text: /* Copyright (c) 2014, Google Inc.
   *
   * Permission to use, copy, modify, and/or distribute this software for any
   * purpose with or without fee is hereby granted, provided that the above
   * copyright notice and this permission notice appear in all copies.
   *
   * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
   * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
   * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
   * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
   * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
   * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
   * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
  
  #include "openssl/bytestring.h"
  
  #include "assert.h"
  #include "string.h"
  
  #include "internal.h"
  #include "../internal.h"
  
  
  // kMaxDepth is a just a sanity limit. The code should be such that the length
  // of the input being processes always decreases. None the less, a very large
  // input could otherwise cause the stack to overflow.
  static const unsigned kMaxDepth = 2048;
  
  // is_string_type returns one if |tag| is a string type and zero otherwise. It
  // ignores the constructed bit.
  static int is_string_type(unsigned tag) {
    switch (tag & ~CBS_ASN1_CONSTRUCTED) {
      case CBS_ASN1_BITSTRING:
      case CBS_ASN1_OCTETSTRING:
      case CBS_ASN1_UTF8STRING:
      case CBS_ASN1_NUMERICSTRING:
      case CBS_ASN1_PRINTABLESTRING:
      case CBS_ASN1_T61STRING:
      case CBS_ASN1_VIDEOTEXSTRING:
      case CBS_ASN1_IA5STRING:
      case CBS_ASN1_GRAPHICSTRING:
      case CBS_ASN1_VISIBLESTRING:
      case CBS_ASN1_GENERALSTRING:
      case CBS_ASN1_UNIVERSALSTRING:
      case CBS_ASN1_BMPSTRING:
        return 1;
      default:
        return 0;
    }
  }
  
  // cbs_find_ber walks an ASN.1 structure in |orig_in| and sets |*ber_found|
  // depending on whether an indefinite length element or constructed string was
  // found. The value of |orig_in| is not changed. It returns one on success (i.e.
  // |*ber_found| was set) and zero on error.
  static int cbs_find_ber(const CBS *orig_in, char *ber_found, unsigned depth) {
    CBS in;
  
    if (depth > kMaxDepth) {
      return 0;
    }
  
    CBS_init(&in, CBS_data(orig_in), CBS_len(orig_in));
    *ber_found = 0;
  
    while (CBS_len(&in) > 0) {
      CBS contents;
      unsigned tag;
      size_t header_len;
  
      if (!CBS_get_any_ber_asn1_element(&in, &contents, &tag, &header_len)) {
        return 0;
      }
      if (CBS_len(&contents) == header_len &&
          header_len > 0 &&
          CBS_data(&contents)[header_len-1] == 0x80) {
        // Found an indefinite-length element.
        *ber_found = 1;
        return 1;
      }
      if (tag & CBS_ASN1_CONSTRUCTED) {
        if (is_string_type(tag)) {
          // Constructed strings are only legal in BER and require conversion.
          *ber_found = 1;
          return 1;
        }
        if (!CBS_skip(&contents, header_len) ||
            !cbs_find_ber(&contents, ber_found, depth + 1)) {
          return 0;
        }
      }
    }
  
    return 1;
  }
  
  // is_eoc returns true if |header_len| and |contents|, as returned by
  // |CBS_get_any_ber_asn1_element|, indicate an "end of contents" (EOC) value.
  static char is_eoc(size_t header_len, CBS *contents) {
    return header_len == 2 && CBS_len(contents) == 2 &&
           OPENSSL_memcmp(CBS_data(contents), "\x00\x00", 2) == 0;
  }
  
  // cbs_convert_ber reads BER data from |in| and writes DER data to |out|. If
  // |string_tag| is non-zero, then all elements must match |string_tag| up to the
  // constructed bit and primitive element bodies are written to |out| without
  // element headers. This is used when concatenating the fragments of a
  // constructed string. If |looking_for_eoc| is set then any EOC elements found
  // will cause the function to return after consuming it. It returns one on
  // success and zero on error.
  static int cbs_convert_ber(CBS *in, CBB *out, unsigned string_tag,
                             char looking_for_eoc, unsigned depth) {
    assert(!(string_tag & CBS_ASN1_CONSTRUCTED));
  
    if (depth > kMaxDepth) {
      return 0;
    }
  
    while (CBS_len(in) > 0) {
      CBS contents;
      unsigned tag, child_string_tag = string_tag;
      size_t header_len;
      CBB *out_contents, out_contents_storage;
  
      if (!CBS_get_any_ber_asn1_element(in, &contents, &tag, &header_len)) {
        return 0;
      }
  
