Mojo cpp bindings: validation logic for incoming messages

mojo/public/cpp/bindings/lib/bounds_checker.cc

+// Copyright 2014 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 "mojo/public/cpp/bindings/lib/bounds_checker.h"
+
+#include <assert.h>
+
+#include "mojo/public/cpp/bindings/lib/bindings_serialization.h"
+#include "mojo/public/cpp/system/core.h"
+
+namespace mojo {
+namespace internal {
+
+BoundsChecker::BoundsChecker(const void* data, uint32_t data_num_bytes,
+                             size_t num_handles)
+    : data_begin_(reinterpret_cast<uintptr_t>(data)),
+      data_end_(data_begin_ + data_num_bytes),
+      handle_begin_(0),
+      handle_end_(static_cast<uint32_t>(num_handles)) {
+  if (data_end_ < data_begin_) {
+    // The calculation of |data_end_| overflowed.
+    // It shouldn't happen but if it does, set the range to empty so
+    // IsValidRange() and ClaimMemory() always fail.
+    assert(false);  // Not reached.
+    data_end_ = data_begin_;
+  }
+  if (handle_end_ < num_handles) {
+    // Assigning |num_handles| to |handle_end_| overflowed.
+    // It shouldn't happen but if it does, set the handle index range to empty.
+    assert(false);  // Not reached.
+    handle_end_ = 0;
+  }
+}
+
+BoundsChecker::~BoundsChecker() {
+}
+
+bool BoundsChecker::ClaimMemory(const void* position, uint32_t num_bytes) {
+  uintptr_t begin = reinterpret_cast<uintptr_t>(position);
+  uintptr_t end = begin + num_bytes;
+
+  if (!InternalIsValidRange(begin, end))
+    return false;
+
+  data_begin_ = end;
+  return true;
+}
+
+bool BoundsChecker::ClaimHandle(const Handle& encoded_handle) {
+  uint32_t index = encoded_handle.value();
+  if (index == kEncodedInvalidHandleValue)
+    return true;
+
+  if (index < handle_begin_ || index >= handle_end_)
+    return false;
+
+  // |index| + 1 shouldn't overflow, because |index| is not the max value of
+  // uint32_t (it is less than |handle_end_|).
+  handle_begin_ = index + 1;
+  return true;
+}
+
+bool BoundsChecker::IsValidRange(const void* position,
+                                 uint32_t num_bytes) const {
+  uintptr_t begin = reinterpret_cast<uintptr_t>(position);
+  uintptr_t end = begin + num_bytes;
+
+  return InternalIsValidRange(begin, end);
+}
+
+bool BoundsChecker::InternalIsValidRange(uintptr_t begin, uintptr_t end) const {
+  return end > begin && begin >= data_begin_ && end <= data_end_;
+}
+
+}  // namespace internal
+}  // namespace mojo