
6 * Bart De Schuymer <bdschuym@pandora.be>
7 *
8 * June, 2002
9 *
10 */
11 #include <linux/module.h>
12 #include <net/sock.h>
13 #include <linux/if_arp.h>
14 #include <net/arp.h>
15 #include <linux/netfilter.h>
16 #include <linux/netfilter/x_tables.h>
17 #include <linux/netfilter_bridge/ebtables.h>
18 #include <linux/netfilter_bridge/ebt_nat.h>
19
20 static unsigned int
ebt_snat_tg(struct sk_buff * skb,const struct xt_action_param * par)21 ebt_snat_tg(struct sk_buff *skb, const struct xt_action_param *par)
22 {
23 const struct ebt_nat_info *info = par->targinfo;
24
25 if (skb_ensure_writable(skb, 0))
26 return EBT_DROP;
27
28 ether_addr_copy(eth_hdr(skb)->h_source, info->mac);
29 if (!(info->target & NAT_ARP_BIT) &&
30 eth_hdr(skb)->h_proto == htons(ETH_P_ARP)) {
31 const struct arphdr *ap;
32 struct arphdr _ah;
33
34 ap = skb_header_pointer(skb, 0, sizeof(_ah), &_ah);
35 if (ap == NULL)
36 return EBT_DROP;
37 if (ap->ar_hln != ETH_ALEN)
38 goto out;
39 if (skb_store_bits(skb, sizeof(_ah), info->mac, ETH_ALEN))
40 return EBT_DROP;
41 }
42 out:
43 return info->target | ~EBT_VERDICT_BITS;
44 }
45
ebt_snat_tg_check(const struct xt_tgchk_param * par)46 static int ebt_snat_tg_check(const struct xt_tgchk_param *par)
47 {
48 const struct ebt_nat_info *info = par->targinfo;
49 int tmp;
50
51 tmp = info->target | ~EBT_VERDICT_BITS;
52 if (BASE_CHAIN && tmp == EBT_RETURN)
53 return -EINVAL;
54
55 if (ebt_invalid_target(tmp))
56 return -EINVAL;
57 tmp = info->target | EBT_VERDICT_BITS;
58 if ((tmp & ~NAT_ARP_BIT) != ~NAT_ARP_BIT)
59 return -EINVAL;
60 return 0;
61 }
62
63 static struct xt_target ebt_snat_tg_reg __read_mostly = {
64 .name = "snat",
65 .revision = 0,
66 .family = NFPROTO_BRIDGE,
67 .table = "nat",
68 .hooks = (1 << NF_BR_NUMHOOKS) | (1 << NF_BR_POST_ROUTING),
69 .target = ebt_snat_tg,
70 .checkentry = ebt_snat_tg_check,
71 .targetsize = sizeof(struct ebt_nat_info),
72 .me = THIS_MODULE,
73 };
74
ebt_snat_init(void)75 static int __init ebt_snat_init(void)
76 {
77 return xt_register_target(&ebt_snat_tg_reg);
78 }
79
ebt_snat_fini(void)80 static void __exit ebt_snat_fini(void)
81 {
82 xt_unregister_target(&ebt_snat_tg_reg);
83 }
84
85 module_init(ebt_snat_init);
86 module_exit(ebt_snat_fini);
87 MODULE_DESCRIPTION("Ebtables: Source MAC address translation");
88 MODULE_LICENSE("GPL");
89