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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("Match for DCCP protocol packets");
  26 MODULE_ALIAS("ipt_dccp");
  27
  28 #define DCCHECK(cond, option, flag, invflag) (!((flag) & (option)) \
  29                                   || (!!((invflag) & (option)) ^ (cond)))
  30
  31 static unsigned char *dccp_optbuf;
  32 static DEFINE_SPINLOCK(dccp_buflock);
  33
  34 static inline bool
  35 dccp_find_option(u_int8_t option,
  36                  const struct sk_buff *skb,
  37                  unsigned int protoff,
  38                  const struct dccp_hdr *dh,
  39                  bool *hotdrop)
  40 {
  41         /* tcp.doff is only 4 bits, ie. max 15 * 4 bytes */
  42         unsigned char *op;
  43         unsigned int optoff = __dccp_hdr_len(dh);
  44         unsigned int optlen = dh->dccph_doff*4 - __dccp_hdr_len(dh);
  45         unsigned int i;
  46
  47         if (dh->dccph_doff * 4 < __dccp_hdr_len(dh)) {
  48                 *hotdrop = true;
  49                 return false;
  50         }
  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                 spin_unlock_bh(&dccp_buflock);
  60                 *hotdrop = true;
  61                 return false;
  62         }
  63
  64         for (i = 0; i < optlen; ) {
  65                 if (op[i] == option) {
  66                         spin_unlock_bh(&dccp_buflock);
  67                         return true;
  68                 }
  69
  70                 if (op[i] < 2)
  71                         i++;
  72                 else
  73                         i += op[i+1]?:1;
  74         }
  75
  76         spin_unlock_bh(&dccp_buflock);
  77         return false;
  78 }
  79
  80
  81 static inline bool
  82 match_types(const struct dccp_hdr *dh, u_int16_t typemask)
  83 {
  84         return (typemask & (1 << dh->dccph_type));
  85 }
  86
  87 static inline bool
  88 match_option(u_int8_t option, const struct sk_buff *skb, unsigned int protoff,
  89              const struct dccp_hdr *dh, bool *hotdrop)
  90 {
  91         return dccp_find_option(option, skb, protoff, dh, hotdrop);
  92 }
  93
  94 static bool
  95 match(const struct sk_buff *skb,
  96       const struct net_device *in,
  97       const struct net_device *out,
  98       const struct xt_match *match,
  99       const void *matchinfo,
 100       int offset,
 101       unsigned int protoff,
 102       bool *hotdrop)
 103 {
 104         const struct xt_dccp_info *info = matchinfo;
 105         struct dccp_hdr _dh, *dh;
 106
 107         if (offset)
 108                 return false;
 109
 110         dh = skb_header_pointer(skb, protoff, sizeof(_dh), &_dh);
 111         if (dh == NULL) {
 112                 *hotdrop = true;
 113                 return false;
 114         }
 115
 116         return  DCCHECK(((ntohs(dh->dccph_sport) >= info->spts[0])
 117                         && (ntohs(dh->dccph_sport) <= info->spts[1])),
 118                         XT_DCCP_SRC_PORTS, info->flags, info->invflags)
 119                 && DCCHECK(((ntohs(dh->dccph_dport) >= info->dpts[0])
 120                         && (ntohs(dh->dccph_dport) <= info->dpts[1])),
 121                         XT_DCCP_DEST_PORTS, info->flags, info->invflags)
 122                 && DCCHECK(match_types(dh, info->typemask),
 123                            XT_DCCP_TYPE, info->flags, info->invflags)
 124                 && DCCHECK(match_option(info->option, skb, protoff, dh,
 125                                         hotdrop),
 126                            XT_DCCP_OPTION, info->flags, info->invflags);
 127 }
 128
 129 static bool
 130 checkentry(const char *tablename,
 131            const void *inf,
 132            const struct xt_match *match,
 133            void *matchinfo,
 134            unsigned int hook_mask)
 135 {
 136         const struct xt_dccp_info *info = matchinfo;
 137
 138         return !(info->flags & ~XT_DCCP_VALID_FLAGS)
 139                 && !(info->invflags & ~XT_DCCP_VALID_FLAGS)
 140                 && !(info->invflags & ~info->flags);
 141 }
 142
 143 static struct xt_match xt_dccp_match[] = {
 144         {
 145                 .name           = "dccp",
 146                 .family         = AF_INET,
 147                 .checkentry     = checkentry,
 148                 .match          = match,
 149                 .matchsize      = sizeof(struct xt_dccp_info),
 150                 .proto          = IPPROTO_DCCP,
 151                 .me             = THIS_MODULE,
 152         },
 153         {
 154                 .name           = "dccp",
 155                 .family         = AF_INET6,
 156                 .checkentry     = checkentry,
 157                 .match          = match,
 158                 .matchsize      = sizeof(struct xt_dccp_info),
 159                 .proto          = IPPROTO_DCCP,
 160                 .me             = THIS_MODULE,
 161         },
 162 };
 163
 164 static int __init xt_dccp_init(void)
 165 {
 166         int ret;
 167
 168         /* doff is 8 bits, so the maximum option size is (4*256).  Don't put
 169          * this in BSS since DaveM is worried about locked TLB's for kernel
 170          * BSS. */
 171         dccp_optbuf = kmalloc(256 * 4, GFP_KERNEL);
 172         if (!dccp_optbuf)
 173                 return -ENOMEM;
 174         ret = xt_register_matches(xt_dccp_match, ARRAY_SIZE(xt_dccp_match));
 175         if (ret)
 176                 goto out_kfree;
 177         return ret;
 178
 179 out_kfree:
 180         kfree(dccp_optbuf);
 181         return ret;
 182 }
 183
 184 static void __exit xt_dccp_fini(void)
 185 {
 186         xt_unregister_matches(xt_dccp_match, ARRAY_SIZE(xt_dccp_match));
 187         kfree(dccp_optbuf);
 188 }
 189
 190 module_init(xt_dccp_init);
 191 module_exit(xt_dccp_fini);