win: Don't attempt to read a nonexistent IMAGE_DIRECTORY_ENTRY_DEBUG

snapshot/win/pe_image_reader.cc

Index: snapshot/win/pe_image_reader.cc
diff --git a/snapshot/win/pe_image_reader.cc b/snapshot/win/pe_image_reader.cc
index 7268358a056eaedd1091a76ca939ecac0e00db23..486bb6d4de236e8d335ab52e850cc2e08e42e8dc 100644
--- a/snapshot/win/pe_image_reader.cc
+++ b/snapshot/win/pe_image_reader.cc
@@ -143,10 +143,19 @@ template <class NtHeadersType>
 bool PEImageReader::ReadDebugDirectoryInformation(UUID* uuid,
                                                   DWORD* age,
                                                   std::string* pdbname) const {
-  WinVMAddress nt_headers_address;
   NtHeadersType nt_headers;
-  if (!ReadNtHeaders(&nt_headers_address, &nt_headers))
+  if (!ReadNtHeaders(nullptr, &nt_headers))
+    return false;
+
+  if (nt_headers.FileHeader.SizeOfOptionalHeader <
+          offsetof(decltype(nt_headers.OptionalHeader),
+                   DataDirectory[IMAGE_DIRECTORY_ENTRY_DEBUG]) +
+              sizeof(nt_headers.OptionalHeader
+                         .DataDirectory[IMAGE_DIRECTORY_ENTRY_DEBUG]) ||
+      nt_headers.OptionalHeader.NumberOfRvaAndSizes <=
+          IMAGE_DIRECTORY_ENTRY_DEBUG) {
     return false;
+  }
 
   const IMAGE_DATA_DIRECTORY& data_directory =
       nt_headers.OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_DEBUG];
@@ -215,9 +224,9 @@ bool PEImageReader::ReadNtHeaders(WinVMAddress* nt_headers_address,
     return false;
   }
 
-  *nt_headers_address = Address() + dos_header.e_lfanew;
+  WinVMAddress local_nt_headers_address = Address() + dos_header.e_lfanew;
   if (!CheckedReadMemory(
-          *nt_headers_address, sizeof(NtHeadersType), nt_headers)) {
+          local_nt_headers_address, sizeof(NtHeadersType), nt_headers)) {
     LOG(WARNING) << "could not read nt headers of " << module_name_;
     return false;
   }
@@ -227,6 +236,9 @@ bool PEImageReader::ReadNtHeaders(WinVMAddress* nt_headers_address,
     return false;
   }
 
+  if (nt_headers_address)
+    *nt_headers_address = local_nt_headers_address;
+
   return true;
 }