android/libwvdrmengine/mediacrypto/src/WVCryptoPlugin.cpp

//
// Copyright 2018 Google LLC. All Rights Reserved. This file and proprietary
// source code may only be used and distributed under the Widevine License
// Agreement.
//

//#define LOG_NDEBUG 0
#define LOG_TAG "WVCdm"
#include <utils/Log.h>

#include "WVCryptoPlugin.h"

#include <algorithm>
#include <endian.h>
#include <iterator>
#include <string.h>
#include <string>
#include <vector>

#include "mapErrors-inl.h"
#include "media/stagefright/MediaErrors.h"
#include "OEMCryptoCENC.h"
#include "openssl/sha.h"
#include "utils/Errors.h"
#include "utils/String8.h"
#include "wv_cdm_constants.h"
#include "WVErrors.h"

namespace wvdrm {

using namespace android;
using namespace std;
using namespace wvcdm;

WVCryptoPlugin::WVCryptoPlugin(const void* data, size_t size,
                               const sp<WvContentDecryptionModule>& cdm)
  : mCDM(cdm),
    mTestMode(false),
    mSessionId(configureTestMode(data, size)) {}

CdmSessionId WVCryptoPlugin::configureTestMode(const void* data, size_t size) {
  CdmSessionId sessionId;
  if (data != NULL) {
    sessionId.assign(static_cast<const char *>(data), size);
    size_t index = sessionId.find("test_mode");
    if (index != string::npos) {
      sessionId = sessionId.substr(0, index);
      mTestMode = true;
    }
  }
  if (!mCDM->IsOpenSession(sessionId)) {
    sessionId.clear();
  }
  return sessionId;
}

bool WVCryptoPlugin::requiresSecureDecoderComponent(const char* mime) const {
  if (!strncasecmp(mime, "video/", 6)) {
    // Type is video, so query CDM to see if we require a secure decoder.
    CdmQueryMap status;

    CdmResponseType res = mCDM->QuerySessionStatus(mSessionId, &status);

    if (!isCdmResponseTypeSuccess(res)) {
      ALOGE("Error querying CDM status: %u", res);
      return false;
    }

    return status[QUERY_KEY_SECURITY_LEVEL] == QUERY_VALUE_SECURITY_LEVEL_L1;
  } else {
    // Type is not video, so never require a secure decoder.
    return false;
  }
}

void WVCryptoPlugin::notifyResolution(uint32_t width, uint32_t height) {
  mCDM->NotifyResolution(mSessionId, width, height);
}

status_t WVCryptoPlugin::setMediaDrmSession(const Vector<uint8_t>& sessionId) {
  CdmSessionId cdmSessionId(reinterpret_cast<const char *>(sessionId.array()),
                            sessionId.size());
  if (sessionId.size() == 0) {
      return android::BAD_VALUE;
  }
  if (!mCDM->IsOpenSession(cdmSessionId)) {
    return android::ERROR_DRM_SESSION_NOT_OPENED;
  } else {
    mSessionId = cdmSessionId;
    return android::NO_ERROR;
  }
}

// Returns negative values for error code and positive values for the size of
// decrypted data.  In theory, the output size can be larger than the input
// size, but in practice this should never happen for AES-CTR.
ssize_t WVCryptoPlugin::decrypt(bool secure, const uint8_t key[KEY_ID_SIZE],
                                const uint8_t iv[KEY_IV_SIZE], Mode mode,
                                const Pattern& pattern, const void* srcPtr,
                                const SubSample* subSamples,
                                size_t numSubSamples, void* dstPtr,
                                AString* errorDetailMsg) {
  if (mode != kMode_Unencrypted &&
      mode != kMode_AES_CTR &&
      mode != kMode_AES_CBC) {
    errorDetailMsg->setTo(
        "The requested encryption mode is not supported by Widevine CDM.");
    return kErrorUnsupportedCrypto;
  } else if (mode == kMode_AES_CTR &&
             (pattern.mEncryptBlocks != 0 || pattern.mSkipBlocks != 0)) {
    errorDetailMsg->setTo(
        "The 'cens' schema is not supported by Widevine CDM.");
    return kErrorUnsupportedCrypto;
  }

  // Convert parameters to the form the CDM wishes to consume them in.
  const KeyId keyId(reinterpret_cast<const char*>(key), KEY_ID_SIZE);
  vector<uint8_t> ivVector(iv, iv + KEY_IV_SIZE);
  const uint8_t* const source = static_cast<const uint8_t*>(srcPtr);
  uint8_t* const dest = static_cast<uint8_t*>(dstPtr);

  // Set up the decrypt params
  CdmDecryptionParametersV16 params;
  params.key_id = keyId;
  params.is_secure = secure;
  if (mode == kMode_AES_CTR) {
    params.cipher_mode = kCipherModeCtr;
  } else if (mode == kMode_AES_CBC) {
    params.cipher_mode = kCipherModeCbc;
  }
  params.pattern.encrypt_blocks = pattern.mEncryptBlocks;
  params.pattern.skip_blocks = pattern.mSkipBlocks;

