ipt_ECN.c 3.5 KB

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  1. // SPDX-License-Identifier: GPL-2.0-only
  2. /* iptables module for the IPv4 and TCP ECN bits, Version 1.5
  3. *
  4. * (C) 2002 by Harald Welte <laforge@netfilter.org>
  5. */
  6. #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  7. #include <linux/in.h>
  8. #include <linux/module.h>
  9. #include <linux/skbuff.h>
  10. #include <linux/ip.h>
  11. #include <net/ip.h>
  12. #include <linux/tcp.h>
  13. #include <net/checksum.h>
  14. #include <linux/netfilter/x_tables.h>
  15. #include <linux/netfilter_ipv4/ip_tables.h>
  16. #include <linux/netfilter_ipv4/ipt_ECN.h>
  17. MODULE_LICENSE("GPL");
  18. MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
  19. MODULE_DESCRIPTION("Xtables: Explicit Congestion Notification (ECN) flag modification");
  20. /* set ECT codepoint from IP header.
  21. * return false if there was an error. */
  22. static inline bool
  23. set_ect_ip(struct sk_buff *skb, const struct ipt_ECN_info *einfo)
  24. {
  25. struct iphdr *iph = ip_hdr(skb);
  26. if ((iph->tos & IPT_ECN_IP_MASK) != (einfo->ip_ect & IPT_ECN_IP_MASK)) {
  27. __u8 oldtos;
  28. if (skb_ensure_writable(skb, sizeof(struct iphdr)))
  29. return false;
  30. iph = ip_hdr(skb);
  31. oldtos = iph->tos;
  32. iph->tos &= ~IPT_ECN_IP_MASK;
  33. iph->tos |= (einfo->ip_ect & IPT_ECN_IP_MASK);
  34. csum_replace2(&iph->check, htons(oldtos), htons(iph->tos));
  35. }
  36. return true;
  37. }
  38. /* Return false if there was an error. */
  39. static inline bool
  40. set_ect_tcp(struct sk_buff *skb, const struct ipt_ECN_info *einfo)
  41. {
  42. struct tcphdr _tcph, *tcph;
  43. __be16 oldval;
  44. /* Not enough header? */
  45. tcph = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_tcph), &_tcph);
  46. if (!tcph)
  47. return false;
  48. if ((!(einfo->operation & IPT_ECN_OP_SET_ECE) ||
  49. tcph->ece == einfo->proto.tcp.ece) &&
  50. (!(einfo->operation & IPT_ECN_OP_SET_CWR) ||
  51. tcph->cwr == einfo->proto.tcp.cwr))
  52. return true;
  53. if (skb_ensure_writable(skb, ip_hdrlen(skb) + sizeof(*tcph)))
  54. return false;
  55. tcph = (void *)ip_hdr(skb) + ip_hdrlen(skb);
  56. oldval = ((__be16 *)tcph)[6];
  57. if (einfo->operation & IPT_ECN_OP_SET_ECE)
  58. tcph->ece = einfo->proto.tcp.ece;
  59. if (einfo->operation & IPT_ECN_OP_SET_CWR)
  60. tcph->cwr = einfo->proto.tcp.cwr;
  61. inet_proto_csum_replace2(&tcph->check, skb,
  62. oldval, ((__be16 *)tcph)[6], false);
  63. return true;
  64. }
  65. static unsigned int
  66. ecn_tg(struct sk_buff *skb, const struct xt_action_param *par)
  67. {
  68. const struct ipt_ECN_info *einfo = par->targinfo;
  69. if (einfo->operation & IPT_ECN_OP_SET_IP)
  70. if (!set_ect_ip(skb, einfo))
  71. return NF_DROP;
  72. if (einfo->operation & (IPT_ECN_OP_SET_ECE | IPT_ECN_OP_SET_CWR) &&
  73. ip_hdr(skb)->protocol == IPPROTO_TCP)
  74. if (!set_ect_tcp(skb, einfo))
  75. return NF_DROP;
  76. return XT_CONTINUE;
  77. }
  78. static int ecn_tg_check(const struct xt_tgchk_param *par)
  79. {
  80. const struct ipt_ECN_info *einfo = par->targinfo;
  81. const struct ipt_entry *e = par->entryinfo;
  82. if (einfo->operation & IPT_ECN_OP_MASK)
  83. return -EINVAL;
  84. if (einfo->ip_ect & ~IPT_ECN_IP_MASK)
  85. return -EINVAL;
  86. if ((einfo->operation & (IPT_ECN_OP_SET_ECE|IPT_ECN_OP_SET_CWR)) &&
  87. (e->ip.proto != IPPROTO_TCP || (e->ip.invflags & XT_INV_PROTO))) {
  88. pr_info_ratelimited("cannot use operation on non-tcp rule\n");
  89. return -EINVAL;
  90. }
  91. return 0;
  92. }
  93. static struct xt_target ecn_tg_reg __read_mostly = {
  94. .name = "ECN",
  95. .family = NFPROTO_IPV4,
  96. .target = ecn_tg,
  97. .targetsize = sizeof(struct ipt_ECN_info),
  98. .table = "mangle",
  99. .checkentry = ecn_tg_check,
  100. .me = THIS_MODULE,
  101. };
  102. static int __init ecn_tg_init(void)
  103. {
  104. return xt_register_target(&ecn_tg_reg);
  105. }
  106. static void __exit ecn_tg_exit(void)
  107. {
  108. xt_unregister_target(&ecn_tg_reg);
  109. }
  110. module_init(ecn_tg_init);
  111. module_exit(ecn_tg_exit);