Run subprocesses as unprivileged user

Dockerfile

@@ -1,8 +1,7 @@
 FROM alpine
 RUN apk add --no-cache bash python3
-RUN adduser -D user
-USER user
-WORKDIR /home/user
-ADD autogolf /home/user/autogolf
-ADD run.py /home/user
+RUN adduser -D -H -u 1337 user
+WORKDIR /root
+ADD autogolf /root/autogolf
+ADD run.py /root
 CMD ["python3", "run.py"]

README.md

@@ -5,5 +5,5 @@ How to run:
 ```
 docker image build --quiet --tag runall-image .
 mkdir output
-docker container run --tty --rm --mount type=bind,src="$(realpath output)",dst=/home/user/output --memory=128m runall-image
+docker container run --tty --rm --mount type=bind,src="$(realpath output)",dst=/root/output --memory=128m runall-image
 ```

autogolf/__init__.py

@@ -2,6 +2,7 @@ from enum import Enum, auto
 from functools import partial
 from itertools import product
 from multiprocessing import Pool
+import os
 from subprocess import DEVNULL, PIPE, Popen, TimeoutExpired
 from time import time
 from typing import List
@@ -17,6 +18,12 @@ class Status(Enum):
     Timeout = auto() # ran for more time than allowed by the timeout value
 
 
+def demote():
+    """Drop root privileges."""
+    os.setgid(1337)
+    os.setuid(1337)
+
+
 def check_pair(script, instr, outstr, timeout) -> Status:
     """
     Check that a Bash script outputs a given string when given a input string.
@@ -29,13 +36,14 @@ def check_pair(script, instr, outstr, timeout) -> Status:
     """
     process = Popen(
         [
-            "/bin/bash", "--restricted", "-c", "--",
+            "/bin/bash", "-c", "--",
             "trap 'kill -9 $(jobs -p) && wait' SIGINT SIGTERM EXIT;\n"
             + script,
         ],
         stdin=PIPE,
         stdout=PIPE,
         stderr=DEVNULL,
+        preexec_fn=demote,
     )
 
     try: