net/netfilter/xt_CHECKSUM.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /* iptables module for the packet checksum mangling
   3  *
   4  * (C) 2002 by Harald Welte <laforge@netfilter.org>
   5  * (C) 2010 Red Hat, Inc.
   6  *
   7  * Author: Michael S. Tsirkin <mst@redhat.com>
   8 */
   9 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  10 #include <linux/module.h>
  11 #include <linux/skbuff.h>
  12
  13 #include <linux/netfilter/x_tables.h>
  14 #include <linux/netfilter/xt_CHECKSUM.h>
  15
  16 #include <linux/netfilter_ipv4/ip_tables.h>
  17 #include <linux/netfilter_ipv6/ip6_tables.h>
  18
  19 MODULE_LICENSE("GPL");
  20 MODULE_AUTHOR("Michael S. Tsirkin <mst@redhat.com>");
  21 MODULE_DESCRIPTION("Xtables: checksum modification");
  22 MODULE_ALIAS("ipt_CHECKSUM");
  23 MODULE_ALIAS("ip6t_CHECKSUM");
  24
  25 static unsigned int
  26 checksum_tg(struct sk_buff *skb, const struct xt_action_param *par)
  27 {
  28         if (skb->ip_summed == CHECKSUM_PARTIAL && !skb_is_gso(skb))
  29                 skb_checksum_help(skb);
  30
  31         return XT_CONTINUE;
  32 }
  33
  34 static int checksum_tg_check(const struct xt_tgchk_param *par)
  35 {
  36         const struct xt_CHECKSUM_info *einfo = par->targinfo;
  37         const struct ip6t_ip6 *i6 = par->entryinfo;
  38         const struct ipt_ip *i4 = par->entryinfo;
  39
  40         if (einfo->operation & ~XT_CHECKSUM_OP_FILL) {
  41                 pr_info_ratelimited("unsupported CHECKSUM operation %x\n",
  42                                     einfo->operation);
  43                 return -EINVAL;
  44         }
  45         if (!einfo->operation)
  46                 return -EINVAL;
  47
  48         switch (par->family) {
  49         case NFPROTO_IPV4:
  50                 if (i4->proto == IPPROTO_UDP &&
  51                     (i4->invflags & XT_INV_PROTO) == 0)
  52                         return 0;
  53                 break;
  54         case NFPROTO_IPV6:
  55                 if ((i6->flags & IP6T_F_PROTO) &&
  56                     i6->proto == IPPROTO_UDP &&
  57                     (i6->invflags & XT_INV_PROTO) == 0)
  58                         return 0;
  59                 break;
  60         }
  61
  62         pr_warn_once("CHECKSUM should be avoided.  If really needed, restrict with \"-p udp\" and only use in OUTPUT\n");
  63         return 0;
  64 }
  65
  66 static struct xt_target checksum_tg_reg __read_mostly = {
  67         .name           = "CHECKSUM",
  68         .family         = NFPROTO_UNSPEC,
  69         .target         = checksum_tg,
  70         .targetsize     = sizeof(struct xt_CHECKSUM_info),
  71         .table          = "mangle",
  72         .checkentry     = checksum_tg_check,
  73         .me             = THIS_MODULE,
  74 };
  75
  76 static int __init checksum_tg_init(void)
  77 {
  78         return xt_register_target(&checksum_tg_reg);
  79 }
  80
  81 static void __exit checksum_tg_exit(void)
  82 {
  83         xt_unregister_target(&checksum_tg_reg);
  84 }
  85
  86 module_init(checksum_tg_init);
  87 module_exit(checksum_tg_exit);