libs/smux/ber_decoder.c

   1 /*-
   2  * Copyright (c) 2003, 2004 Lev Walkin <vlm@lionet.info>. All rights reserved.
   3  * Redistribution and modifications are permitted subject to BSD license.
   4  */
   5 #include <asn_internal.h>
   6
   7 #undef  ADVANCE
   8 #define ADVANCE(num_bytes)      do {                                    \
   9                 size_t num = num_bytes;                                 \
  10                 ptr = ((const char *)ptr) + num;                        \
  11                 size -= num;                                            \
  12                 consumed_myself += num;                                 \
  13         } while(0)
  14 #undef  RETURN
  15 #define RETURN(_code)   do {                                            \
  16                 asn_dec_rval_t rval;                                    \
  17                 rval.code = _code;                                      \
  18                 if(opt_ctx) opt_ctx->step = step; /* Save context */    \
  19                 if(_code == RC_OK || opt_ctx)                           \
  20                         rval.consumed = consumed_myself;                \
  21                 else                                                    \
  22                         rval.consumed = 0;      /* Context-free */      \
  23                 return rval;                                            \
  24         } while(0)
  25
  26 /*
  27  * The BER decoder of any type.
  28  */
  29 asn_dec_rval_t
  30 ber_decode(asn_codec_ctx_t *opt_codec_ctx,
  31         asn_TYPE_descriptor_t *type_descriptor,
  32         void **struct_ptr, const void *ptr, size_t size) {
  33         asn_codec_ctx_t s_codec_ctx;
  34
  35         /*
  36          * Stack checker requires that the codec context
  37          * must be allocated on the stack.
  38          */
  39         if(opt_codec_ctx) {
  40                 if(opt_codec_ctx->max_stack_size) {
  41                         s_codec_ctx = *opt_codec_ctx;
  42                         opt_codec_ctx = &s_codec_ctx;
  43                 }
  44         } else {
  45                 /* If context is not given, be security-conscious anyway */
  46                 memset(&s_codec_ctx, 0, sizeof(s_codec_ctx));
  47                 s_codec_ctx.max_stack_size = _ASN_DEFAULT_STACK_MAX;
  48                 opt_codec_ctx = &s_codec_ctx;
  49         }
  50
  51         /*
  52          * Invoke type-specific decoder.
  53          */
  54         return type_descriptor->ber_decoder(opt_codec_ctx, type_descriptor,
  55                 struct_ptr,     /* Pointer to the destination structure */
  56                 ptr, size,      /* Buffer and its size */
  57                 0               /* Default tag mode is 0 */
  58                 );
  59 }
  60
  61 /*
  62  * Check the set of <TL<TL<TL...>>> tags matches the definition.
  63  */
  64 asn_dec_rval_t
  65 ber_check_tags(asn_codec_ctx_t *opt_codec_ctx,
  66                 asn_TYPE_descriptor_t *td, asn_struct_ctx_t *opt_ctx,
  67                 const void *ptr, size_t size, int tag_mode, int last_tag_form,
  68                 ber_tlv_len_t *last_length, int *opt_tlv_form) {
  69         ssize_t consumed_myself = 0;
  70         ssize_t tag_len;
  71         ssize_t len_len;
  72         ber_tlv_tag_t tlv_tag;
  73         ber_tlv_len_t tlv_len;
  74         ber_tlv_len_t limit_len = -1;
  75         int expect_00_terminators = 0;
  76         int tlv_constr = -1;    /* If CHOICE, opt_tlv_form is not given */
  77         int step = opt_ctx ? opt_ctx->step : 0; /* Where we left previously */
  78         int tagno;
  79
  80         /*
  81          * Make sure we didn't exceed the maximum stack size.
  82          */
  83         if(_ASN_STACK_OVERFLOW_CHECK(opt_codec_ctx))
  84                 RETURN(RC_FAIL);
  85
  86         /*
  87          * So what does all this implicit skip stuff mean?