  // Set up the sample
  // Android's API only supports one at a time
  params.samples.emplace_back();
  CdmDecryptionSample& sample = params.samples.back();
  sample.encrypt_buffer = source;
  sample.decrypt_buffer = dest;
  sample.decrypt_buffer_offset = 0;
  sample.iv = ivVector;

  // Set up the subsamples
  // We abuse std::transform() here to also do some side-effects: Tallying the
  // total size of the sample and checking if any of the data is protected.
  size_t totalSize = 0;
  bool hasProtectedData = false;
  sample.subsamples.reserve(numSubSamples);
  std::transform(subSamples, subSamples + numSubSamples,
      std::back_inserter(sample.subsamples),
      [&](const SubSample& subSample) -> CdmDecryptionSubsample {
        totalSize +=
            subSample.mNumBytesOfClearData + subSample.mNumBytesOfEncryptedData;
        hasProtectedData |= subSample.mNumBytesOfEncryptedData > 0;
        return CdmDecryptionSubsample(subSample.mNumBytesOfClearData,
                                      subSample.mNumBytesOfEncryptedData);
      });

  sample.encrypt_buffer_length = totalSize;
  sample.decrypt_buffer_size = totalSize;

  if (mode == kMode_Unencrypted && hasProtectedData) {
    errorDetailMsg->setTo("Protected ranges found in allegedly clear data.");
    return kErrorExpectedUnencrypted;
  }

  // Decrypt
  status_t res = attemptDecrypt(params, hasProtectedData, errorDetailMsg);
  if (res != android::OK) {
    return res;
  }

  // In test mode, we return an error that causes a detailed error
  // message string containing a SHA256 hash of the decrypted data
  // to get passed to the java app via CryptoException.  The test app
  // can then use the hash to verify that decryption was successful.

  if (mTestMode) {
      if (secure) {
          // can't access data in secure mode
          errorDetailMsg->setTo("secure");
      } else {
          SHA256_CTX ctx;
          uint8_t digest[SHA256_DIGEST_LENGTH];
          SHA256_Init(&ctx);
          SHA256_Update(&ctx, dstPtr, totalSize);
          SHA256_Final(digest, &ctx);
          String8 buf;
          for (size_t i = 0; i < sizeof(digest); i++) {
              buf.appendFormat("%02x", digest[i]);
          }
          errorDetailMsg->setTo(buf.string());
      }

      return kErrorTestMode;
  }

  return static_cast<ssize_t>(totalSize);
}

status_t WVCryptoPlugin::attemptDecrypt(
    const CdmDecryptionParametersV16& params, bool hasProtectedData,
    AString* errorDetailMsg) {
  CdmResponseType res = mCDM->DecryptV16(mSessionId, hasProtectedData,
                                         params);

  if (isCdmResponseTypeSuccess(res)) {
    return android::OK;
  } else {
    ALOGE("Decrypt error in session %s during a sample %s protected data: %d",
          mSessionId.c_str(),
          hasProtectedData ? "with" : "without",
          res);
    bool actionableError = true;
    switch (res) {
      case wvcdm::INSUFFICIENT_CRYPTO_RESOURCES:
        errorDetailMsg->setTo(
            "Error decrypting data: insufficient crypto resources");
        break;
      case wvcdm::NEED_KEY:
      case wvcdm::KEY_NOT_FOUND_IN_SESSION:
        errorDetailMsg->setTo(
            "Error decrypting data: requested key has not been loaded");
        break;
      case wvcdm::DECRYPT_NOT_READY:
        errorDetailMsg->setTo(
            "Error decrypting data: license validity period is in the future");
        break;
      case wvcdm::SESSION_NOT_FOUND_FOR_DECRYPT:
        errorDetailMsg->setTo(
            "Error decrypting data: session not found, possibly reclaimed");
        break;
      case wvcdm::DECRYPT_ERROR:
        errorDetailMsg->setTo(
            "Error decrypting data: unspecified error");
        break;
      case wvcdm::INSUFFICIENT_OUTPUT_PROTECTION:
      case wvcdm::ANALOG_OUTPUT_ERROR:
        errorDetailMsg->setTo(
            "Error decrypting data: insufficient output protection");
        break;
      case wvcdm::KEY_PROHIBITED_FOR_SECURITY_LEVEL:
        errorDetailMsg->setTo(
            "Error decrypting data: key prohibited for security level");
        break;
      default:
        actionableError = false;
        break;
    }

    if (actionableError) {
      // This error is actionable by the app and should be passed up.
      return mapCdmResponseType(res);
    } else {
      // Swallow the specifics of other errors to obscure decrypt internals.
      return kErrorCDMGeneric;
    }
  }
}

}  // namespace wvdrm