Fixing Insufficient Buffer Size For Large Payloads In Project CHIP
Introduction
Hey guys, let's dive into a critical bug discovered in the Project CHIP's connectedhomeip SDK. This issue revolves around insufficient buffer sizes when reading large payloads, specifically when dealing with attributes like provisioned TLS root certificates. This can lead to a frustrating CHIP Error 0x0000000B: No memory situation, which basically means the system can't handle the data being thrown at it. Understanding and resolving this bug is crucial for ensuring the reliability and robustness of our connected devices, so let's get into the details and see how we can tackle it together. We'll explore the reproduction steps, the consistency of the bug, and potential solutions to this buffer size problem, ensuring our systems can handle large payloads effectively.
Reproduction Steps
To reproduce this bug, you need to read a large payload attribute over TCP. A prime example is attempting to read provisioned TLS root certificates. The error manifests in the chip::app::ReadClient::Callback, specifically within src/system/TLVPacketBufferBackingStore.cpp at line 91. The error message CHIP Error 0x0000000B: No memory pops up because the system's buffer is too small to propagate the response or report. Here’s a snippet of the log illustrating the issue:
[DMG] [
[DMG] AttributeReportIB =
[DMG] {
[DMG] AttributeDataIB =
[DMG] {
[DMG] DataVersion = 0x70fa6c33,
[DMG] AttributePathIB =
[DMG] {
[DMG] Endpoint = 0x1,
[DMG] Cluster = 0x801,
[DMG] Attribute = 0x0000_0001,
[DMG] }
[DMG] Data = [
[DMG] {
[DMG] 0x0 = 0 (unsigned),
[DMG] 0x1 = [
[DMG] 0x30, 0x82, 0x05, 0x6b, 0x30, 0x82, 0x03, 0x53, 0xa0, 0x03, 0x02, 0x01, 0x02, 0x02, 0x11, 0x00, 0x82, 0x10, 0xcf, 0xb0, 0xd2, 0x40, 0xe3, 0x59, 0x44, 0x63, 0xe0, 0xbb, 0x63, 0x82, 0x8b, 0x00, 0x30, 0x0d, 0x06, 0x09, 0x2a, 0x86, 0x48, 0x86, 0xf7, 0
[DMG] ] (1391 bytes)
[DMG] 0xfe = 1 (unsigned),
[DMG] },
[DMG] {
[DMG] 0x0 = 1 (unsigned),
[DMG] 0x1 = [
[DMG] 0x30, 0x82, 0x03, 0x41, 0x30, 0x82, 0x02, 0x29, 0xa0, 0x03, 0x02, 0x01, 0x02, 0x02, 0x13, 0x06, 0x6c, 0x9f, 0xcf, 0x99, 0xbf, 0x8c, 0x0a, 0x39, 0xe2, 0xf0, 0x78, 0x8a, 0x43, 0xe6, 0x96, 0x36, 0x5b, 0xca, 0x30, 0x0d, 0x06, 0x09, 0x2a, 0x86, 0x48,
[DMG] ] (837 bytes)
[DMG] 0xfe = 1 (unsigned),
[DMG] },
[DMG] ],
[DMG] }
[DMG] },
[DMG] ],
[DMG] SuppressResponse = true,
[DMG] InteractionModelRevision = 12
[DMG] }
From the logs, you can see the AttributeReportIB containing AttributeDataIB, which holds the actual data. The Data field contains byte arrays representing the TLS root certificates. The sizes of these arrays (1391 bytes and 837 bytes) highlight the large payload, which the buffer struggles to handle. This error is consistently reproducible, making it a significant concern for applications dealing with substantial data transfers. Ensuring sufficient buffer size is critical for the reliable operation of connected devices, especially when managing security-related information like TLS certificates. Therefore, addressing this issue is paramount to maintaining the integrity and security of the system.
Bug Prevalence and SDK Details
This insufficient buffer size bug is consistently reproducible, meaning it will likely occur every time you attempt to read large payloads. This makes it a high-priority issue to address. The bug was identified in the SDK with the GitHub hash f6dc93a. Although the platform is marked as “other,” the underlying issue pertains to how the SDK handles large payloads over TCP, making it relevant across various platforms. This consistency underscores the need for a robust solution to prevent data loss and ensure reliable communication. The fact that the bug is consistently reproducible simplifies the testing and validation process once a fix is implemented. It allows developers to confidently confirm that the issue is resolved and prevent its recurrence in future releases. This reliability is essential for maintaining the stability of connected devices and the overall user experience.
