arpt_mangle.c 2.4 KB

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  1. // SPDX-License-Identifier: GPL-2.0-only
  2. /* module that allows mangling of the arp payload */
  3. #include <linux/module.h>
  4. #include <linux/netfilter.h>
  5. #include <linux/netfilter_arp/arpt_mangle.h>
  6. #include <net/sock.h>
  7. MODULE_LICENSE("GPL");
  8. MODULE_AUTHOR("Bart De Schuymer <bdschuym@pandora.be>");
  9. MODULE_DESCRIPTION("arptables arp payload mangle target");
  10. static unsigned int
  11. target(struct sk_buff *skb, const struct xt_action_param *par)
  12. {
  13. const struct arpt_mangle *mangle = par->targinfo;
  14. const struct arphdr *arp;
  15. unsigned char *arpptr;
  16. int pln, hln;
  17. if (skb_ensure_writable(skb, skb->len))
  18. return NF_DROP;
  19. arp = arp_hdr(skb);
  20. arpptr = skb_network_header(skb) + sizeof(*arp);
  21. pln = arp->ar_pln;
  22. hln = arp->ar_hln;
  23. /* We assume that pln and hln were checked in the match */
  24. if (mangle->flags & ARPT_MANGLE_SDEV) {
  25. if (ARPT_DEV_ADDR_LEN_MAX < hln ||
  26. (arpptr + hln > skb_tail_pointer(skb)))
  27. return NF_DROP;
  28. memcpy(arpptr, mangle->src_devaddr, hln);
  29. }
  30. arpptr += hln;
  31. if (mangle->flags & ARPT_MANGLE_SIP) {
  32. if (ARPT_MANGLE_ADDR_LEN_MAX < pln ||
  33. (arpptr + pln > skb_tail_pointer(skb)))
  34. return NF_DROP;
  35. memcpy(arpptr, &mangle->u_s.src_ip, pln);
  36. }
  37. arpptr += pln;
  38. if (mangle->flags & ARPT_MANGLE_TDEV) {
  39. if (ARPT_DEV_ADDR_LEN_MAX < hln ||
  40. (arpptr + hln > skb_tail_pointer(skb)))
  41. return NF_DROP;
  42. memcpy(arpptr, mangle->tgt_devaddr, hln);
  43. }
  44. arpptr += hln;
  45. if (mangle->flags & ARPT_MANGLE_TIP) {
  46. if (ARPT_MANGLE_ADDR_LEN_MAX < pln ||
  47. (arpptr + pln > skb_tail_pointer(skb)))
  48. return NF_DROP;
  49. memcpy(arpptr, &mangle->u_t.tgt_ip, pln);
  50. }
  51. return mangle->target;
  52. }
  53. static int checkentry(const struct xt_tgchk_param *par)
  54. {
  55. const struct arpt_mangle *mangle = par->targinfo;
  56. if (mangle->flags & ~ARPT_MANGLE_MASK ||
  57. !(mangle->flags & ARPT_MANGLE_MASK))
  58. return -EINVAL;
  59. if (mangle->target != NF_DROP && mangle->target != NF_ACCEPT &&
  60. mangle->target != XT_CONTINUE)
  61. return -EINVAL;
  62. return 0;
  63. }
  64. static struct xt_target arpt_mangle_reg __read_mostly = {
  65. .name = "mangle",
  66. .family = NFPROTO_ARP,
  67. .target = target,
  68. .targetsize = sizeof(struct arpt_mangle),
  69. .checkentry = checkentry,
  70. .me = THIS_MODULE,
  71. };
  72. static int __init arpt_mangle_init(void)
  73. {
  74. return xt_register_target(&arpt_mangle_reg);
  75. }
  76. static void __exit arpt_mangle_fini(void)
  77. {
  78. xt_unregister_target(&arpt_mangle_reg);
  79. }
  80. module_init(arpt_mangle_init);
  81. module_exit(arpt_mangle_fini);