[5494bc]: extensions / xt_DHCPMAC.c  Maximize  Restore  History

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/*
* "DHCPMAC" extensions for Xtables
* Copyright Š Jan Engelhardt, 2008
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License; either
* version 2 of the License, or any later version, as published by the
* Free Software Foundation.
*/
#include <linux/ip.h>
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/types.h>
#include <linux/udp.h>
#include <net/ip.h>
#include <linux/netfilter/x_tables.h>
#include "xt_DHCPMAC.h"
#include "compat_xtables.h"
struct dhcp_message {
uint8_t op, htype, hlen, hops;
__be32 xid;
__be16 secs, flags;
__be32 ciaddr, yiaddr, siaddr, giaddr;
char chaddr[16];
/* Omitting all unneeded fields saves runtime memory */
/* char sname[64], file[128]; */
};
static void ether_set(unsigned char *addr, const unsigned char *op,
uint8_t mask)
{
uint8_t lo_mask;
unsigned int i;
for (i = 0; i < ETH_ALEN && mask > 0; ++i) {
lo_mask = mask % 8;
/* FF << 4 >> 4 = 0F */
lo_mask = ~(uint8_t)0U << lo_mask >> lo_mask;
addr[i] &= lo_mask;
addr[i] |= op[i] & ~lo_mask;
if (mask >= 8)
mask -= 8;
else
mask = 0;
}
}
static bool ether_cmp(const unsigned char *lh, const unsigned char *rh,
uint8_t mask)
{
uint8_t lo_mask;
unsigned int i;
#define ZMAC_FMT "%02X:%02X:%02X:%02X:%02X:%02X"
#define ZMACHEX(s) s[0], s[1], s[2], s[3], s[4], s[5]
for (i = 0; i < ETH_ALEN && mask > 0; ++i) {
lo_mask = mask % 8;
/* ~(0xFF << 4 >> 4) = ~0x0F = 0xF0 */
lo_mask = ~(~(uint8_t)0U << lo_mask >> lo_mask);
if ((lh[i] ^ rh[i]) & lo_mask)
return false;
if (mask >= 8)
mask -= 8;
else
mask = 0;
}
return true;
}
static bool
dhcpmac_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
const struct dhcpmac_info *info = par->matchinfo;
const struct dhcp_message *dh;
struct dhcp_message dhcpbuf;
dh = skb_header_pointer(skb, par->thoff + sizeof(struct udphdr),
sizeof(dhcpbuf), &dhcpbuf);
if (dh == NULL)
/*
* No hotdrop. This packet does not look like DHCP, but other
* matches may still have a valid reason to get their chance
* to match on this.
*/
return false;
return ether_cmp((const void *)dh->chaddr, info->addr, info->mask);
}
static unsigned int
dhcpmac_tg(struct sk_buff **pskb, const struct xt_action_param *par)
{
const struct dhcpmac_info *info = par->targinfo;
struct dhcp_message dhcpbuf, *dh;
struct udphdr udpbuf, *udph;
struct sk_buff *skb = *pskb;
unsigned int i;
if (!skb_make_writable(pskb, 0))
return NF_DROP;
udph = skb_header_pointer(skb, ip_hdrlen(skb),
sizeof(udpbuf), &udpbuf);
if (udph == NULL)
return NF_DROP;
dh = skb_header_pointer(skb, ip_hdrlen(skb) + sizeof(udpbuf),
sizeof(dhcpbuf), &dhcpbuf);
if (dh == NULL)
return NF_DROP;
for (i = 0; i < sizeof(dh->chaddr); i += 2)
csum_replace2(&udph->check, *(const __be16 *)dh->chaddr, 0);
memset(dh->chaddr, 0, sizeof(dh->chaddr));
ether_set(dh->chaddr, info->addr, info->mask);
for (i = 0; i < sizeof(dh->chaddr); i += 2)
csum_replace2(&udph->check, 0, *(const __be16 *)dh->chaddr);
return XT_CONTINUE;
}
static struct xt_target dhcpmac_tg_reg __read_mostly = {
.name = "DHCPMAC",
.revision = 0,
.family = NFPROTO_IPV4,
.proto = IPPROTO_UDP,
.table = "mangle",
.target = dhcpmac_tg,
.targetsize = XT_ALIGN(sizeof(struct dhcpmac_info)),
.me = THIS_MODULE,
};
static struct xt_match dhcpmac_mt_reg __read_mostly = {
.name = "dhcpmac",
.revision = 0,
.family = NFPROTO_IPV4,
.proto = IPPROTO_UDP,
.match = dhcpmac_mt,
.matchsize = sizeof(struct dhcpmac_info),
.me = THIS_MODULE,
};
static int __init dhcpmac_init(void)
{
int ret;
ret = xt_register_target(&dhcpmac_tg_reg);
if (ret != 0)
return ret;
ret = xt_register_match(&dhcpmac_mt_reg);
if (ret != 0) {
xt_unregister_target(&dhcpmac_tg_reg);
return ret;
}
return 0;
}
static void __exit dhcpmac_exit(void)
{
xt_unregister_target(&dhcpmac_tg_reg);
xt_unregister_match(&dhcpmac_mt_reg);
}
module_init(dhcpmac_init);
module_exit(dhcpmac_exit);
MODULE_DESCRIPTION("Xtables: Clamp DHCP MAC to packet MAC addresses");
MODULE_AUTHOR("Jan Engelhardt ");
MODULE_LICENSE("GPL");
MODULE_ALIAS("ipt_DHCPMAC");
MODULE_ALIAS("ipt_dhcpmac");

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