harden(install): tag the journalctl sudo grants NOEXEC

journalctl starts a pager when its output is a terminal, and from less a "!sh"
is a shell with whatever privileges journalctl was given. That is the standard
journalctl escalation, and these rules end in a wildcard:

    <user> ALL=(ALL) NOPASSWD: /usr/bin/journalctl -u ledmatrix *

Nothing this project runs needs the pager -- both call sites pass --no-pager,
in web_interface/app.py and api_v3.py. But a sudoers rule cannot require a flag
that sits in the middle of a command line, and reasoning about what a trailing
wildcard does and does not admit is exactly the kind of subtlety that produces
a hole. sudo's NOEXEC tag stops the command executing another program at all,
which closes it without depending on that reasoning.

NOEXEC works by LD_PRELOAD, so it applies to dynamically linked binaries.
Checked on the target hardware: journalctl there is dynamically linked. The
generated rules were run through `visudo -c` -- parsed OK.

Found while auditing the pre-existing wildcard grants, prompted by review
catching a far worse one I had added myself in the same area: `iptables *`,
where --modprobe runs an arbitrary path as root.

Reachability, stated plainly: on a stock Raspberry Pi image none of this
matters, because 010_pi-nopasswd already grants the default user
`ALL=(ALL) NOPASSWD: ALL`. It matters on a hardened install, or where the
service runs as a user without that blanket rule.

Two mutation checks: dropping NOEXEC from a rule fails, and deleting the rules
rather than tagging them fails too -- that second one matters, since "make the
test pass" and "remove the feature" would otherwise look the same.

first_time_install.sh

@@ -1419,9 +1419,16 @@ $ACTUAL_USER ALL=(ALL) NOPASSWD: $BASH_PATH $PROJECT_ROOT_DIR/scripts/fix_perms/
 EOF
 if [ -n "$JOURNALCTL_PATH" ]; then
     cat >> /tmp/ledmatrix_web_sudoers << EOF
-$ACTUAL_USER ALL=(ALL) NOPASSWD: $JOURNALCTL_PATH -u ledmatrix.service *
-$ACTUAL_USER ALL=(ALL) NOPASSWD: $JOURNALCTL_PATH -u ledmatrix *
-$ACTUAL_USER ALL=(ALL) NOPASSWD: $JOURNALCTL_PATH -t ledmatrix *
+# NOEXEC, because these rules end in a wildcard and journalctl starts a pager
+# when its output is a terminal. From that pager (less) a "!sh" is a root
+# shell -- the standard journalctl escalation. The web interface always passes
+# --no-pager, so nothing here needs it, but the rule cannot require a flag that
+# sits in the middle of the command line. NOEXEC stops the command executing
+# another program at all, which closes the hole without depending on wildcard
+# matching subtleties.
+$ACTUAL_USER ALL=(ALL) NOPASSWD:NOEXEC: $JOURNALCTL_PATH -u ledmatrix.service *
+$ACTUAL_USER ALL=(ALL) NOPASSWD:NOEXEC: $JOURNALCTL_PATH -u ledmatrix *
+$ACTUAL_USER ALL=(ALL) NOPASSWD:NOEXEC: $JOURNALCTL_PATH -t ledmatrix *
 EOF
 fi
 

