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