aboutsummaryrefslogtreecommitdiffstats
path: root/tests/test_nsjail.py
blob: 85bee680b714b35c908ea16dc31ed94d019d6fb9 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
import io
import logging
import shutil
import sys
import tempfile
import unittest
import unittest.mock
from itertools import product
from pathlib import Path
from textwrap import dedent

from snekbox.nsjail import DEFAULT_EXECUTABLE_PATH, NsJail
from snekbox.snekio import FileAttachment
from snekbox.snekio.filesystem import Size


class NsJailTests(unittest.TestCase):
    def setUp(self):
        super().setUp()

        # Specify lower limits for unit tests to complete within time limits
        self.nsjail = NsJail(memfs_instance_size=2 * Size.MiB)
        self.logger = logging.getLogger("snekbox.nsjail")
        self.logger.setLevel(logging.WARNING)

        # Hard-coded because it's non-trivial to parse the mount options.
        self.shm_mount_size = 40 * Size.MiB

    def eval_code(self, code: str):
        return self.nsjail.python3(["-c", code])

    def eval_file(self, code: str, name: str = "test.py", **kwargs):
        file = FileAttachment(name, code.encode())
        return self.nsjail.python3([name], [file], **kwargs)

    def test_print_returns_0(self):
        for fn in (self.eval_code, self.eval_file):
            with self.subTest(fn.__name__):
                result = fn("print('test')")
                self.assertEqual(result.returncode, 0)
                self.assertEqual(result.stdout, "test\n")
                self.assertEqual(result.stderr, None)

    def test_timeout_returns_137(self):
        code = "while True: pass"

        with self.assertLogs(self.logger) as log:
            result = self.eval_file(code)

        self.assertEqual(result.returncode, 137)
        self.assertEqual(result.stdout, "")
        self.assertEqual(result.stderr, None)
        self.assertIn("run time >= time limit", "\n".join(log.output))

    def test_memory_returns_137(self):
        # Add a kilobyte just to be safe.
        code = f"x = ' ' * {self.nsjail.config.cgroup_mem_max + 1000}"

        result = self.eval_file(code)
        self.assertEqual(result.stdout, "")
        self.assertEqual(result.returncode, 137)
        self.assertEqual(result.stderr, None)

    def test_multi_files(self):
        files = [
            FileAttachment("main.py", "import lib; print(lib.x)".encode()),
            FileAttachment("lib.py", "x = 'hello'".encode()),
        ]

        result = self.nsjail.python3(["main.py"], files)
        self.assertEqual(result.returncode, 0)
        self.assertEqual(result.stdout, "hello\n")
        self.assertEqual(result.stderr, None)

    def test_subprocess_resource_unavailable(self):
        max_pids = self.nsjail.config.cgroup_pids_max
        code = dedent(
            f"""
            import subprocess

            # Should fail at n (max PIDs) since the caller python process counts as well
            for _ in range({max_pids}):
                print(subprocess.Popen(
                    [
                        '/snekbin/python/default/bin/python',
                        '-c',
                        'import time; time.sleep(1)'
                    ],
                ).pid)
            """
        ).strip()

        result = self.eval_file(code)
        self.assertEqual(result.returncode, 1)
        self.assertIn("Resource temporarily unavailable", result.stdout)
        # Expect n-1 processes to be opened by the presence of string like "2\n3\n4\n"
        expected = "\n".join(map(str, range(2, max_pids + 1)))
        self.assertIn(expected, result.stdout)
        self.assertEqual(result.stderr, None)

    def test_multiprocess_resource_limits(self):
        code = dedent(
            """
            import time
            from multiprocessing import Process

            def f():
                object = "A" * 40_000_000
                time.sleep(0.5)

            if __name__ == "__main__":
                proc_1 = Process(target=f)
                proc_2 = Process(target=f)

                proc_1.start()
                proc_2.start()

                proc_1.join()
                proc_2.join()

                print(proc_1.exitcode, proc_2.exitcode)
            """
        )

        result = self.eval_file(code)

        exit_codes = result.stdout.strip().split()
        self.assertIn("-9", exit_codes)
        self.assertEqual(result.stderr, None)

    def test_multiprocessing_pool(self):
        # Validates that shm is working as expected
        code = dedent(
            """
            from multiprocessing import Pool

            def f(x):
                return x*x

            if __name__ == "__main__":
                with Pool(2) as p:
                    print(p.map(f, [1, 2, 3]))
        """
        )

        result = self.eval_file(code)

