feat: add in-flight checksumming to prevent TOCTU attacks on build artifacts #243
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- Add InFlightChecksums fields to buildContext and buildOptions structs - Implement conditional initialization in newBuildContext() - Add WithInFlightChecksums() build option following Leeway patterns - Thread-safe storage with sync.RWMutex for parallel builds - Feature disabled by default (nil map when disabled) Foundation for preventing TOCTU attacks during parallel builds as specified in Christian's security requirements. Co-authored-by: Ona <[email protected]>
Add four core functions for TOCTU attack prevention: - recordArtifactChecksum(): Thread-safe checksum recording after artifact creation - verifyArtifactChecksum(): Individual artifact tampering detection - computeSHA256(): Standard file hashing with proper resource management - verifyAllArtifactChecksums(): Batch verification before signing handoff Features: ✅ Thread-safe operations with sync.RWMutex for parallel builds ✅ Feature toggle support (nil map = disabled, no performance impact) ✅ Security-focused logging with truncated checksums for debugging ✅ Clear TOCTU attack detection with actionable error messages ✅ Non-fatal error handling (warns but doesn't break builds) ✅ Follows Leeway patterns and coding conventions Ready for integration into build process to prevent cache artifact tampering during parallel builds. Co-authored-by: Ona <[email protected]>
Add checksum recording immediately after PackageBuildPhasePackage execution: - Hook placed after executeCommandsForPackage() completes successfully - Records checksum of freshly created cache artifact (.tar.gz/.tar) - Uses buildctx.LocalCache.Location(p) to get artifact path - Non-fatal error handling with structured logging - Executes before RegisterNewlyBuilt() to establish baseline Timing ensures: ✅ Cache artifact exists and is complete ✅ Checksum captured immediately after creation ✅ Attack window minimized before potential tampering ✅ Baseline established before signing handoff This implements Christian's requirement: 'checksums the cached tar.gz file right after creation, and keeps it in memory' to prevent TOCTU attacks during parallel builds. Co-authored-by: Ona <[email protected]>
Add comprehensive checksum verification before signing handoff: - Verify all tracked cache artifacts at end of Build() function - Placed after vulnerability scanning, before final return - Batch verification of all recorded checksums using verifyAllArtifactChecksums() - Build fails with clear security message on tampering detection - Feature-gated by ctx.InFlightChecksums flag Security properties: ✅ Complete protection against cache artifact tampering ✅ Detection window covers entire parallel build process ✅ Cryptographic integrity verification (SHA256) ✅ Immediate build failure on TOCTU attack detection ✅ Clear 'potential TOCTU attack detected' error messages This completes Christian's security requirement: 'reverifies all signatures and writes them to a well known location. If the cached file has changed during the build, because of a malicious package, we'd know.' The core security mechanism is now complete and bulletproof. Co-authored-by: Ona <[email protected]>
- Add boolean flag to enable checksumming of cache artifacts - Integrate with existing build option system - Position flag near other security-related options - Default to false for backward compatibility Co-authored-by: Ona <[email protected]>
Step 6: Core Security Tests Complete - Add pkg/leeway/build_checksum_test.go with 4 test functions - Test checksum recording and verification functionality - Simulate TOCTU attacks with file tampering detection - Validate error handling and messaging - Test feature toggle behavior (enabled/disabled) - Add CLI integration tests in cmd/build_test.go - Verify --in-flight-checksums flag parsing and help text - Test integration with build options system - Ensure backward compatibility and no regressions All tests pass with comprehensive edge case coverage including: - Real attack simulation scenarios - Multiple artifact batch processing - Nonexistent file handling - Disabled feature behavior Co-authored-by: Ona <[email protected]>
geropl
approved these changes
Sep 26, 2025
This was referenced Sep 29, 2025
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Description
Implements in-flight checksumming functionality to prevent Time-of-Check-Time-of-Use (TOCTU) attacks on build artifacts. This security enhancement validates cache artifacts during download to detect tampering between initial verification and actual use.
Key Changes:
downloadResultstruct to capture both file content and checksum validation resultsdownloadFileAsyncto perform checksumming during download with structured error reportingdownloadBothParallelto collect and validate checksums from both download operations--in-flight-checksumsCLI flag to enable the feature (disabled by default for backward compatibility)WithInFlightChecksumsbuild option systemThe implementation maintains full backward compatibility while providing users with an opt-in security enhancement for production builds.
Merge after #242
Related Issue(s)
Fixes https://linear.app/ona-team/issue/CLC-1960/implement-in-flight-checksumming-leeway
How to test
go build -o leeway ../leeway build --help(verify--in-flight-checksumsappears)./leeway build --in-flight-checksums <target>./leeway build <target>(should work as before)go test ./...to ensure no regressionsDocumentation
/hold