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   1 /*
   2  * iptables module for DCCP protocol header matching
   3  *
   4  * (C) 2005 by Harald Welte <laforge@netfilter.org>
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License version 2 as
   8  * published by the Free Software Foundation.
   9  */
  10
  11 #include <linux/module.h>
  12 #include <linux/skbuff.h>
  13 #include <linux/slab.h>
  14 #include <linux/spinlock.h>
  15 #include <net/ip.h>
  16 #include <linux/dccp.h>
  17
  18 #include <linux/netfilter/x_tables.h>
  19 #include <linux/netfilter/xt_dccp.h>
  20
  21 #include <linux/netfilter_ipv4/ip_tables.h>
  22 #include <linux/netfilter_ipv6/ip6_tables.h>
  23
  24 MODULE_LICENSE("GPL");
  25 MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
  26 MODULE_DESCRIPTION("Xtables: DCCP protocol packet match");
  27 MODULE_ALIAS("ipt_dccp");
  28 MODULE_ALIAS("ip6t_dccp");
  29
  30 #define DCCHECK(cond, option, flag, invflag) (!((flag) & (option)) \
  31                                   || (!!((invflag) & (option)) ^ (cond)))
  32
  33 static unsigned char *dccp_optbuf;
  34 static DEFINE_SPINLOCK(dccp_buflock);
  35
  36 static inline bool
  37 dccp_find_option(u_int8_t option,
  38                  const struct sk_buff *skb,
  39                  unsigned int protoff,
  40                  const struct dccp_hdr *dh,
  41                  bool *hotdrop)
  42 {
  43         /* tcp.doff is only 4 bits, ie. max 15 * 4 bytes */
  44         const unsigned char *op;
  45         unsigned int optoff = __dccp_hdr_len(dh);
  46         unsigned int optlen = dh->dccph_doff*4 - __dccp_hdr_len(dh);
  47         unsigned int i;
  48
  49         if (dh->dccph_doff * 4 < __dccp_hdr_len(dh))
  50                 goto invalid;
  51
  52         if (!optlen)
  53                 return false;
  54
  55         spin_lock_bh(&dccp_buflock);
  56         op = skb_header_pointer(skb, protoff + optoff, optlen, dccp_optbuf);
  57         if (op == NULL) {
  58                 /* If we don't have the whole header, drop packet. */
  59                 goto partial;
  60         }
  61
  62         for (i = 0; i < optlen; ) {
  63                 if (op[i] == option) {
  64                         spin_unlock_bh(&dccp_buflock);
  65                         return true;
  66                 }
  67
  68                 if (op[i] < 2)
  69                         i++;
  70                 else
  71                         i += op[i+1]?:1;
  72         }
  73
  74         spin_unlock_bh(&dccp_buflock);
  75         return false;
  76
  77 partial:
  78         spin_unlock_bh(&dccp_buflock);
  79 invalid:
  80         *hotdrop = true;
  81         return false;
  82 }
  83
  84
  85 static inline bool
  86 match_types(const struct dccp_hdr *dh, u_int16_t typemask)
  87 {
  88         return typemask & (1 << dh->dccph_type);
  89 }
  90
  91 static inline bool
  92 match_option(u_int8_t option, const struct sk_buff *skb, unsigned int protoff,
  93              const struct dccp_hdr *dh, bool *hotdrop)
  94 {
  95         return dccp_find_option(option, skb, protoff, dh, hotdrop);
  96 }
  97
  98 static bool
  99 dccp_mt(const struct sk_buff *skb, const struct xt_match_param *par)
 100 {
 101         const struct xt_dccp_info *info = par->matchinfo;
 102         const struct dccp_hdr *dh;
 103         struct dccp_hdr _dh;
 104
 105         if (par->fragoff != 0)
 106                 return false;
 107
 108         dh = skb_header_pointer(skb, par->thoff, sizeof(_dh), &_dh);
 109         if (dh == NULL) {
 110                 *par->hotdrop = true;
 111                 return false;
 112         }
 113
 114         return  DCCHECK(ntohs(dh->dccph_sport) >= info->spts[0]
 115                         && ntohs(dh->dccph_sport) <= info->spts[1],
 116                         XT_DCCP_SRC_PORTS, info->flags, info->invflags)
 117                 && DCCHECK(ntohs(dh->dccph_dport) >= info->dpts[0]
 118                         && ntohs(dh->dccph_dport) <= info->dpts[1],
 119                         XT_DCCP_DEST_PORTS, info->flags, info->invflags)
 120                 && DCCHECK(match_types(dh, info->typemask),
 121                            XT_DCCP_TYPE, info->flags, info->invflags)
 122                 && DCCHECK(match_option(info->option, skb, par->thoff, dh,
 123                                         par->hotdrop),
 124                            XT_DCCP_OPTION, info->flags, info->invflags);
 125 }
 126
 127 static bool dccp_mt_check(const struct xt_mtchk_param *par)
 128 {
 129         const struct xt_dccp_info *info = par->matchinfo;
 130
 131         return !(info->flags & ~XT_DCCP_VALID_FLAGS)
 132                 && !(info->invflags & ~XT_DCCP_VALID_FLAGS)
 133                 && !(info->invflags & ~info->flags);
 134 }
 135
 136 static struct xt_match dccp_mt_reg[] __read_mostly = {
 137         {
 138                 .name           = "dccp",
 139                 .family         = NFPROTO_IPV4,
 140                 .checkentry     = dccp_mt_check,
 141                 .match          = dccp_mt,
 142                 .matchsize      = sizeof(struct xt_dccp_info),
 143                 .proto          = IPPROTO_DCCP,
 144                 .me             = THIS_MODULE,
 145         },
 146         {
 147                 .name           = "dccp",
 148                 .family         = NFPROTO_IPV6,
 149                 .checkentry     = dccp_mt_check,
 150                 .match          = dccp_mt,
 151                 .matchsize      = sizeof(struct xt_dccp_info),
 152                 .proto          = IPPROTO_DCCP,
 153                 .me             = THIS_MODULE,
 154         },
 155 };
 156
 157 static int __init dccp_mt_init(void)
 158 {
 159         int ret;
 160
 161         /* doff is 8 bits, so the maximum option size is (4*256).  Don't put
 162          * this in BSS since DaveM is worried about locked TLB's for kernel
 163          * BSS. */
 164         dccp_optbuf = kmalloc(256 * 4, GFP_KERNEL);
 165         if (!dccp_optbuf)
 166                 return -ENOMEM;
 167         ret = xt_register_matches(dccp_mt_reg, ARRAY_SIZE(dccp_mt_reg));
 168         if (ret)
 169                 goto out_kfree;
 170         return ret;
 171
 172 out_kfree:
 173         kfree(dccp_optbuf);
 174         return ret;
 175 }
 176
 177 static void __exit dccp_mt_exit(void)
 178 {
 179         xt_unregister_matches(dccp_mt_reg, ARRAY_SIZE(dccp_mt_reg));
 180         kfree(dccp_optbuf);
 181 }
 182
 183 module_init(dccp_mt_init);
 184 module_exit(dccp_mt_exit);