net/netfilter/xt_sctp.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
   3 #include <linux/module.h>
   4 #include <linux/skbuff.h>
   5 #include <net/ip.h>
   6 #include <net/ipv6.h>
   7 #include <net/sctp/sctp.h>
   8 #include <linux/sctp.h>
   9
  10 #include <linux/netfilter/x_tables.h>
  11 #include <linux/netfilter/xt_sctp.h>
  12 #include <linux/netfilter_ipv4/ip_tables.h>
  13 #include <linux/netfilter_ipv6/ip6_tables.h>
  14
  15 MODULE_LICENSE("GPL");
  16 MODULE_AUTHOR("Kiran Kumar Immidi");
  17 MODULE_DESCRIPTION("Xtables: SCTP protocol packet match");
  18 MODULE_ALIAS("ipt_sctp");
  19 MODULE_ALIAS("ip6t_sctp");
  20
  21 #define SCCHECK(cond, option, flag, invflag) (!((flag) & (option)) \
  22                                               || (!!((invflag) & (option)) ^ (cond)))
  23
  24 static bool
  25 match_flags(const struct xt_sctp_flag_info *flag_info,
  26             const int flag_count,
  27             u_int8_t chunktype,
  28             u_int8_t chunkflags)
  29 {
  30         int i;
  31
  32         for (i = 0; i < flag_count; i++)
  33                 if (flag_info[i].chunktype == chunktype)
  34                         return (chunkflags & flag_info[i].flag_mask) == flag_info[i].flag;
  35
  36         return true;
  37 }
  38
  39 static inline bool
  40 match_packet(const struct sk_buff *skb,
  41              unsigned int offset,
  42              const struct xt_sctp_info *info,
  43              bool *hotdrop)
  44 {
  45         u_int32_t chunkmapcopy[256 / sizeof (u_int32_t)];
  46         const struct sctp_chunkhdr *sch;
  47         struct sctp_chunkhdr _sch;
  48         int chunk_match_type = info->chunk_match_type;
  49         const struct xt_sctp_flag_info *flag_info = info->flag_info;
  50         int flag_count = info->flag_count;
  51
  52 #ifdef DEBUG
  53         int i = 0;
  54 #endif
  55
  56         if (chunk_match_type == SCTP_CHUNK_MATCH_ALL)
  57                 SCTP_CHUNKMAP_COPY(chunkmapcopy, info->chunkmap);
  58
  59         do {
  60                 sch = skb_header_pointer(skb, offset, sizeof(_sch), &_sch);
  61                 if (sch == NULL || sch->length == 0) {
  62                         pr_debug("Dropping invalid SCTP packet.\n");
  63                         *hotdrop = true;
  64                         return false;
  65                 }
  66 #ifdef DEBUG
  67                 pr_debug("Chunk num: %d\toffset: %d\ttype: %d\tlength: %d"
  68                          "\tflags: %x\n",
  69                          ++i, offset, sch->type, htons(sch->length),
  70                          sch->flags);
  71 #endif
  72                 offset += SCTP_PAD4(ntohs(sch->length));
  73
  74                 pr_debug("skb->len: %d\toffset: %d\n", skb->len, offset);
  75
  76                 if (SCTP_CHUNKMAP_IS_SET(info->chunkmap, sch->type)) {
  77                         switch (chunk_match_type) {
  78                         case SCTP_CHUNK_MATCH_ANY:
  79                                 if (match_flags(flag_info, flag_count,
  80                                         sch->type, sch->flags)) {
  81                                         return true;
  82                                 }
  83                                 break;
  84
  85                         case SCTP_CHUNK_MATCH_ALL:
  86                                 if (match_flags(flag_info, flag_count,
  87                                     sch->type, sch->flags))
  88                                         SCTP_CHUNKMAP_CLEAR(chunkmapcopy, sch->type);
  89                                 break;
  90
  91                         case SCTP_CHUNK_MATCH_ONLY:
  92                                 if (!match_flags(flag_info, flag_count,
  93                                     sch->type, sch->flags))
  94                                         return false;
  95                                 break;
  96                         }
  97                 } else {
  98                         switch (chunk_match_type) {
