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