Harden container startup (#24718)

* keep /config out of the root environment in the frigate run script

The script exported HOME=/config and prepended /config/.local/lib to LD_LIBRARY_PATH while still root, then ran python3, ffmpeg, grep, and opt_in_out as root. The runtime user owns /config, so it could plant a .pth file in the user site-packages or a library on the loader path and get code run as root on the next start. Root helpers now run with root's environment (and python3 -I), and HOME, LD_LIBRARY_PATH, and PATH reach only the dropped process through env on the s6-setuidgid line. opt_in_out runs as the runtime user, so the openvino marker no longer gets written into /config by root.

* don't follow a planted symlink when writing /dev/shm/go2rtc.yaml

After the first start the go2rtc user owned /dev/shm/go2rtc.yaml and could swap it for a dangling symlink. The run script's -f test was false for a dangling link, so the link survived, and root's create_config.py then created the link target and the chown handed it to go2rtc. The run script now removes any existing entry, create_config.py creates the file with O_EXCL and O_NOFOLLOW at mode 0640, and the chown uses -h.

* run root python helpers in isolated mode and keep HOME=/config for non-root containers

The previous commit only set HOME=/config when dropping from root, so a container started with --user lost it. The other root-run helpers in the go2rtc, nginx, and certsync scripts now use python3 -I too, so they never load user site-packages or PYTHON* variables.

* validate networking.listen values before rendering them into nginx config

ListenConfig and get_nginx_settings.py only checked that the text after the last colon parsed as an int, and tempio rendered the raw string into the listen directive, so a value like "5000; location /x/ { alias /; } #:5000" injected nginx directives. Both now go through parse_listen_address, which accepts only a port, IPv4:port, or [IPv6]:port with a 1 to 65535 port and rebuilds the value from the parsed parts. get_nginx_settings.py falls back to the default port on an invalid value so nginx still serves the safe-mode UI.

* tighten comments

* accept hostnames, wildcards, and padded values in networking.listen

The stricter parser broke localhost:5000, *:5000, and values with surrounding whitespace that the old int() parsing accepted. parse_listen_address now strips the value and accepts RFC 1123 hostnames and *, still rebuilding the rendered value from the parsed parts. The ListenConfig validator runs in before mode, because pydantic coerced true to port 1 while get_nginx_settings.py rejected it and fell back to 5000, so the auth internal port and nginx disagreed.

* always create go2rtc.yaml after removing it and don't let opt_in_out stop frigate

The go2rtc else-branch was only reachable when a regular file was planted between rm and the test, and then loaded that file as go2rtc's config. create_config.py now runs unconditionally and its exclusive create fails closed. opt_in_out runs after s6-svc -O, so a failure there was terminal under errexit.

* fall back to default listen ports when either is invalid or they collide

* keep valid listen values and refuse to start nginx when the ports collide

frigate/util/config.py

@@ -1,8 +1,10 @@
 """configuration utils."""
 
 import asyncio
+import ipaddress
 import logging
 import os
+import re
 import shutil
 from functools import cache
 from typing import Any
@@ -126,6 +128,49 @@ def redact_credential(obj: dict[str, Any], key: str) -> None:
         obj.pop(key, None)
 
 
+LISTEN_HOSTNAME = re.compile(
+    r"[A-Za-z0-9](?:[A-Za-z0-9-]{0,61}[A-Za-z0-9])?"
+    r"(?:\.[A-Za-z0-9](?:[A-Za-z0-9-]{0,61}[A-Za-z0-9])?)*"
+)
+
+
+def parse_listen_address(value: int | str) -> tuple[int | str, int]:
+    """Validate a networking.listen value and rebuild it from its parsed parts.
+
+    Accepts a port, "host:port", "*:port", or "[IPv6]:port", where host is an
+    IPv4 address or an RFC 1123 hostname. nginx receives the rebuilt value
+    verbatim, so anything else raises ValueError.
+
+    Returns:
+        The normalized value (an int for a bare port) and the port
+    """
+    if isinstance(value, bool) or not isinstance(value, int | str):
+        raise ValueError(f"invalid listen value: {value!r}")
+
+    host, sep, port_text = str(value).strip().rpartition(":")
+
+    if not re.fullmatch(r"[0-9]{1,5}", port_text) or not (1 <= int(port_text) <= 65535):
+        raise ValueError(f"invalid listen port: {value!r}")
+
+    port = int(port_text)
+
+    if not sep:
+        return port, port
+
+    if host.startswith("[") and host.endswith("]"):
+        address = ipaddress.IPv6Address(host[1:-1])
+
+        if address.scope_id:
+            raise ValueError(f"listen address must not have a scope ID: {value!r}")
+
+        return f"[{address}]:{port}", port
+
+    if host != "*" and not LISTEN_HOSTNAME.fullmatch(host):
+        raise ValueError(f"invalid listen address: {value!r}")
+
+    return f"{host}:{port}", port
+
+
 def find_config_file() -> str:
     """Return the path of the config file to use.