| 1 | /* module that allows mangling of the arp payload */ |
| 2 | #include <linux/module.h> |
| 3 | #include <linux/netfilter_arp/arpt_mangle.h> |
| 4 | #include <net/sock.h> |
| 5 | |
| 6 | MODULE_LICENSE("GPL"); |
| 7 | MODULE_AUTHOR("Bart De Schuymer <bdschuym@pandora.be>"); |
| 8 | MODULE_DESCRIPTION("arptables arp payload mangle target"); |
| 9 | |
| 10 | static unsigned int |
| 11 | target(struct sk_buff **pskb, const struct net_device *in, |
| 12 | const struct net_device *out, unsigned int hooknum, const void *targinfo, |
| 13 | void *userinfo) |
| 14 | { |
| 15 | const struct arpt_mangle *mangle = targinfo; |
| 16 | struct arphdr *arp; |
| 17 | unsigned char *arpptr; |
| 18 | int pln, hln; |
| 19 | |
| 20 | if (skb_shared(*pskb) || skb_cloned(*pskb)) { |
| 21 | struct sk_buff *nskb; |
| 22 | |
| 23 | nskb = skb_copy(*pskb, GFP_ATOMIC); |
| 24 | if (!nskb) |
| 25 | return NF_DROP; |
| 26 | if ((*pskb)->sk) |
| 27 | skb_set_owner_w(nskb, (*pskb)->sk); |
| 28 | kfree_skb(*pskb); |
| 29 | *pskb = nskb; |
| 30 | } |
| 31 | |
| 32 | arp = (*pskb)->nh.arph; |
| 33 | arpptr = (*pskb)->nh.raw + sizeof(*arp); |
| 34 | pln = arp->ar_pln; |
| 35 | hln = arp->ar_hln; |
| 36 | /* We assume that pln and hln were checked in the match */ |
| 37 | if (mangle->flags & ARPT_MANGLE_SDEV) { |
| 38 | if (ARPT_DEV_ADDR_LEN_MAX < hln || |
| 39 | (arpptr + hln > (**pskb).tail)) |
| 40 | return NF_DROP; |
| 41 | memcpy(arpptr, mangle->src_devaddr, hln); |
| 42 | } |
| 43 | arpptr += hln; |
| 44 | if (mangle->flags & ARPT_MANGLE_SIP) { |
| 45 | if (ARPT_MANGLE_ADDR_LEN_MAX < pln || |
| 46 | (arpptr + pln > (**pskb).tail)) |
| 47 | return NF_DROP; |
| 48 | memcpy(arpptr, &mangle->u_s.src_ip, pln); |
| 49 | } |
| 50 | arpptr += pln; |
| 51 | if (mangle->flags & ARPT_MANGLE_TDEV) { |
| 52 | if (ARPT_DEV_ADDR_LEN_MAX < hln || |
| 53 | (arpptr + hln > (**pskb).tail)) |
| 54 | return NF_DROP; |
| 55 | memcpy(arpptr, mangle->tgt_devaddr, hln); |
| 56 | } |
| 57 | arpptr += hln; |
| 58 | if (mangle->flags & ARPT_MANGLE_TIP) { |
| 59 | if (ARPT_MANGLE_ADDR_LEN_MAX < pln || |
| 60 | (arpptr + pln > (**pskb).tail)) |
| 61 | return NF_DROP; |
| 62 | memcpy(arpptr, &mangle->u_t.tgt_ip, pln); |
| 63 | } |
| 64 | return mangle->target; |
| 65 | } |
| 66 | |
| 67 | static int |
| 68 | checkentry(const char *tablename, const void *e, void *targinfo, |
| 69 | unsigned int targinfosize, unsigned int hook_mask) |
| 70 | { |
| 71 | const struct arpt_mangle *mangle = targinfo; |
| 72 | |
| 73 | if (mangle->flags & ~ARPT_MANGLE_MASK || |
| 74 | !(mangle->flags & ARPT_MANGLE_MASK)) |
| 75 | return 0; |
| 76 | |
| 77 | if (mangle->target != NF_DROP && mangle->target != NF_ACCEPT && |
| 78 | mangle->target != ARPT_CONTINUE) |
| 79 | return 0; |
| 80 | return 1; |
| 81 | } |
| 82 | |
| 83 | static struct arpt_target arpt_mangle_reg = { |
| 84 | .name = "mangle", |
| 85 | .target = target, |
| 86 | .targetsize = sizeof(struct arpt_mangle), |
| 87 | .checkentry = checkentry, |
| 88 | .me = THIS_MODULE, |
| 89 | }; |
| 90 | |
| 91 | static int __init init(void) |
| 92 | { |
| 93 | if (arpt_register_target(&arpt_mangle_reg)) |
| 94 | return -EINVAL; |
| 95 | |
| 96 | return 0; |
| 97 | } |
| 98 | |
| 99 | static void __exit fini(void) |
| 100 | { |
| 101 | arpt_unregister_target(&arpt_mangle_reg); |
| 102 | } |
| 103 | |
| 104 | module_init(init); |
| 105 | module_exit(fini); |