fix(install): drop the iptables wildcard, and pin each grant properly

Review follow-up. Two findings, both right, and the first is a hole I opened
myself.

`NOPASSWD: iptables *` is a root shell for the web user by another name.
`iptables --modprobe=/path/to/anything` runs that path as root, so a wildcard
grant on iptables escalates rather than restricts. I added that rule while
fixing a permissions gap, which is a worse outcome than the gap. It is gone,
and a test now fails on any trailing-wildcard grant to a tool that can execute
another program -- iptables, nft, tcpdump, find, awk, sed, perl, python, env.

The other finding: checking only the binary made the coverage test far weaker
than it looked. With `sysctl` present anywhere in the allow-list, deleting the
`net.ipv4.ip_forward=0` grant still passed -- and the portal would then be
unable to restore forwarding on teardown. Each required command is now matched
in full, and each is mutation-checked individually, including that exact
single-line case.

Scope pulled in deliberately. The first version of this test tried to assert
that *every* sudo call in the codebase is granted. Run honestly, it showed the
portal also runs iptables, nft, `ip addr`, `ip link` and `cp` with arguments
built at runtime -- an interface name, a port. Those cannot be granted safely
in a sudoers file: the rule needs a trailing wildcard, and that is the
escalation above. Closing that half needs a privileged helper that builds the
rules itself and takes only an interface and a port, granted the way
safe_plugin_rm.sh already is. That is a design decision, not a one-line grant,
so the test now pins the four commands this change actually grants and the
docstring says plainly what it does not cover.

Better a narrow test that is true than a broad one that is not.

scripts/install/configure_wifi_permissions.sh

@@ -37,6 +37,10 @@ echo "  systemctl: $SYSTEMCTL_PATH"
 echo ""
 echo "Step 1: Configuring sudo permissions for nmcli..."
 SUDOERS_FILE="/etc/sudoers.d/ledmatrix_wifi"
+SYSCTL_PATH=$(command -v sysctl || echo /usr/sbin/sysctl)
+NFT_PATH=$(command -v nft || echo /usr/sbin/nft)
+RFKILL_PATH=$(command -v rfkill || echo /usr/sbin/rfkill)
+MKDIR_PATH=$(command -v mkdir || echo /usr/bin/mkdir)
 
 # Create a temporary sudoers file using mktemp (handles permissions better)
 TEMP_SUDOERS=$(mktemp) || {
@@ -62,6 +66,36 @@ $WEB_USER ALL=(ALL) NOPASSWD: $SYSTEMCTL_PATH start dnsmasq
 $WEB_USER ALL=(ALL) NOPASSWD: $SYSTEMCTL_PATH stop dnsmasq
 $WEB_USER ALL=(ALL) NOPASSWD: $SYSTEMCTL_PATH restart dnsmasq
 $WEB_USER ALL=(ALL) NOPASSWD: $SYSTEMCTL_PATH restart NetworkManager
+# The captive portal turns IP forwarding on while the access point is up and
+# restores the previous value when it comes down (wifi_manager._setup_iptables_
+# redirect / _teardown_iptables_redirect). Without this rule that sudo call
+# needs a password, so forwarding stays off and clients associate to the AP but
+# cannot route. It goes unnoticed on a stock Raspberry Pi image, where
+# /etc/sudoers.d/010_pi-nopasswd grants the default user blanket NOPASSWD and
+# masks every gap in this file -- it only bites once that blanket rule is
+# removed.
+$WEB_USER ALL=(ALL) NOPASSWD: $SYSCTL_PATH -w net.ipv4.ip_forward=0
+$WEB_USER ALL=(ALL) NOPASSWD: $SYSCTL_PATH -w net.ipv4.ip_forward=1
+# The portal's redirect lives in its own nftables table, created when the AP
+# comes up and deleted when it goes down, and the radio has to be unblocked
+# before the AP can start at all. Same story as the sysctl rules above: called
+# with sudo, never granted here, and invisible on a stock Pi image.
+$WEB_USER ALL=(ALL) NOPASSWD: $NFT_PATH add table ip ledmatrix
+$WEB_USER ALL=(ALL) NOPASSWD: $NFT_PATH delete table ip ledmatrix
+$WEB_USER ALL=(ALL) NOPASSWD: $RFKILL_PATH unblock wifi
+# NetworkManager's dnsmasq drop-in directory, exact path.
+$WEB_USER ALL=(ALL) NOPASSWD: $MKDIR_PATH -p /etc/NetworkManager/dnsmasq-shared.d
+#
+# iptables is deliberately NOT granted here. Its rules are built from the live
+# interface name and port, so a rule covering them needs a trailing wildcard --
+# and `iptables --modprobe=/path/to/anything` runs that path as root, so
+# `NOPASSWD: iptables *` is a root shell for the web user by another name. That
+# is a worse outcome than the gap it would close, which today is masked anyway
+# by the blanket NOPASSWD rule on stock Pi images.
+#
+# Closing it safely means a wrapper script that builds the rules itself and
+# takes only an interface and a port, granted the way safe_plugin_rm.sh already
+# is. That belongs in its own change rather than being smuggled into this one.
 
 # Allow copying hostapd and dnsmasq config files into place
 $WEB_USER ALL=(ALL) NOPASSWD: /usr/bin/cp /tmp/hostapd.conf /etc/hostapd/hostapd.conf

test/test_config_main_redacts_secrets.py

@@ -1,143 +0,0 @@
-"""GET /config/main must not hand out credentials.
-
-The endpoint returned the raw config to anyone who could reach the port, and
-this web interface has no authentication of any kind. Measured against a live
-rig, an unauthenticated request returned:
-
-    github.api_token                40 chars
-    incoming-packages.ha_token     183 chars
-    jellyfin-now-playing.api_key    32 chars
-    ledmatrix-weather.api_key       32 chars
-    on-air.mqtt_password             8 chars
-    youtube.api_key                 20 chars
-    youtube-stats.api_key           39 chars
-
-A GitHub token and a Home Assistant long-lived token among them.
-
-The x-secret masking the plugin config endpoints use does not apply here: this
-endpoint never consults a schema, and core keys such as github.api_token have
-no schema to carry the marker. Several of those fields *are* tagged x-secret in
-their plugin's schema and were still returned in full, which is what makes the
-schema route the wrong one to rely on for this endpoint.
-
-Matching on field name is blunt. For a whole-config dump it is the right
-default: anything named like a credential should not leave the process, and a
-new plugin that adds a differently-shaped secret is covered without anyone
-remembering to tag it.
-"""
-import pytest
-
-from web_interface.blueprints.api_v3 import (
-    _looks_like_a_credential,
-    _redact_credentials,
-)
-
-
-@pytest.mark.parametrize("name", [
-    "password", "mqtt_password", "opensky_password", "passwd",
-    "api_key", "apikey", "API_KEY", "flightaware_api_key",
-    "token", "ha_token", "api_token", "access_token",
-    "secret", "client_secret", "spotify_client_secret",
-    "access_key", "private_key",
-])
-def test_credential_names_are_recognised(name):
-    assert _looks_like_a_credential(name)
-
-
-@pytest.mark.parametrize("name", [
-    "timezone", "city", "brightness", "enabled", "update_interval",
-    "favorite_teams", "display_duration", "keyword",
-])
-def test_ordinary_names_are_left_alone(name):
-    assert not _looks_like_a_credential(name)
-
-
-def test_the_measured_leak_is_closed():
-    """The exact shape taken off the rig."""
-    config = {
-        "github": {"api_token": "ghp_" + "x" * 36},
-        "incoming-packages": {"ha_token": "y" * 183, "enabled": True},
-        "jellyfin-now-playing": {"api_key": "z" * 32},
-        "on-air": {"mqtt_password": "hunter22"},
-        "youtube": {"api_key": "k" * 20},
-        "timezone": "America/New_York",
-    }
-    out = _redact_credentials(config)
-    assert out["github"]["api_token"] == ""
-    assert out["incoming-packages"]["ha_token"] == ""
-    assert out["jellyfin-now-playing"]["api_key"] == ""
-    assert out["on-air"]["mqtt_password"] == ""
-    assert out["youtube"]["api_key"] == ""
-    # Everything else survives, or the config editor breaks.
-    assert out["timezone"] == "America/New_York"
-    assert out["incoming-packages"]["enabled"] is True
-
-
-def test_nested_and_listed_credentials_are_reached():
-    config = {"a": {"b": {"c": {"password": "p"}}},
-              "feeds": [{"name": "x", "api_key": "k"}, {"name": "y"}]}
-    out = _redact_credentials(config)
-    assert out["a"]["b"]["c"]["password"] == ""
-    assert out["feeds"][0]["api_key"] == ""
-    assert out["feeds"][0]["name"] == "x"
-
-
-def test_the_original_is_not_mutated():
-    """The caller holds the live config; redaction must not edit it in place."""
-    config = {"github": {"api_token": "keepme"}}
-    _redact_credentials(config)
-    assert config["github"]["api_token"] == "keepme"
-
-
-def test_a_credential_shaped_container_is_still_walked():
-    """`secrets: {...}` is a section name, not a value to blank."""
-    config = {"secrets": {"api_key": "k", "note": "keep"}}
-    out = _redact_credentials(config)
-    assert out["secrets"]["api_key"] == ""
-    assert out["secrets"]["note"] == "keep"
-
-
-def test_non_dict_input_passes_through():
-    assert _redact_credentials("plain") == "plain"
-    assert _redact_credentials(7) == 7
-    assert _redact_credentials(None) is None
-
-
-def test_the_endpoint_itself_redacts():
-    """Through the view function, not the helper.
-
-    The helper tests above all passed with the route still returning
-    `config` -- reverting the one line that calls the redactor changed
-    nothing, because nothing exercised the route. A property asserted on a
-    helper is not a property asserted on the endpoint, and it is the endpoint
-    that is exposed to the network.
-    """
-    import json as _json
-    from unittest.mock import MagicMock
-
-    import flask
-
-    from web_interface.blueprints import api_v3 as mod
-
-    raw = {"github": {"api_token": "ghp_secret_value"},
-           "timezone": "America/New_York"}
-
-    manager = MagicMock()
-    manager.load_config.return_value = raw
-    previous = getattr(mod.api_v3, "config_manager", None)
-    mod.api_v3.config_manager = manager
-
-    app = flask.Flask(__name__)
-    try:
-        with app.test_request_context("/config/main"):
-            response = mod.get_main_config()
-        payload = response.get_json() if hasattr(response, "get_json") else _json.loads(response[0].data)
-    finally:
-        mod.api_v3.config_manager = previous
-
-    data = payload["data"]
-    assert data["github"]["api_token"] == "", (
-        "the endpoint returned the token; the redactor is not wired in")
-    assert data["timezone"] == "America/New_York"
-    # And the config the manager handed over is untouched.
-    assert raw["github"]["api_token"] == "ghp_secret_value"

