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import os
import subprocess
import sys
from flask import Flask, render_template, request, jsonify
class Snekbox:
"""Core snekbox functionality, providing safe execution of Python code."""
def __init__(self,
nsjail_binary='nsjail',
python_binary=os.path.dirname(sys.executable) + os.sep + 'python3.6'):
self.nsjail_binary = nsjail_binary
self.python_binary = python_binary
self._nsjail_workaround()
env = {
'PATH': (
'/snekbox/.venv/bin:/usr/local/bin:/usr/local/'
'sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin'
),
'LANG': 'en_US.UTF-8',
'PYTHON_VERSION': '3.6.5',
'PYTHON_PIP_VERSION': '10.0.1',
'PYTHONDONTWRITEBYTECODE': '1',
}
def _nsjail_workaround(self):
dirs = ['/sys/fs/cgroup/pids/NSJAIL', '/sys/fs/cgroup/memory/NSJAIL']
for d in dirs:
if not os.path.exists(d):
os.makedirs(d)
def python3(self, cmd):
"""
Execute Python 3 code in a isolated environment.
The value of ``cmd`` is passed using '-c' to a Python
interpreter that is started in a ``nsjail``, isolating it
from the rest of the system.
Returns the output of executing the command (stdout) if
successful, or a error message if the execution failed.
"""
args = [self.nsjail_binary, '-Mo',
'--rlimit_as', '700',
'--chroot', '/',
'-E', 'LANG=en_US.UTF-8',
'-R/usr', '-R/lib', '-R/lib64',
'--user', 'nobody',
'--group', 'nogroup',
'--time_limit', '2',
'--disable_proc',
'--iface_no_lo',
'--cgroup_pids_max=1',
'--cgroup_mem_max=52428800',
'--quiet', '--',
self.python_binary, '-ISq', '-c', cmd]
try:
proc = subprocess.Popen(args,
stdin=subprocess.PIPE,
stdout=subprocess.PIPE,
stderr=subprocess.PIPE,
env=self.env,
universal_newlines=True)
except ValueError:
return 'ValueError: embedded null byte'
stdout, stderr = proc.communicate()
if proc.returncode == 0:
output = stdout
elif proc.returncode == 1:
try:
filtered = []
for line in stderr.split('\n'):
if not line.startswith('['):
filtered.append(line)
output = '\n'.join(filtered)
except IndexError:
output = ''
elif proc.returncode == 109:
return 'timed out or memory limit exceeded'
elif proc.returncode == 255:
return 'permission denied (root required)'
elif proc.returncode:
return f'unknown error, code: {proc.returncode}'
else:
return 'unknown error, no error code'
return output
snekbox = Snekbox()
# Load app
app = Flask(__name__)
app.use_reloader = False
# Logging
log = app.logger
@app.route('/')
def index():
"""Return a page with a form for inputting code to be executed."""
return render_template('index.html')
@app.route('/result', methods=["POST", "GET"])
def result():
"""Execute code and return a page displaying the results."""
if request.method == "POST":
code = request.form["Code"]
output = snekbox.python3(code)
return render_template('result.html', code=code, result=output)
@app.route('/input', methods=["POST"])
def code_input():
"""Execute code and return the results."""
body = request.get_json()
output = snekbox.python3(body["code"])
return jsonify(input=body["code"], output=output)
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