Record Code Signature of Downloaded DMG files

chrome/utility/safe_browsing/mac/udif.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/udif.h"
 
 #include <CoreFoundation/CoreFoundation.h>
 #include <bzlib.h>
 #include <libkern/OSByteOrder.h>
 #include <uuid/uuid.h>
@@ skipping 330 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(UDIFBlockChunkReadStream);
 };
 
 }  // namespace
 
 UDIFParser::UDIFParser(ReadStream* stream)
     : stream_(stream),
       partition_names_(),
       blocks_(),
-      block_size_(kSectorSize) {
-}
+      block_size_(kSectorSize) {}
 
 UDIFParser::~UDIFParser() {}
 
 bool UDIFParser::Parse() {
   if (!ParseBlkx())
     return false;
 
   return true;
 }
 
+const std::vector<uint8_t>& UDIFParser::GetDmgSignatureData() {
+  return signature_blob_;
+}
+
 size_t UDIFParser::GetNumberOfPartitions() {
   return blocks_.size();
 }
 
 std::string UDIFParser::GetPartitionName(size_t part_number) {
   DCHECK_LT(part_number, partition_names_.size());
   return partition_names_[part_number];
 }
 
 std::string UDIFParser::GetPartitionType(size_t part_number) {
@@ skipping 177 matching lines @@
                  << ", SectorCount = " << chunk->sector_count
                  << ", CompressOffset = " << chunk->compressed_offset
                  << ", CompressLen = " << chunk->compressed_length;
       }
     }
 
     blocks_.push_back(std::move(block));
     partition_names_.push_back(partition_name);
   }
 
+  // The offsets in the trailer could be garbage in DMGs that aren't signed.
+  // Need a sanity check that the DMG has legit values for these fields.
+  if (trailer.code_signature_length != 0 && trailer_start > 0) {
+    auto code_signature_end =
+        base::CheckedNumeric<size_t>(trailer.code_signature_offset) +
+        trailer.code_signature_length;
+    if (code_signature_end.IsValid() &&
+        code_signature_end.ValueOrDie() <=
+            base::checked_cast<size_t>(trailer_start)) {
+      signature_blob_.resize(trailer.code_signature_length);
+
+      off_t code_signature_start =
+          stream_->Seek(trailer.code_signature_offset, SEEK_SET);
+      if (code_signature_start == -1)
+        return false;
+
+      size_t bytes_read = 0;
+
+      if (!stream_->Read(signature_blob_.data(), trailer.code_signature_length,
+                         &bytes_read)) {
+        DLOG(ERROR) << "Failed to read raw signature bytes";
+        return false;
+      }
+
+      if (bytes_read != trailer.code_signature_length)

[Robert Sesek, 2017/06/28 18:21:06]

DLOGing here would be helpful too, I think.

[mortonm, 2017/06/28 23:07:09]

Done.

+        return false;
+    }
+  }
+
   return true;
 }
 
 namespace {
 
 UDIFPartitionReadStream::UDIFPartitionReadStream(
     ReadStream* stream,
     uint16_t block_size,
     const UDIFBlock* partition_block)
     : stream_(stream),
@@ skipping 295 matching lines @@
                 << chunk_->compressed_offset;
     return false;
   }
   return true;
 }
 
 }  // namespace
 
 }  // namespace dmg
 }  // namespace safe_browsing