1 | // SPDX-License-Identifier: GPL-2.0-only |
2 | /* module that allows mangling of the arp payload */ |
3 | #include <linux/module.h> |
4 | #include <linux/netfilter.h> |
5 | #include <linux/netfilter_arp/arpt_mangle.h> |
6 | #include <net/sock.h> |
7 | |
8 | MODULE_LICENSE("GPL" ); |
9 | MODULE_AUTHOR("Bart De Schuymer <bdschuym@pandora.be>" ); |
10 | MODULE_DESCRIPTION("arptables arp payload mangle target" ); |
11 | |
12 | static unsigned int |
13 | target(struct sk_buff *skb, const struct xt_action_param *par) |
14 | { |
15 | const struct arpt_mangle *mangle = par->targinfo; |
16 | const struct arphdr *arp; |
17 | unsigned char *arpptr; |
18 | int pln, hln; |
19 | |
20 | if (skb_ensure_writable(skb, write_len: skb->len)) |
21 | return NF_DROP; |
22 | |
23 | arp = arp_hdr(skb); |
24 | arpptr = skb_network_header(skb) + sizeof(*arp); |
25 | pln = arp->ar_pln; |
26 | hln = arp->ar_hln; |
27 | /* We assume that pln and hln were checked in the match */ |
28 | if (mangle->flags & ARPT_MANGLE_SDEV) { |
29 | if (ARPT_DEV_ADDR_LEN_MAX < hln || |
30 | (arpptr + hln > skb_tail_pointer(skb))) |
31 | return NF_DROP; |
32 | memcpy(arpptr, mangle->src_devaddr, hln); |
33 | } |
34 | arpptr += hln; |
35 | if (mangle->flags & ARPT_MANGLE_SIP) { |
36 | if (ARPT_MANGLE_ADDR_LEN_MAX < pln || |
37 | (arpptr + pln > skb_tail_pointer(skb))) |
38 | return NF_DROP; |
39 | memcpy(arpptr, &mangle->u_s.src_ip, pln); |
40 | } |
41 | arpptr += pln; |
42 | if (mangle->flags & ARPT_MANGLE_TDEV) { |
43 | if (ARPT_DEV_ADDR_LEN_MAX < hln || |
44 | (arpptr + hln > skb_tail_pointer(skb))) |
45 | return NF_DROP; |
46 | memcpy(arpptr, mangle->tgt_devaddr, hln); |
47 | } |
48 | arpptr += hln; |
49 | if (mangle->flags & ARPT_MANGLE_TIP) { |
50 | if (ARPT_MANGLE_ADDR_LEN_MAX < pln || |
51 | (arpptr + pln > skb_tail_pointer(skb))) |
52 | return NF_DROP; |
53 | memcpy(arpptr, &mangle->u_t.tgt_ip, pln); |
54 | } |
55 | return mangle->target; |
56 | } |
57 | |
58 | static int checkentry(const struct xt_tgchk_param *par) |
59 | { |
60 | const struct arpt_mangle *mangle = par->targinfo; |
61 | |
62 | if (mangle->flags & ~ARPT_MANGLE_MASK || |
63 | !(mangle->flags & ARPT_MANGLE_MASK)) |
64 | return -EINVAL; |
65 | |
66 | if (mangle->target != NF_DROP && mangle->target != NF_ACCEPT && |
67 | mangle->target != XT_CONTINUE) |
68 | return -EINVAL; |
69 | return 0; |
70 | } |
71 | |
72 | static struct xt_target arpt_mangle_reg __read_mostly = { |
73 | .name = "mangle" , |
74 | .family = NFPROTO_ARP, |
75 | .target = target, |
76 | .targetsize = sizeof(struct arpt_mangle), |
77 | .checkentry = checkentry, |
78 | .me = THIS_MODULE, |
79 | }; |
80 | |
81 | static int __init arpt_mangle_init(void) |
82 | { |
83 | return xt_register_target(target: &arpt_mangle_reg); |
84 | } |
85 | |
86 | static void __exit arpt_mangle_fini(void) |
87 | { |
88 | xt_unregister_target(target: &arpt_mangle_reg); |
89 | } |
90 | |
91 | module_init(arpt_mangle_init); |
92 | module_exit(arpt_mangle_fini); |
93 | |