grp is not thread safe #126316
Description
Crash report
What happened?
It's possible to crash grp in a no-gil build by repeatedly calling functions in threads, it only happens with PYTHON_GIL=0.
from threading import Thread
import grp
for x in range(5000):
alive = [
Thread(target=grp.getgrgid, args=(1,)),
Thread(target=grp.getgrall),
Thread(target=grp.getgrnam, args=('root',)),
]
for obj in alive:
print('START', obj)
obj.start()Backtrace is:
(gdb) bt
#0 __strlen_avx2 ()
at ../sysdeps/x86_64/multiarch/strlen-avx2.S:74
#1 0x00005555557ad3cb in PyUnicode_DecodeFSDefault (
s=s@entry=0x3838323432353a78 <error: Cannot access memory at address 0x3838323432353a78>) at Objects/unicodeobject.c:4058
#2 0x00007ffff7c3f952 in mkgrent (
module=module@entry=0x20000795b80, p=<optimized out>)
at ./Modules/grpmodule.c:83
#3 0x00007ffff7c3fc41 in grp_getgrall_impl (
module=0x20000795b80) at ./Modules/grpmodule.c:291
#4 0x00007ffff7c3fcad in grp_getgrall (
module=<optimized out>, _unused_ignored=<optimized out>)
at ./Modules/clinic/grpmodule.c.h:83
#5 0x00005555556fca83 in cfunction_vectorcall_NOARGS (
func=0x2000079f820, args=<optimized out>,
nargsf=<optimized out>, kwnames=<optimized out>)
at Objects/methodobject.c:495
#6 0x000055555567b4bc in _PyVectorcall_Call (
tstate=tstate@entry=0x555555d2ac70,
func=0x5555556fc8b5 <cfunction_vectorcall_NOARGS>,
callable=callable@entry=0x2000079f820,
tuple=tuple@entry=0x555555c5d1d8 <_PyRuntime+128984>,
kwargs=kwargs@entry=0x2001a0400d0) at Objects/call.c:273
#7 0x000055555567b894 in _PyObject_Call (
tstate=0x555555d2ac70,
callable=callable@entry=0x2000079f820,
args=args@entry=0x555555c5d1d8 <_PyRuntime+128984>,
kwargs=kwargs@entry=0x2001a0400d0) at Objects/call.c:348
#8 0x000055555567b8f1 in PyObject_Call (
callable=callable@entry=0x2000079f820,
args=args@entry=0x555555c5d1d8 <_PyRuntime+128984>,
kwargs=kwargs@entry=0x2001a0400d0) at Objects/call.c:373Found using fusil by @vstinner.
CPython versions tested on:
CPython main branch
Operating systems tested on:
Linux
Output from running 'python -VV' on the command line:
Python 3.14.0a1+ experimental free-threading build (heads/main:d467d9246c, Nov 1 2024, 09:05:56) [GCC 11.4.0]
Linked PRs
- gh-126316: Use critical sections in grp module #126488
- gh-126316: Use mutexes in the grp module #126504
- gh-126316: Use getgrent_r() in grp.getgrall() #126506
- gh-126316: Make grp.getgrall() thread-safe: add a mutex #127055
- [3.13] gh-126316: Make grp.getgrall() thread-safe: add a mutex (#127055) #127104