False positive: Critical Artifact poisoning

[AdnaneKhan]

Description of the false positive

The artifact poisoning CodeQL query creates a Critical false-positive under the following scenario:

• Download Artifact with path set to start with ${{ runner.temp }}
• Use of a PoisonableCommandStep

Below is an example that reproduces the false positive:

name: Test False Positive
on:
  workflow_run:
    workflows:
      - Benchmark
    types:
      - completed

permissions:
  contents: read

jobs:
  benchmark:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - name: Download From PR
        uses: actions/download-artifact@v4
        with:
          github-token: ${{ secrets.GITHUB_TOKEN }}
          run-id: ${{ github.event.workflow_run.id }}
          path: ${{ runner.temp }}/artifacts/
      - run: npm install

This is particularly a problem because the examples for a secure workflow specifically calls out this fix.

name: Secure Workflow

on:
  workflow_run:
    workflows: ["Prev"]
    types:
      - completed

jobs:
  Download:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - run: mkdir -p ${{ runner.temp }}/artifacts/
      - uses: dawidd6/action-download-artifact@v2
        with:
          name: pr_number
          path: ${{ runner.temp }}/artifacts/

      - name: Run command
        run: |
          sh cmd.sh

I took a stab at fixing it in #19388 but no one looked at it - if my fix is appropriate could it get a review :)?