fix(spanner): catch recursion and decode errors in proto parsing to p… - #16561
fix(spanner): catch recursion and decode errors in proto parsing to p…#16561sinhasubham merged 1 commit into
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Code Review
This pull request introduces error handling for Protobuf parsing within the _parse_proto helper, ensuring that DecodeError or RecursionError results in returning raw bytes rather than a failure. Review feedback identifies that the log variable is undefined and should be replaced with _LOGGER, along with removing redundant prefixes in the log message. Furthermore, the newly added unit tests require a fix to decode base64 encoded bytes into UTF-8 strings to avoid TypeError when populating Protobuf Value messages.
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| proto_message.ParseFromString(bytes_value) | ||
| return proto_message | ||
| try: | ||
| proto_message.ParseFromString(bytes_value) |
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is there a way to enforce nesting level?
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The standard Python Protobuf API (ParseFromString) does not expose a parameter to enforce a custom recursion or nesting limit during parsing.
Although, we did consider using sys.setrecursionlimit() to force a lower limit (e.g. 100) right before parsing but had to reject it because sys.setrecursionlimit is process-wide. In a multi-threaded environment, lowering the limit for this one call could cause arbitrary valid code run by other threads to crash.
I couldn't find any other thread-safe way to enforce a custom limit during parsing in Python Protobuf, the most robust solution is to catch the errors the parser naturally throws (DecodeError and RecursionError) and fall back.
In Java, we can explicitly enforce and set a custom nesting level while parsing which is not possible in Python.
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This PR fixes a Persistent Stored Denial of Service (DoS) vulnerability in the google-cloud-spanner Python SDK (Issue 479858035).
The Problem
When the SDK attempts to deserialize a Protobuf-encoded row (via _parse_proto() in _helpers.py) that contains a maliciously crafted "recursion bomb" (e.g., a ListValue nested 1,000+ times), it triggers a DecodeError or RecursionError. This unhandled exception crashes the consumer thread and blocks the entire result set stream ("pipeline blackhole").
The Solution
We modify _parse_proto to wrap the ParseFromString() call in a defensive try...except block:
Catch RecursionError (triggered if Python hits its stack limit first in pure Python implementations).
Catch google.protobuf.message.DecodeError (triggered by the C++ extension's internal limits).
If an error is caught: A warning is logged. The original raw bytes_value is returned as a fallback (consistent with existing behavior when no prototype is found). This allows the stream iterator to continue processing subsequent rows.