Restrict go2rtc ffmpeg and ngrok options without arbitrary exec (#24709)

* restrict go2rtc ffmpeg and ngrok options without arbitrary exec

The GO2RTC_ALLOW_ARBITRARY_EXEC checks only looked at go2rtc.streams, so an admin could save a config with a custom ffmpeg.bin or ngrok.command and run any command as the go2rtc user after a restart. go2rtc builds every ffmpeg: source into a command that starts with ffmpeg.bin, and it runs ngrok.command at startup. A custom template also brought back arbitrary ffmpeg arguments, since a stream can reference any template key with #video=<name>.

config/save and config/set now reject any added or changed key under go2rtc.ffmpeg or go2rtc.ngrok unless arbitrary exec is enabled. Keys already in the saved config are left alone, the same as stream sources. At startup, ffmpeg.bin is always Frigate's ffmpeg and ngrok is dropped unless arbitrary exec is enabled. Templates already in the config file, such as the documented vaapi global, keep working.

* reject ffmpeg paths with spaces, quotes or shell characters

ffmpeg.path was used as-is when absolute, and several ffmpeg commands are built as strings and split on spaces before running. A path like `/bin/sh -c <cmd>;#` ran a shell command instead of ffmpeg in the preview and export processes, and in go2rtc through the birdseye restream exec source. The path is now validated as a version alias or an absolute path of plain characters, so config/save and config/set reject an unsafe value. resolve_ffmpeg_path falls back to the default ffmpeg for one, and the go2rtc startup script prints an error.

docker/main/rootfs/usr/local/go2rtc/create_config.py

@@ -10,13 +10,15 @@ from ruamel.yaml import YAML
 
 sys.path.insert(0, "/opt/frigate")
 from frigate.config.env import substitute_frigate_vars
-from frigate.const import (
-    BIRDSEYE_PIPE,
-    LIBAVFORMAT_VERSION_MAJOR,
-)
+from frigate.const import BIRDSEYE_PIPE
 from frigate.ffmpeg_presets import parse_preset_hardware_acceleration_encode
-from frigate.util.config import find_config_file, resolve_ffmpeg_path
+from frigate.util.config import (
+    find_config_file,
+    is_valid_ffmpeg_path,
+    resolve_ffmpeg_path,
+)
 from frigate.util.services import (
+    apply_go2rtc_ffmpeg_config,
     is_go2rtc_arbitrary_exec_allowed,
     is_restricted_go2rtc_source,
 )
@@ -92,20 +94,17 @@ if go2rtc_config.get("rtsp", {}).get("password") is not None:
 
 # ensure ffmpeg path is set correctly
 path = config.get("ffmpeg", {}).get("path", "default")
+if not is_valid_ffmpeg_path(path):
+    print(
+        "[ERROR] ffmpeg path contains spaces, quotes or shell characters, using the default ffmpeg instead."
+    )
 ffmpeg_path = resolve_ffmpeg_path(path, "ffmpeg")
 
-if go2rtc_config.get("ffmpeg") is None:
-    go2rtc_config["ffmpeg"] = {"bin": ffmpeg_path}
-elif go2rtc_config["ffmpeg"].get("bin") is None:
-    go2rtc_config["ffmpeg"]["bin"] = ffmpeg_path
-
-# need to replace ffmpeg command when using ffmpeg4
-if LIBAVFORMAT_VERSION_MAJOR < 59:
-    rtsp_args = "-fflags nobuffer -flags low_delay -stimeout 10000000 -user_agent go2rtc/ffmpeg -rtsp_transport tcp -i {input}"
-    if go2rtc_config.get("ffmpeg") is None:
-        go2rtc_config["ffmpeg"] = {"rtsp": rtsp_args}
-    elif go2rtc_config["ffmpeg"].get("rtsp") is None:
-        go2rtc_config["ffmpeg"]["rtsp"] = rtsp_args
+for key in apply_go2rtc_ffmpeg_config(go2rtc_config, ffmpeg_path):
+    print(
+        f"[ERROR] go2rtc option '{key}' was ignored because it is disabled by default for security. "
+        f"Set GO2RTC_ALLOW_ARBITRARY_EXEC=true to enable arbitrary exec."
+    )
 
 
 for name in list(go2rtc_config.get("streams", {})):