Add subprocess isolation setup and git credential helper (#1132)

- Add optional bubblewrap setup step for Linux subprocess isolation
  when allowed_non_write_users is configured
- Use git credential helper instead of embedding token in remote URL
- edit-issue-labels.sh: read issue number from workflow event payload
  instead of CLI arg
- Add CLAUDE_CODE_SCRIPT_CAPS env for per-script call limit config
- docs/security.md: note recommended github_token configuration

🏠 Remote-Dev: homespace

.claude/commands/label-issue.md

@@ -45,7 +45,7 @@ TASK OVERVIEW:
    - If you find similar issues using ./scripts/gh.sh search, consider using a "duplicate" label if appropriate. Only do so if the issue is a duplicate of another OPEN issue.
 
 5. Apply the selected labels:
-   - Use `./scripts/edit-issue-labels.sh --issue NUMBER --add-label LABEL1 --add-label LABEL2` to apply your selected labels
+   - Use `./scripts/edit-issue-labels.sh --add-label LABEL1 --add-label LABEL2` to apply your selected labels (issue number is read from the workflow event)
    - DO NOT post any comments explaining your decision
    - DO NOT communicate directly with users
    - If no labels are clearly applicable, do not apply any labels

.github/workflows/issue-triage.yml

@@ -20,6 +20,8 @@ jobs:
 
       - name: Run Claude Code for Issue Triage
         uses: anthropics/claude-code-action@main
+        env:
+          CLAUDE_CODE_SCRIPT_CAPS: '{"edit-issue-labels.sh":2}'
         with:
           prompt: "/label-issue REPO: ${{ github.repository }} ISSUE_NUMBER: ${{ github.event.issue.number }}"
           anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}

action.yml

@@ -195,6 +195,26 @@ runs:
         cd ${GITHUB_ACTION_PATH}
         bun install --production
 
+    - name: Install subprocess isolation dependencies
+      # Install subprocess isolation dependencies when processing content from non-write users.
+      # Best-effort: skips on non-Linux or when sudo/apt unavailable (self-hosted runners).
+      if: ${{ inputs.allowed_non_write_users != '' && env.CLAUDE_CODE_SUBPROCESS_ENV_SCRUB != '0' && runner.os == 'Linux' }}
+      continue-on-error: true
+      shell: bash
+      run: |
+        if command -v apt-get >/dev/null && command -v sudo >/dev/null; then
+          for i in 1 2 3; do
+            sudo apt-get update -qq && sudo apt-get install -y --no-install-recommends bubblewrap socat && break
+            echo "apt-get attempt $i failed, retrying..."
+            sleep 5
+          done
+        fi
+        # Ubuntu 24.04+ restricts unprivileged user namespaces via AppArmor.
+        # The sysctl doesn't exist on older kernels — that's fine.
+        if [ -f /proc/sys/kernel/apparmor_restrict_unprivileged_userns ] && command -v sudo >/dev/null; then
+          sudo sysctl -w kernel.apparmor_restrict_unprivileged_userns=0
+        fi
+
     - name: Run Claude Code Action
       id: run
       shell: bash
@@ -214,6 +234,7 @@ runs:
         ALLOWED_BOTS: ${{ inputs.allowed_bots }}
         ALLOWED_NON_WRITE_USERS: ${{ inputs.allowed_non_write_users }}
         CLAUDE_CODE_SUBPROCESS_ENV_SCRUB: ${{ env.CLAUDE_CODE_SUBPROCESS_ENV_SCRUB || (inputs.allowed_non_write_users != '' && '1') || '' }}
+        CLAUDE_CODE_SCRIPT_CAPS: ${{ env.CLAUDE_CODE_SCRIPT_CAPS || '' }}
         INCLUDE_COMMENTS_BY_ACTOR: ${{ inputs.include_comments_by_actor }}
         EXCLUDE_COMMENTS_BY_ACTOR: ${{ inputs.exclude_comments_by_actor }}
         GITHUB_RUN_ID: ${{ github.run_id }}

docs/security.md

@@ -13,7 +13,9 @@
   - Accepts either a comma-separated list of specific usernames or `*` to allow all users
   - **Should be used with extreme caution** as it bypasses the primary security mechanism of this action
   - Is designed for automation workflows where user permissions are already restricted by the workflow's permission scope
-  - When set, Claude does a best-effort scrub of Anthropic, cloud, and GitHub Actions secrets from subprocess environments. This reduces but does not eliminate prompt injection risk — keep workflow permissions minimal and validate all outputs. Set `CLAUDE_CODE_SUBPROCESS_ENV_SCRUB: 0` in your workflow or job `env:` block to opt out.
+  - When set, Claude does a best-effort scrub of Anthropic, cloud, and GitHub Actions secrets from subprocess environments. On Linux runners with bubblewrap available, subprocesses additionally run with PID-namespace isolation. This reduces but does not eliminate prompt injection risk — keep workflow permissions minimal and validate all outputs. Set `CLAUDE_CODE_SUBPROCESS_ENV_SCRUB: 0` in your workflow or job `env:` block to opt out.
+  - Optionally set `CLAUDE_CODE_SCRIPT_CAPS` in your workflow `env:` block to limit how many times Claude can call specific scripts per run. Value is JSON: `{"script-name.sh": maxCalls}`. Example: `CLAUDE_CODE_SCRIPT_CAPS: '{"edit-issue-labels.sh":2}'` allows at most 2 calls to `edit-issue-labels.sh`. Useful for write-capable helper scripts.
+  - When using `allowed_non_write_users`, always pass `github_token: ${{ secrets.GITHUB_TOKEN }}`. The auto-generated workflow token is scoped to the job's declared permissions and expires automatically, which limits blast radius. Personal access tokens are not recommended for untrusted-input workflows.
 - **Token Permissions**: The GitHub app receives only a short-lived token scoped specifically to the repository it's operating in
 - **No Cross-Repository Access**: Each action invocation is limited to the repository where it was triggered
 - **Limited Scope**: The token cannot access other repositories or perform actions beyond the configured permissions

