crypto/libressl/ssl/bs_ber.c

   1 /*      $OpenBSD: bs_ber.c,v 1.7 2015/06/17 07:20:39 doug Exp $ */
   2 /*
   3  * Copyright (c) 2014, Google Inc.
   4  *
   5  * Permission to use, copy, modify, and/or distribute this software for any
   6  * purpose with or without fee is hereby granted, provided that the above
   7  * copyright notice and this permission notice appear in all copies.
   8  *
   9  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  10  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  11  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
  12  * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  13  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
  14  * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
  15  * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
  16
  17 #include <string.h>
  18
  19 #include <openssl/opensslconf.h>
  20
  21 #include "bytestring.h"
  22
  23 /*
  24  * kMaxDepth is a just a sanity limit. The code should be such that the length
  25  * of the input being processes always decreases. None the less, a very large
  26  * input could otherwise cause the stack to overflow.
  27  */
  28 static const unsigned int kMaxDepth = 2048;
  29
  30 /* Non-strict version that allows a relaxed DER with indefinite form. */
  31 static int
  32 cbs_nonstrict_get_any_asn1_element(CBS *cbs, CBS *out, unsigned int *out_tag,
  33     size_t *out_header_len)
  34 {
  35         return cbs_get_any_asn1_element_internal(cbs, out,
  36             out_tag, out_header_len, 0);
  37 }
  38
  39 /*
  40  * cbs_find_indefinite walks an ASN.1 structure in |orig_in| and sets
  41  * |*indefinite_found| depending on whether an indefinite length element was
  42  * found. The value of |orig_in| is not modified.
  43  *
  44  * Returns one on success (i.e. |*indefinite_found| was set) and zero on error.
  45  */
  46 static int
  47 cbs_find_indefinite(const CBS *orig_in, char *indefinite_found,
  48     unsigned int depth)
  49 {
  50         CBS in;
  51
  52         if (depth > kMaxDepth)
  53                 return 0;
  54
  55         CBS_init(&in, CBS_data(orig_in), CBS_len(orig_in));
  56
  57         while (CBS_len(&in) > 0) {
  58                 CBS contents;
  59                 unsigned int tag;
  60                 size_t header_len;
  61
  62                 if (!cbs_nonstrict_get_any_asn1_element(&in, &contents, &tag,
  63                     &header_len))
  64                         return 0;
  65
  66                 /* Indefinite form not allowed by DER. */
  67                 if (CBS_len(&contents) == header_len && header_len > 0 &&
  68                     CBS_data(&contents)[header_len - 1] == 0x80) {
  69                         *indefinite_found = 1;
  70                         return 1;
  71                 }
  72                 if (tag & CBS_ASN1_CONSTRUCTED) {
  73                         if (!CBS_skip(&contents, header_len) ||
  74                             !cbs_find_indefinite(&contents, indefinite_found,
  75                             depth + 1))
  76                                 return 0;
  77                 }
  78         }
  79
  80         *indefinite_found = 0;
  81         return 1;
  82 }
  83
  84 /*
  85  * is_primitive_type returns true if |tag| likely a primitive type. Normally
  86  * one can just test the "constructed" bit in the tag but, in BER, even
  87  * primitive tags can have the constructed bit if they have indefinite
  88  * length.
  89  */
  90 static char
  91 is_primitive_type(unsigned int tag)
  92 {
  93         return (tag & 0xc0) == 0 &&
  94             (tag & 0x1f) != (CBS_ASN1_SEQUENCE & 0x1f) &&
  95             (tag & 0x1f) != (CBS_ASN1_SET & 0x1f);
  96 }
  97
  98 /*
  99  * is_eoc returns true if |header_len| and |contents|, as returned by
 100  * |cbs_nonstrict_get_any_asn1_element|, indicate an "end of contents" (EOC)
 101  * value.
 102  */
 103 static char
 104 is_eoc(size_t header_len, CBS *contents)
 105 {
 106         return header_len == 2 && CBS_mem_equal(contents, "\x00\x00", 2);
 107 }
 108
 109 /*
 110  * cbs_convert_indefinite reads data with DER encoding (but relaxed to allow
 111  * indefinite form) from |in| and writes definite form DER data to |out|. If
 112  * |squash_header| is set then the top-level of elements from |in| will not
 113  * have their headers written. This is used when concatenating the fragments of
 114  * an indefinite length, primitive value. If |looking_for_eoc| is set then any
 115  * EOC elements found will cause the function to return after consuming it.
 116  * It returns one on success and zero on error.
