/* Copyright (C) 2014 by Bundesamt für Sicherheit in der Informationstechnik
 * Software engineering by Intevation GmbH
 *
 * This file is Free Software under the GNU GPL (v>=2)
 * and comes with ABSOLUTELY NO WARRANTY!
 * See LICENSE.txt for details.
 */

#include "binverify.h"

#include "strhelp.h"
#include "logging.h"
#ifdef RELEASE_BUILD
#include "pubkey-release.h"
#else
#include "pubkey-test.h"
#endif

bin_verify_result
verify_binary(const char *filename, size_t name_len) {
  if (!filename || !name_len)
    return VerifyUnknownError;
#ifdef WIN32
  return verify_binary_win(filename, name_len);
#else
  return verify_binary_linux(filename, name_len);
#endif
}

#ifdef WIN32

#include <polarssl/x509_crt.h>

#include <windows.h>
#include <wincrypt.h>
#include <wintrust.h>
#include <stdio.h>


/** @brief Check if the certificate @a pCCertContext is pinned
  *
  * Compares the certificate's binary data (public key and attributes)
  * with each other to validate that the certificate pCCertContext has
  * exactly the same data as the builtin public certificate.
  *
  * @param[in] pCCertContext pointer to the certificate to check
  *
  * @returns true if the certificate matches, false otherwise.
  */
static bool
check_certificate (PCCERT_CONTEXT pCCertContext)
{
  x509_crt codesign_cert;
  int ret = 0;
  DWORD dwI = 0;
  bool retval = false;

  if (pCCertContext == NULL)
    {
      ERRORPRINTF ("Invalid call to check_certificate");
      return false;
    }

  x509_crt_init(&codesign_cert);

  /* Parse the pinned certificate */
  ret = x509_crt_parse(&codesign_cert,
                       public_key_codesign_pem,
                       public_key_codesign_pem_size);
  if (ret != 0)
    {
      ERRORPRINTF ("x509_crt_parse failed with -0x%04x\n\n", -ret);
      goto done;
    }

  if (codesign_cert.raw.len != pCCertContext->cbCertEncoded ||
      codesign_cert.raw.len <= 0)
    {
      ERRORPRINTF ("Certificate size mismatch");
      goto done;
    }

  /* Check that the certificate is exactly the same as the pinned one */
  for (dwI = 0; dwI < pCCertContext->cbCertEncoded; dwI++)
    {
      if (pCCertContext->pbCertEncoded[dwI] != codesign_cert.raw.p[dwI])
        {
          ERRORPRINTF ("Certificate content mismatch");
          goto done;
        }
    }

  retval = true;

done:
  x509_crt_free(&codesign_cert);
  return retval;
}

bin_verify_result
verify_binary_win(const char *filename, size_t name_len) {
  bin_verify_result retval = VerifyUnknownError;
  WCHAR *filenameW = NULL;
  BOOL result = FALSE;
  DWORD dwEncoding = 0,
        dwContentType = 0,
        dwFormatType = 0,
        dwSignerInfoSize = 0;
  HCERTSTORE hStore = NULL;
  HCRYPTMSG hMsg = NULL;
  PCERT_INFO pSignerCert = NULL;
  PCCERT_CONTEXT pSignerCertContext = NULL;

  if (!filename || name_len > MAX_PATH || strlen(filename) != name_len)
    {
      ERRORPRINTF ("Invalid parameters\n");
      return VerifyUnknownError;
    }

  filenameW = utf8_to_wchar(filename, name_len);

  result = CryptQueryObject (CERT_QUERY_OBJECT_FILE,
                             filenameW,
                             CERT_QUERY_CONTENT_FLAG_PKCS7_SIGNED_EMBED,
                             CERT_QUERY_FORMAT_FLAG_BINARY,
                             0,
                             &dwEncoding,
                             &dwContentType,
                             &dwFormatType,
                             &hStore,
                             &hMsg,
                             NULL);

  if (!result || !hMsg)
    {
      PRINTLASTERROR ("Failed to query crypto object");
      retval = VerifyReadFailed;
      goto done;
    }

  /* Get the cert info so that we can look up the signer in the store later */
  if (CryptMsgGetParam(hMsg,
                       CMSG_SIGNER_CERT_INFO_PARAM,
                       0,
                       NULL,
                       &dwSignerInfoSize) && dwSignerInfoSize > 0)
    {
      pSignerCert = xmalloc (dwSignerInfoSize);
    }
  else
    {
      ERRORPRINTF ("Failed to get signer cert size.");
      retval = VerifyUnknownError;
      goto done;
    }

  if (!(CryptMsgGetParam(hMsg,
                         CMSG_SIGNER_CERT_INFO_PARAM,
                         0,
                         pSignerCert,
                         &dwSignerInfoSize)))
    {
      ERRORPRINTF ("Failed to get signer cert.");
      retval = VerifyUnknownError;
      goto done;
    }

  pSignerCertContext = CertGetSubjectCertificateFromStore(
          hStore,
          PKCS_7_ASN_ENCODING | X509_ASN_ENCODING,
          pSignerCert);

  if (!pSignerCertContext)
    {
      ERRORPRINTF ("Failed to find signer cert in store.");
      retval = VerifyUnknownError;
      goto done;
    }