docs/solutions.md

@@ -421,7 +421,8 @@ jobs:
             - `./scripts/gh.sh label list` to see available labels
 
             Based on your analysis, add the appropriate labels using:
-            `./scripts/edit-issue-labels.sh --issue [number] --add-label "label1" --add-label "label2"`
+            `./scripts/edit-issue-labels.sh --add-label "label1" --add-label "label2"`
+            (the issue number is read automatically from the workflow event)
 
             If it appears to be a duplicate, post a comment mentioning the original issue.
 

scripts/edit-issue-labels.sh

@@ -1,22 +1,26 @@
 #!/usr/bin/env bash
 #
 # Edits labels on a GitHub issue.
-# Usage: ./scripts/edit-issue-labels.sh --issue 123 --add-label bug --add-label needs-triage --remove-label untriaged
+# Usage: ./scripts/edit-issue-labels.sh --add-label bug --add-label needs-triage --remove-label untriaged
+#
+# The issue number is read from the workflow event payload.
 #
 
 set -euo pipefail
 
-ISSUE=""
+# Read from event payload so the issue number is bound to the triggering event
+ISSUE=$(jq -r '.issue.number // empty' "${GITHUB_EVENT_PATH:?GITHUB_EVENT_PATH not set}")
+if ! [[ "$ISSUE" =~ ^[0-9]+$ ]]; then
+  echo "Error: no issue number in event payload" >&2
+  exit 1
+fi
+
 ADD_LABELS=()
 REMOVE_LABELS=()
 
 # Parse arguments
 while [[ $# -gt 0 ]]; do
   case $1 in
-    --issue)
-      ISSUE="$2"
-      shift 2
-      ;;
     --add-label)
       ADD_LABELS+=("$2")
       shift 2
@@ -26,20 +30,12 @@ while [[ $# -gt 0 ]]; do
       shift 2
       ;;
     *)
+      echo "Error: unknown argument (only --add-label and --remove-label are accepted)" >&2
       exit 1
       ;;
   esac
 done
 
-# Validate issue number
-if [[ -z "$ISSUE" ]]; then
-  exit 1
-fi
-
-if ! [[ "$ISSUE" =~ ^[0-9]+$ ]]; then
-  exit 1
-fi
-
 if [[ ${#ADD_LABELS[@]} -eq 0 && ${#REMOVE_LABELS[@]} -eq 0 ]]; then
   exit 1
 fi

src/github/operations/git-config.ts

@@ -51,11 +51,34 @@ export async function configureGitAuth(
     console.log("No existing authentication headers to remove");
   }
 
+  if (process.env.ALLOWED_NON_WRITE_USERS) {
+    // When processing content from non-write users, use a credential helper
+    // instead of embedding the token in the remote URL. The helper script reads
+    // from GH_TOKEN at auth time, so .git/config stays token-free. Written as a
+    // file to avoid shell-escaping the helper body; placed under
+    // GITHUB_ACTION_PATH so it sits alongside the action source.
+    console.log("Configuring git credential helper...");
+    process.env.GH_TOKEN = githubToken;
+    const helperPath = join(
+      process.env.GITHUB_ACTION_PATH || homedir(),
+      ".git-credential-gh-token",
+    );
+    await writeFile(
+      helperPath,
+      '#!/bin/sh\necho username=x-access-token\necho password="$GH_TOKEN"\n',
+      { mode: 0o700 },
+    );
+    const cleanUrl = `https://${serverUrl.host}/${context.repository.owner}/${context.repository.repo}.git`;
+    await $`git remote set-url origin ${cleanUrl}`;
+    await $`git config credential.helper ${helperPath}`;
+    console.log("✓ Configured credential helper");
+  } else {
     // Update the remote URL to include the token for authentication
     console.log("Updating remote URL with authentication...");
     const remoteUrl = `https://x-access-token:${githubToken}@${serverUrl.host}/${context.repository.owner}/${context.repository.repo}.git`;
     await $`git remote set-url origin ${remoteUrl}`;
     console.log("✓ Updated remote URL with authentication token");
+  }
 
   console.log("Git authentication configured successfully");
 }