runner-guard: block workflows that hand a self-hosted runner to strangers (Boss 10-01)

R1 pull_request_target; R2 fork pull_request on self-hosted without a same-repo/environment
gate; R3 outsider events (issue_comment, workflow_run, ...) on self-hosted; R0 unparseable.
PR mode in the 5-min sync posts windy-git/runner-guard on open PRs of public sneakyfree repos
that change a workflow (each status once). Nightly sweep (Windy 0 timer) over every public
repo: page + BOARD line on new hits + red windy-job heartbeat.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

api/tests/test_runner_guard.py

@@ -0,0 +1,70 @@
+"""runner-guard: workflow shapes that hand a self-hosted runner to strangers."""
+
+from __future__ import annotations
+
+import importlib.util
+import sys
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parents[2]
+_spec = importlib.util.spec_from_file_location("runner_guard", ROOT / "scripts" / "runner_guard.py")
+rg = importlib.util.module_from_spec(_spec)
+sys.modules["runner_guard"] = rg
+_spec.loader.exec_module(rg)
+
+
+def rules(text):
+    return [(r, ln) for _p, ln, r, _m in rg.lint_text("w.yml", text)]
+
+
+def test_pull_request_target_always_fails():
+    assert rules("on: pull_request_target\njobs:\n  a:\n    runs-on: ubuntu-latest\n    steps: []\n")[0][0] == "R1"
+
+
+def test_fork_pr_on_self_hosted_fails_and_points_at_runs_on():
+    wf = "on:\n  pull_request:\njobs:\n  t:\n    runs-on: [self-hosted, linux, x64]\n    steps: []\n"
+    assert rules(wf) == [("R2", 5)]
+
+
+def test_same_repo_gate_or_environment_passes():
+    gated = ("on: [pull_request]\njobs:\n  t:\n    if: github.event.pull_request.head.repo.full_name == github.repository\n"
+             "    runs-on: [self-hosted]\n    steps: []\n")
+    env = "on: [pull_request]\njobs:\n  t:\n    environment: ci\n    runs-on: self-hosted\n    steps: []\n"
+    assert rules(gated) == [] and rules(env) == []
+
+
+def test_outsider_events_on_self_hosted_fail_but_writer_events_pass():
+    wf = "on:\n  issue_comment:\n  workflow_run:\n    workflows: [x]\njobs:\n  t:\n    runs-on: self-hosted\n    steps: []\n"
+    assert sorted(r for r, _ in rules(wf)) == ["R3", "R3"]
+    ok = "on:\n  push:\n    tags: ['v*']\n  workflow_dispatch:\n  schedule:\n    - cron: '0 3 * * *'\njobs:\n  t:\n    runs-on: self-hosted\n    steps: []\n"
+    assert rules(ok) == []
+
+
+def test_expression_runs_on_is_treated_as_self_hosted_and_hosted_runner_is_fine():
+    expr = "on: pull_request\njobs:\n  t:\n    runs-on: ${{ matrix.os }}\n    steps: []\n"
+    hosted = "on: pull_request\njobs:\n  t:\n    runs-on: ubuntu-latest\n    steps: []\n"
+    assert rules(expr) == [("R2", 4)] and rules(hosted) == []
+
+
+def test_broken_yaml_is_a_finding_and_non_workflows_are_ignored():
+    assert rules("on: [push\njobs: {")[0][0] == "R0"
+    assert rules("name: just a file\n") == []
+
+
+def test_pr_mode_posts_each_status_once(monkeypatch, tmp_path):
+    calls = []
+    monkeypatch.setattr(rg, "STATE", str(tmp_path / "s.json"))
+    monkeypatch.setattr(rg, "public_repos", lambda owners: [("o/r", "main")])
+    monkeypatch.setattr(rg, "file_at", lambda *a: "on: push\\njobs:\\n  t:\\n    runs-on: self-hosted\\n    steps: []\\n")
+
+    def fake_gh(*args, check=True):
+        if args[0].startswith("repos/o/r/pulls?"):
+            return "7 abc123 o/r\\n"
+        if args[0].endswith("/files?per_page=100"):
+            return ".github/workflows/ci.yml\\n"
+        calls.append(args[0])
+        return ""
+    monkeypatch.setattr(rg, "gh", fake_gh)
+    rg.cmd_pr(["o"], post=True)
+    rg.cmd_pr(["o"], post=True)
+    assert calls == ["repos/o/r/statuses/abc123"]

