reader-pcsc: allow fixing the length of a PIN

fixes OpenSC#1221
closes OpenSC#1288

etc/opensc.conf.in

@@ -103,6 +103,12 @@ app default {
  # Default: true
  # enable_pinpad = false;
  #
+ # Some pinpad readers can only handle one exact length of the PIN.
+ # fixed_pinlength sets this value so that OpenSC expands the padding to
+ # this length.
+ # Default: 0 (i.e. not fixed)
+ # fixed_pinlength = 6;
+ #
  # Detect reader capabilities with escape commands (wrapped APDUs with
  # CLA=0xFF as defined by PC/SC pt. 3 and BSI TR-03119, e.g. for getting
  # the UID, escaped PIN commands and the reader's firmware version)

src/libopensc/reader-pcsc.c

@@ -82,6 +82,7 @@ struct pcsc_global_private_data {
  SCARDCONTEXT pcsc_ctx;
  SCARDCONTEXT pcsc_wait_ctx;
  int enable_pinpad;
+ int fixed_pinlength;
  int enable_pace;
  size_t force_max_recv_size;
  size_t force_max_send_size;
@@ -766,6 +767,7 @@ static int pcsc_init(sc_context_t *ctx)
  gpriv->transaction_end_action = SCARD_LEAVE_CARD;
  gpriv->reconnect_action = SCARD_LEAVE_CARD;
  gpriv->enable_pinpad = 1;
+ gpriv->fixed_pinlength = 0;
  gpriv->enable_pace = 1;
  gpriv->pcsc_ctx = -1;
  gpriv->pcsc_wait_ctx = -1;
@@ -788,6 +790,8 @@ static int pcsc_init(sc_context_t *ctx)
  pcsc_reset_action(scconf_get_str(conf_block, "reconnect_action", "leave"));
  gpriv->enable_pinpad = scconf_get_bool(conf_block, "enable_pinpad",
  gpriv->enable_pinpad);
+ gpriv->fixed_pinlength = scconf_get_bool(conf_block, "fixed_pinlength",
+ gpriv->fixed_pinlength);
  gpriv->enable_pace = scconf_get_bool(conf_block, "enable_pace",
  gpriv->enable_pace);
  gpriv->force_max_send_size = scconf_get_int(conf_block,
@@ -1887,10 +1891,17 @@ part10_check_pin_min_max(sc_reader_t *reader, struct sc_pin_cmd_data *data)
  unsigned char buffer[256];
  size_t length = sizeof buffer;
  struct pcsc_private_data *priv = reader->drv_data;
+ struct pcsc_global_private_data *gpriv = (struct pcsc_global_private_data *) reader->ctx->reader_drv_data;
  struct sc_pin_cmd_pin *pin_ref =
  data->flags & SC_PIN_CMD_IMPLICIT_CHANGE ?
  &data->pin1 : &data->pin2;
 
+ if (gpriv->fixed_pinlength != 0) {
+ pin_ref->min_length = gpriv->fixed_pinlength;
+ pin_ref->max_length = gpriv->fixed_pinlength;
+ return 0;
+ }
+
  if (!priv->get_tlv_properties)
  return 0;