Distrust received pack indexes (behind config flag, with perf fixes) #1846
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The GVFS protocol includes an index file along with pack file in the prefetch workflow (primarily used on a new clone to fetch all commits and trees). Currently, GVFS blindly accepts that index file. This pull request changes GVFS prefetch to discard the index sent by the server and always create an index locally. This provides improved security and verification of the pack file, at the expense of performance for the first clone of a repository on a new drive.
mjcheetham
reviewed
Jun 23, 2025
mjcheetham
approved these changes
Jun 24, 2025
Merged
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This pull request contains 4 things:
This is intended to be a temporary configuration setting, to be removed (or defaulted to false) once more mitigations have been completed for the performance.
git index-packis changed from running in the GVFS enlistment to running outside the enlistment. This was the reason for the unexpected performance issues.It was expected that the first prefetch on a new clone would take longer due to indexing the pack locally; however users who deleted their prefetch cache (but not the rest of the cache or local loose objects) in order to re-fetch it with local indexing enabled experienced many times longer delays than expected, because
git index-packreads all the existing pack indexes and loose objects and considers them when indexing a pack in order to support validating that all referenced objects exist - even when the command-line options to act on nonexistent references are not enabled. Since we aren't using --validate or its variants, we can rungit index-packoutside the enlistment to avoid this issue.