deploy/windy0/nightly-runner-guard-sweep.sh

@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+# Nightly (Boss 10-01): runner-guard over the default branch of EVERY public repo in Grant's
+# 5 GitHub accounts (runs on Veron: windy-git scripts/runner_guard.py report). Writes
+# ~/windy-orchestra/RUNNER_GUARD.md (repo, file:line, rule; no file content), appends ONE
+# BOARD line per NEW hit vs the last run, and prints "runner-guard sweep: N hit(s)" last, so
+# the windy-job heartbeat (--expect "runner-guard sweep: 0 hit") goes red while any hit exists.
+set -euo pipefail
+page=~/windy-orchestra/RUNNER_GUARD.md
+state=~/.local/state/runner-guard-sweep.txt
+mkdir -p "$(dirname "$state")"
+out=$(timeout 900 ssh -o BatchMode=yes -o ConnectTimeout=15 ts-veron \
+  'cd /srv/windygit/src && timeout 850 python3 scripts/runner_guard.py report' || true)
+summary=$(grep '^# runner-guard sweep:' <<<"$out" || echo "# runner-guard sweep: ERROR (no summary)")
+hits=$(grep -v '^#' <<<"$out" | grep . || true)
+{
+  echo "# Runner guard: stranger-code paths to self-hosted runners ($(date -u '+%Y-%m-%d %H:%MZ'))"
+  echo "_Nightly; windy-git scripts/runner_guard.py. R1 pull_request_target · R2 fork PR on self-hosted without a same-repo/environment gate · R3 outsider events (issue_comment, workflow_run, ...) on self-hosted · R0 unparseable._"
+  echo; echo "${summary#\# }"; echo
+  echo "| repo | file:line | rule | fix |"; echo "|---|---|---|---|"
+  while IFS=$'\t' read -r repo loc rule msg; do [[ -n $repo ]] && echo "| $repo | $loc | $rule | $msg |"; done <<<"$hits"
+} > "$page"
+new=$(comm -13 <(sort -u "$state" 2>/dev/null || true) <(cut -f1-3 <<<"$hits" | sort -u))
+cut -f1-3 <<<"$hits" | sort -u > "$state"
+if [[ -n "$new" ]]; then
+  n=$(grep -c . <<<"$new")
+  echo "$(date -u +%Y-%m-%dT%H:%MZ) Windy Git: 🚨 runner-guard: $n NEW stranger-code path(s) to a self-hosted runner in public repos; see ~/windy-orchestra/RUNNER_GUARD.md" >> ~/windy-orchestra/BOARD.md
+fi
+echo "${summary#\# }"

deploy/windy0/windy-runner-guard-sweep.service

@@ -0,0 +1,7 @@
+[Unit]
+Description=Nightly runner-guard sweep of every PUBLIC repo's workflows (Windy Git lane)
+
+[Service]
+Type=oneshot
+ExecStart=/usr/local/bin/windy-job windy-runner-guard-sweep 26h --expect "runner-guard sweep: 0 hit" --owner 13 -- %h/bin/nightly-runner-guard-sweep.sh
+TimeoutStartSec=1200

deploy/windy0/windy-runner-guard-sweep.timer

@@ -0,0 +1,9 @@
+[Unit]
+Description=Nightly runner-guard sweep
+
+[Timer]
+OnCalendar=*-*-* 09:40:00 UTC
+Persistent=true
+
+[Install]
+WantedBy=timers.target

