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

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "mojo/public/cpp/bindings/lib/bounds_checker.h"
   6
   7 #include "mojo/public/cpp/bindings/lib/bindings_serialization.h"
   8 #include "mojo/public/cpp/environment/logging.h"
   9 #include "mojo/public/cpp/system/handle.h"
  10
  11 namespace mojo {
  12 namespace internal {
  13
  14 BoundsChecker::BoundsChecker(const void* data, uint32_t data_num_bytes,
  15                              size_t num_handles)
  16     : data_begin_(reinterpret_cast<uintptr_t>(data)),
  17       data_end_(data_begin_ + data_num_bytes),
  18       handle_begin_(0),
  19       handle_end_(static_cast<uint32_t>(num_handles)) {
  20   if (data_end_ < data_begin_) {
  21     // The calculation of |data_end_| overflowed.
  22     // It shouldn't happen but if it does, set the range to empty so
  23     // IsValidRange() and ClaimMemory() always fail.
  24     MOJO_DCHECK(false) << "Not reached";
  25     data_end_ = data_begin_;
  26   }
  27   if (handle_end_ < num_handles) {
  28     // Assigning |num_handles| to |handle_end_| overflowed.
  29     // It shouldn't happen but if it does, set the handle index range to empty.
  30     MOJO_DCHECK(false) << "Not reached";
  31     handle_end_ = 0;
  32   }
  33 }
  34
  35 BoundsChecker::~BoundsChecker() {
  36 }
  37
  38 bool BoundsChecker::ClaimMemory(const void* position, uint32_t num_bytes) {
  39   uintptr_t begin = reinterpret_cast<uintptr_t>(position);
  40   uintptr_t end = begin + num_bytes;
  41
  42   if (!InternalIsValidRange(begin, end))
  43     return false;
  44
  45   data_begin_ = end;
  46   return true;
  47 }
  48
  49 bool BoundsChecker::ClaimHandle(const Handle& encoded_handle) {
  50   uint32_t index = encoded_handle.value();
  51   if (index == kEncodedInvalidHandleValue)
  52     return true;
  53
  54   if (index < handle_begin_ || index >= handle_end_)
  55     return false;
  56
  57   // |index| + 1 shouldn't overflow, because |index| is not the max value of
  58   // uint32_t (it is less than |handle_end_|).
  59   handle_begin_ = index + 1;
  60   return true;
  61 }
  62
  63 bool BoundsChecker::IsValidRange(const void* position,
  64                                  uint32_t num_bytes) const {
  65   uintptr_t begin = reinterpret_cast<uintptr_t>(position);
  66   uintptr_t end = begin + num_bytes;
  67
  68   return InternalIsValidRange(begin, end);
  69 }
  70
  71 bool BoundsChecker::InternalIsValidRange(uintptr_t begin, uintptr_t end) const {
  72   return end > begin && begin >= data_begin_ && end <= data_end_;
  73 }
  74
  75 }  // namespace internal
  76 }  // namespace mojo