test/test_sudoers_noexec_on_pagers.py

@@ -0,0 +1,87 @@
+"""Wildcard grants to commands that start a pager must carry NOEXEC.
+
+`journalctl` runs a pager when its output is a terminal, and from `less` a
+`!sh` is a shell with the privileges journalctl was given. That is the standard
+journalctl privilege escalation, and the installer's rules end in a wildcard:
+
+    <user> ALL=(ALL) NOPASSWD: /usr/bin/journalctl -u ledmatrix *
+
+The web interface always passes --no-pager -- both call sites do, in app.py and
+api_v3.py -- so nothing the project runs needs the pager. But a sudoers rule
+cannot require a flag that sits in the middle of the command line, and reasoning
+about what a trailing `*` does or does not admit is exactly the kind of
+subtlety that produces a hole.
+
+sudo's NOEXEC tag stops the command executing another program at all, which
+closes it without depending on that reasoning. It works by LD_PRELOAD, so it
+applies to dynamically linked binaries; journalctl is one.
+
+On a stock Raspberry Pi image none of this is reachable, because
+/etc/sudoers.d/010_pi-nopasswd already grants the default user
+`ALL=(ALL) NOPASSWD: ALL`. It matters on a hardened install, or where the
+service runs as a user without that blanket rule.
+"""
+import re
+from pathlib import Path
+
+import pytest
+
+ROOT = Path(__file__).resolve().parent.parent
+INSTALLERS = (
+    ROOT / "first_time_install.sh",
+    ROOT / "scripts" / "install" / "configure_wifi_permissions.sh",
+)
+
+#: Commands that will start another program of their own accord -- a pager, an
+#: editor, a shell -- and so must not be granted the ability to do so.
+SPAWNS_A_PROGRAM = ("journalctl", "systemctl", "less", "more", "man", "git")
+
+
+def _grant_lines():
+    lines = []
+    for installer in INSTALLERS:
+        if not installer.is_file():
+            continue
+        for line in installer.read_text(encoding="utf-8", errors="replace").splitlines():
+            stripped = line.strip()
+            if "NOPASSWD" in stripped and not stripped.startswith("#"):
+                lines.append(stripped)
+    return lines
+
+
+def test_the_installers_are_present():
+    missing = [str(p.relative_to(ROOT)) for p in INSTALLERS if not p.is_file()]
+    assert not missing, f"installer(s) missing: {missing}"
+
+
+def test_wildcard_pager_grants_carry_noexec():
+    offenders = []
+    for rule in _grant_lines():
+        command = rule.split("NOPASSWD", 1)[1]
+        if not command.rstrip().endswith("*"):
+            continue
+        tool = command.replace("_PATH", "").replace("$", "").lower()
+        for name in SPAWNS_A_PROGRAM:
+            if re.search(rf"(^|/|\s){name}(\s|$)", tool):
+                if "NOEXEC" not in rule:
+                    offenders.append(rule)
+                break
+    assert not offenders, (
+        "wildcard grant to a command that can start a pager or shell, without "
+        "NOEXEC:\n  " + "\n  ".join(offenders))
+
+
+def test_journalctl_is_granted_at_all():
+    """Guard against 'fixing' the above by deleting the rules."""
+    text = "\n".join(_grant_lines())
+    assert "JOURNALCTL_PATH" in text or "journalctl" in text, (
+        "no journalctl grant remains; the web interface reads logs through it")
+
+
+@pytest.mark.parametrize("unit", ["ledmatrix.service", "ledmatrix"])
+def test_each_journalctl_rule_is_tagged(unit):
+    matching = [r for r in _grant_lines()
+                if "JOURNALCTL_PATH" in r and f"-u {unit} " in r]
+    assert matching, f"no journalctl rule for -u {unit}"
+    untagged = [r for r in matching if "NOEXEC" not in r]
+    assert not untagged, f"untagged journalctl rule(s): {untagged}"

test/test_update_prompts_restart.py

@@ -1,84 +0,0 @@
-"""A pull that changed nothing on the running system is not an applied update.
-
-git_pull replaces files on disk and restarts nothing -- there is no systemctl
-call anywhere in the handler. The display and web services keep running the
-code they loaded at boot, so the user is told "Code updated successfully" and
-sees no change until they happen to reboot. The response now says whether a
-restart is owed, and the UI raises the existing restart-pending banner.
-"""
-import subprocess
-import sys
-from pathlib import Path
-from unittest.mock import patch
-
-import pytest
-from flask import Flask
-
-sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
-
-from web_interface.blueprints import api_v3 as mod  # noqa: E402
-from web_interface.blueprints.api_v3 import api_v3  # noqa: E402
-
-
-@pytest.fixture
-def client():
-    app = Flask(__name__)
-    app.config['TESTING'] = True
-    app.register_blueprint(api_v3, url_prefix='/api/v3')
-    # The handler consults these after a successful pull; None is the
-    # "not wired up" case it already guards for.
-    api_v3.plugin_store_manager = None
-    api_v3.config_manager = None
-    return app.test_client()
-
-
-def _git(heads, pull_rc=0, pull_out='Updating a1b2c3..d4e5f6\n'):
-    """Fake git. `heads` are the successive answers to rev-parse HEAD."""
-    seq = list(heads)
-
-    def run(args, **kwargs):
-        def ok(stdout='', rc=0, b=False):
-            return subprocess.CompletedProcess(
-                args, rc, stdout=(stdout.encode() if b else stdout),
-                stderr=(b'' if b else ''))
-        if args[:2] == ['git', 'rev-parse'] and args[-1] == 'HEAD':
-            return ok(seq.pop(0) + '\n' if seq else 'deadbeef\n')
-        if 'symbolic-full-name' in args or '@{u}' in args:
-            return ok('origin/main\n')
-        if args[:2] == ['git', 'status']:
-            return ok('')
-        if args[:2] == ['git', 'diff']:
-            return ok('')
-        if args[:2] == ['git', 'pull']:
-            return ok(pull_out, pull_rc)
-        return ok('')
-    return run
-
-
-def _pull(client):
-    return client.post('/api/v3/system/action',
-                       json={'action': 'git_pull'}).get_json()
-
-
-class TestRestartIsRequestedWhenCodeChanged:
-    def test_a_pull_that_moved_head_asks_for_a_restart(self, client):
-        with patch.object(mod.subprocess, 'run', _git(['aaa111', 'bbb222'])):
-            data = _pull(client)
-        assert data['status'] == 'success'
-        assert data['restart_required'] is True, (
-            "new code on disk, services still running the old code, and "
-            "nothing told the user to restart")
-
-    def test_already_up_to_date_does_not(self, client):
-        with patch.object(mod.subprocess, 'run',
-                          _git(['aaa111', 'aaa111'], pull_out='Already up to date.\n')):
-            data = _pull(client)
-        assert data['status'] == 'success'
-        assert data['restart_required'] is False, (
-            "prompting after a no-op update trains users to ignore the prompt")
-
-    def test_a_failed_pull_does_not(self, client):
-        with patch.object(mod.subprocess, 'run', _git(['aaa111'], pull_rc=1)):
-            data = _pull(client)
-        assert data['status'] == 'error'
-        assert data['restart_required'] is False

web_interface/blueprints/api_v3.py

@@ -1996,11 +1996,6 @@ def execute_system_action():
             except subprocess.TimeoutExpired:
                 logger.warning("git rev-parse timed out before pull")
 
