fix(packer): use Uint64() to prevent silent overflow on GasAllocated

[Aboudjem]

Summary

UnpackCheckResult in packer.go uses big.Int.Int64() to populate the uint64 field GasAllocated. If the on-chain value exceeds math.MaxInt64 (2^63-1), Int64() silently truncates and returns a negative value, which then wraps to a large positive uint64. This could cause upkeep gas budgets to be wildly incorrect.

The fix extracts the *big.Int, checks IsUint64(), and returns an error if the value overflows. Otherwise it uses .Uint64() for a safe conversion.

Changes

• core/services/ocr2/plugins/ocr2keeper/evmregistry/v21/encoding/packer.go - 7 lines added, 1 removed

Test plan

• go build passes on the target package
• Diff limited to single target file
• Existing unit tests pass (CI will verify)

[Copilot]

Pull request overview

This PR fixes a silent integer overflow bug in UnpackCheckResult in the OCR2 Keeper V21 ABI packer. Previously, the GasAllocated field (a uint64) was populated via big.Int.Int64(), which silently truncates values above math.MaxInt64 (2^63-1) and returns a negative value that wraps to a large positive uint64. The fix extracts the *big.Int, validates it via IsUint64(), and returns an error with a proper ineligible check result if it overflows.

Changes:

• Extracts GasAllocated as a *big.Int before conversion, validates range with IsUint64(), and switches from Int64() to Uint64() for the safe cast.

[Copilot]

The new overflow check path lacks a unit test. The existing test file (packer_test.go) has dedicated tests for the decode failed and unpack failed error paths in UnpackCheckResult, but there is no test case covering the new GasAllocated overflows uint64 error path. A test case should be added with a raw hex payload whose out[4] encodes a value larger than math.MaxUint64 (e.g., a 256-bit integer with bits set above the 64-bit boundary), verifying that the error is returned and the result has PipelineExecutionState set to PackUnpackDecodeFailed.

[Aboudjem]

The test is already there - see the "gas allocated overflow" case in packer_test.go (added in commit 875fbcb). It encodes GasAllocated as 2^64 (math.MaxUint64+1) and asserts the overflow error.