      if (is_eoc(header_len, &contents)) {
        return looking_for_eoc;
      }
  
      if (string_tag != 0) {
        // This is part of a constructed string. All elements must match
        // |string_tag| up to the constructed bit and get appended to |out|
        // without a child element.
        if ((tag & ~CBS_ASN1_CONSTRUCTED) != string_tag) {
          return 0;
        }
        out_contents = out;
      } else {
        unsigned out_tag = tag;
        if ((tag & CBS_ASN1_CONSTRUCTED) && is_string_type(tag)) {
          // If a constructed string, clear the constructed bit and inform
          // children to concatenate bodies.
          out_tag &= ~CBS_ASN1_CONSTRUCTED;
          child_string_tag = out_tag;
        }
        if (!CBB_add_asn1(out, &out_contents_storage, out_tag)) {
          return 0;
        }
        out_contents = &out_contents_storage;
      }
  
      if (CBS_len(&contents) == header_len && header_len > 0 &&
          CBS_data(&contents)[header_len - 1] == 0x80) {
        // This is an indefinite length element.
        if (!cbs_convert_ber(in, out_contents, child_string_tag,
                             1 /* looking for eoc */, depth + 1) ||
            !CBB_flush(out)) {
          return 0;
        }
        continue;
      }
  
      if (!CBS_skip(&contents, header_len)) {
        return 0;
      }
  
      if (tag & CBS_ASN1_CONSTRUCTED) {
        // Recurse into children.
        if (!cbs_convert_ber(&contents, out_contents, child_string_tag,
                             0 /* not looking for eoc */, depth + 1)) {
          return 0;
        }
      } else {
        // Copy primitive contents as-is.
        if (!CBB_add_bytes(out_contents, CBS_data(&contents),
                           CBS_len(&contents))) {
          return 0;
        }
      }
  
      if (!CBB_flush(out)) {
        return 0;
      }
    }
  
    return looking_for_eoc == 0;
  }
  
  int CBS_asn1_ber_to_der(CBS *in, CBS *out, uint8_t **out_storage) {
    CBB cbb;
  
    // First, do a quick walk to find any indefinite-length elements. Most of the
    // time we hope that there aren't any and thus we can quickly return.
    char conversion_needed;
    if (!cbs_find_ber(in, &conversion_needed, 0)) {
      return 0;
    }
  
    if (!conversion_needed) {
      if (!CBS_get_any_asn1_element(in, out, NULL, NULL)) {
        return 0;
      }
      *out_storage = NULL;
      return 1;
    }
  
    size_t len;
    if (!CBB_init(&cbb, CBS_len(in)) ||
        !cbs_convert_ber(in, &cbb, 0, 0, 0) ||
        !CBB_finish(&cbb, out_storage, &len)) {
      CBB_cleanup(&cbb);
      return 0;
    }
  
    CBS_init(out, *out_storage, len);
    return 1;
  }
  
  int CBS_get_asn1_implicit_string(CBS *in, CBS *out, uint8_t **out_storage,
                                   unsigned outer_tag, unsigned inner_tag) {
    assert(!(outer_tag & CBS_ASN1_CONSTRUCTED));
    assert(!(inner_tag & CBS_ASN1_CONSTRUCTED));
    assert(is_string_type(inner_tag));
  
    if (CBS_peek_asn1_tag(in, outer_tag)) {
      // Normal implicitly-tagged string.
      *out_storage = NULL;
      return CBS_get_asn1(in, out, outer_tag);
    }
  
    // Otherwise, try to parse an implicitly-tagged constructed string.
    // |CBS_asn1_ber_to_der| is assumed to have run, so only allow one level deep
    // of nesting.
    CBB result;
    CBS child;
    if (!CBB_init(&result, CBS_len(in)) ||
        !CBS_get_asn1(in, &child, outer_tag | CBS_ASN1_CONSTRUCTED)) {
      goto err;
    }
  
    while (CBS_len(&child) > 0) {
      CBS chunk;
      if (!CBS_get_asn1(&child, &chunk, inner_tag) ||
          !CBB_add_bytes(&result, CBS_data(&chunk), CBS_len(&chunk))) {
        goto err;
      }
    }
  
    uint8_t *data;
    size_t len;
    if (!CBB_finish(&result, &data, &len)) {
      goto err;
    }
  
    CBS_init(out, data, len);
    *out_storage = data;
    return 1;
  
  err:
    CBB_cleanup(&result);
    return 0;
  }
  