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/* module that allows mangling of the arp payload */
#include <linux/module.h>
#include <linux/netfilter.h>
#include <linux/netfilter_arp/arpt_mangle.h>
#include <net/sock.h>
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Bart De Schuymer <bdschuym@pandora.be>");
MODULE_DESCRIPTION("arptables arp payload mangle target");
static unsigned int
target(struct sk_buff *skb,
const struct net_device *in, const struct net_device *out,
unsigned int hooknum, const struct xt_target *target,
const void *targinfo)
{
const struct arpt_mangle *mangle = targinfo;
const struct arphdr *arp;
unsigned char *arpptr;
int pln, hln;
if (!skb_make_writable(skb, skb->len))
return NF_DROP;
arp = arp_hdr(skb);
arpptr = skb_network_header(skb) + sizeof(*arp);
pln = arp->ar_pln;
hln = arp->ar_hln;
/* We assume that pln and hln were checked in the match */
if (mangle->flags & ARPT_MANGLE_SDEV) {
if (ARPT_DEV_ADDR_LEN_MAX < hln ||
(arpptr + hln > skb_tail_pointer(skb)))
return NF_DROP;
memcpy(arpptr, mangle->src_devaddr, hln);
}
arpptr += hln;
if (mangle->flags & ARPT_MANGLE_SIP) {
if (ARPT_MANGLE_ADDR_LEN_MAX < pln ||
(arpptr + pln > skb_tail_pointer(skb)))
return NF_DROP;
memcpy(arpptr, &mangle->u_s.src_ip, pln);
}
arpptr += pln;
if (mangle->flags & ARPT_MANGLE_TDEV) {
if (ARPT_DEV_ADDR_LEN_MAX < hln ||
(arpptr + hln > skb_tail_pointer(skb)))
return NF_DROP;
memcpy(arpptr, mangle->tgt_devaddr, hln);
}
arpptr += hln;
if (mangle->flags & ARPT_MANGLE_TIP) {
if (ARPT_MANGLE_ADDR_LEN_MAX < pln ||
(arpptr + pln > skb_tail_pointer(skb)))
return NF_DROP;
memcpy(arpptr, &mangle->u_t.tgt_ip, pln);
}
return mangle->target;
}
static bool
checkentry(const char *tablename, const void *e, const struct xt_target *target,
void *targinfo, unsigned int hook_mask)
{
const struct arpt_mangle *mangle = targinfo;
if (mangle->flags & ~ARPT_MANGLE_MASK ||
!(mangle->flags & ARPT_MANGLE_MASK))
return false;
if (mangle->target != NF_DROP && mangle->target != NF_ACCEPT &&
mangle->target != ARPT_CONTINUE)
return false;
return true;
}
static struct xt_target arpt_mangle_reg __read_mostly = {
.name = "mangle",
.target = target,
.targetsize = sizeof(struct arpt_mangle),
.checkentry = checkentry,
.me = THIS_MODULE,
};
static int __init arpt_mangle_init(void)
{
if (arpt_register_target(&arpt_mangle_reg))
return -EINVAL;
return 0;
}
static void __exit arpt_mangle_fini(void)
{
arpt_unregister_target(&arpt_mangle_reg);
}
module_init(arpt_mangle_init);
module_exit(arpt_mangle_fini);
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