scripts/runner_guard.py

@@ -0,0 +1,209 @@
+#!/usr/bin/env python3
+"""Runner guard: no workflow may let a STRANGER's code reach a self-hosted runner (Boss 10-01).
+
+Our self-hosted GitHub runners run on Veron as `github-runner`, which is in the docker group
+(= root on Veron). Until ephemeral containerised runners exist (after launch), the cheap
+guard is to refuse the workflow shapes that hand a self-hosted runner to outsiders:
+
+  R1 pull_request_target            : runs with secrets/write token in the BASE repo context
+  R2 pull_request on self-hosted    : fork PRs run their own code, unless the job is gated to
+                                      same-repo heads (`if:` on head.repo.full_name == github.repository
+                                      or head.repo.fork == false) or an `environment:`
+  R3 issue_comment / workflow_run / issues / discussion* / pull_request_review* / fork / watch
+                                    : anyone can fire these; never on self-hosted without an environment gate
+  (push, tags, schedule, workflow_dispatch, repository_dispatch, workflow_call: writers only, fine)
+
+A job counts as self-hosted when its runs-on names `self-hosted`, or is an expression we
+can't resolve (conservative). Findings carry file:line, never file content beyond that.
+
+  python3 scripts/runner_guard.py lint FILE...              # local files
+  python3 scripts/runner_guard.py report [--owners a,b]     # default branch of every PUBLIC repo
+  python3 scripts/runner_guard.py pr [--owners a,b] [--post]  # open PRs on public repos: changed workflows
+"""
+from __future__ import annotations
+
+import argparse
+import base64
+import json
+import os
+import subprocess
+import sys
+
+import yaml
+
+OWNERS = ["sneakyfree", "VERONTECH", "Windstorm-Institute", "Windstorm-Labs", "Public-Streamer"]
+CTX = "windy-git/runner-guard"
+OUTSIDE = {"issue_comment", "workflow_run", "issues", "discussion", "discussion_comment",
+           "pull_request_review", "pull_request_review_comment", "fork", "watch"}
+SAME_REPO_GATES = ("head.repo.full_name == github.repository", "github.repository == github.event.pull_request.head.repo.full_name",
+                   "head.repo.fork == false", "!github.event.pull_request.head.repo.fork")
+
+
+def _node_map(node):
+    """{key: (value_node, line)} for a YAML mapping node."""
+    if not isinstance(node, yaml.MappingNode):
+        return {}
+    return {k.value: (v, k.start_mark.line + 1) for k, v in node.value if isinstance(k, yaml.ScalarNode)}
+
+
+def _triggers(on_node) -> dict[str, int]:
+    """{event: line}."""
+    if isinstance(on_node, yaml.ScalarNode):
+        return {on_node.value: on_node.start_mark.line + 1}
+    if isinstance(on_node, yaml.SequenceNode):
+        return {n.value: n.start_mark.line + 1 for n in on_node.value if isinstance(n, yaml.ScalarNode)}
+    return {k: line for k, (_v, line) in _node_map(on_node).items()}
+
+
+def _self_hosted(runs_on) -> bool:
+    if runs_on is None:
+        return False
+    text = yaml.serialize(runs_on) if isinstance(runs_on, yaml.Node) else str(runs_on)
+    return "self-hosted" in text or "${{" in text
+
+
+def lint_text(path: str, text: str) -> list[tuple[str, int, str, str]]:
+    """[(path, line, rule, message)]. Unparseable YAML is a finding (it cannot be reviewed)."""
+    try:
+        root = yaml.compose(text)
+    except yaml.YAMLError as e:
+        line = getattr(getattr(e, "problem_mark", None), "line", 0) + 1
+        return [(path, line, "R0", "workflow YAML does not parse; cannot be checked")]
