Commit message: re-applied sanity check patch
CVE: CVE-2013-2116
CWE: CWE-20
Vulnerability description: The _gnutls_ciphertext2compressed function in lib/gnutls_cipher.c in GnuTLS 2.12.23 allows remote attackers to cause a denial of service (buffer over-read and crash) via a crafted padding length.  NOTE: this might be due to an incorrect fix for CVE-2013-0169.

Project: gnutls
File: gnutls_cipher.c

_gnutls_ciphertext2compressed (gnutls_session_t session,
                               opaque * compress_data,
                               int compress_size,
                               gnutls_datum_t ciphertext, uint8_t type,
                               record_parameters_st * params)
{
  uint8_t MAC[MAX_HASH_SIZE];
  uint16_t c_length;
  unsigned int pad = 0;
  int length;
  uint16_t blocksize;
  int ret, i, pad_failed = 0;
  opaque preamble[PREAMBLE_SIZE];
  int preamble_size = 0;
  int ver = gnutls_protocol_get_version (session);
  int hash_size = _gnutls_hash_get_algo_len (params->mac_algorithm);

  blocksize = gnutls_cipher_get_block_size (params->cipher_algorithm);


  /* actual decryption (inplace)
   */
  switch (_gnutls_cipher_is_block (params->cipher_algorithm))
    {
    case CIPHER_STREAM:
      if ((ret =
           _gnutls_cipher_decrypt (&params->read.cipher_state,
                                   ciphertext.data, ciphertext.size)) < 0)
        {
          gnutls_assert ();
          return ret;
        }

      length = ciphertext.size - hash_size;

      break;
    case CIPHER_BLOCK:
      if ((ciphertext.size < blocksize) || (ciphertext.size % blocksize != 0))
        {
          gnutls_assert ();
          return GNUTLS_E_DECRYPTION_FAILED;
        }

      if ((ret =
           _gnutls_cipher_decrypt (&params->read.cipher_state,
                                   ciphertext.data, ciphertext.size)) < 0)
        {
          gnutls_assert ();
          return ret;
        }

      /* ignore the IV in TLS 1.1.
       */
      if (_gnutls_version_has_explicit_iv
          (session->security_parameters.version))
        {
          ciphertext.size -= blocksize;
          ciphertext.data += blocksize;
        }

      if (ciphertext.size < hash_size)
        {
          gnutls_assert ();
          return GNUTLS_E_DECRYPTION_FAILED;
        }
      pad = ciphertext.data[ciphertext.size - 1];   /* pad */

      /* Check the pading bytes (TLS 1.x). 
       * Note that we access all 256 bytes of ciphertext for padding check
       * because there is a timing channel in that memory access (in certain CPUs).
       */
      if (_gnutls_version_has_variable_padding (ver) && pad_failed == 0)
        for (i = 2; i <= pad; i++)
          {
            if (ciphertext.data[ciphertext.size - i] != pad)
              pad_failed = GNUTLS_E_DECRYPTION_FAILED;
          }
          
      if (pad_failed)
        pad = 0;
      length = ciphertext.size - hash_size - pad - 1;

      break;
    default:
      gnutls_assert ();
      return GNUTLS_E_INTERNAL_ERROR;
    }

  if (length < 0)
    length = 0;
  c_length = _gnutls_conv_uint16 ((uint16_t) length);

  /* Pass the type, version, length and compressed through
   * MAC.
   */
  if (params->mac_algorithm != GNUTLS_MAC_NULL)
    {
      digest_hd_st td;

      ret = mac_init (&td, params->mac_algorithm,
                      params->read.mac_secret.data,
                      params->read.mac_secret.size, ver);

      if (ret < 0)
        {
          gnutls_assert ();
          return GNUTLS_E_INTERNAL_ERROR;
        }

      preamble_size =
        make_preamble (UINT64DATA
                       (params->read.sequence_number), type,
                       c_length, ver, preamble);
      mac_hash (&td, preamble, preamble_size, ver);
      if (length > 0)
        mac_hash (&td, ciphertext.data, length, ver);

      mac_deinit (&td, MAC, ver);
    }

  /* HMAC was not the same. 
   */
  if (memcmp (MAC, &ciphertext.data[length], hash_size) != 0 || pad_failed != 0)
    {
      gnutls_datum_t compressed = {compress_data, compress_size};
      /* HMAC was not the same. */
      dummy_wait(params, &compressed, pad_failed, pad, length+preamble_size, ver);

      gnutls_assert ();
      return GNUTLS_E_DECRYPTION_FAILED;
    }

  /* copy the decrypted stuff to compressed_data.
   */
  if (compress_size < length)
    {
      gnutls_assert ();
      return GNUTLS_E_DECOMPRESSION_FAILED;
    }
  memcpy (compress_data, ciphertext.data, length);

  return length;
}