Harden allocator for file-backed memory.

components/metrics/file_metrics_provider.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/metrics/file_metrics_provider.h"
 
 #include "base/command_line.h"
 #include "base/files/file.h"
 #include "base/files/file_enumerator.h"
 #include "base/files/file_util.h"
@@ skipping 317 matching lines @@
   // Ensure any problems below don't occur repeatedly.
   source->last_seen = info.last_modified;
 
   // Test the validity of the file contents.
   const bool read_only = kSourceOptions[source->type].is_read_only;
   if (!base::FilePersistentMemoryAllocator::IsFileAcceptable(*mapped,
                                                              read_only)) {
     return ACCESS_RESULT_INVALID_CONTENTS;
   }
 
+  // Map the file and validate it.
+  std::unique_ptr<base::PersistentMemoryAllocator> memory_allocator =
+      base::MakeUnique<base::FilePersistentMemoryAllocator>(
+          std::move(mapped), 0, 0, base::StringPiece(), read_only);
+  if (memory_allocator->GetMemoryState() ==
+      base::PersistentMemoryAllocator::MEMORY_DELETED) {
+    return ACCESS_RESULT_MEMORY_DELETED;
+  }
+
   // Create an allocator for the mapped file. Ownership passes to the allocator.
-  source->allocator.reset(new base::PersistentHistogramAllocator(
-      base::MakeUnique<base::FilePersistentMemoryAllocator>(
-          std::move(mapped), 0, 0, base::StringPiece(), read_only)));
+  source->allocator = base::MakeUnique<base::PersistentHistogramAllocator>(
+      std::move(memory_allocator));
 
   return ACCESS_RESULT_SUCCESS;
 }
 
 // static
 void FileMetricsProvider::MergeHistogramDeltasFromSource(SourceInfo* source) {
   DCHECK(source->allocator);
   base::PersistentHistogramAllocator::Iterator histogram_iter(
       source->allocator.get());
 
@@ skipping 208 matching lines @@
   // important to know how much total "jank" may be introduced.
   SCOPED_UMA_HISTOGRAM_TIMER("UMA.FileMetricsProvider.SnapshotTime.Total");
 
   for (std::unique_ptr<SourceInfo>& source : sources_mapped_) {
     SCOPED_UMA_HISTOGRAM_TIMER("UMA.FileMetricsProvider.SnapshotTime.File");
     MergeHistogramDeltasFromSource(source.get());
   }
 }
 
 }  // namespace metrics