[llvm] [workflows] Split pr-code-format into two parts to make it more secure (PR #78216)

[Aiden Grossman via llvm-commits]

================
@@ -0,0 +1,72 @@
+name: Comment on an issue
+
+on:
+  workflow_run:
+    workflows: ["Check code formatting"]
+    types:
+      - completed
+
+permissions:
+  contents: read
+
+jobs:
+  pr-comment:
+    runs-on: ubuntu-latest
+    permissions:
+      pull-requests: write
+    if: >
+      github.event.workflow_run.event == 'pull_request'
+    steps:
+      - name: 'Download artifact'
+        # v7.0.1
+        uses: actions/github-script at 60a0d83039c74a4aee543508d2ffcb1c3799cdea
+        with:
+          script: |
+            let allArtifacts = await github.rest.actions.listWorkflowRunArtifacts({
+               owner: context.repo.owner,
+               repo: context.repo.repo,
+               run_id: context.payload.workflow_run.id,
+            });
+            let matchArtifact = allArtifacts.data.artifacts.filter((artifact) => {
+              return artifact.name == "workflow-args"
+            })[0];
+            let download = await github.rest.actions.downloadArtifact({
+               owner: context.repo.owner,
+               repo: context.repo.repo,
+               artifact_id: matchArtifact.id,
+               archive_format: 'zip',
+            });
+            let fs = require('fs');
+            fs.writeFileSync(`${process.env.GITHUB_WORKSPACE}/workflow-args.zip`, Buffer.from(download.data));
+
+      - run: unzip workflow-args.zip
+
+      - name: 'Comment on PR'
+        uses: actions/github-script at v3
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          script: |
+            var fs = require('fs');
+            const comments = JSON.parse(fs.readFileSync('./comments'));
+            if (!comments) {
+              return;
+            }
+            console.log(comments);
+            await comments.forEach(function (comment) {
+              if (comment.id) {
+                github.issues.updateComment({
+                  owner: context.repo.owner,
+                  repo: context.repo.repo,
+                  issue_number: comment.number,
+                  comment_id: comment.id,
+                  body: comment.body
----------------
boomanaiden154 wrote:

I'm not sure input validation is that necessary here, but this change means that the JSON artifact sent over should be completely untrusted as anyone can theoretically modify the workflow and make it send whatever. I don't think this should happen much in practice (depending upon the settings for whether or not new contributors need approval for workflow runs), but it theoretically gives the ability for anyone to post a comment on any PR/Issue under the Github moniker.

https://github.com/llvm/llvm-project/pull/78216