Optimize OEMCrypto_ShrinkUsageTableHeader fuzzing

Merge from Widevine repo of http://go/wvgerrit/159057

Increase fuzzing efficiency by generating the header_buffer_length
parameter from the input data and pre-creating a usage table header.

Test: tested with http://go/ag/20420224

Change-Id: Idab4c3d0ae879854202e5ffd24bf031b946aeb6a

libwvdrmengine/oemcrypto/test/fuzz_tests/oemcrypto_fuzz_helper.h

@@ -20,9 +20,10 @@ extern "C" size_t LLVMFuzzerMutate(uint8_t* Data, size_t Size, size_t MaxSize)
     __attribute__((weak));
 
 const size_t KB = 1024;
-// Maximum signature length. If fuzzed signature length is greater that this,
-// this value will be used for signature length.
-const size_t MAX_FUZZ_SIGNATURE_LENGTH = 5 * KB;
+
+// Default maximum length of fuzzing output parameters.
+const size_t MAX_FUZZ_OUTPUT_LENGTH = 5 * KB;
+
 // Initial setup to create a valid OEMCrypto state such as initializing crypto
 // firmware/hardware, installing golden key box etc. in order to fuzz
 // OEMCrypto APIs.

libwvdrmengine/oemcrypto/test/fuzz_tests/oemcrypto_generate_rsa_signature_fuzz.cc

@@ -23,7 +23,7 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
   // We cannot allocate buffers of random huge lengths in memory.
   // This also slows down the fuzzer.
   size_t signature_length =
-      std::min(MAX_FUZZ_SIGNATURE_LENGTH, fuzzed_structure.signature_length);
+      std::min(MAX_FUZZ_OUTPUT_LENGTH, fuzzed_structure.signature_length);
   vector<uint8_t> signature(signature_length);
   OEMCrypto_GenerateRSASignature(
       license_api_fuzz.session()->session_id(), data + sizeof(fuzzed_structure),

libwvdrmengine/oemcrypto/test/fuzz_tests/oemcrypto_generic_verify_fuzz.cc

@@ -57,7 +57,7 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
                       session->license().keys[0].key_id_length,
                       fuzzed_structure.cipher_mode);
   signature_length =
-      std::min(MAX_FUZZ_SIGNATURE_LENGTH, fuzzed_structure.signature_length);
+      std::min(MAX_FUZZ_OUTPUT_LENGTH, fuzzed_structure.signature_length);
   signature.resize(signature_length);
   OEMCrypto_Generic_Verify(session->session_id(), in_buffer.data(),
                            in_buffer.size(), fuzzed_structure.algorithm,

libwvdrmengine/oemcrypto/test/fuzz_tests/oemcrypto_shrink_usage_table_header_fuzz.cc

@@ -2,6 +2,7 @@
 // source code may only be used and distributed under the Widevine
 // License Agreement.
 
+#include "FuzzedDataProvider.h"
 #include "OEMCryptoCENC.h"
 #include "oemcrypto_fuzz_helper.h"
 
@@ -11,15 +12,17 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
   // reduce noise
   RedirectStdoutToFile();
 
-  if (size < sizeof(uint32_t)) {
+  if (size < sizeof(uint32_t) + sizeof(size_t)) {
     return 0;
   }
 
   LicenseWithUsageEntryFuzz entry;
-  uint32_t new_entry_count = 0;
-  memcpy(&new_entry_count, data, sizeof(uint32_t));
-  std::vector<uint8_t> header_buffer(size - sizeof(uint32_t));
-  size_t header_buffer_length = header_buffer.size();
+  entry.CreateUsageTableHeader();
+  FuzzedDataProvider fuzzed_data(data, size);
+  const uint32_t new_entry_count = fuzzed_data.ConsumeIntegral<uint32_t>();
+  size_t header_buffer_length =
+      fuzzed_data.ConsumeIntegralInRange<size_t>(0, MAX_FUZZ_OUTPUT_LENGTH);
+  std::vector<uint8_t> header_buffer(header_buffer_length);
   OEMCrypto_ShrinkUsageTableHeader(new_entry_count, header_buffer.data(),
                                    &header_buffer_length);