Return EACCES when authentication to a DESFire tag fails

Note that in case the tag didn't authenticate us, we've also
tag->last_picc_error = AUTHENTICATION_ERROR
But in the unlikely event that we didn't authenticate the tag
(e.g. if the tag is fake and pretends the auth was ok)
only errno = EACCES will be set

libfreefare/mifare_desfire.c

@@ -192,6 +192,8 @@ static ssize_t read_data (MifareTag tag, uint8_t command, uint8_t file_no, off_
  res[__##res##_n-2] = __res[__##res##_n-1]; \
  __##res##_n--; \
  if ((1 == __##res##_n) && (ADDITIONAL_FRAME != res[__##res##_n-1]) && (OPERATION_OK != res[__##res##_n-1])) { \
+ if (res[0] == AUTHENTICATION_ERROR) \
+ errno = EACCES; \
  return MIFARE_DESFIRE (tag)->last_picc_error = res[0], -1; \
  } \
  memcpy (res, __res, __##res##_n - 1); \
@@ -416,6 +418,7 @@ authenticate (MifareTag tag, uint8_t cmd, uint8_t key_no, MifareDESFireKey key)
  hexdump (PCD_RndA_s, key_length, "PCD ", 0);
  hexdump (PICC_RndA_s, key_length, "PICC ", 0);
 #endif
+ errno = EACCES;
  return -1;
  }