CSRSS lockdown: destroy CSRSS heap

sandbox/win/src/heap_helper.cc

+// Copyright 2017 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 "sandbox/win/src/heap_helper.h"
+
+#include <windows.h>
+
+#include "base/memory/ref_counted.h"
+#include "base/win/windows_version.h"
+
+namespace sandbox {
+
+// These are undocumented, but readily found on the internet.
+#define HEAP_CLASS_8 0x00008000  // CSR port heap
+#define HEAP_CLASS_MASK 0x0000f000
+
+// This structure is not documented, but the flags field is the only relevant
+// field.
+struct _HEAP {
+  char reserved[0x70];
+  DWORD flags;
+};
+
+bool HeapFlags(HANDLE handle, DWORD* flags) {
+  if (!handle || !flags) {
+    // This is an error.
+    return false;
+  }
+  _HEAP* heap = reinterpret_cast<_HEAP*>(handle);
+  *flags = heap->flags;
+  return true;
+}
+
+HANDLE FindCsrPortHeap() {
+  if (base::win::GetVersion() < base::win::VERSION_WIN10) {
+    // This functionality has not been verified on versions before Win10.
+    return nullptr;
+  }
+  DWORD number_of_heaps = ::GetProcessHeaps(0, NULL);
+  std::unique_ptr<HANDLE[]> all_heaps(new HANDLE[number_of_heaps]);
+  if (::GetProcessHeaps(number_of_heaps, all_heaps.get()) != number_of_heaps)
+    return nullptr;
+
+  // Search for the CSR port heap handle, identified purely based on flags.
+  HANDLE csr_port_heap = nullptr;
+  for (size_t i = 0; i < number_of_heaps; ++i) {
+    HANDLE handle = all_heaps[i];
+    DWORD flags = 0;
+    if (!HeapFlags(handle, &flags)) {
+      LOG(ERROR) << "Unable to get flags for this heap";

[dcheng, 2017/05/03 23:26:04]

Is there a reason these are LOG(ERROR) instead of DLOG? It doesn't seem
particularly actionable to end users and takes up binary space (logging strings
aren't dropped, even in official builds).

+      continue;
+    }
+    if ((flags & HEAP_CLASS_MASK) == HEAP_CLASS_8) {
+      if (nullptr != csr_port_heap) {
+        LOG(ERROR) << "Found multiple suitable CSR Port heaps";
+        return nullptr;
+      }
+      csr_port_heap = handle;
+    }
+  }
+  return csr_port_heap;
+}
+
+}  // namespace sandbox