net/ipv4/netfilter/arpt_mangle.c

   1 /* module that allows mangling of the arp payload */
   2 #include <linux/module.h>
   3 #include <linux/netfilter_arp/arpt_mangle.h>
   4 #include <net/sock.h>
   5
   6 MODULE_LICENSE("GPL");
   7 MODULE_AUTHOR("Bart De Schuymer <bdschuym@pandora.be>");
   8 MODULE_DESCRIPTION("arptables arp payload mangle target");
   9
  10 static unsigned int
  11 target(struct sk_buff **pskb, unsigned int hooknum, const struct net_device *in,
  12    const struct net_device *out, const void *targinfo, void *userinfo)
  13 {
  14         const struct arpt_mangle *mangle = targinfo;
  15         struct arphdr *arp;
  16         unsigned char *arpptr;
  17         int pln, hln;
  18
  19         if (skb_shared(*pskb) || skb_cloned(*pskb)) {
  20                 struct sk_buff *nskb;
  21
  22                 nskb = skb_copy(*pskb, GFP_ATOMIC);
  23                 if (!nskb)
  24                         return NF_DROP;
  25                 if ((*pskb)->sk)
  26                         skb_set_owner_w(nskb, (*pskb)->sk);
  27                 kfree_skb(*pskb);
  28                 *pskb = nskb;
  29         }
  30
  31         arp = (*pskb)->nh.arph;
  32         arpptr = (*pskb)->nh.raw + sizeof(*arp);
  33         pln = arp->ar_pln;
  34         hln = arp->ar_hln;
  35         /* We assume that pln and hln were checked in the match */
  36         if (mangle->flags & ARPT_MANGLE_SDEV) {
  37                 if (ARPT_DEV_ADDR_LEN_MAX < hln ||
  38                    (arpptr + hln > (**pskb).tail))
  39                         return NF_DROP;
  40                 memcpy(arpptr, mangle->src_devaddr, hln);
  41         }
  42         arpptr += hln;
  43         if (mangle->flags & ARPT_MANGLE_SIP) {
  44                 if (ARPT_MANGLE_ADDR_LEN_MAX < pln ||
  45                    (arpptr + pln > (**pskb).tail))
  46                         return NF_DROP;
  47                 memcpy(arpptr, &mangle->u_s.src_ip, pln);
  48         }
  49         arpptr += pln;
  50         if (mangle->flags & ARPT_MANGLE_TDEV) {
  51                 if (ARPT_DEV_ADDR_LEN_MAX < hln ||
  52                    (arpptr + hln > (**pskb).tail))
  53                         return NF_DROP;
  54                 memcpy(arpptr, mangle->tgt_devaddr, hln);
  55         }
  56         arpptr += hln;
  57         if (mangle->flags & ARPT_MANGLE_TIP) {
  58                 if (ARPT_MANGLE_ADDR_LEN_MAX < pln ||
  59                    (arpptr + pln > (**pskb).tail))
  60                         return NF_DROP;
  61                 memcpy(arpptr, &mangle->u_t.tgt_ip, pln);
  62         }
  63         return mangle->target;
  64 }
  65
  66 static int
  67 checkentry(const char *tablename, const struct arpt_entry *e, void *targinfo,
  68    unsigned int targinfosize, unsigned int hook_mask)
  69 {
  70         const struct arpt_mangle *mangle = targinfo;
  71
  72         if (mangle->flags & ~ARPT_MANGLE_MASK ||
  73             !(mangle->flags & ARPT_MANGLE_MASK))
  74                 return 0;
  75
  76         if (mangle->target != NF_DROP && mangle->target != NF_ACCEPT &&
  77            mangle->target != ARPT_CONTINUE)
  78                 return 0;
  79         return 1;
  80 }
  81
  82 static struct arpt_target arpt_mangle_reg
  83 = {
  84         .name           = "mangle",
  85         .target         = target,
  86         .checkentry     = checkentry,
  87         .me             = THIS_MODULE,
  88 };
  89
  90 static int __init init(void)
  91 {
  92         if (arpt_register_target(&arpt_mangle_reg))
  93                 return -EINVAL;
  94
  95         return 0;
  96 }
  97
  98 static void __exit fini(void)
  99 {
 100         arpt_unregister_target(&arpt_mangle_reg);
 101 }
 102
 103 module_init(init);
 104 module_exit(fini);