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("Match for DCCP protocol packets");
  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 match(const struct sk_buff *skb,
  97       const struct net_device *in,
  98       const struct net_device *out,
  99       const struct xt_match *match,
 100       const void *matchinfo,
 101       int offset,
 102       unsigned int protoff,
 103       bool *hotdrop)
 104 {
 105         const struct xt_dccp_info *info = matchinfo;
 106         struct dccp_hdr _dh, *dh;
 107
 108         if (offset)
 109                 return false;
 110
 111         dh = skb_header_pointer(skb, protoff, sizeof(_dh), &_dh);
 112         if (dh == NULL) {
 113                 *hotdrop = true;
 114                 return false;
 115         }
 116
 117         return  DCCHECK(ntohs(dh->dccph_sport) >= info->spts[0]
 118                         && ntohs(dh->dccph_sport) <= info->spts[1],
 119                         XT_DCCP_SRC_PORTS, info->flags, info->invflags)
 120                 && DCCHECK(ntohs(dh->dccph_dport) >= info->dpts[0]
 121                         && ntohs(dh->dccph_dport) <= info->dpts[1],
 122                         XT_DCCP_DEST_PORTS, info->flags, info->invflags)
 123                 && DCCHECK(match_types(dh, info->typemask),
 124                            XT_DCCP_TYPE, info->flags, info->invflags)
 125                 && DCCHECK(match_option(info->option, skb, protoff, dh,
 126                                         hotdrop),
 127                            XT_DCCP_OPTION, info->flags, info->invflags);
 128 }
 129
 130 static bool
 131 checkentry(const char *tablename,
 132            const void *inf,
 133            const struct xt_match *match,
 134            void *matchinfo,
 135            unsigned int hook_mask)
 136 {
 137         const struct xt_dccp_info *info = matchinfo;
 138
 139         return !(info->flags & ~XT_DCCP_VALID_FLAGS)
 140                 && !(info->invflags & ~XT_DCCP_VALID_FLAGS)
 141                 && !(info->invflags & ~info->flags);
 142 }
 143
 144 static struct xt_match xt_dccp_match[] __read_mostly = {
 145         {
 146                 .name           = "dccp",
 147                 .family         = AF_INET,
 148                 .checkentry     = checkentry,
 149                 .match          = match,
 150                 .matchsize      = sizeof(struct xt_dccp_info),
 151                 .proto          = IPPROTO_DCCP,
 152                 .me             = THIS_MODULE,
 153         },
 154         {
 155                 .name           = "dccp",
 156                 .family         = AF_INET6,
 157                 .checkentry     = checkentry,
 158                 .match          = match,
 159                 .matchsize      = sizeof(struct xt_dccp_info),
 160                 .proto          = IPPROTO_DCCP,
 161                 .me             = THIS_MODULE,
 162         },
 163 };
 164
 165 static int __init xt_dccp_init(void)
 166 {
 167         int ret;
 168
 169         /* doff is 8 bits, so the maximum option size is (4*256).  Don't put
 170          * this in BSS since DaveM is worried about locked TLB's for kernel
 171          * BSS. */
 172         dccp_optbuf = kmalloc(256 * 4, GFP_KERNEL);
 173         if (!dccp_optbuf)
 174                 return -ENOMEM;
 175         ret = xt_register_matches(xt_dccp_match, ARRAY_SIZE(xt_dccp_match));
 176         if (ret)
 177                 goto out_kfree;
 178         return ret;
 179
 180 out_kfree:
 181         kfree(dccp_optbuf);
 182         return ret;
 183 }
 184
 185 static void __exit xt_dccp_fini(void)
 186 {
 187         xt_unregister_matches(xt_dccp_match, ARRAY_SIZE(xt_dccp_match));
 188         kfree(dccp_optbuf);
 189 }
 190
 191 module_init(xt_dccp_init);
 192 module_exit(xt_dccp_fini);