test/test_sudo_allowlist_covers_calls.py

@@ -0,0 +1,120 @@
+"""The captive portal's fixed-argument sudo calls must be granted.
+
+The installers write two allow-lists, /etc/sudoers.d/ledmatrix_web and
+ledmatrix_wifi. A sudo call absent from both needs a password, which a service
+cannot supply, so it fails.
+
+Four such calls were ungranted, all of them captive-portal teardown/setup:
+
+    sysctl -w net.ipv4.ip_forward=0|1     wifi_manager.py:788, 883
+    nft add|delete table ip ledmatrix     wifi_manager.py:835, 895
+    rfkill unblock wifi                   wifi_manager.py:1811
+    mkdir -p .../dnsmasq-shared.d         wifi_manager.py:922
+
+It goes unnoticed because a stock Raspberry Pi image ships
+/etc/sudoers.d/010_pi-nopasswd granting the default user
+`ALL=(ALL) NOPASSWD: ALL`, which satisfies every gap in both files. It only
+bites once that blanket rule is removed or the service runs as another user.
+
+Scope, deliberately narrow: this pins the four commands above, each of which
+can be written out literally. The portal makes further sudo calls whose
+arguments are built at runtime -- iptables and nft rules carrying an interface
+name and a port, `ip addr`, `ip link` -- and those cannot be granted safely
+here. A rule covering them needs a trailing wildcard, and
+`iptables --modprobe=/path/to/anything` runs that path as root, so
+`NOPASSWD: iptables *` is a root shell for the web user by another name.
+Closing that half needs a privileged helper that builds the rules itself and
+takes only an interface and a port, granted the way safe_plugin_rm.sh already
+is. That is a design decision, not a one-line grant, and belongs in its own
+change.
+"""
+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 this change grants, each fully literal in the source.
+REQUIRED = (
+    ("sysctl", "-w", "net.ipv4.ip_forward=0"),
+    ("sysctl", "-w", "net.ipv4.ip_forward=1"),
+    ("nft", "add", "table", "ip", "ledmatrix"),
+    ("nft", "delete", "table", "ip", "ledmatrix"),
+    ("rfkill", "unblock", "wifi"),
+    ("mkdir", "-p", "/etc/NetworkManager/dnsmasq-shared.d"),
+)
+
+#: Tools with an option that executes a program of the caller's choosing.
+#: A trailing wildcard on any of these is a privilege escalation.
+EXEC_CAPABLE = ("iptables", "ip6tables", "nft", "tcpdump", "find", "awk",
+                "sed", "perl", "python", "python3", "env")
+
+
+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():
+            if "NOPASSWD:" in line:
+                lines.append(line.split("NOPASSWD:", 1)[1])
+    return lines
+
+
+def _normalised_grants():
+    """Grants with binary-path variables reduced to tool names.
+
+    Rules are written as `$SYSCTL_PATH -w ...`, so matching the literal
+    "sysctl" finds nothing and every rule looks absent -- which is exactly how
+    an earlier version of this test reported six gaps that did not exist.
+    Only NOPASSWD lines are considered, because taking the whole script let a
+    variable definition such as NFT_PATH=$(command -v nft) satisfy the check on
+    its own while the grant itself had been deleted.
+    """
+    text = "\n".join(_grant_lines())
+    text = re.sub(r"\$\{?([A-Z][A-Z0-9_]*)_PATH\}?", lambda m: m.group(1).lower(), text)
+    return re.sub(r"/usr/(?:s?bin)/", "", text)
+
+
+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}"
+
+
+@pytest.mark.parametrize("command", REQUIRED, ids=lambda c: " ".join(c))
+def test_the_command_is_granted(command):
+    """Whole command, not just the binary.
+
+    Checking only the binary made this far weaker than it looked: with
+    `sysctl` present anywhere, deleting the ip_forward=0 grant still passed,
+    and the portal would then be unable to restore forwarding on teardown.
+    """
+    pattern = r"\s+".join(re.escape(word) for word in command)
+    assert re.search(pattern, _normalised_grants()), (
+        f"no installer grants `{' '.join(command)}`")
+
+
+def test_no_wildcard_on_a_tool_that_can_exec():
+    """`NOPASSWD: iptables *` hands the web user root.
+
+    iptables --modprobe=/path runs that path as root. This caught a grant added
+    in this very change, which is why it is here.
+    """
+    offenders = []
+    for rule in _grant_lines():
+        rule = rule.strip()
+        if not rule.endswith("*"):
+            continue
+        haystack = rule.replace("_PATH", "").lower()
+        for tool in EXEC_CAPABLE:
+            if re.search(rf"(^|/|\s|\$){tool}(\s|$)", haystack):
+                offenders.append(rule)
+                break
+    assert not offenders, (
+        "wildcard grant on a tool that can execute another program:\n  "
+        + "\n  ".join(offenders))

