net/netfilter/xt_dccp.c

   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                 *hotdrop = true;
  50                 return false;
  51         }
  52
  53         if (!optlen)
  54                 return false;
  55
  56         spin_lock_bh(&dccp_buflock);
  57         op = skb_header_pointer(skb, protoff + optoff, optlen, dccp_optbuf);
  58         if (op == NULL) {
  59                 /* If we don't have the whole header, drop packet. */
  60                 spin_unlock_bh(&dccp_buflock);
  61                 *hotdrop = true;
  62                 return false;
  63         }
  64
  65         for (i = 0; i < optlen; ) {
  66                 if (op[i] == option) {
  67                         spin_unlock_bh(&dccp_buflock);
  68                         return true;
  69                 }
  70
  71                 if (op[i] < 2)
  72                         i++;
  73                 else
  74                         i += op[i+1]?:1;
  75         }
  76
  77         spin_unlock_bh(&dccp_buflock);
  78         return false;
  79 }
  80
  81
  82 static inline bool
  83 match_types(const struct dccp_hdr *dh, u_int16_t typemask)
  84 {
  85         return typemask & (1 << dh->dccph_type);
  86 }
  87
  88 static inline bool
  89 match_option(u_int8_t option, const struct sk_buff *skb, unsigned int protoff,
  90              const struct dccp_hdr *dh, bool *hotdrop)
  91 {
  92         return dccp_find_option(option, skb, protoff, dh, hotdrop);
  93 }
  94
  95 static bool
  96 dccp_mt(const struct sk_buff *skb, const struct net_device *in,
  97         const struct net_device *out, const struct xt_match *match,
  98         const void *matchinfo, int offset, unsigned int protoff, bool *hotdrop)
  99 {
 100         const struct xt_dccp_info *info = matchinfo;
 101         struct dccp_hdr _dh, *dh;
 102
 103         if (offset)
 104                 return false;
 105
 106         dh = skb_header_pointer(skb, protoff, sizeof(_dh), &_dh);
 107         if (dh == NULL) {
 108                 *hotdrop = true;
 109                 return false;
 110         }
 111
 112         return  DCCHECK(ntohs(dh->dccph_sport) >= info->spts[0]
 113                         && ntohs(dh->dccph_sport) <= info->spts[1],
 114                         XT_DCCP_SRC_PORTS, info->flags, info->invflags)
 115                 && DCCHECK(ntohs(dh->dccph_dport) >= info->dpts[0]
 116                         && ntohs(dh->dccph_dport) <= info->dpts[1],
 117                         XT_DCCP_DEST_PORTS, info->flags, info->invflags)
 118                 && DCCHECK(match_types(dh, info->typemask),
 119                            XT_DCCP_TYPE, info->flags, info->invflags)
 120                 && DCCHECK(match_option(info->option, skb, protoff, dh,
 121                                         hotdrop),
 122                            XT_DCCP_OPTION, info->flags, info->invflags);
 123 }
 124
 125 static bool
 126 dccp_mt_check(const char *tablename, const void *inf,
 127               const struct xt_match *match, void *matchinfo,
 128               unsigned int hook_mask)
 129 {
 130         const struct xt_dccp_info *info = matchinfo;
 131
 132         return !(info->flags & ~XT_DCCP_VALID_FLAGS)
 133                 && !(info->invflags & ~XT_DCCP_VALID_FLAGS)
 134                 && !(info->invflags & ~info->flags);
 135 }
 136
 137 static struct xt_match dccp_mt_reg[] __read_mostly = {
 138         {
 139                 .name           = "dccp",
 140                 .family         = AF_INET,
 141                 .checkentry     = dccp_mt_check,
 142                 .match          = dccp_mt,
 143                 .matchsize      = sizeof(struct xt_dccp_info),
 144                 .proto          = IPPROTO_DCCP,
 145                 .me             = THIS_MODULE,
 146         },
 147         {
 148                 .name           = "dccp",
 149                 .family         = AF_INET6,
 150                 .checkentry     = dccp_mt_check,
 151                 .match          = dccp_mt,
 152                 .matchsize      = sizeof(struct xt_dccp_info),
 153                 .proto          = IPPROTO_DCCP,
 154                 .me             = THIS_MODULE,
 155         },
 156 };
 157
 158 static int __init dccp_mt_init(void)
 159 {
 160         int ret;
 161
 162         /* doff is 8 bits, so the maximum option size is (4*256).  Don't put
 163          * this in BSS since DaveM is worried about locked TLB's for kernel
 164          * BSS. */
 165         dccp_optbuf = kmalloc(256 * 4, GFP_KERNEL);
 166         if (!dccp_optbuf)
 167                 return -ENOMEM;
 168         ret = xt_register_matches(dccp_mt_reg, ARRAY_SIZE(dccp_mt_reg));
 169         if (ret)
 170                 goto out_kfree;
 171         return ret;
 172
 173 out_kfree:
 174         kfree(dccp_optbuf);
 175         return ret;
 176 }
 177
 178 static void __exit dccp_mt_exit(void)
 179 {
 180         xt_unregister_matches(dccp_mt_reg, ARRAY_SIZE(dccp_mt_reg));
 181         kfree(dccp_optbuf);
 182 }
 183
 184 module_init(dccp_mt_init);
 185 module_exit(dccp_mt_exit);