Files
frigate/docker/main/rootfs/usr/local/bin/safe-sentinel
T
Josh HawkinsandNicolas Mowen 3be59c9c18 Container security hardening (phase 3, breaking) (#24081)
* Run the frigate service as the frigate user

* Run go2rtc as its own restricted user

* Run nginx as the frigate user with writable state in /tmp/nginx

* Disable bandwidth stats gracefully when not running as root

* Hand TensorRT model cache ownership to the runtime user

* Document non-root operation and per-hardware device access

* Create /media/frigate after the ownership sweep

* Assert non-root services, JWT migration, and escape hatch in CI

* only write the sweep sentinel when a media volume is mounted

* tolerate homekit config chown failures in the go2rtc run script

* chown the s6 log pipe so non-root nginx can reopen /dev/stdout

* set HOME to /config for non-root services

* run smoke nginx -t and the write probe as the runtime user

* re-own the nginx shm cache on service restart

* discard stdout for the unprivileged smoke nginx -t

* unwrap hard-wrapped prose in the installation docs

* report progress during the ownership sweep

* document EXTRA_GROUPS as the only device access path for dropped services

* expand the non-root device access docs with diagnosis steps and udev rules

* document network storage ownership and the remaining detector hardware

* skip lost+found during the ownership sweep

* hand /tmp/cache to the runtime user before services start

* make bundled models readable by the runtime user

* reload nginx by signaling the master instead of parsing its config as root

* harden root writes into unprivileged-owned paths

Restrict the sweep sentinel to a mount at or below /media/frigate so a
parent /media mount cannot bless a later-shadowed volume. Rebuild
/tmp/nginx root-owned each start so root's cp and tempio writes cannot
follow a symlink an unprivileged nginx planted in the previous run.

* collapse the duplicated sentinel comment

* add a service-runs-as-root helper for granular root services

* validate FRIGATE_ROOT_SERVICES and fail fast on unknown names

* let services listed in FRIGATE_ROOT_SERVICES skip the privilege drop

* record the root-services mode in the sentinel and sweep small trees each boot

* cache the runtime ids in the ownership helper

* chown recordings, previews, and exports to the runtime user at create

* chown the database files after init

* recommend FRIGATE_ROOT_SERVICES in the bandwidth stats warning

* assert granular root services in CI

* document FRIGATE_ROOT_SERVICES

* own every directory level created for a recording segment

* clear the cached runtime ids when ownership tests finish

* skip missing media paths in the per-boot ownership sweep

* clarify granular root services docs

* clean up

* install acl for device access grants

* grant runtime users access to mapped device nodes at boot

* assert device access grants in CI

* document automatic device access grants

* stop telling users device access needs host side setup

* clarify the non-root docs

* link the migration script to the repo

* group the manual device setup under one section

* harden against symlink attacks

/config is owned by the unprivileged runtime user after the ownership sweep, so root operations on files there could be redirected by a planted symlink.

- go2rtc HomeKit setup: replace the root yq/jq normalization and chown with an O_NOFOLLOW helper (prepare_homekit.py), so a symlink at go2rtc_homekit.yml can't redirect a root write or chown onto another file
- go2rtc binary override: ignore /config/go2rtc whenever the service runs as root, so a planted binary can't exec as root under FRIGATE_ROOT_SERVICES
- sweep sentinel: read and write it through safe-sentinel, which trusts only a root-owned regular file and never follows a symlink, so it can't be forged to skip the migration or symlinked to clobber a root file
- ownership sweep: chown with -execdir so a parent directory swapped for a symlink mid-walk can't redirect the chown out of the volume
- validate inputs: restrict DEVICE_ACL_PATHS to /dev, require nonzero numeric EXTRA_GROUPS, and reject PUID/PGID that collide with the go2rtc ids
- docs: correct the TLS key ownership note to match what actually happens

* tweak docs

* stop the ownership sweep chasing entries other mechanisms own

* keep custom binaries out of root services only under granular root
2026-09-12 07:30:04 -06:00

75 lines
2.1 KiB
Python
Executable File

#!/usr/bin/env python3
"""Read or write the ownership sweep sentinel without following symlinks.
The sentinel lives in /config, which the unprivileged runtime user owns, so it
can be swapped for a symlink. read trusts only a root-owned regular file; write
never follows a symlink or fifo onto another file.
Usage:
safe-sentinel read PATH print content, exit 0 only if root-owned regular file
safe-sentinel write PATH CONTENT write CONTENT to a regular file at PATH
"""
import errno
import os
import stat
import sys
MODE = 0o644
def do_read(path: str) -> int:
try:
fd = os.open(path, os.O_RDONLY | os.O_NOFOLLOW)
except OSError:
return 1
try:
st = os.fstat(fd)
if not stat.S_ISREG(st.st_mode) or st.st_uid != 0:
return 1
sys.stdout.buffer.write(os.read(fd, 4096))
finally:
os.close(fd)
return 0
def do_write(path: str, content: str) -> int:
# O_NONBLOCK so a fifo fails fast (ENXIO) instead of blocking the open.
flags = os.O_WRONLY | os.O_CREAT | os.O_NOFOLLOW | os.O_NONBLOCK
replace = (errno.ELOOP, errno.ENXIO)
try:
fd = os.open(path, flags, MODE)
if not stat.S_ISREG(os.fstat(fd).st_mode):
os.close(fd)
raise OSError(errno.ELOOP, "not a regular file")
except OSError as err:
if err.errno not in replace:
raise
os.unlink(path)
fd = os.open(path, flags | os.O_EXCL, MODE)
try:
os.ftruncate(fd, 0)
os.write(fd, content.encode())
# keep it root-owned so a later sweep that chowned the old sentinel to
# the runtime user can't make the next read reject and re-sweep
os.fchown(fd, 0, 0)
finally:
os.close(fd)
return 0
def main(argv: list[str]) -> int:
if len(argv) == 3 and argv[1] == "read":
return do_read(argv[2])
if len(argv) == 4 and argv[1] == "write":
try:
return do_write(argv[2], argv[3])
except OSError:
return 1
print("usage: safe-sentinel read PATH | write PATH CONTENT", file=sys.stderr)
return 2
if __name__ == "__main__":
sys.exit(main(sys.argv))