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Linux/net/ipv4/netfilter/ipt_ah.c

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  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);
 92 

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