net/ipv6/netfilter/ip6t_hbh.c

   1 /* Kernel module to match Hop-by-Hop and Destination parameters. */
   2
   3 /* (C) 2001-2002 Andras Kis-Szabo <kisza@sch.bme.hu>
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License version 2 as
   7  * published by the Free Software Foundation.
   8  */
   9 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  10 #include <linux/module.h>
  11 #include <linux/skbuff.h>
  12 #include <linux/ipv6.h>
  13 #include <linux/types.h>
  14 #include <net/checksum.h>
  15 #include <net/ipv6.h>
  16
  17 #include <asm/byteorder.h>
  18
  19 #include <linux/netfilter/x_tables.h>
  20 #include <linux/netfilter_ipv6/ip6_tables.h>
  21 #include <linux/netfilter_ipv6/ip6t_opts.h>
  22
  23 MODULE_LICENSE("GPL");
  24 MODULE_DESCRIPTION("Xtables: IPv6 Hop-By-Hop and Destination Header match");
  25 MODULE_AUTHOR("Andras Kis-Szabo <kisza@sch.bme.hu>");
  26 MODULE_ALIAS("ip6t_dst");
  27
  28 /*
  29  *  (Type & 0xC0) >> 6
  30  *      0       -> ignorable
  31  *      1       -> must drop the packet
  32  *      2       -> send ICMP PARM PROB regardless and drop packet
  33  *      3       -> Send ICMP if not a multicast address and drop packet
  34  *  (Type & 0x20) >> 5
  35  *      0       -> invariant
  36  *      1       -> can change the routing
  37  *  (Type & 0x1F) Type
  38  *      0       -> Pad1 (only 1 byte!)
  39  *      1       -> PadN LENGTH info (total length = length + 2)
  40  *      C0 | 2  -> JUMBO 4 x x x x ( xxxx > 64k )
  41  *      5       -> RTALERT 2 x x
  42  */
  43
  44 static struct xt_match hbh_mt6_reg[] __read_mostly;
  45
  46 static bool
  47 hbh_mt6(const struct sk_buff *skb, struct xt_action_param *par)
  48 {
  49         struct ipv6_opt_hdr _optsh;
  50         const struct ipv6_opt_hdr *oh;
  51         const struct ip6t_opts *optinfo = par->matchinfo;
  52         unsigned int temp;
  53         unsigned int ptr;
  54         unsigned int hdrlen = 0;
  55         bool ret = false;
  56         u8 _opttype;
  57         u8 _optlen;
  58         const u_int8_t *tp = NULL;
  59         const u_int8_t *lp = NULL;
  60         unsigned int optlen;
  61         int err;
  62
  63         err = ipv6_find_hdr(skb, &ptr,
  64                             (par->match == &hbh_mt6_reg[0]) ?
  65                             NEXTHDR_HOP : NEXTHDR_DEST, NULL);
  66         if (err < 0) {
  67                 if (err != -ENOENT)
  68                         par->hotdrop = true;
  69                 return false;
  70         }
  71
  72         oh = skb_header_pointer(skb, ptr, sizeof(_optsh), &_optsh);
  73         if (oh == NULL) {
  74                 par->hotdrop = true;
  75                 return false;
  76         }
  77
  78         hdrlen = ipv6_optlen(oh);
  79         if (skb->len - ptr < hdrlen) {
  80                 /* Packet smaller than it's length field */
  81                 return false;
  82         }
  83
  84         pr_debug("IPv6 OPTS LEN %u %u ", hdrlen, oh->hdrlen);
  85
  86         pr_debug("len %02X %04X %02X ",
  87                  optinfo->hdrlen, hdrlen,
  88                  (!(optinfo->flags & IP6T_OPTS_LEN) ||
  89                   ((optinfo->hdrlen == hdrlen) ^
  90                    !!(optinfo->invflags & IP6T_OPTS_INV_LEN))));
  91
  92         ret = (oh != NULL) &&
  93               (!(optinfo->flags & IP6T_OPTS_LEN) ||
  94                ((optinfo->hdrlen == hdrlen) ^
  95                 !!(optinfo->invflags & IP6T_OPTS_INV_LEN)));
  96
  97         ptr += 2;
  98         hdrlen -= 2;
  99         if (!(optinfo->flags & IP6T_OPTS_OPTS)) {
 100                 return ret;
 101         } else {
 102                 pr_debug("Strict ");
 103                 pr_debug("#%d ", optinfo->optsnr);
 104                 for (temp = 0; temp < optinfo->optsnr; temp++) {
 105                         /* type field exists ? */
 106                         if (hdrlen < 1)
 107                                 break;
 108                         tp = skb_header_pointer(skb, ptr, sizeof(_opttype),
 109                                                 &_opttype);
 110                         if (tp == NULL)
 111                                 break;
 112
 113                         /* Type check */