+    top = _node_map(root)
+    if "on" not in top or "jobs" not in top:
+        return []
+    trig = _triggers(top["on"][0])
+    jobs = _node_map(top["jobs"][0])
+    out = []
+    if "pull_request_target" in trig:
+        out.append((path, trig["pull_request_target"], "R1",
+                    "pull_request_target runs fork code with base-repo secrets; not allowed"))
+    for name, (jnode, jline) in jobs.items():
+        j = _node_map(jnode)
+        ro = j.get("runs-on", (None, jline))
+        if not _self_hosted(ro[0]):
+            continue
+        has_env = "environment" in j
+        cond = j["if"][0].value if "if" in j and isinstance(j["if"][0], yaml.ScalarNode) else ""
+        same_repo = any(g in cond.replace("  ", " ") for g in SAME_REPO_GATES)
+        if "pull_request" in trig and not (has_env or same_repo):
+            out.append((path, ro[1], "R2", f"job '{name}' runs fork PR code on a self-hosted runner "
+                        "(gate it: if: github.event.pull_request.head.repo.full_name == github.repository, or an environment)"))
+        for ev in sorted(OUTSIDE & trig.keys()):
+            if not has_env:
+                out.append((path, trig[ev], "R3", f"'{ev}' can be fired by anyone and job '{name}' is self-hosted "
+                            "without an environment gate"))
+    return out
+
+
+# ---------------------------------------------------------------- GitHub side
+def gh(*args: str, check=True) -> str:
+    r = subprocess.run(["gh", "api", *args], capture_output=True, text=True, timeout=60)
+    if check and r.returncode != 0:
+        raise RuntimeError(f"gh api {args[0]} failed")
+    return r.stdout
+
+
+def public_repos(owners) -> list[tuple[str, str]]:
+    out = []
+    for o in owners:
+        txt = gh(f"users/{o}/repos?per_page=100&type=owner", "--paginate",
+                 "--jq", '.[]|select(.private==false and .archived==false)|.full_name+" "+.default_branch', check=False)
+        out += [tuple(row.split()) for row in txt.splitlines() if row.strip()]
+    return out
+
+
+def workflows_at(full: str, ref: str) -> list[tuple[str, str]]:
+    txt = gh(f"repos/{full}/contents/.github/workflows?ref={ref}", "--jq",
+             '.[]|select(.type=="file")|.path', check=False)
+    files = [p for p in txt.splitlines() if p.endswith((".yml", ".yaml"))]
+    return [(p, file_at(full, p, ref)) for p in files]
+
+
+def file_at(full: str, path: str, ref: str) -> str:
+    raw = gh(f"repos/{full}/contents/{path}?ref={ref}", "--jq", ".content", check=False).strip()
+    return base64.b64decode(raw).decode("utf-8", "replace") if raw else ""
+
+
+def cmd_report(owners) -> int:
+    hits = 0
+    repos = public_repos(owners)
+    for full, branch in repos:
+        for path, text in workflows_at(full, branch):
+            for p, line, rule, msg in lint_text(path, text):
+                hits += 1
+                print(f"{full}\t{p}:{line}\t{rule}\t{msg}")
+    print(f"# runner-guard sweep: {hits} hit(s) in {len(repos)} public repos")
+    return 1 if hits else 0
+
+
+STATE = os.environ.get("RUNNER_GUARD_STATE", "/var/lib/windy-git/runner-guard-posted.json")
+
+
+def cmd_pr(owners, post: bool) -> int:
+    # Post each (repo, sha, state, description) ONCE: the sync runs every 5 min and GitHub caps
+    # statuses per sha+context at 1000.
+    try:
+        with open(STATE) as fh:
+            posted = set(json.load(fh))
+    except (OSError, ValueError):
+        posted = set()
+    seen = set()
+    for full, _branch in public_repos(owners):