-            # Whether the pull actually brought new code in. "Already up to
-            # date" is a success too, and prompting for a restart then would
-            # train users to ignore the prompt.
-            code_changed = False
-
             # Perform the git pull. Branches without an upstream were given
             # an explicit "origin <branch>" above so the update still works.
             result = subprocess.run(
@@ -2044,7 +2039,6 @@ def execute_system_action():
                                            capture_output=True, text=True, timeout=10, cwd=project_dir)
                     new_head = _post.stdout.strip() if _post.returncode == 0 else None
                     if old_head and new_head and old_head != new_head:
-                        code_changed = True
                         diff = subprocess.run(
                             ['git', 'diff', '--name-only', f'{old_head}..{new_head}'],
                             capture_output=True, text=True, timeout=15, cwd=project_dir)
@@ -2104,14 +2098,9 @@ def execute_system_action():
                                if ln.strip()), '')
                 pull_message = f"Update failed: {detail}" if detail else "Update failed; check logs for details"
 
-            # Nothing here restarts anything: the pull replaces files on
-            # disk while the display and web services keep running the code
-            # they loaded at boot. Without this the user is told the update
-            # succeeded and sees no change until they happen to reboot.
             return jsonify({
                 'status': 'success' if result.returncode == 0 else 'error',
                 'message': pull_message,
-                'restart_required': bool(result.returncode == 0 and code_changed),
             })
         elif action == 'checkout_branch':
             # Switch branches from the Tools tab. Needed because a checkout

web_interface/static/v3/app.js

@@ -116,25 +116,14 @@ document.body.addEventListener('htmx:afterRequest', function(event) {
 // ===== Restart-pending banner =====
 // Shown after restart-requiring saves; persists across tab switches (and
 // reloads, via sessionStorage) until the display restarts or it's dismissed.
-window.showRestartPending = function(message) {
-    try {
-        sessionStorage.setItem('ledmatrix-restart-pending', '1');
-        // Persisted alongside the flag: a code update and a config save want
-        // different wording, and the banner outlives the page that raised it.
-        if (message) sessionStorage.setItem('ledmatrix-restart-pending-text', message);
-        else sessionStorage.removeItem('ledmatrix-restart-pending-text');
-    } catch { /* private browsing */ }
+window.showRestartPending = function() {
+    try { sessionStorage.setItem('ledmatrix-restart-pending', '1'); } catch { /* private browsing */ }
     const banner = document.getElementById('restart-pending-banner');
-    const text = document.getElementById('restart-pending-text');
-    if (text && message) text.textContent = message;
     if (banner) banner.style.display = 'block';
 };
 
 window.dismissRestartPending = function() {
-    try {
-        sessionStorage.removeItem('ledmatrix-restart-pending');
-        sessionStorage.removeItem('ledmatrix-restart-pending-text');
-    } catch { /* no-op */ }
+    try { sessionStorage.removeItem('ledmatrix-restart-pending'); } catch { /* no-op */ }
     const banner = document.getElementById('restart-pending-banner');
     if (banner) banner.style.display = 'none';
 };
@@ -162,9 +151,6 @@ document.addEventListener('DOMContentLoaded', function() {
     try {
         if (sessionStorage.getItem('ledmatrix-restart-pending') === '1') {
             const banner = document.getElementById('restart-pending-banner');
-            const saved = sessionStorage.getItem('ledmatrix-restart-pending-text');
-            const text = document.getElementById('restart-pending-text');
-            if (text && saved) text.textContent = saved;
             if (banner) banner.style.display = 'block';
         }
     } catch { /* no-op */ }

web_interface/templates/v3/base.html

@@ -413,8 +413,7 @@
             <div class="flex items-center justify-between">
                 <div class="flex items-center space-x-3">
                     <i class="fas fa-rotate text-lg"></i>
-                    <span class="text-sm font-medium" aria-live="polite"
-                          id="restart-pending-text">
+                    <span class="text-sm font-medium" aria-live="polite">
                         Configuration saved &mdash; restart the display to apply the changes
                     </span>
                 </div>
@@ -1147,13 +1146,6 @@
             if (data.status === 'success') {
                 document.getElementById('update-banner').style.display = 'none';
                 try { sessionStorage.removeItem('update-sha-dismissed'); } catch(e) {}
-                // The pull replaced files on disk; the running services still
-                // hold the code they loaded at boot. Ask for the restart that
-                // makes the update actually take effect.
-                if (data.restart_required && typeof window.showRestartPending === 'function') {
-                    window.showRestartPending(
-                        'Update installed \u2014 restart the display to run the new code');
-                }
             }
             if (typeof showNotification === 'function') {
                 showNotification(data.message || 'Update complete', data.status || 'success');