 117  */
 118 static int
 119 cbs_convert_indefinite(CBS *in, CBB *out, char squash_header,
 120     char looking_for_eoc, unsigned int depth)
 121 {
 122         if (depth > kMaxDepth)
 123                 return 0;
 124
 125         while (CBS_len(in) > 0) {
 126                 CBS contents;
 127                 unsigned int tag;
 128                 size_t header_len;
 129                 CBB *out_contents, out_contents_storage;
 130
 131                 if (!cbs_nonstrict_get_any_asn1_element(in, &contents, &tag,
 132                     &header_len))
 133                         return 0;
 134
 135                 out_contents = out;
 136
 137                 if (CBS_len(&contents) == header_len) {
 138                         if (is_eoc(header_len, &contents))
 139                                 return looking_for_eoc;
 140
 141                         if (header_len > 0 &&
 142                             CBS_data(&contents)[header_len - 1] == 0x80) {
 143                                 /*
 144                                  * This is an indefinite length element. If
 145                                  * it's a SEQUENCE or SET then we just need to
 146                                  * write the out the contents as normal, but
 147                                  * with a concrete length prefix.
 148                                  *
 149                                  * If it's a something else then the contents
 150                                  * will be a series of DER elements of the same
 151                                  * type which need to be concatenated.
 152                                  */
 153                                 const char context_specific = (tag & 0xc0)
 154                                     == 0x80;
 155                                 char squash_child_headers =
 156                                     is_primitive_type(tag);
 157
 158                                 /*
 159                                  * This is a hack, but it sufficies to handle
 160                                  * NSS's output. If we find an indefinite
 161                                  * length, context-specific tag with a definite,
 162                                  * primtive tag inside it, then we assume that
 163                                  * the context-specific tag is implicit and the
 164                                  * tags within are fragments of a primitive type
 165                                  * that need to be concatenated.
 166                                  */
 167                                 if (context_specific &&
 168                                     (tag & CBS_ASN1_CONSTRUCTED)) {
 169                                         CBS in_copy, inner_contents;
 170                                         unsigned int inner_tag;
 171                                         size_t inner_header_len;
 172
 173                                         CBS_init(&in_copy, CBS_data(in),
 174                                             CBS_len(in));
 175                                         if (!cbs_nonstrict_get_any_asn1_element(
 176                                             &in_copy, &inner_contents,
 177                                             &inner_tag, &inner_header_len))
 178                                                 return 0;
 179
 180                                         if (CBS_len(&inner_contents) >
 181                                             inner_header_len &&
 182                                             is_primitive_type(inner_tag))
 183                                                 squash_child_headers = 1;
 184                                 }
 185
 186                                 if (!squash_header) {
 187                                         unsigned int out_tag = tag;
 188
 189                                         if (squash_child_headers)
 190                                                 out_tag &=
 191                                                     ~CBS_ASN1_CONSTRUCTED;
 192
 193                                         if (!CBB_add_asn1(out,
 194                                             &out_contents_storage, out_tag))
 195                                                 return 0;
 196
 197                                         out_contents = &out_contents_storage;
 198                                 }
 199
 200                                 if (!cbs_convert_indefinite(in, out_contents,
 201                                     squash_child_headers,
 202                                     1 /* looking for eoc */, depth + 1))
 203                                         return 0;
 204
 205                                 if (out_contents != out && !CBB_flush(out))
 206                                         return 0;
 207
 208                                 continue;
 209                         }
 210                 }
 211
 212                 if (!squash_header) {
 213                         if (!CBB_add_asn1(out, &out_contents_storage, tag))
 214                                 return 0;
 215
 216                         out_contents = &out_contents_storage;
 217                 }
 218
 219                 if (!CBS_skip(&contents, header_len))
 220                         return 0;
 221
 222                 if (tag & CBS_ASN1_CONSTRUCTED) {
 223                         if (!cbs_convert_indefinite(&contents, out_contents,
 224                             0 /* don't squash header */,
 225                             0 /* not looking for eoc */, depth + 1))
 226                                 return 0;
 227                 } else {
 228                         if (!CBB_add_bytes(out_contents, CBS_data(&contents),
 229                             CBS_len(&contents)))
 230                                 return 0;
 231                 }
 232
 233                 if (out_contents != out && !CBB_flush(out))
 234                         return 0;
 235         }
 236
 237         return looking_for_eoc == 0;
 238 }
 239
 240 int
 241 CBS_asn1_indefinite_to_definite(CBS *in, uint8_t **out, size_t *out_len)
 242 {
 243         CBB cbb;
 244
 245         /*
 246          * First, do a quick walk to find any indefinite-length elements. Most
 247          * of the time we hope that there aren't any and thus we can quickly
 248          * return.
 249          */
 250         char conversion_needed;
 251         if (!cbs_find_indefinite(in, &conversion_needed, 0))
 252                 return 0;
 253
 254         if (!conversion_needed) {
 255                 *out = NULL;
 256                 *out_len = 0;
 257                 return 1;
 258         }
 259
 260         if (!CBB_init(&cbb, CBS_len(in)))
 261                 return 0;
 262         if (!cbs_convert_indefinite(in, &cbb, 0, 0, 0)) {
 263                 CBB_cleanup(&cbb);
 264                 return 0;
 265         }
 266
 267         return CBB_finish(&cbb, out, out_len);
 268 }