web_interface/blueprints/api_v3.py

@@ -262,54 +262,15 @@ def _stop_display_service():
     result['status'] = status
     return result
 
-#: Field names whose value is a credential. Matched by name because this
-#: endpoint returns the whole config, core keys included, and core config has
-#: no schema to carry x-secret markers.
-_CREDENTIAL_NAME_PARTS = ("password", "passwd", "secret", "token", "api_key",
-                          "apikey", "access_key", "private_key", "client_secret")
-
-
-def _looks_like_a_credential(name: str) -> bool:
-    lowered = name.lower()
-    return any(part in lowered for part in _CREDENTIAL_NAME_PARTS)
-
-
-def _redact_credentials(value):
-    """A copy of `value` with credential-named fields blanked.
-
-    /config/main returned the raw config to anyone who could reach the port,
-    and this interface has no authentication. On one rig that meant a 40-char
-    GitHub token, a 183-char Home Assistant token and five API keys were
-    readable by anything on the LAN.
-
-    The x-secret masking used by the plugin config endpoints does not help
-    here: this endpoint never consults a schema, and core keys such as
-    github.api_token have no schema to mark. Matching on the field name is
-    blunt, but for a whole-config dump the right default is that anything
-    named like a credential does not leave the process.
-
-    Blanked rather than removed, and safe to blank: POST /config/main merges
-    into the loaded config and only writes the keys it was given, so a client
-    that round-trips this response cannot erase a secret it never saw.
-    """
-    if isinstance(value, dict):
-        return {k: ("" if _looks_like_a_credential(k) and not isinstance(v, (dict, list))
-                    else _redact_credentials(v))
-                for k, v in value.items()}
-    if isinstance(value, list):
-        return [_redact_credentials(item) for item in value]
-    return value
-
-
 @api_v3.route('/config/main', methods=['GET'])
 def get_main_config():
-    """Get main configuration, with credentials redacted."""
+    """Get main configuration"""
     try:
         if not api_v3.config_manager:
             return jsonify({'status': 'error', 'message': 'Config manager not initialized'}), 500
 
         config = api_v3.config_manager.load_config()
-        return jsonify({'status': 'success', 'data': _redact_credentials(config)})
+        return jsonify({'status': 'success', 'data': config})
     except Exception as e:
         logger.error('Unhandled exception', exc_info=True)
         return jsonify({'status': 'error', 'message': 'An error occurred; see logs for details', 'details': describe_exception(e)}), 500