        self.assertEqual(result.stdout, "[1, 4, 9]\n")
        self.assertEqual(result.returncode, 0)

    def test_read_only_file_system(self):
        for path in ("/", "/etc", "/lib", "/lib64", "/snekbox", "/usr"):
            with self.subTest(path=path):
                code = dedent(
                    f"""
                    with open('{path}/hello', 'w') as f:
                        f.write('world')
                    """
                ).strip()

                result = self.eval_file(code)
                self.assertEqual(result.returncode, 1)
                self.assertIn("Read-only file system", result.stdout)
                self.assertEqual(result.stderr, None)

    def test_write(self):
        code = dedent(
            """
            from pathlib import Path
            with open('test.txt', 'w') as f:
                f.write('hello')
            print(Path('test.txt').read_text())
            """
        ).strip()

        result = self.eval_file(code)
        self.assertEqual(result.returncode, 0)
        self.assertEqual(result.stdout, "hello\n")
        self.assertEqual(result.stderr, None)

    def test_write_exceed_space(self):
        code = dedent(
            f"""
            size = {self.nsjail.memfs_instance_size} // 2048
            with open('f.bin', 'wb') as f:
                for i in range(size):
                    f.write(b'1' * 2048)
            """
        ).strip()

        result = self.eval_file(code)
        self.assertEqual(result.returncode, 1)
        self.assertIn("No space left on device", result.stdout)
        self.assertEqual(result.stderr, None)

    def test_write_hidden_exclude(self):
        """Hidden paths should be excluded from output."""
        code = dedent(
            """
            from pathlib import Path

            Path("normal").mkdir()
            Path("normal/a.txt").write_text("a")
            Path("normal/.hidden.txt").write_text("a")
            Path(".hidden").mkdir()
            Path(".hidden/b.txt").write_text("b")
            """
        ).strip()

        result = self.eval_file(code)
        self.assertEqual(result.returncode, 0)
        self.assertEqual(len(result.files), 1)
        self.assertEqual(result.files[0].content, b"a")

    def test_forkbomb_resource_unavailable(self):
        code = dedent(
            """
            import os
            while 1:
                os.fork()
            """
        ).strip()

        result = self.eval_file(code)
        self.assertEqual(result.returncode, 1)
        self.assertIn("Resource temporarily unavailable", result.stdout)
        self.assertEqual(result.stderr, None)

    def test_file_parsing_timeout(self):
        code = dedent(
            """
            import os
            data = "a" * 1024
            size = 32 * 1024 * 1024

            with open("file", "w") as f:
                for _ in range(size // 1024):
                    f.write(data)

            for i in range(100):
                os.symlink("file", f"file{i}")
            """
        ).strip()
        # A value higher than the actual memory needed is used to avoid the limit
        # on total file size being reached before the timeout when reading.
        nsjail = NsJail(memfs_instance_size=128 * Size.MiB, files_timeout=0.1)
        result = nsjail.python3(["-c", code])
        self.assertEqual(result.returncode, None)
        self.assertEqual(
            result.stdout, "TimeoutError: Exceeded time limit while parsing attachments"
        )
        self.assertEqual(result.stderr, None)

    def test_filename_encoding_illegal_chars(self):
        code = dedent(
            r"""
            with open(b"\xC3.txt", "w") as f:
                f.write("test")
            """
        ).strip()
        result = self.eval_file(code)
        self.assertEqual(result.returncode, None)
        self.assertEqual(
            result.stdout, "FileParsingError: invalid bytes in filename while parsing attachments"
        )
        self.assertEqual(result.stderr, None)

    def test_file_parsing_depth_limit(self):
        code = dedent(
            """
            import os

            x = ""
            for _ in range(1000):
                x += "a/"
                os.mkdir(x)

            open(f"{x}test.txt", "w").write("test")
            """
        ).strip()

        nsjail = NsJail(memfs_instance_size=32 * Size.MiB, files_timeout=5)
        result = nsjail.python3(["-c", code])
        self.assertEqual(result.returncode, None)
        self.assertEqual(
            result.stdout,
            "FileParsingError: Exceeded directory depth limit while parsing attachments",
        )
        self.assertEqual(result.stderr, None)

    def test_file_parsing_size_limit_sparse_files(self):
        tmpfs_size = 8 * Size.MiB
        code = dedent(
            f"""
            import os
            with open("test.txt", "w") as f:
                os.truncate(f.fileno(), {tmpfs_size // 2 + 1})

