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