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
   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 #ifdef DEBUG_CONNTRACK
  22 #define duprintf(format, args...) printk(format , ## args)
  23 #else
  24 #define duprintf(format, args...)
  25 #endif
  26
  27 /* Returns 1 if the spi is matched by the range, 0 otherwise */
  28 static inline bool
  29 spi_match(u_int32_t min, u_int32_t max, u_int32_t spi, bool invert)
  30 {
  31         bool r;
  32         duprintf("ah spi_match:%c 0x%x <= 0x%x <= 0x%x",invert? '!':' ',
  33                 min,spi,max);
  34         r=(spi >= min && spi <= max) ^ invert;
  35         duprintf(" result %s\n",r? "PASS" : "FAILED");
  36         return r;
  37 }
  38
  39 static bool ah_mt(const struct sk_buff *skb, const struct xt_match_param *par)
  40 {
  41         struct ip_auth_hdr _ahdr;
  42         const struct ip_auth_hdr *ah;
  43         const struct ipt_ah *ahinfo = par->matchinfo;
  44
  45         /* Must not be a fragment. */
  46         if (par->fragoff != 0)
  47                 return false;
  48
  49         ah = skb_header_pointer(skb, par->thoff, sizeof(_ahdr), &_ahdr);
  50         if (ah == NULL) {
  51                 /* We've been asked to examine this packet, and we
  52                  * can't.  Hence, no choice but to drop.
  53                  */
  54                 duprintf("Dropping evil AH tinygram.\n");
  55                 *par->hotdrop = true;
  56                 return 0;
  57         }
  58
  59         return spi_match(ahinfo->spis[0], ahinfo->spis[1],
  60                          ntohl(ah->spi),
  61                          !!(ahinfo->invflags & IPT_AH_INV_SPI));
  62 }
  63
  64 static bool ah_mt_check(const struct xt_mtchk_param *par)
  65 {
  66         const struct ipt_ah *ahinfo = par->matchinfo;
  67
  68         /* Must specify no unknown invflags */
  69         if (ahinfo->invflags & ~IPT_AH_INV_MASK) {
  70                 duprintf("ipt_ah: unknown flags %X\n", ahinfo->invflags);
  71                 return false;
  72         }
  73         return true;
  74 }
  75
  76 static struct xt_match ah_mt_reg __read_mostly = {
  77         .name           = "ah",
  78         .family         = NFPROTO_IPV4,
  79         .match          = ah_mt,
  80         .matchsize      = sizeof(struct ipt_ah),
  81         .proto          = IPPROTO_AH,
  82         .checkentry     = ah_mt_check,
  83         .me             = THIS_MODULE,
  84 };
  85
  86 static int __init ah_mt_init(void)
  87 {
  88         return xt_register_match(&ah_mt_reg);
  89 }
  90
  91 static void __exit ah_mt_exit(void)
  92 {
  93         xt_unregister_match(&ah_mt_reg);
  94 }
  95
  96 module_init(ah_mt_init);
  97 module_exit(ah_mt_exit);