tool_getparam: ensure string termination in parse_cert_parameter()

  size_t span;

  const char *param_place = NULL;

  char *certname_place = NULL;

  *certname = NULL;

  *passphrase = NULL;

  /* most trivial assumption: cert_parameter is empty */

  if(param_length == 0) {

    *certname = NULL;

  if(param_length == 0)

    return;

  }

  /* next less trivial: cert_parameter contains no colon nor backslash; this

   * means no passphrase was given and no characters escaped */

  if(!strpbrk(cert_parameter, ":\\")) {

    return;

  }

  /* deal with escaped chars; find unescaped colon if it exists */

  *certname = (char *) malloc(param_length + 1);

  param_place = cert_parameter;

  certname_place = *certname;

  certname_place = malloc(param_length + 1);

  if(!certname_place)

    return;

  *certname = certname_place;

  param_place = cert_parameter;

  while(*param_place) {

    span = strcspn(param_place, ":\\");

    strncpy(certname_place, param_place, span);

    param_place += span;

    certname_place += span;

    *certname_place = '\0';

    /* we just ate all the non-special chars. now we're on either a special

     * char or the end of the string. */

    switch(*param_place) {

      if(strlen(param_place) > 0) {

        *passphrase = strdup(param_place);

      }

      return;

      goto done;

    }

  }

done:

  *certname_place = '\0';

}

ParameterError getparameter(char *flag,    /* f or -long-flag */