net/ipv4/netfilter/ipt_ah.c

   1 /* Kernel module to match AH parameters. */
   2 /* (C) 1999-2000 Yon Uriarte <yon@astaro.de>
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License version 2 as
   6  * published by the Free Software Foundation.
   7  */
   8 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
   9 #include <linux/in.h>
  10 #include <linux/module.h>
  11 #include <linux/skbuff.h>
  12 #include <linux/ip.h>
  13
  14 #include <linux/netfilter_ipv4/ipt_ah.h>
  15 #include <linux/netfilter/x_tables.h>
  16
  17 MODULE_LICENSE("GPL");
  18 MODULE_AUTHOR("Yon Uriarte <yon@astaro.de>");
  19 MODULE_DESCRIPTION("Xtables: IPv4 IPsec-AH SPI match");
  20
  21 /* Returns 1 if the spi is matched by the range, 0 otherwise */
  22 static inline bool
  23 spi_match(u_int32_t min, u_int32_t max, u_int32_t spi, bool invert)
  24 {
  25         bool r;
  26         pr_debug("spi_match:%c 0x%x <= 0x%x <= 0x%x\n",
  27                  invert ? '!' : ' ', min, spi, max);
  28         r=(spi >= min && spi <= max) ^ invert;
  29         pr_debug(" result %s\n", r ? "PASS" : "FAILED");
  30         return r;
  31 }
  32
  33 static bool ah_mt(const struct sk_buff *skb, struct xt_action_param *par)
  34 {
  35         struct ip_auth_hdr _ahdr;
  36         const struct ip_auth_hdr *ah;
  37         const struct ipt_ah *ahinfo = par->matchinfo;
  38
  39         /* Must not be a fragment. */
  40         if (par->fragoff != 0)
  41                 return false;
  42
  43         ah = skb_header_pointer(skb, par->thoff, sizeof(_ahdr), &_ahdr);
  44         if (ah == NULL) {
  45                 /* We've been asked to examine this packet, and we
  46                  * can't.  Hence, no choice but to drop.
  47                  */
  48                 pr_debug("Dropping evil AH tinygram.\n");
  49                 par->hotdrop = true;
  50                 return 0;
  51         }
  52
  53         return spi_match(ahinfo->spis[0], ahinfo->spis[1],
  54                          ntohl(ah->spi),
  55                          !!(ahinfo->invflags & IPT_AH_INV_SPI));
  56 }
  57
  58 static int ah_mt_check(const struct xt_mtchk_param *par)
  59 {
  60         const struct ipt_ah *ahinfo = par->matchinfo;
  61
  62         /* Must specify no unknown invflags */
  63         if (ahinfo->invflags & ~IPT_AH_INV_MASK) {
  64                 pr_debug("unknown flags %X\n", ahinfo->invflags);
  65                 return -EINVAL;
  66         }
  67         return 0;
  68 }
  69
  70 static struct xt_match ah_mt_reg __read_mostly = {
  71         .name           = "ah",
  72         .family         = NFPROTO_IPV4,
  73         .match          = ah_mt,
  74         .matchsize      = sizeof(struct ipt_ah),
  75         .proto          = IPPROTO_AH,
  76         .checkentry     = ah_mt_check,
  77         .me             = THIS_MODULE,
  78 };
  79
  80 static int __init ah_mt_init(void)
  81 {
  82         return xt_register_match(&ah_mt_reg);
  83 }
  84
  85 static void __exit ah_mt_exit(void)
  86 {
  87         xt_unregister_match(&ah_mt_reg);
  88 }
  89
  90 module_init(ah_mt_init);
  91 module_exit(ah_mt_exit);