  88          * Imagine two types,
  89          *      A ::= [5] IMPLICIT      T
  90          *      B ::= [2] EXPLICIT      T
  91          * Where T is defined as
  92          *      T ::= [4] IMPLICIT SEQUENCE { ... }
  93          *
  94          * Let's say, we are starting to decode type A, given the
  95          * following TLV stream: <5> <0>. What does this mean?
  96          * It means that the type A contains type T which is,
  97          * in turn, empty.
  98          * Remember though, that we are still in A. We cannot
  99          * just pass control to the type T decoder. Why? Because
 100          * the type T decoder expects <4> <0>, not <5> <0>.
 101          * So, we must make sure we are going to receive <5> while
 102          * still in A, then pass control to the T decoder, indicating
 103          * that the tag <4> was implicitly skipped. The decoder of T
 104          * hence will be prepared to treat <4> as valid tag, and decode
 105          * it appropriately.
 106          */
 107
 108         tagno = step    /* Continuing where left previously */
 109                 + (tag_mode==1?-1:0)
 110                 ;
 111         ASN_DEBUG("ber_check_tags(%s, size=%ld, tm=%d, step=%d, tagno=%d)",
 112                 td->name, (long)size, tag_mode, step, tagno);
 113         /* assert(td->tags_count >= 1) May not be the case for CHOICE or ANY */
 114
 115         if(tag_mode == 0 && tagno == td->tags_count) {
 116                 /*
 117                  * This must be the _untagged_ ANY type,
 118                  * which outermost tag isn't known in advance.
 119                  * Fetch the tag and length separately.
 120                  */
 121                 tag_len = ber_fetch_tag(ptr, size, &tlv_tag);
 122                 switch(tag_len) {
 123                 case -1: RETURN(RC_FAIL);
 124                 case 0: RETURN(RC_WMORE);
 125                 }
 126                 tlv_constr = BER_TLV_CONSTRUCTED(ptr);
 127                 len_len = ber_fetch_length(tlv_constr,
 128                         (const char *)ptr + tag_len, size - tag_len, &tlv_len);
 129                 switch(len_len) {
 130                 case -1: RETURN(RC_FAIL);
 131                 case 0: RETURN(RC_WMORE);
 132                 }
 133                 ASN_DEBUG("Advancing %ld in ANY case",
 134                         (long)(tag_len + len_len));
 135                 ADVANCE(tag_len + len_len);
 136         } else {
 137                 assert(tagno < td->tags_count); /* At least one loop */
 138         }
 139         for((void)tagno; tagno < td->tags_count; tagno++, step++) {
 140
 141                 /*
 142                  * Fetch and process T from TLV.
 143                  */
 144                 tag_len = ber_fetch_tag(ptr, size, &tlv_tag);
 145                         ASN_DEBUG("Fetching tag from {%p,%ld}: "
 146                                 "len %ld, step %d, tagno %d got %s",
 147                                 ptr, (long)size,
 148                                 (long)tag_len, step, tagno,
 149                                 ber_tlv_tag_string(tlv_tag));
 150                 switch(tag_len) {
 151                 case -1: RETURN(RC_FAIL);
 152                 case 0: RETURN(RC_WMORE);
 153                 }
 154
 155                 tlv_constr = BER_TLV_CONSTRUCTED(ptr);
 156
 157                 /*
 158                  * If {I}, don't check anything.
 159                  * If {I,B,C}, check B and C unless we're at I.
 160                  */
 161                 if(tag_mode != 0 && step == 0) {
 162                         /*
 163                          * We don't expect tag to match here.
 164                          * It's just because we don't know how the tag
 165                          * is supposed to look like.
 166                          */
 167                 } else {
 168                     assert(tagno >= 0); /* Guaranteed by the code above */
 169                     if(tlv_tag != td->tags[tagno]) {
 170                         /*
 171                          * Unexpected tag. Too bad.