Proposed Solution: Adjusting the Response Buffer
To address this bug, we need to adjust the response buffer in src/app/BufferedReadCallback.cpp. Currently, the buffer size is limited, causing the “No memory” error when handling large payloads. A potential solution involves increasing the buffer size dynamically, similar to how command responses are handled in src/app/CommandResponseSender.cpp. Here's a snippet of the proposed change:
diff --git a/src/app/BufferedReadCallback.cpp b/src/app/BufferedReadCallback.cpp
index 3752a3e65ae..76d2b8937f8 100644
--- a/src/app/BufferedReadCallback.cpp
+++ b/src/app/BufferedReadCallback.cpp
@@ -117,7 +117,11 @@ CHIP_ERROR BufferedReadCallback::BufferListItem(TLV::TLVReader & reader)
// TLV element. Since the tag can vary in size, for now, let's just do the safe thing. In the future, if this is a problem,
// we can improve this.
//
- handle = System::PacketBufferHandle::New(chip::app::kMaxSecureSduLengthBytes);
+ size_t bufSize = chip::app::kMaxSecureSduLengthBytes;
+ if (mAllowLargePayload) {
+ bufSize = chip::app::kMaxLargeSecureSduLengthBytes;
+ }
+ handle = System::PacketBufferHandle::New(bufSize);
VerifyOrReturnError(!handle.IsNull(), CHIP_ERROR_NO_MEMORY);
diff --git a/src/app/BufferedReadCallback.h b/src/app/BufferedReadCallback.h
index b24257884e1..124d41e9681 100644
--- a/src/app/BufferedReadCallback.h
+++ b/src/app/BufferedReadCallback.h
@@ -40,7 +40,8 @@ namespace app {
class BufferedReadCallback : public ReadClient::Callback
{
public:
- BufferedReadCallback(Callback & callback) : mCallback(callback) {}
+ BufferedReadCallback(Callback & callback) : mAllowLargePayload(false), mCallback(callback){}
+ BufferedReadCallback(bool allowLargePayload, Callback & callback) : mAllowLargePayload(allowLargePayload), mCallback(callback){}
private:
/*
* Called when an individual list item is ready to be buffered.
@@ -130,6 +131,7 @@ private:
CHIP_ERROR BufferListItem(TLV::TLVReader & reader);
ConcreteDataAttributePath mBufferedPath;
std::vector<System::PacketBufferHandle> mBufferedList;
+ bool mAllowLargePayload;
Callback & mCallback;
};
This proposed solution introduces a parameter to the BufferedReadCallback that allows bumping the buffer size. The mAllowLargePayload flag determines whether to use the standard buffer size (chip::app::kMaxSecureSduLengthBytes) or the larger buffer size (chip::app::kMaxLargeSecureSduLengthBytes). This adjustment ensures that reads can support large payloads, similar to how command responses are handled. The key idea here is to create a more flexible buffer management system that can adapt to the size of the incoming data. By allowing the buffer size to be dynamically adjusted, we can prevent the “No memory” error and ensure that large payloads are processed correctly. This approach also aligns with the handling of command responses, providing a consistent strategy for managing data within the system. Implementing this change should significantly improve the system's ability to handle large data transfers, enhancing its overall robustness and reliability.
Further Considerations and Next Steps
With reads now supporting large payloads, similar to command invokes, the response buffer needs careful adjustment. The current approach mirrors the handling of command responses, using the exchange context to determine large payload ability. However, a more refined approach might involve constructing a buffer read callback with a parameter that bumps the buffer, allowing call sites to use appropriate values based on the session or type of request. This ensures optimal memory utilization and prevents potential buffer overflows. The suggested code diff provides a starting point, but further testing and refinement are necessary to ensure the solution is robust and doesn't introduce new issues. It's also essential to consider the implications of larger buffer sizes on memory usage and overall system performance. Performance testing should be conducted to ensure that the changes don't negatively impact other aspects of the system. Additionally, thorough documentation of the changes and the rationale behind them is crucial for maintainability and future development. Addressing this bug effectively requires a holistic approach, considering both the immediate issue and the long-term implications for the system's architecture and performance.
Conclusion
In conclusion, the insufficient buffer size bug in Project CHIP’s connectedhomeip SDK is a significant issue that needs addressing. It consistently manifests when reading large payloads, such as provisioned TLS root certificates, leading to a “No memory” error. The proposed solution involves adjusting the response buffer in src/app/BufferedReadCallback.cpp to dynamically accommodate larger payloads, similar to how command responses are handled. This adjustment ensures that the system can reliably process large data transfers, enhancing its overall robustness. While the provided code diff offers a solid starting point, further testing and refinement are necessary to ensure the solution is foolproof and doesn't introduce unintended consequences. This includes performance testing to evaluate the impact on memory usage and system performance, as well as thorough documentation for maintainability. By addressing this bug effectively, we can ensure the stability and reliability of connected devices, providing a seamless and secure user experience.