            with open("test2.txt", "w") as f:
                os.truncate(f.fileno(), {tmpfs_size // 2 + 1})
            """
        )
        nsjail = NsJail(memfs_instance_size=tmpfs_size, files_timeout=5)
        result = nsjail.python3(["-c", code])
        self.assertEqual(result.returncode, 0)
        self.assertEqual(len(result.files), 1)

    def test_file_parsing_size_limit_sparse_files_large(self):
        tmpfs_size = 8 * Size.MiB
        code = dedent(
            f"""
            import os
            with open("test.txt", "w") as f:
                # Use a very large value to ensure the test fails if the
                # file is read even if would have been discarded later.
                os.truncate(f.fileno(), {1024 * Size.TiB})
            """
        )
        nsjail = NsJail(memfs_instance_size=tmpfs_size, files_timeout=5)
        result = nsjail.python3(["-c", code])
        self.assertEqual(result.returncode, 0)
        self.assertEqual(len(result.files), 0)

    def test_file_parsing_size_limit_symlinks(self):
        tmpfs_size = 8 * Size.MiB
        code = dedent(
            f"""
            import os
            data = "a" * 1024
            size = {tmpfs_size // 8}

            with open("file", "w") as f:
                for _ in range(size // 1024):
                    f.write(data)

            for i in range(20):
                os.symlink("file", f"file{{i}}")
            """
        )
        nsjail = NsJail(memfs_instance_size=tmpfs_size, files_timeout=5)
        result = nsjail.python3(["-c", code])
        self.assertEqual(result.returncode, 0)
        self.assertEqual(len(result.files), 8)

    def test_file_write_error(self):
        """Test errors during file write."""
        result = self.nsjail.python3(
            [""],
            [
                FileAttachment("dir/test.txt", b"abc"),
                FileAttachment("dir", b"xyz"),
            ],
        )

        self.assertEqual(result.stdout, "IsADirectoryError: Failed to create file 'dir'.")
        self.assertEqual(result.stderr, None)
        self.assertEqual(result.returncode, None)

    def test_sigsegv_returns_139(self):  # In honour of Juan.
        code = dedent(
            """
            import ctypes
            ctypes.string_at(0)
            """
        ).strip()

        result = self.eval_file(code)
        self.assertEqual(result.returncode, 139)
        self.assertEqual(result.stdout, "")
        self.assertEqual(result.stderr, None)

    def test_null_byte_value_error(self):
        # This error only occurs with `-c` mode
        result = self.eval_code("\0")
        self.assertEqual(result.returncode, None)
        self.assertEqual(result.stdout, "ValueError: embedded null byte")
        self.assertEqual(result.stderr, None)

    def test_print_bad_unicode_encode_error(self):
        result = self.eval_file("print(chr(56550))")
        self.assertEqual(result.returncode, 1)
        self.assertIn("UnicodeEncodeError", result.stdout)
        self.assertEqual(result.stderr, None)

    def test_unicode_env_erase_escape_fails(self):
        result = self.eval_file(
            dedent(
                """
                import os
                import sys
                os.unsetenv('PYTHONIOENCODING')
                os.execl(sys.executable, 'python', '-c', 'print(chr(56550))')
                """
            ).strip()
        )
        self.assertEqual(result.returncode, None)
        self.assertEqual(result.stdout, "UnicodeDecodeError: invalid Unicode in output pipe")
        self.assertEqual(result.stderr, None)

    @unittest.mock.patch("snekbox.nsjail.DEBUG", new=False)
    def test_log_parser(self):
        log_lines = (
            "[D][2019-06-22T20:07:00+0000][16] void foo::bar()():100 This is a debug message.",
            "[I][2019-06-22T20:07:48+0000] pid=20 ([STANDALONE MODE]) "
            "exited with status: 2, (PIDs left: 0)",
            "[W][2019-06-22T20:06:04+0000][14] void cmdline::logParams(nsjconf_t*)():250 "
            "Process will be UID/EUID=0 in the global user namespace, and will have user "
            "root-level access to files",
            "[W][2019-06-22T20:07:00+0000][16] void foo::bar()():100 This is a warning!",
            "[E][2019-06-22T20:07:00+0000][16] bool "
            "cmdline::setupArgv(nsjconf_t*, int, char**, int)():316 No command-line provided",
            "[F][2019-06-22T20:07:00+0000][16] int main(int, char**)():204 "
            "Couldn't parse cmdline options",
            "Invalid Line",
        )

        with self.assertLogs(self.logger, logging.DEBUG) as log:
            self.nsjail._parse_log(log_lines)

