net/netfilter/xt_CHECKSUM.c

   1 /* iptables module for the packet checksum mangling
   2  *
   3  * (C) 2002 by Harald Welte <laforge@netfilter.org>
   4  * (C) 2010 Red Hat, Inc.
   5  *
   6  * Author: Michael S. Tsirkin <mst@redhat.com>
   7  *
   8  * This program is free software; you can redistribute it and/or modify
   9  * it under the terms of the GNU General Public License version 2 as
  10  * published by the Free Software Foundation.
  11 */
  12 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  13 #include <linux/module.h>
  14 #include <linux/skbuff.h>
  15
  16 #include <linux/netfilter/x_tables.h>
  17 #include <linux/netfilter/xt_CHECKSUM.h>
  18
  19 #include <linux/netfilter_ipv4/ip_tables.h>
  20 #include <linux/netfilter_ipv6/ip6_tables.h>
  21
  22 MODULE_LICENSE("GPL");
  23 MODULE_AUTHOR("Michael S. Tsirkin <mst@redhat.com>");
  24 MODULE_DESCRIPTION("Xtables: checksum modification");
  25 MODULE_ALIAS("ipt_CHECKSUM");
  26 MODULE_ALIAS("ip6t_CHECKSUM");
  27
  28 static unsigned int
  29 checksum_tg(struct sk_buff *skb, const struct xt_action_param *par)
  30 {
  31         if (skb->ip_summed == CHECKSUM_PARTIAL && !skb_is_gso(skb))
  32                 skb_checksum_help(skb);
  33
  34         return XT_CONTINUE;
  35 }
  36
  37 static int checksum_tg_check(const struct xt_tgchk_param *par)
  38 {
  39         const struct xt_CHECKSUM_info *einfo = par->targinfo;
  40         const struct ip6t_ip6 *i6 = par->entryinfo;
  41         const struct ipt_ip *i4 = par->entryinfo;
  42
  43         if (einfo->operation & ~XT_CHECKSUM_OP_FILL) {
  44                 pr_info_ratelimited("unsupported CHECKSUM operation %x\n",
  45                                     einfo->operation);
  46                 return -EINVAL;
  47         }
  48         if (!einfo->operation)
  49                 return -EINVAL;
  50
  51         switch (par->family) {
  52         case NFPROTO_IPV4:
  53                 if (i4->proto == IPPROTO_UDP &&
  54                     (i4->invflags & XT_INV_PROTO) == 0)
  55                         return 0;
  56                 break;
  57         case NFPROTO_IPV6:
  58                 if ((i6->flags & IP6T_F_PROTO) &&
  59                     i6->proto == IPPROTO_UDP &&
  60                     (i6->invflags & XT_INV_PROTO) == 0)
  61                         return 0;
  62                 break;
  63         }
  64
  65         pr_warn_once("CHECKSUM should be avoided.  If really needed, restrict with \"-p udp\" and only use in OUTPUT\n");
  66         return 0;
  67 }
  68
  69 static struct xt_target checksum_tg_reg __read_mostly = {
  70         .name           = "CHECKSUM",
  71         .family         = NFPROTO_UNSPEC,
  72         .target         = checksum_tg,
  73         .targetsize     = sizeof(struct xt_CHECKSUM_info),
  74         .table          = "mangle",
  75         .checkentry     = checksum_tg_check,
  76         .me             = THIS_MODULE,
  77 };
  78
  79 static int __init checksum_tg_init(void)
  80 {
  81         return xt_register_target(&checksum_tg_reg);
  82 }
  83
  84 static void __exit checksum_tg_exit(void)
  85 {
  86         xt_unregister_target(&checksum_tg_reg);
  87 }
  88
  89 module_init(checksum_tg_init);
  90 module_exit(checksum_tg_exit);