Fix cens Mode in Android CDM

(This is a merge of go/wvgerrit/20500)

This patch removes the logic that calculates the "pattern offset" from
the Android glue layer. There is no such thing as a pattern offset, and
setting this value to anything other than zero may break cens mode on
some devices.

To reduce the risk of setting this value to anything other than zero,
the offset_blocks parameter has been removed from the pattern descriptor
in the CDM Core. It will have to remain part of OEMCrypto v11,
unfortunately, but the code to set it to zero is now centralized in
CryptoSession.

Bug: 28726863
Change-Id: I9c5bfe470fe251c7a57901dc2e998f4dab7fe7d7

libwvdrmengine/cdm/core/include/wv_cdm_types.h

@@ -282,11 +282,9 @@ enum CdmCipherMode {
 struct CdmCencPatternEncryptionDescriptor {
   size_t encrypt_blocks;  // number of 16 byte blocks to decrypt
   size_t skip_blocks;     // number of 16 byte blocks to leave in clear
-  size_t offset_blocks;   // offset into the pattern for this call, in blocks
   CdmCencPatternEncryptionDescriptor()
       : encrypt_blocks(0),
-        skip_blocks(0),
+        skip_blocks(0) {}
-        offset_blocks(0) {}
 };
 
 struct CdmDecryptionParameters {

libwvdrmengine/cdm/core/src/crypto_session.cpp

@@ -689,7 +689,7 @@ CdmResponseType CryptoSession::Decrypt(const CdmDecryptionParameters& params) {
     OEMCrypto_CENCEncryptPatternDesc pattern_descriptor;
     pattern_descriptor.encrypt = params.pattern_descriptor.encrypt_blocks;
     pattern_descriptor.skip = params.pattern_descriptor.skip_blocks;
-    pattern_descriptor.offset = params.pattern_descriptor.offset_blocks;
+    pattern_descriptor.offset = 0;  // Deprecated field
     AutoLock auto_lock(crypto_lock_);
     // Check if key needs to be selected
     if (params.is_encrypted) {

libwvdrmengine/mediacrypto/include/WVCryptoPlugin.h

@@ -47,7 +47,7 @@ class WVCryptoPlugin : public android::CryptoPlugin {
   wvcdm::CdmSessionId configureTestMode(const void* data, size_t size);
   static wvcdm::CdmResponseType countEncryptedBlocksInPatternedRange(
       size_t range, size_t startingOffset, const Pattern& pattern,
-      size_t startingPatternOffset, uint64_t* result);
+      uint64_t* result);
   static void incrementIV(uint64_t increaseBy, std::vector<uint8_t>* ivPtr);
 };
 

libwvdrmengine/mediacrypto/src/WVCryptoPlugin.cpp

@@ -146,7 +146,6 @@ ssize_t WVCryptoPlugin::decrypt(bool secure, const uint8_t key[KEY_ID_SIZE],
   size_t blockOffset = 0;
   const size_t patternLengthInBytes =
       (pattern.mEncryptBlocks + pattern.mSkipBlocks) * kAESBlockSize;
-  size_t patternOffsetInBytes = 0;
 
   for (size_t i = 0; i < numSubSamples; ++i) {
     const SubSample& subSample = subSamples[i];
@@ -187,7 +186,6 @@ ssize_t WVCryptoPlugin::decrypt(bool secure, const uint8_t key[KEY_ID_SIZE],
       params.encrypt_buffer = source + offset;
       params.encrypt_length = subSample.mNumBytesOfClearData;
       params.block_offset = 0;
-      params.pattern_descriptor.offset_blocks = 0;
       params.decrypt_buffer_offset = offset;
       params.subsample_flags = clearFlags;
 
@@ -238,12 +236,6 @@ ssize_t WVCryptoPlugin::decrypt(bool secure, const uint8_t key[KEY_ID_SIZE],
       params.encrypt_buffer = source + offset;
       params.encrypt_length = subSample.mNumBytesOfEncryptedData;
       params.block_offset = blockOffset;
-      // Note that the pattern offset calculation relies intentionally on
-      // integer division's flooring behavior. If we are partway through a
-      // crypto block, we should return the offset of the pattern block we are
-      // partway through.
-      size_t patternOffsetInBlocks = patternOffsetInBytes / kAESBlockSize;
-      params.pattern_descriptor.offset_blocks = patternOffsetInBlocks;
       params.decrypt_buffer_offset = offset;
       params.subsample_flags = encryptedFlags;
 
@@ -301,7 +293,7 @@ ssize_t WVCryptoPlugin::decrypt(bool secure, const uint8_t key[KEY_ID_SIZE],
         } else {
           res = countEncryptedBlocksInPatternedRange(
               subSample.mNumBytesOfEncryptedData, blockOffset, pattern,
-              patternOffsetInBlocks, &increment);
+              &increment);
           if (!isCdmResponseTypeSuccess(res)) {
             // Swallow the specifics of the error to obscure decrypt internals.
             return kErrorCDMGeneric;
@@ -312,12 +304,6 @@ ssize_t WVCryptoPlugin::decrypt(bool secure, const uint8_t key[KEY_ID_SIZE],
         // Update the block offset
         blockOffset = (blockOffset + subSample.mNumBytesOfEncryptedData) %
             kAESBlockSize;
-
-        if (patternLengthInBytes > 0) {
-          patternOffsetInBytes =
-              (patternOffsetInBytes + subSample.mNumBytesOfEncryptedData) %
-                  patternLengthInBytes;
-        }
       } else if (mode == kMode_AES_CBC && patternLengthInBytes == 0) {
         // If there is no pattern, assume cbc1 mode and update the IV.
 
@@ -363,14 +349,13 @@ ssize_t WVCryptoPlugin::decrypt(bool secure, const uint8_t key[KEY_ID_SIZE],
 
 CdmResponseType WVCryptoPlugin::countEncryptedBlocksInPatternedRange(
     size_t range, size_t startingOffset, const Pattern& pattern,
-    size_t startingPatternOffset, uint64_t* result) {
+    uint64_t* result) {
   uint64_t blocksPassed = 0;
   size_t bytesRemaining = range;
-  size_t patternOffset = startingPatternOffset;
+  size_t patternPosition = 0;
   size_t patternLength = pattern.mEncryptBlocks + pattern.mSkipBlocks;
 
-  if (result == NULL || startingOffset >= kAESBlockSize ||
+  if (result == NULL || startingOffset >= kAESBlockSize) {
-      startingPatternOffset >= patternLength) {
     return wvcdm::UNKNOWN_ERROR;
   }
 
@@ -379,10 +364,10 @@ CdmResponseType WVCryptoPlugin::countEncryptedBlocksInPatternedRange(
   size_t bytesNeededToCompleteABlock = kAESBlockSize - startingOffset;
   while (bytesRemaining >= bytesNeededToCompleteABlock) {
     bytesRemaining -= bytesNeededToCompleteABlock;
-    if (patternOffset < pattern.mEncryptBlocks) {
+    if (patternPosition < pattern.mEncryptBlocks) {
       ++blocksPassed;
     }
-    patternOffset = (patternOffset + 1) % patternLength;
+    patternPosition = (patternPosition + 1) % patternLength;
 
     // After the first block, we only concern ourselves with complete blocks.
     bytesNeededToCompleteABlock = kAESBlockSize;