        self.assertIn("DEBUG:snekbox.nsjail:This is a debug message.", log.output)
        self.assertIn("ERROR:snekbox.nsjail:Couldn't parse cmdline options", log.output)
        self.assertIn("ERROR:snekbox.nsjail:No command-line provided", log.output)
        self.assertIn("WARNING:snekbox.nsjail:Failed to parse log line 'Invalid Line'", log.output)
        self.assertIn("WARNING:snekbox.nsjail:This is a warning!", log.output)
        self.assertIn(
            "INFO:snekbox.nsjail:pid=20 ([STANDALONE MODE]) exited with status: 2, (PIDs left: 0)",
            log.output,
        )

    def test_tmp_not_mounted(self):
        code = dedent(
            """
            with open('/tmp/test', 'wb') as file:
                file.write(bytes([255]))
        """
        ).strip()

        result = self.eval_file(code)
        self.assertEqual(result.returncode, 1)
        self.assertIn("No such file or directory", result.stdout)
        self.assertEqual(result.stderr, None)

    def test_multiprocessing_shared_memory(self):
        cases = (
            (self.shm_mount_size, self.shm_mount_size, 0),
            # Even if the shared memory object is larger than the mount,
            # writing data within the size of the mount should succeed.
            (self.shm_mount_size + 1, self.shm_mount_size, 0),
            (self.shm_mount_size + 1, self.shm_mount_size + 1, 135),
        )

        for shm_size, buffer_size, return_code in cases:
            with self.subTest(shm_size=shm_size, buffer_size=buffer_size):
                # Need enough memory for buffer and bytearray plus some overhead.
                mem_max = (buffer_size * 2) + (400 * Size.MiB)
                code = dedent(
                    f"""
                    from multiprocessing.shared_memory import SharedMemory

                    shm = SharedMemory(create=True, size={shm_size})
                    shm.buf[:{buffer_size}] = bytearray([1] * {buffer_size})
                    shm.close()
                    shm.unlink()
                """
                ).strip()

                result = self.eval_file(code, nsjail_args=("--cgroup_mem_max", str(mem_max)))

                self.assertEqual(result.returncode, return_code)
                self.assertEqual(result.stdout, "")
                self.assertEqual(result.stderr, None)

    def test_multiprocessing_shared_memory_mmap_limited(self):
        """The mmap call should be OOM trying to map a large & sparse shared memory object."""
        code = dedent(
            f"""
            from multiprocessing.shared_memory import SharedMemory

            SharedMemory(create=True, size={self.nsjail.config.cgroup_mem_max + Size.GiB})
        """
        ).strip()

        result = self.eval_file(code)
        self.assertEqual(result.returncode, 1)
        self.assertIn("[Errno 12] Cannot allocate memory", result.stdout)
        self.assertEqual(result.stderr, None)

    def test_numpy_import(self):
        result = self.eval_file("import numpy")
        self.assertEqual(result.returncode, 0)
        self.assertEqual(result.stdout, "")
        self.assertEqual(result.stderr, None)

    def test_output_order(self):
        stdout_msg = "greetings from stdout!"
        stderr_msg = "hello from stderr!"
        code = dedent(
            f"""
            print({stdout_msg!r})
            raise ValueError({stderr_msg!r})
            """
        ).strip()

        result = self.eval_file(code)
        self.assertLess(
            result.stdout.find(stdout_msg),
            result.stdout.find(stderr_msg),
            msg="stdout does not come before stderr",
        )
        self.assertEqual(result.stderr, None)

    def test_stdout_flood_results_in_graceful_sigterm(self):
        code = "while True: print('abcdefghij')"

        result = self.eval_file(code)
        self.assertEqual(result.returncode, 143)

    def test_large_output_is_truncated(self):
        chunk = "a" * self.nsjail.read_chunk_size
        expected_chunks = self.nsjail.max_output_size // sys.getsizeof(chunk) + 1

        nsjail_subprocess = unittest.mock.MagicMock()

