CertStoreBearSSL.cpp

/*
  CertStoreBearSSL.cpp - Library for Arduino ESP8266
  Copyright (c) 2018 Earle F. Philhower, III

  This library is free software; you can redistribute it and/or
  modify it under the terms of the GNU Lesser General Public
  License as published by the Free Software Foundation; either
  version 2.1 of the License, or (at your option) any later version.

  This library is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public
  License along with this library; if not, write to the Free Software
  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/

#include "CertStoreBearSSL.h"
#include <memory>


#if defined(DEBUG_ESP_SSL) && defined(DEBUG_ESP_PORT)
#define DEBUG_BSSL(fmt, ...)  DEBUG_ESP_PORT.printf_P((PGM_P)PSTR( "BSSL:" fmt), ## __VA_ARGS__)
#else
#define DEBUG_BSSL(...)
#endif

namespace BearSSL {

extern "C" {
  // Callback for the x509 decoder
  static void dn_append(void *ctx, const void *buf, size_t len) {
    br_sha256_context *sha1 = (br_sha256_context*)ctx;
    br_sha256_update(sha1, buf, len);
  }
}


CertStore::~CertStore() {
  free(_indexName);
  free(_dataName);
}

CertStore::CertInfo CertStore::_preprocessCert(uint32_t length, uint32_t offset, const void *raw) {
  CertStore::CertInfo ci;

  // Clear the CertInfo
  memset(&ci, 0, sizeof(ci));

  // Process it using SHA256, same as the hashed_dn
  br_x509_decoder_context *ctx = new (std::nothrow) br_x509_decoder_context;
  br_sha256_context *sha256 = new (std::nothrow) br_sha256_context;
  if (!ctx || !sha256) {
    if (ctx)
      delete ctx;
    if (sha256)
      delete sha256;
    DEBUG_BSSL("CertStore::_preprocessCert: OOM\n");
    return ci;
  }

  br_sha256_init(sha256);
  br_x509_decoder_init(ctx, dn_append, sha256, nullptr, nullptr);
  br_x509_decoder_push(ctx, (const void*)raw, length);

  // Copy result to structure
  br_sha256_out(sha256, &ci.sha256);
  ci.length = length;
  ci.offset = offset;

  // Clean up allocated memory
  delete sha256;
  delete ctx;

  // Return result
  return ci;
}

// The certs.ar file is a UNIX ar format file, concatenating all the 
// individual certificates into a single blob in a space-efficient way.
int CertStore::initCertStore(fs::FS &fs, const char *indexFileName, const char *dataFileName) {
  int count = 0;
  uint32_t offset = 0;

  _fs = &fs;

  // In case initCertStore called multiple times, don't leak old filenames
  free(_indexName);
  free(_dataName);

  // No strdup_P, so manually do it
  _indexName = (char *)malloc(strlen_P(indexFileName) + 1);
  _dataName = (char *)malloc(strlen_P(dataFileName) + 1);
  if (!_indexName || !_dataName) {
    free(_indexName);
    free(_dataName);
    return 0;
  }
  memcpy_P(_indexName, indexFileName, strlen_P(indexFileName) + 1);
  memcpy_P(_dataName, dataFileName, strlen_P(dataFileName) + 1);

  fs::File index = _fs->open(_indexName, "w");
  if (!index) {
    return 0;
  }

  fs::File data = _fs->open(_dataName, "r");
  if (!data) {
    index.close();
    return 0;
  }

  uint8_t magic[8];
  if (data.read(magic, sizeof(magic)) != sizeof(magic) ||
      memcmp(magic, "!<arch>\n", sizeof(magic)) ) {
    data.close();
    index.close();
    return 0;
  }
  offset += sizeof(magic);

  while (true) {
    uint8_t fileHeader[60];
    // 0..15 = filename in ASCII
    // 48...57 = length in decimal ASCII
    int32_t length;
    if (data.read(fileHeader, sizeof(fileHeader)) != sizeof(fileHeader)) {
      break;
    }
    offset += sizeof(fileHeader);
    fileHeader[58] = 0;
    if (1 != sscanf((char *)(fileHeader + 48), "%d", &length) || !length) {
      break;
    }

    void *raw = malloc(length);
    if (!raw) {
      break;
    }
    if (data.read((uint8_t *)raw, length) != length) {
      free(raw);
      break;
    }

    // If the filename starts with "//" then this is a rename file, skip it
    if (fileHeader[0] != '/' || fileHeader[1] != '/') {
      CertStore::CertInfo ci = _preprocessCert(length, offset, raw);
      if (index.write((uint8_t *)&ci, sizeof(ci)) != (ssize_t)sizeof(ci)) {
        free(raw);
        break;
      }
      count++;
    }

    offset += length;
    free(raw);
    if (offset & 1) {
      uint8_t x;
      data.read(&x, 1);
      offset++;
    }
  }
  data.close();
  index.close();
  return count;
}

void CertStore::installCertStore(br_x509_minimal_context *ctx) {
  br_x509_minimal_set_dynamic(ctx, (void*)this, findHashedTA, freeHashedTA);
}

const br_x509_trust_anchor *CertStore::findHashedTA(void *ctx, void *hashed_dn, size_t len) {
  CertStore *cs = static_cast<CertStore*>(ctx);
  CertStore::CertInfo ci;

  if (!cs || len != sizeof(ci.sha256) || !cs->_indexName || !cs->_dataName || !cs->_fs) {
    return nullptr;
  }

  fs::File index = cs->_fs->open(cs->_indexName, "r");
  if (!index) {
    return nullptr;
  }

  while (index.read((uint8_t *)&ci, sizeof(ci)) == sizeof(ci)) {
    if (!memcmp(ci.sha256, hashed_dn, sizeof(ci.sha256))) {
      index.close();
      uint8_t *der = (uint8_t*)malloc(ci.length);
      if (!der) {
        return nullptr;
      }
      fs::File data = cs->_fs->open(cs->_dataName, "r");
      if (!data) {
        free(der);
        return nullptr;
      }
      if (!data.seek(ci.offset, fs::SeekSet)) {
        data.close();
        free(der);
        return nullptr;
      }
      if (data.read(der, ci.length) != (int)ci.length) {
        free(der);
        return nullptr;
      }
      data.close();
      cs->_x509 = new (std::nothrow) X509List(der, ci.length);
      free(der);
      if (!cs->_x509) {
        DEBUG_BSSL("CertStore::findHashedTA: OOM\n");
        return nullptr;
      }

      br_x509_trust_anchor *ta = (br_x509_trust_anchor*)cs->_x509->getTrustAnchors();
      memcpy(ta->dn.data, ci.sha256, sizeof(ci.sha256));
      ta->dn.len = sizeof(ci.sha256);

      return ta;
    }
  }
  index.close();
  return nullptr;
}

void CertStore::freeHashedTA(void *ctx, const br_x509_trust_anchor *ta) {
  CertStore *cs = static_cast<CertStore*>(ctx);
  (void) ta; // Unused
  delete cs->_x509;
  cs->_x509 = nullptr;
}

}