  /* Verify that the signature is actually valid */
  if(!CryptMsgControl(hMsg,
                      0,
                      CMSG_CTRL_VERIFY_SIGNATURE,
                      pSignerCertContext->pCertInfo))
    {
      ERRORPRINTF ("The signature is invalid. \n");
      retval = VerifyInvalidSignature;
      syslog_error_printf ("Software update embedded signature is invalid.");
      goto done;
    }

  if(check_certificate(pSignerCertContext))
    {
      DEBUGPRINTF ("Valid signature with pinned certificate.");
      retval = VerifyValid;
      goto done;
    }
  else
    {
      ERRORPRINTF ("Certificate mismatch. \n");
      retval = VerifyInvalidCertificate;
      syslog_error_printf ("Software update embedded signature "
                           "created with wrong certificate.");
      goto done;
    }

done:
  xfree(filenameW);
  xfree(pSignerCert);

  if(pSignerCertContext)
    {
      CertFreeCertificateContext(pSignerCertContext);
    }
  if (hStore)
    {
      CertCloseStore(hStore, 0);
    }
  if (hMsg)
    {
      CryptMsgClose(hMsg);
    }
  return retval;
}
#else /* WIN32 */

#include "listutil.h"

#pragma GCC diagnostic ignored "-Wconversion"
/* Polarssl mh.h contains a conversion which gcc warns about */
#include <polarssl/pk.h>
#include <polarssl/base64.h>
#include <polarssl/sha256.h>
#include <polarssl/error.h>
#include <polarssl/x509_crt.h>
#pragma GCC diagnostic pop

bin_verify_result
verify_binary_linux(const char *filename, size_t name_len)
{
  int ret = -1;
  const size_t sig_b64_size = TRUSTBRIDGE_RSA_KEY_SIZE / 8 * 4 / 3;
  char *data = NULL,
       signature_b64[sig_b64_size + 1];
  size_t data_size = 0,
         sig_size = TRUSTBRIDGE_RSA_KEY_SIZE / 8;
  unsigned char signature[sig_size],
                hash[32];

  bin_verify_result retval = VerifyUnknownError;
  x509_crt codesign_cert;

  if (strnlen(filename, name_len + 1) != name_len || name_len == 0)
    {
      ERRORPRINTF ("Invalid call to verify_binary_linux\n");
      return VerifyUnknownError;
    }

  ret = read_file(filename, &data, &data_size, MAX_VALID_BIN_SIZE);

  if (ret != 0)
    {
      ERRORPRINTF ("Read file failed with error: %i\n", ret);
      return VerifyReadFailed;
    }

  /* Fetch the signature from the end of data */
  if (data_size < sig_b64_size + 5)
    {
      ERRORPRINTF ("File to small to contain a signature.\n");
      retval = VerifyInvalidSignature;
      goto done;
    }

  if (data[data_size - sig_b64_size - 2] != ':' ||
      data[data_size - sig_b64_size - 3] != 'S' ||
      data[data_size - sig_b64_size - 4] != '\n'||
      data[data_size - sig_b64_size - 5] != '\r')
    {
      ERRORPRINTF ("Failed to find valid signature line.\n");
      retval = VerifyInvalidSignature;
      goto done;
    }

  strncpy(signature_b64, data + (data_size - sig_b64_size - 1), sig_b64_size);
  signature_b64[sig_b64_size] = '\0';

  ret = base64_decode(signature, &sig_size,
                      (unsigned char *)signature_b64, sig_b64_size);

  if (ret != 0 || sig_size != TRUSTBRIDGE_RSA_KEY_SIZE / 8)
    {
      ERRORPRINTF ("Base 64 decode failed with error: %i\n", ret);
      goto done;
    }

  /* Hash is calculated over the data without the signature at the end. */
  sha256((unsigned char *)data, data_size - sig_b64_size - 5, hash, 0);

  x509_crt_init(&codesign_cert);

  /* Parse the pinned certificate */
  ret = x509_crt_parse(&codesign_cert,
                       public_key_codesign_pem,
                       public_key_codesign_pem_size);
  if (ret != 0)
    {
      char errbuf[1020];
      polarssl_strerror(ret, errbuf, 1020);
      errbuf[1019] = '\0'; /* Just to be sure */
      ERRORPRINTF ("x509_crt_parse failed with -0x%04x\n%s\n", -ret, errbuf);
      x509_crt_free(&codesign_cert);
      return VerifyUnknownError;
    }

  ret = pk_verify(&codesign_cert.pk, POLARSSL_MD_SHA256, hash, 0,
                  signature, sig_size);

  if (ret != 0)
    {
      char errbuf[1020];
      polarssl_strerror(ret, errbuf, 1020);
      errbuf[1019] = '\0'; /* Just to be sure */
      ERRORPRINTF ("pk_verify failed with -0x%04x\n %s\n", -ret, errbuf);
      x509_crt_free(&codesign_cert);
      retval = VerifyInvalidSignature;
      goto done;
    }
  x509_crt_free(&codesign_cert);

  retval = VerifyValid;

done:
  xfree (data);
  return retval;
}

#endif /* WIN32 */