 172                          */
 173                         ASN_DEBUG("Expected: %s, "
 174                                 "expectation failed (tn=%d, tm=%d)",
 175                                 ber_tlv_tag_string(td->tags[tagno]),
 176                                 tagno, tag_mode
 177                         );
 178                         RETURN(RC_FAIL);
 179                     }
 180                 }
 181
 182                 /*
 183                  * Attention: if there are more tags expected,
 184                  * ensure that the current tag is presented
 185                  * in constructed form (it contains other tags!).
 186                  * If this one is the last one, check that the tag form
 187                  * matches the one given in descriptor.
 188                  */
 189                 if(tagno < (td->tags_count - 1)) {
 190                         if(tlv_constr == 0) {
 191                                 ASN_DEBUG("tlv_constr = %d, expfail",
 192                                         tlv_constr);
 193                                 RETURN(RC_FAIL);
 194                         }
 195                 } else {
 196                         if(last_tag_form != tlv_constr
 197                         && last_tag_form != -1) {
 198                                 ASN_DEBUG("last_tag_form %d != %d",
 199                                         last_tag_form, tlv_constr);
 200                                 RETURN(RC_FAIL);
 201                         }
 202                 }
 203
 204                 /*
 205                  * Fetch and process L from TLV.
 206                  */
 207                 len_len = ber_fetch_length(tlv_constr,
 208                         (const char *)ptr + tag_len, size - tag_len, &tlv_len);
 209                 ASN_DEBUG("Fetchinig len = %ld", (long)len_len);
 210                 switch(len_len) {
 211                 case -1: RETURN(RC_FAIL);
 212                 case 0: RETURN(RC_WMORE);
 213                 }
 214
 215                 /*
 216                  * FIXME
 217                  * As of today, the chain of tags
 218                  * must either contain several indefinite length TLVs,
 219                  * or several definite length ones.
 220                  * No mixing is allowed.
 221                  */
 222                 if(tlv_len == -1) {
 223                         /*
 224                          * Indefinite length.
 225                          */
 226                         if(limit_len == -1) {
 227                                 expect_00_terminators++;
 228                         } else {
 229                                 ASN_DEBUG("Unexpected indefinite length "
 230                                         "in a chain of definite lengths");
 231                                 RETURN(RC_FAIL);
 232                         }
 233                         ADVANCE(tag_len + len_len);
 234                         continue;
 235                 } else {
 236                         if(expect_00_terminators) {
 237                                 ASN_DEBUG("Unexpected definite length "
 238                                         "in a chain of indefinite lengths");
 239                                 RETURN(RC_FAIL);
 240                         }
 241                 }
 242
 243                 /*
 244                  * Check that multiple TLVs specify ever decreasing length,
 245                  * which is consistent.
 246                  */
 247                 if(limit_len == -1) {
 248                         limit_len    = tlv_len + tag_len + len_len;
 249                         if(limit_len < 0) {
 250                                 /* Too great tlv_len value? */
 251                                 RETURN(RC_FAIL);
 252                         }
 253                 } else if(limit_len != tlv_len + tag_len + len_len) {
 254                         /*
 255                          * Inner TLV specifies length which is inconsistent
 256                          * with the outer TLV's length value.
 257                          */
 258                         ASN_DEBUG("Outer TLV is %ld and inner is %ld",
 259                                 (long)limit_len, (long)tlv_len);
 260                         RETURN(RC_FAIL);
 261                 }
 262
 263                 ADVANCE(tag_len + len_len);
 264
 265                 limit_len -= (tag_len + len_len);
 266                 if((ssize_t)size > limit_len) {
 267                         /*
 268                          * Make sure that we won't consume more bytes
 269                          * from the parent frame than the inferred limit.
 270                          */
 271                         size = limit_len;
 272                 }
 273         }
 274
 275         if(opt_tlv_form)
 276                 *opt_tlv_form = tlv_constr;
 277         if(expect_00_terminators)
 278                 *last_length = -expect_00_terminators;
 279         else
 280                 *last_length = tlv_len;
 281
 282         RETURN(RC_OK);
 283 }