Pad block with random bytes.

Add a test for all possible sizes of record - to see that padding works
correctly for all.

Bug: b:157943388
Change-Id: Iafb432365fb57ff4fad3fbebd81f8ece93c32033
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2300683Reviewed-by: Zach Trudo <zatrudo@google.com>
Commit-Queue: Leonid Baraz <lbaraz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#788840}

chrome/browser/policy/messaging_layer/storage/storage_queue.cc

@@ -21,7 +21,6 @@
 #include "base/hash/hash.h"
 #include "base/memory/ptr_util.h"
 #include "base/memory/weak_ptr.h"
-#include "base/rand_util.h"
 #include "base/sequence_checker.h"
 #include "base/strings/strcat.h"
 #include "base/strings/string_number_conversions.h"
@@ -34,6 +33,7 @@
 #include "chrome/browser/policy/messaging_layer/util/status_macros.h"
 #include "chrome/browser/policy/messaging_layer/util/statusor.h"
 #include "chrome/browser/policy/messaging_layer/util/task_runner_context.h"
+#include "crypto/random.h"
 
 namespace reporting {
 
@@ -344,10 +344,11 @@ Status StorageQueue::WriteHeaderAndBlock(
     const size_t pad_size =
         GetPaddingToNextFrameSize(sizeof(header) + data.size());
     if (pad_size != FRAME_SIZE) {
-      // TODO(b/157943388): Fill in with random bytes.
+      // Fill in with random bytes.
       uint8_t junk_bytes[FRAME_SIZE];
-      memset(&junk_bytes[0], 0, FRAME_SIZE);
-      write_status = file->Append(base::make_span(&junk_bytes[0], pad_size));
+      const auto pad_span = base::make_span(&junk_bytes[0], pad_size);
+      crypto::RandBytes(pad_span);
+      write_status = file->Append(pad_span);
       if (!write_status.ok()) {
         return Status(error::RESOURCE_EXHAUSTED, "Cannot pad file");
       }

chrome/browser/policy/messaging_layer/storage/storage_queue_unittest.cc

@@ -252,6 +252,29 @@ TEST_P(StorageQueueTest, WriteIntoNewStorageQueueAndFlush) {
   storage_queue_->Flush();
 }
 
+TEST_P(StorageQueueTest, ValidateVariousRecordSizes) {
+  std::vector<std::string> blobs;
+  for (size_t i = 16; i < 16 + 16; ++i) {
+    blobs.emplace_back(i, 'R');
+  }
+  CreateStorageQueueOrDie(BuildStorageQueueOptionsOnlyManual());
+  for (const auto& blob : blobs) {
+    WriteStringOrDie(blob);
+  }
+
+  // Set uploader expectations.
+  EXPECT_CALL(set_mock_uploader_expectations_, Call(NotNull()))
+      .WillOnce(Invoke([&blobs](MockUploadClient* mock_upload_client) {
+        MockUploadClient::SetUp client_setup(mock_upload_client);
+        for (const auto& blob : blobs) {
+          client_setup.Required(blob);
+        }
+      }));
+
+  // Flush manually.
+  storage_queue_->Flush();
+}
+
 TEST_P(StorageQueueTest, WriteAndRepeatedlyUploadWithConfirmations) {
   CreateStorageQueueOrDie(BuildStorageQueueOptionsPeriodic());