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