/* module that allows mangling of the arp payload */#include <linux/module.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 inttarget(struct sk_buff **pskb, unsigned int hooknum, const struct net_device *in,   const struct net_device *out, const void *targinfo, void *userinfo){	const struct arpt_mangle *mangle = targinfo;	struct arphdr *arp;	unsigned char *arpptr;	int pln, hln;	if (skb_shared(*pskb) || skb_cloned(*pskb)) {		struct sk_buff *nskb;		nskb = skb_copy(*pskb, GFP_ATOMIC);		if (!nskb)			return NF_DROP;		if ((*pskb)->sk)			skb_set_owner_w(nskb, (*pskb)->sk);		kfree_skb(*pskb);		*pskb = nskb;	}	arp = (*pskb)->nh.arph;	arpptr = (*pskb)->nh.raw + 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 > (**pskb).tail))			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 > (**pskb).tail))			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 > (**pskb).tail))			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 > (**pskb).tail))			return NF_DROP;		memcpy(arpptr, &mangle->u_t.tgt_ip, pln);	}	return mangle->target;}static intcheckentry(const char *tablename, const struct arpt_entry *e, void *targinfo,   unsigned int targinfosize, unsigned int hook_mask){	const struct arpt_mangle *mangle = targinfo;	if (mangle->flags & ~ARPT_MANGLE_MASK ||	    !(mangle->flags & ARPT_MANGLE_MASK))		return 0;	if (mangle->target != NF_DROP && mangle->target != NF_ACCEPT &&	   mangle->target != ARPT_CONTINUE)		return 0;	return 1;}static struct arpt_target arpt_mangle_reg= {        .name		= "mangle",        .target		= target,        .checkentry	= checkentry,        .me		= THIS_MODULE,};static int __init init(void){	if (arpt_register_target(&arpt_mangle_reg))		return -EINVAL;	return 0;}static void __exit fini(void){	arpt_unregister_target(&arpt_mangle_reg);}module_init(init);module_exit(fini);