Segmentation fault when create hashlimit match about python-iptables

[ldx]

I can reproduce the issue with python 3.7. Looking into the stacktrace:

Program received signal SIGSEGV, Segmentation fault.                                                               [53/866]
0x00000000004d1e7a in PyObject_ClearWeakRefs (object=object@entry=0x7ffff68e8eb8) at ../Objects/weakrefobject.c:899        899     ../Objects/weakrefobject.c: No such file or directory.                                                             (gdb) bt                                                                                                                   #0  0x00000000004d1e7a in PyObject_ClearWeakRefs (object=object@entry=0x7ffff68e8eb8) at ../Objects/weakrefobject.c:899    #1  0x0000000000446991 in func_dealloc (op=op@entry=0x7ffff68e8eb8) at ../Objects/funcobject.c:531                         #2  0x0000000000469a59 in _Py_Dealloc (op=0x7ffff68e8eb8) at ../Objects/object.c:1971
#3  0x00000000004e8e16 in call_function (kwnames=0x0, oparg=<optimized out>, pp_stack=<synthetic pointer>)
    at ../Python/ceval.c:4629
#4  _PyEval_EvalFrameDefault (f=0x928a08, throwflag=<optimized out>) at ../Python/ceval.c:3124
#5  0x00000000004dda6a in PyEval_EvalFrameEx (f=f@entry=0x928a08, throwflag=throwflag@entry=0) at ../Python/ceval.c:547
#6  0x00000000004de488 in _PyEval_EvalCodeWithName (_co=0x7ffff7238400, globals=<optimized out>, locals=<optimized out>,
    args=<optimized out>, argcount=argcount@entry=0, kwnames=0x0, kwargs=0x0, kwcount=0, kwstep=2, defs=0x0, defcount=0,
    kwdefs=0x0, closure=0x0, name=0x0, qualname=0x0) at ../Python/ceval.c:3930
#7  0x00000000004de5f2 in PyEval_EvalCodeEx (_co=_co@entry=0x7ffff7238400, globals=globals@entry=0x7ffff72ca148,
    locals=locals@entry=0x7ffff72ca148, args=args@entry=0x0, argcount=argcount@entry=0, kws=kws@entry=0x0, kwcount=0,
    defs=0x0, defcount=0, kwdefs=0x0, closure=0x0) at ../Python/ceval.c:3959
#8  0x00000000004de620 in PyEval_EvalCode (co=co@entry=0x7ffff7238400, globals=globals@entry=0x7ffff72ca148,
    locals=locals@entry=0x7ffff72ca148) at ../Python/ceval.c:524
#9  0x0000000000519a99 in run_mod (mod=mod@entry=0x96ae60, filename=filename@entry=0x7ffff7202a50,
    globals=globals@entry=0x7ffff72ca148, locals=locals@entry=0x7ffff72ca148, flags=flags@entry=0x7fffffffe41c,
    arena=arena@entry=0x7ffff726a4c0) at ../Python/pythonrun.c:1035
#10 0x000000000051c6ab in PyRun_FileExFlags (fp=fp@entry=0x9541b0,
    filename_str=filename_str@entry=0x7ffff72a1190 "issue318.py", start=start@entry=257,
    globals=globals@entry=0x7ffff72ca148, locals=locals@entry=0x7ffff72ca148, closeit=closeit@entry=1,
    flags=0x7fffffffe41c) at ../Python/pythonrun.c:988
#11 0x000000000051ca10 in PyRun_SimpleFileExFlags (fp=fp@entry=0x9541b0, filename=<optimized out>,
    filename@entry=0x7ffff72a1190 "issue318.py", closeit=closeit@entry=1, flags=flags@entry=0x7fffffffe41c)
    at ../Python/pythonrun.c:429
#12 0x000000000051cbdf in PyRun_AnyFileExFlags (fp=fp@entry=0x9541b0, filename=0x7ffff72a1190 "issue318.py",
    closeit=closeit@entry=1, flags=flags@entry=0x7fffffffe41c) at ../Python/pythonrun.c:84
#13 0x0000000000425daa in pymain_run_file (fp=0x9541b0, filename=0x8d98d0 L"issue318.py", p_cf=p_cf@entry=0x7fffffffe41c)
    at ../Modules/main.c:427
#14 0x0000000000425e6a in pymain_run_filename (pymain=pymain@entry=0x7fffffffe440, cf=cf@entry=0x7fffffffe41c)
    at ../Modules/main.c:1627
#15 0x0000000000425f77 in pymain_run_python (pymain=pymain@entry=0x7fffffffe440) at ../Modules/main.c:2877
#16 0x0000000000429571 in pymain_main (pymain=pymain@entry=0x7fffffffe440) at ../Modules/main.c:3038
#17 0x0000000000429654 in _Py_UnixMain (argc=<optimized out>, argv=<optimized out>) at ../Modules/main.c:3073
#18 0x0000000000422e5b in main (argc=<optimized out>, argv=<optimized out>) at ../Programs/python.c:15

Which is weird - it looks more like a python bug than memory corruption or a segfault in the C lib.

I also tried to repro it with python2.7 and python3.9 - both worked fine. So my conclusion is that we're triggering some CPython bug in some way (your experiment to use a set instead of a list also confirms this).

A few things you can try:

• You don't really need the output from set_parameters(), any reason you're using a list comprehension?
• Using a for loop instead of the list also avoids the problem.
• Can you try upgrading your Python install?

[ntcong]

Will try the latest 3.7 and also 3.8 to see if the issue is there. But since 18.04 is widely used (LTS), should we do something about this?

[ldx]

This is the first time this issue is reported, so I'm unsure how common it is. It's also limited what we can do, unfortunately: I was poking around yesterday to see if tweaking gc might make a difference, but it does not seem so.

I'll keep this on my radar in case someone else also bumps into it. Thanks for reporting it!