ipc: Update Message::FindNext to parse brokered attachments.

ipc/ipc_message.cc

 // Copyright (c) 2012 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 "ipc/ipc_message.h"
 
 #include "base/atomic_sequence_num.h"
 #include "base/logging.h"
 #include "build/build_config.h"
 #include "ipc/ipc_message_attachment.h"
@@ skipping 115 matching lines @@
   const char* data = end_of_payload();
   data -= sizeof(int64);
   return *(reinterpret_cast<const int64*>(data));
 }
 
 void Message::set_received_time(int64 time) const {
   received_time_ = time;
 }
 #endif
 
+Message::NextMessageInfo::NextMessageInfo()
+    : message_found(false),
+      parsing_error(false),
+      pickle_end(nullptr),
+      message_end(nullptr) {}
+Message::NextMessageInfo::~NextMessageInfo() {}
+
+// static
+Message::NextMessageInfo Message::FindNext(const char* range_start,
+                                           const char* range_end) {
+  NextMessageInfo info;
+  const char* pickle_end =
+      base::Pickle::FindNext(sizeof(Header), range_start, range_end);
+  if (pickle_end == nullptr)

[Tom Sepez, 2015/09/01 18:01:54]

nit: if (!pickle_end)

[erikchen, 2015/09/04 02:13:39]

Done.

+    return info;
+  info.pickle_end = pickle_end;
+
+#if USE_ATTACHMENT_BROKER
+  // The data is not copied.
+  size_t pickle_len = static_cast<size_t>(pickle_end - range_start);
+  Message message(range_start, static_cast<int>(pickle_len));
+  int num_attachments = message.header()->num_brokered_attachments;
+
+  // Each brokered attachment adds kNonceSize bytes of data to the message. We
+  // want to avoid overflows in our computations, so we limit the number of
+  // brokerable attachments to 100.
+  if (num_attachments > 100) {

[Tom Sepez, 2015/09/01 18:01:54]

nit: this should be a constant kSomethingOrOther in a header file.

[erikchen, 2015/09/04 02:13:39]

The previous code didn't actually prevent overflows. I've updated the logic to
correctly check for overflows, which also doesn't rely on an arbitrary constant.

I also removed the field parsing_error in NextMessageInfo, since there's no
point in providing different behavior for certain overflows (too many
attachments) from the existing behavior for a message with an unreasonable
pickle size.

+    info.parsing_error = true;
+    return info;
+  }
+
+  // Check whether the range includes the attachments.
+  size_t attachment_length = num_attachments * BrokerableAttachment::kNonceSize;
+  size_t buffer_length = static_cast<size_t>(range_end - range_start);
+  if (buffer_length < attachment_length + pickle_len)
+    return info;
+
+  for (int i = 0; i < num_attachments; ++i) {
+    const char* attachment_start =
+        pickle_end + i * (BrokerableAttachment::kNonceSize);

[Tom Sepez, 2015/09/01 18:01:54]

nit: unnecessary ()

[erikchen, 2015/09/04 02:13:39]

removed

+    BrokerableAttachment::AttachmentId id(attachment_start,
+                                          BrokerableAttachment::kNonceSize);
+    info.attachment_ids.push_back(id);
+  }
+  info.message_end =
+      pickle_end + num_attachments * BrokerableAttachment::kNonceSize;
+#else
+  info.message_end = pickle_end;
+#endif  // USE_ATTACHMENT_BROKER
+
+  info.message_found = true;
+  return info;
+}
+
 bool Message::WriteAttachment(scoped_refptr<MessageAttachment> attachment) {
   // We write the index of the descriptor so that we don't have to
   // keep the current descriptor as extra decoding state when deserialising.
   WriteInt(attachment_set()->size());
 
 #if USE_ATTACHMENT_BROKER
   if (attachment->GetType() == MessageAttachment::TYPE_BROKERABLE_ATTACHMENT)
     header()->num_brokered_attachments += 1;
 #endif
 
@@ skipping 22 matching lines @@
 bool Message::HasMojoHandles() const {
   return attachment_set_.get() && attachment_set_->num_mojo_handles() > 0;
 }
 
 bool Message::HasBrokerableAttachments() const {
   return attachment_set_.get() &&
          attachment_set_->num_brokerable_attachments() > 0;
 }
 
 }  // namespace IPC