        # Go 10 chunks over to make sure we exceed the limit
        nsjail_subprocess.stdout = io.StringIO((expected_chunks + 10) * chunk)
        nsjail_subprocess.poll.return_value = None

        output = self.nsjail._consume_stdout(nsjail_subprocess)
        self.assertEqual(output, chunk * expected_chunks)

    def test_nsjail_args(self):
        args = ["foo", "bar"]
        result = self.nsjail.python3((), nsjail_args=args)

        end = result.args.index("--")
        self.assertEqual(result.args[end - len(args) : end], args)

    def test_py_args(self):
        cases = [
            # Normal args
            (["-c", "print('hello')"], ["-c", "print('hello')"]),
            # Leading empty strings should be removed
            (["", "-m", "timeit"], ["-m", "timeit"]),
            (["", "", "-m", "timeit"], ["-m", "timeit"]),
            (["", "", "", "-m", "timeit"], ["-m", "timeit"]),
            # Non-leading empty strings should be preserved
            (["-m", "timeit", ""], ["-m", "timeit", ""]),
        ]

        for args, expected in cases:
            with self.subTest(args=args):
                result = self.nsjail.python3(py_args=args)
                idx = result.args.index(DEFAULT_EXECUTABLE_PATH)
                self.assertEqual(result.args[idx + 1 :], expected)
                self.assertEqual(result.returncode, 0)


class NsJailArgsTests(unittest.TestCase):
    def setUp(self):
        self._temp_dir = tempfile.TemporaryDirectory()
        self.addClassCleanup(self._temp_dir.cleanup)

        self.nsjail_path = shutil.copy2("/usr/sbin/nsjail", self._temp_dir.name)
        self.config_path = shutil.copy2("./config/snekbox.cfg", self._temp_dir.name)
        self.max_output_size = 1_234_567
        self.read_chunk_size = 12_345

        self.nsjail = NsJail(
            self.nsjail_path, self.config_path, self.max_output_size, self.read_chunk_size
        )

        logging.getLogger("snekbox.nsjail").setLevel(logging.WARNING)

    def test_nsjail_path(self):
        result = self.nsjail.python3("")

        self.assertEqual(result.args[0], self.nsjail_path)

    def test_config_path(self):
        result = self.nsjail.python3("")

        i = result.args.index("--config") + 1
        self.assertEqual(result.args[i], self.config_path)

    def test_init_args(self):
        self.assertEqual(self.nsjail.nsjail_path, self.nsjail_path)
        self.assertEqual(self.nsjail.config_path, self.config_path)
        self.assertEqual(self.nsjail.max_output_size, self.max_output_size)
        self.assertEqual(self.nsjail.read_chunk_size, self.read_chunk_size)


class NsJailCgroupTests(unittest.TestCase):
    # This should still pass for v2, even if this test isn't relevant.
    def test_cgroupv1(self):
        logging.getLogger("snekbox.nsjail").setLevel(logging.ERROR)
        logging.getLogger("snekbox.limits.swap").setLevel(logging.ERROR)

        config_base = dedent(
            """
            mode: ONCE
            mount {
                src: "/"
                dst: "/"
                is_bind: true
                rw: false
            }
            exec_bin {
                path: "/bin/su"
                arg: ""
            }
            """
        ).strip()

        cases = (
            (
                (
                    "cgroup_mem_max: 52428800",
                    # memory.limit_in_bytes must be set before memory.memsw.limit_in_bytes
                    "cgroup_mem_max: 52428800\ncgroup_mem_memsw_max: 104857600",
                    "cgroup_mem_max: 52428800\ncgroup_mem_swap_max: 52428800",
                ),
                "cgroup_mem_mount: '/sys/fs/cgroup/memory'",
                "cgroup_mem_parent: 'NSJAILTEST1'",
            ),
            (
                ("cgroup_pids_max: 20",),
                "cgroup_pids_mount: '/sys/fs/cgroup/pids'",
                "cgroup_pids_parent: 'NSJAILTEST2'",
            ),
            (
                ("cgroup_net_cls_classid: 1048577",),
                "cgroup_net_cls_mount: '/sys/fs/cgroup/net_cls'",
                "cgroup_net_cls_parent: 'NSJAILTEST3'",
            ),
            (
                ("cgroup_cpu_ms_per_sec: 800",),
                "cgroup_cpu_mount: '/sys/fs/cgroup/cpu'",
                "cgroup_cpu_parent: 'NSJAILTEST4'",
            ),
        )

        # protobuf doesn't parse correctly when NamedTemporaryFile is used directly.
        with tempfile.TemporaryDirectory() as directory:
            for values, mount, parent in cases:
                for lines in product(values, (mount, ""), (parent, "")):
                    with self.subTest(config=lines):
                        config_path = str(Path(directory, "config.cfg"))
                        with open(config_path, "w", encoding="utf8") as f:
                            f.write("\n".join(lines + (config_base,)))

                        nsjail = NsJail(config_path=config_path)

                        result = nsjail.python3("")

                        self.assertNotEqual(result.returncode, 255)