From 6e9e8c6ab5e5cc560e45a606c47ab83b8c261d64 Mon Sep 17 00:00:00 2001
From: jenkins <jenkins@bstein.dev>
Date: Mon, 17 Aug 2026 20:37:30 -0300
Subject: [PATCH] hermes: reject regex literals in polkit grants

A regex literal embedding a quote desynced the string tokenizer and
swallowed an unconditional Result.YES, so the grant read as unscoped and
slipped past the literal-identity check. Fail closed on any slash outside
a string or comment; neither regex nor division belongs in an
identity-scoped grant.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
---
 services/hermes/scripts/node_polkit_audit.py  |  7 +++
 .../tests/test_hermes_node_polkit_identity.py | 56 +++++++++++++++++++
 2 files changed, 63 insertions(+)

diff --git a/services/hermes/scripts/node_polkit_audit.py b/services/hermes/scripts/node_polkit_audit.py
index 281f1484..d45a0134 100644
--- a/services/hermes/scripts/node_polkit_audit.py
+++ b/services/hermes/scripts/node_polkit_audit.py
@@ -85,6 +85,13 @@ def _split_strings(text: str) -> tuple[str, list[str]]:
             code.append(" ")
             index = closing + 2
             continue
+        if character == "/":
+            # Any remaining slash is a regex literal or a division operator.
+            # A regex literal may embed a quote character, which would desync
+            # the string scanner and swallow an unconditional grant.  Neither
+            # regex nor division has a place in an identity-scoped grant, so
+            # both fail closed before they can hide a Result.YES.
+            raise HardeningError("polkit rule uses a regex or division operator")
         code.append(character)
         index += 1
     return "".join(code), strings
diff --git a/testing/tests/test_hermes_node_polkit_identity.py b/testing/tests/test_hermes_node_polkit_identity.py
index 059f05f2..3af8d095 100644
--- a/testing/tests/test_hermes_node_polkit_identity.py
+++ b/testing/tests/test_hermes_node_polkit_identity.py
@@ -124,6 +124,62 @@ def test_unprovable_rule_constructs_fail_closed(text: str, match: str):
         _rules(module, text)
 
 
+def test_regex_literal_tokenizer_desync_grant_is_rejected():
+    """A regex literal embedding a quote must not open a phantom string.
+
+    Without regex awareness the two /'/ literals fool the string scanner into
+    swallowing the unconditional Result.YES between their quotes; the grant
+    then reads as unscoped and would slip past every later check.
+    """
+    module = _load()
+    exploit = (
+        "polkit.addRule(function(action, subject) { "
+        "var a = /'/; "
+        'if (action.id == "org.freedesktop.policykit.exec") '
+        "{ return polkit.Result.YES; } "
+        "var b = /'/; });\n"
+    )
+    with pytest.raises(module.HardeningError, match="regex or division"):
+        _rules(module, exploit)
+
+
+@pytest.mark.parametrize(
+    "snippet",
+    [
+        "var a = /'/;",
+        'var a = /"/;',
+        "var a = /abc/;",
+        "var a = /[/'\"]/;",
+        "var a = /x\\/y/;",
+        "var a = subject.user / 2;",
+        "// a comment / with a slash then\nvar a = /'/;",
+        '/* block */ var a = /"/;',
+        "return polkit.Result.YES / 1;",
+    ],
+)
+def test_every_slash_form_outside_a_comment_fails_closed(snippet: str):
+    module = _load()
+    text = f"polkit.addRule(function(action, subject) {{ {snippet} }});\n"
+    with pytest.raises(module.HardeningError, match="regex or division"):
+        _rules(module, text)
+
+
+def test_slashes_confined_to_strings_and_comments_stay_legal():
+    module = _load()
+    # Slashes inside string literals and // or /* */ comments are inert.
+    _rules(
+        module,
+        "// path-like /usr/bin comment\n"
+        "/* another /etc/ comment */\n"
+        "polkit.addRule(function(action, subject) {\n"
+        '    if (action.id == "org.freedesktop.systemd1.manage-units" &&\n'
+        '        subject.user == "systemd-network") {\n'
+        "        return polkit.Result.YES;\n"
+        "    }\n"
+        "});\n",
+    )
+
+
 def test_string_and_comment_handling_keeps_literal_rules_auditable():
     module = _load()
     code, strings = module._split_strings(