 114                         if (*tp != (optinfo->opts[temp] & 0xFF00) >> 8) {
 115                                 pr_debug("Tbad %02X %02X\n", *tp,
 116                                          (optinfo->opts[temp] & 0xFF00) >> 8);
 117                                 return false;
 118                         } else {
 119                                 pr_debug("Tok ");
 120                         }
 121                         /* Length check */
 122                         if (*tp) {
 123                                 u16 spec_len;
 124
 125                                 /* length field exists ? */
 126                                 if (hdrlen < 2)
 127                                         break;
 128                                 lp = skb_header_pointer(skb, ptr + 1,
 129                                                         sizeof(_optlen),
 130                                                         &_optlen);
 131                                 if (lp == NULL)
 132                                         break;
 133                                 spec_len = optinfo->opts[temp] & 0x00FF;
 134
 135                                 if (spec_len != 0x00FF && spec_len != *lp) {
 136                                         pr_debug("Lbad %02X %04X\n", *lp,
 137                                                  spec_len);
 138                                         return false;
 139                                 }
 140                                 pr_debug("Lok ");
 141                                 optlen = *lp + 2;
 142                         } else {
 143                                 pr_debug("Pad1\n");
 144                                 optlen = 1;
 145                         }
 146
 147                         /* Step to the next */
 148                         pr_debug("len%04X\n", optlen);
 149
 150                         if ((ptr > skb->len - optlen || hdrlen < optlen) &&
 151                             temp < optinfo->optsnr - 1) {
 152                                 pr_debug("new pointer is too large!\n");
 153                                 break;
 154                         }
 155                         ptr += optlen;
 156                         hdrlen -= optlen;
 157                 }
 158                 if (temp == optinfo->optsnr)
 159                         return ret;
 160                 else
 161                         return false;
 162         }
 163
 164         return false;
 165 }
 166
 167 static int hbh_mt6_check(const struct xt_mtchk_param *par)
 168 {
 169         const struct ip6t_opts *optsinfo = par->matchinfo;
 170
 171         if (optsinfo->invflags & ~IP6T_OPTS_INV_MASK) {
 172                 pr_debug("unknown flags %X\n", optsinfo->invflags);
 173                 return -EINVAL;
 174         }
 175
 176         if (optsinfo->flags & IP6T_OPTS_NSTRICT) {
 177                 pr_debug("Not strict - not implemented");
 178                 return -EINVAL;
 179         }
 180
 181         return 0;
 182 }
 183
 184 static struct xt_match hbh_mt6_reg[] __read_mostly = {
 185         {
 186                 /* Note, hbh_mt6 relies on the order of hbh_mt6_reg */
 187                 .name           = "hbh",
 188                 .family         = NFPROTO_IPV6,
 189                 .match          = hbh_mt6,
 190                 .matchsize      = sizeof(struct ip6t_opts),
 191                 .checkentry     = hbh_mt6_check,
 192                 .me             = THIS_MODULE,
 193         },
 194         {
 195                 .name           = "dst",
 196                 .family         = NFPROTO_IPV6,
 197                 .match          = hbh_mt6,
 198                 .matchsize      = sizeof(struct ip6t_opts),
 199                 .checkentry     = hbh_mt6_check,
 200                 .me             = THIS_MODULE,
 201         },
 202 };
 203
 204 static int __init hbh_mt6_init(void)
 205 {
 206         return xt_register_matches(hbh_mt6_reg, ARRAY_SIZE(hbh_mt6_reg));
 207 }
 208
 209 static void __exit hbh_mt6_exit(void)
 210 {
 211         xt_unregister_matches(hbh_mt6_reg, ARRAY_SIZE(hbh_mt6_reg));
 212 }
 213
 214 module_init(hbh_mt6_init);
 215 module_exit(hbh_mt6_exit);