  99                         case SCTP_CHUNK_MATCH_ONLY:
 100                                 return false;
 101                         }
 102                 }
 103         } while (offset < skb->len);
 104
 105         switch (chunk_match_type) {
 106         case SCTP_CHUNK_MATCH_ALL:
 107                 return SCTP_CHUNKMAP_IS_CLEAR(chunkmapcopy);
 108         case SCTP_CHUNK_MATCH_ANY:
 109                 return false;
 110         case SCTP_CHUNK_MATCH_ONLY:
 111                 return true;
 112         }
 113
 114         /* This will never be reached, but required to stop compiler whine */
 115         return false;
 116 }
 117
 118 static bool
 119 sctp_mt(const struct sk_buff *skb, struct xt_action_param *par)
 120 {
 121         const struct xt_sctp_info *info = par->matchinfo;
 122         const struct sctphdr *sh;
 123         struct sctphdr _sh;
 124
 125         if (par->fragoff != 0) {
 126                 pr_debug("Dropping non-first fragment.. FIXME\n");
 127                 return false;
 128         }
 129
 130         sh = skb_header_pointer(skb, par->thoff, sizeof(_sh), &_sh);
 131         if (sh == NULL) {
 132                 pr_debug("Dropping evil TCP offset=0 tinygram.\n");
 133                 par->hotdrop = true;
 134                 return false;
 135         }
 136         pr_debug("spt: %d\tdpt: %d\n", ntohs(sh->source), ntohs(sh->dest));
 137
 138         return  SCCHECK(ntohs(sh->source) >= info->spts[0]
 139                         && ntohs(sh->source) <= info->spts[1],
 140                         XT_SCTP_SRC_PORTS, info->flags, info->invflags) &&
 141                 SCCHECK(ntohs(sh->dest) >= info->dpts[0]
 142                         && ntohs(sh->dest) <= info->dpts[1],
 143                         XT_SCTP_DEST_PORTS, info->flags, info->invflags) &&
 144                 SCCHECK(match_packet(skb, par->thoff + sizeof(_sh),
 145                                      info, &par->hotdrop),
 146                         XT_SCTP_CHUNK_TYPES, info->flags, info->invflags);
 147 }
 148
 149 static int sctp_mt_check(const struct xt_mtchk_param *par)
 150 {
 151         const struct xt_sctp_info *info = par->matchinfo;
 152
 153         if (info->flags & ~XT_SCTP_VALID_FLAGS)
 154                 return -EINVAL;
 155         if (info->invflags & ~XT_SCTP_VALID_FLAGS)
 156                 return -EINVAL;
 157         if (info->invflags & ~info->flags)
 158                 return -EINVAL;
 159         if (!(info->flags & XT_SCTP_CHUNK_TYPES))
 160                 return 0;
 161         if (info->chunk_match_type & (SCTP_CHUNK_MATCH_ALL |
 162             SCTP_CHUNK_MATCH_ANY | SCTP_CHUNK_MATCH_ONLY))
 163                 return 0;
 164         return -EINVAL;
 165 }
 166
 167 static struct xt_match sctp_mt_reg[] __read_mostly = {
 168         {
 169                 .name           = "sctp",
 170                 .family         = NFPROTO_IPV4,
 171                 .checkentry     = sctp_mt_check,
 172                 .match          = sctp_mt,
 173                 .matchsize      = sizeof(struct xt_sctp_info),
 174                 .proto          = IPPROTO_SCTP,
 175                 .me             = THIS_MODULE
 176         },
 177         {
 178                 .name           = "sctp",
 179                 .family         = NFPROTO_IPV6,
 180                 .checkentry     = sctp_mt_check,
 181                 .match          = sctp_mt,
 182                 .matchsize      = sizeof(struct xt_sctp_info),
 183                 .proto          = IPPROTO_SCTP,
 184                 .me             = THIS_MODULE
 185         },
 186 };
 187
 188 static int __init sctp_mt_init(void)
 189 {
 190         return xt_register_matches(sctp_mt_reg, ARRAY_SIZE(sctp_mt_reg));
 191 }
 192
 193 static void __exit sctp_mt_exit(void)
 194 {
 195         xt_unregister_matches(sctp_mt_reg, ARRAY_SIZE(sctp_mt_reg));
 196 }
 197
 198 module_init(sctp_mt_init);
 199 module_exit(sctp_mt_exit);