[EventPipe] Fix user_events metadata label scope#118474
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mdh1418 merged 1 commit intodotnet:mainfrom Aug 7, 2025
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Pull Request Overview
This PR fixes a critical memory corruption bug in the EventPipe session tracepoint writing functionality. The issue was caused by a stack-allocated variable going out of scope during a writev operation, leading to potential data corruption in the first 5 bytes of metadata extensions.
Key changes:
- Move stack variable declaration to correct scope to prevent memory corruption
- Ensure metadata extension buffer remains valid during
writevsystem call
lateralusX
approved these changes
Aug 7, 2025
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Alternate internal testing showed that the first 5 bytes of the metadata extension were zeroed out. I missed that the stack allocated variable corresponding to the metadata label + metadata size would be out of scope during the writev, and thus prone to corruption.
The corruption never occurred during my manual testing which read the values from sys/kernel/tracing/trace.