Validate safe_browsing::dmg::UDIFBlock data before attempting to read at its offsets.

chrome/utility/safe_browsing/mac/hfs.cc

 // Copyright 2015 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 "chrome/utility/safe_browsing/mac/hfs.h"
 
 #include <libkern/OSByteOrder.h>
 #include <stddef.h>
 #include <sys/stat.h>
 
@@ skipping 351 matching lines @@
 
     auto extent_size =
         base::CheckedNumeric<size_t>(extent->blockCount) * hfs_->block_size();
     if (!extent_size.IsValid()) {
       DLOG(ERROR) << "Extent blockCount overflows";
       return false;
     }
 
     // Read the entire extent now, to avoid excessive seeking and re-reading.
     if (!read_current_extent_) {
-      hfs_->SeekToBlock(extent->startBlock);
+      if (!hfs_->SeekToBlock(extent->startBlock)) {
+        DLOG(ERROR) << "Failed to seek to block " << extent->startBlock;
+        return false;
+      }
       current_extent_data_.resize(extent_size.ValueOrDie());
       if (!hfs_->stream()->ReadExact(&current_extent_data_[0],
                                      extent_size.ValueOrDie())) {
         DLOG(ERROR) << "Failed to read extent " << current_extent_;
         return false;
       }
 
       read_current_extent_ = true;
     }
 
@@ skipping 259 matching lines @@
   return object;
 }
 
 bool HFSBTreeIterator::IsKeyUnexported(const base::string16& key) {
   return key == kHFSDirMetadataFolder ||
          key == kHFSMetadataFolder;
 }
 
 }  // namespace dmg
 }  // namespace safe_browsing