net/ipv4/netfilter/arpt_mangle.c

   1 /* module that allows mangling of the arp payload */
   2 #include <linux/module.h>
   3 #include <linux/netfilter.h>
   4 #include <linux/netfilter_arp/arpt_mangle.h>
   5 #include <net/sock.h>
   6
   7 MODULE_LICENSE("GPL");
   8 MODULE_AUTHOR("Bart De Schuymer <bdschuym@pandora.be>");
   9 MODULE_DESCRIPTION("arptables arp payload mangle target");
  10
  11 static unsigned int
  12 target(struct sk_buff *skb, const struct xt_target_param *par)
  13 {
  14         const struct arpt_mangle *mangle = par->targinfo;
  15         const struct arphdr *arp;
  16         unsigned char *arpptr;
  17         int pln, hln;
  18
  19         if (!skb_make_writable(skb, skb->len))
  20                 return NF_DROP;
  21
  22         arp = arp_hdr(skb);
  23         arpptr = skb_network_header(skb) + sizeof(*arp);
  24         pln = arp->ar_pln;
  25         hln = arp->ar_hln;
  26         /* We assume that pln and hln were checked in the match */
  27         if (mangle->flags & ARPT_MANGLE_SDEV) {
  28                 if (ARPT_DEV_ADDR_LEN_MAX < hln ||
  29                    (arpptr + hln > skb_tail_pointer(skb)))
  30                         return NF_DROP;
  31                 memcpy(arpptr, mangle->src_devaddr, hln);
  32         }
  33         arpptr += hln;
  34         if (mangle->flags & ARPT_MANGLE_SIP) {
  35                 if (ARPT_MANGLE_ADDR_LEN_MAX < pln ||
  36                    (arpptr + pln > skb_tail_pointer(skb)))
  37                         return NF_DROP;
  38                 memcpy(arpptr, &mangle->u_s.src_ip, pln);
  39         }
  40         arpptr += pln;
  41         if (mangle->flags & ARPT_MANGLE_TDEV) {
  42                 if (ARPT_DEV_ADDR_LEN_MAX < hln ||
  43                    (arpptr + hln > skb_tail_pointer(skb)))
  44                         return NF_DROP;
  45                 memcpy(arpptr, mangle->tgt_devaddr, hln);
  46         }
  47         arpptr += hln;
  48         if (mangle->flags & ARPT_MANGLE_TIP) {
  49                 if (ARPT_MANGLE_ADDR_LEN_MAX < pln ||
  50                    (arpptr + pln > skb_tail_pointer(skb)))
  51                         return NF_DROP;
  52                 memcpy(arpptr, &mangle->u_t.tgt_ip, pln);
  53         }
  54         return mangle->target;
  55 }
  56
  57 static bool checkentry(const struct xt_tgchk_param *par)
  58 {
  59         const struct arpt_mangle *mangle = par->targinfo;
  60
  61         if (mangle->flags & ~ARPT_MANGLE_MASK ||
  62             !(mangle->flags & ARPT_MANGLE_MASK))
  63                 return false;
  64
  65         if (mangle->target != NF_DROP && mangle->target != NF_ACCEPT &&
  66            mangle->target != ARPT_CONTINUE)
  67                 return false;
  68         return true;
  69 }
  70
  71 static struct xt_target arpt_mangle_reg __read_mostly = {
  72         .name           = "mangle",
  73         .family         = NFPROTO_ARP,
  74         .target         = target,
  75         .targetsize     = sizeof(struct arpt_mangle),
  76         .checkentry     = checkentry,
  77         .me             = THIS_MODULE,
  78 };
  79
  80 static int __init arpt_mangle_init(void)
  81 {
  82         return xt_register_target(&arpt_mangle_reg);
  83 }
  84
  85 static void __exit arpt_mangle_fini(void)
  86 {
  87         xt_unregister_target(&arpt_mangle_reg);
  88 }
  89
  90 module_init(arpt_mangle_init);
  91 module_exit(arpt_mangle_fini);