Mac Archive Type Sniffing

chrome/utility/safe_browsing/mac/udif.cc

Index: chrome/utility/safe_browsing/mac/udif.cc
diff --git a/chrome/utility/safe_browsing/mac/udif.cc b/chrome/utility/safe_browsing/mac/udif.cc
index 0c4be3fa310747ef84226969a5ea536f630e8b6c..a2a335681a50fb72d5161ca2c72066628f49550d 100644
--- a/chrome/utility/safe_browsing/mac/udif.cc
+++ b/chrome/utility/safe_browsing/mac/udif.cc
@@ -348,13 +348,57 @@ UDIFParser::UDIFParser(ReadStream* stream)
     : stream_(stream),
       partition_names_(),
       blocks_(),
-      block_size_(kSectorSize) {
-}
+      block_size_(kSectorSize),
+      trailer_successfully_parsed_(false) {}
 
 UDIFParser::~UDIFParser() {}
 
+bool UDIFParser::ParseTrailer() {
+  // Makes sure that trailer is only ever parsed single time during execution of
+  // constuctor, so position of ReadStream is not moved after constructor runs.
+  if (trailer_successfully_parsed_)
+    return true;
+
+  UDIFResourceFile trailer;
+
+  off_t trailer_start = stream_->Seek(-sizeof(trailer), SEEK_END);
+  if (trailer_start == -1)
+    return false;
+
+  if (!stream_->ReadType(&trailer)) {
+    DLOG(ERROR) << "Failed to read UDIFResourceFile";
+    return false;
+  }
+  ConvertBigEndian(&trailer);
+
+  if (trailer.signature != trailer.kSignature) {
+    DLOG(ERROR) << "blkx signature does not match, is 0x" << std::hex
+                << trailer.signature;
+    return false;
+  }
+  if (trailer.version != trailer.kVersion) {
+    DLOG(ERROR) << "blkx version does not match, is " << trailer.version;
+    return false;
+  }
+
+  auto plist_end =
+      base::CheckedNumeric<size_t>(trailer.plist_offset) + trailer.plist_length;
+  if (!plist_end.IsValid() ||
+      plist_end.ValueOrDie() > base::checked_cast<size_t>(trailer_start)) {
+    DLOG(ERROR) << "blkx plist extends past UDIF trailer";
+    return false;
+  }
+
+  trailer_signature_ = trailer.signature;
+  plist_length_ = trailer.plist_length;
+  plist_offset_ = trailer.plist_offset;
+  return true;
+}
+
 bool UDIFParser::Parse() {
-  if (!ParseBlkx())
+  // First parses trailer and then parses blocks.
+  trailer_successfully_parsed_ = ParseTrailer();
+  if (!trailer_successfully_parsed_ || !ParseBlkx())
     return false;
 
   return true;
@@ -407,41 +451,15 @@ std::unique_ptr<ReadStream> UDIFParser::GetPartitionReadStream(
 }
 
 bool UDIFParser::ParseBlkx() {
-  UDIFResourceFile trailer;
-  off_t trailer_start = stream_->Seek(-sizeof(trailer), SEEK_END);
-  if (trailer_start == -1)
+  if (!trailer_successfully_parsed_)
     return false;
 
-  if (!stream_->ReadType(&trailer)) {
-    DLOG(ERROR) << "Failed to read UDIFResourceFile";
-    return false;
-  }
-  ConvertBigEndian(&trailer);
-
-  if (trailer.signature != trailer.kSignature) {
-    DLOG(ERROR) << "blkx signature does not match, is 0x"
-                << std::hex << trailer.signature;
-    return false;
-  }
-  if (trailer.version != trailer.kVersion) {
-    DLOG(ERROR) << "blkx version does not match, is " << trailer.version;
-    return false;
-  }
-
-  auto plist_end = base::CheckedNumeric<size_t>(trailer.plist_offset) +
-                   trailer.plist_length;
-  if (!plist_end.IsValid() ||
-      plist_end.ValueOrDie() > base::checked_cast<size_t>(trailer_start)) {
-    DLOG(ERROR) << "blkx plist extends past UDIF trailer";
-    return false;
-  }
-
-  std::vector<uint8_t> plist_bytes(trailer.plist_length, 0);
+  std::vector<uint8_t> plist_bytes(plist_length_, 0);
 
-  if (stream_->Seek(trailer.plist_offset, SEEK_SET) == -1)
+  if (stream_->Seek(plist_offset_, SEEK_SET) == -1)
     return false;
 
-  if (!stream_->ReadExact(&plist_bytes[0], trailer.plist_length)) {
+  if (!stream_->ReadExact(&plist_bytes[0], plist_length_)) {
     DLOG(ERROR) << "Failed to read blkx plist data";
     return false;
   }