LXR linux/net/ipv4/netfilter/arpt

   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
   8MODULE_LICENSE("GPL");
   9MODULE_AUTHOR("Bart De Schuymer <bdschuym@pandora.be>");
  10MODULE_DESCRIPTION("arptables arp payload mangle target");
  11
  12static unsigned int
  13target(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, 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
  58static 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
  72static 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
  81static int __init arpt_mangle_init(void)
  82{
  83        return xt_register_target(&arpt_mangle_reg);
  84}
  85
  86static void __exit arpt_mangle_fini(void)
  87{
  88        xt_unregister_target(&arpt_mangle_reg);
  89}
  90
  91module_init(arpt_mangle_init);
  92module_exit(arpt_mangle_fini);
  93