+        prs = gh(f"repos/{full}/pulls?state=open&per_page=50", "--jq",
+                 '.[]|(.number|tostring)+" "+.head.sha+" "+.head.repo.full_name', check=False)
+        for line in prs.splitlines():
+            num, sha, head_repo = line.split(" ", 2)
+            files = gh(f"repos/{full}/pulls/{num}/files?per_page=100", "--jq",
+                       '.[]|select(.status!="removed")|.filename', check=False).split()
+            wf = [f for f in files if f.startswith(".github/workflows/") and f.endswith((".yml", ".yaml"))]
+            # a fork's own content is read from the head repo at the head sha
+            src = head_repo if head_repo and head_repo != "null" else full
+            found = [h for f in wf for h in lint_text(f, file_at(src, f, sha))]
+            if found:
+                p, ln, rule, msg = found[0]
+                state, desc = "failure", f"BLOCKED: {rule} {p}:{ln}: {msg}"[:140]
+            else:
+                state, desc = "success", ("OK: no workflow changes" if not wf else
+                                          "OK: no stranger-code path to a self-hosted runner")
+            key = f"{full}@{sha}:{state}:{desc}"
+            seen.add(key)
+            if key in posted:
+                continue
+            print(f"{full}#{num}@{sha[:7]} {state} {desc}")
+            if post:
+                gh(f"repos/{full}/statuses/{sha}", "-f", f"state={state}", "-f", f"context={CTX}",
+                   "-f", f"description={desc}", check=False)
+                posted.add(key)
+    if post:  # keep only keys for PRs still open, so the file never grows without bound
+        os.makedirs(os.path.dirname(STATE), exist_ok=True)
+        with open(STATE, "w") as fh:
+            json.dump(sorted(posted & seen), fh)
+    return 0
+
+
+def main(argv=None) -> int:
+    ap = argparse.ArgumentParser(prog="runner_guard")
+    sub = ap.add_subparsers(dest="cmd", required=True)
+    lint_p = sub.add_parser("lint")
+    lint_p.add_argument("files", nargs="+")
+    rep = sub.add_parser("report")
+    rep.add_argument("--owners", default=",".join(OWNERS))
+    prp = sub.add_parser("pr")
+    prp.add_argument("--owners", default="sneakyfree")  # self-hosted runners exist only there
+    prp.add_argument("--post", action="store_true")
+    a = ap.parse_args(argv)
+    if a.cmd == "lint":
+        hits = []
+        for f in a.files:
+            with open(f, errors="replace") as fh:
+                hits += lint_text(f, fh.read())
+        for p_, ln, rule, msg in hits:
+            print(f"{p_}:{ln}\t{rule}\t{msg}")
+        return 1 if hits else 0
+    owners = a.owners.split(",")
+    return cmd_report(owners) if a.cmd == "report" else cmd_pr(owners, a.post)
+
+
+if __name__ == "__main__":
+    sys.exit(main())

scripts/sync_from_github.sh

@@ -94,6 +94,11 @@ if ! python3 "$(dirname "$0")/pr_status_bridge.py"; then
   log "FAILED pr status bridge"; FAILED=1
 fi
 
+# Runner guard (Boss 10-01): PUBLIC sneakyfree repos have self-hosted GitHub runners on Veron.
+# A PR that changes a workflow so a stranger's code could reach one gets a red
+# windy-git/runner-guard status. Each status is posted once; never fails the sync.
+timeout -k 10 120 python3 "$(dirname "$0")/runner_guard.py" pr --post || log "runner-guard failed or timed out (non-fatal)"
+
 # CI telemetry -> admin.windyword.ai (shapes declared with Windy Telemetry 40).
 # Sends nothing until WINDYGIT_TELEMETRY_TOKEN is set; never fails the sync.
 timeout -k 10 180 python3 "$(dirname "$0")/telemetry_emit.py" || log "telemetry emit failed or timed out (non-fatal)"