Repository navigation
subprocess module does not check WIFSTOPPED on SIGCHLD #73521
Description
Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.
Show more details
GitHub fields:
assignee = 'https://github.com/gpshead'
closed_at = <Date 2017-05-24.01:36:09.178>
created_at = <Date 2017-01-20.20:48:08.437>
labels = ['type-bug', 'library']
title = 'subprocess module does not check WIFSTOPPED on SIGCHLD'
updated_at = <Date 2017-06-26.22:00:53.909>
user = 'https://bugs.python.org/ZachRiggle'bugs.python.org fields:
activity = <Date 2017-06-26.22:00:53.909>
actor = 'vstinner'
assignee = 'gregory.p.smith'
closed = True
closed_date = <Date 2017-05-24.01:36:09.178>
closer = 'gregory.p.smith'
components = ['Library (Lib)']
creation = <Date 2017-01-20.20:48:08.437>
creator = 'Zach Riggle'
dependencies = []
files = ['46363', '46385', '46386']
hgrepos = []
issue_num = 29335
keywords = ['patch']
message_count = 17.0
messages = ['285921', '285996', '286023', '286031', '286036', '286046', '286050', '286057', '286099', '286100', '286102', '294251', '294308', '296907', '296910', '296957', '296959']
nosy_count = 5.0
nosy_names = ['gregory.p.smith', 'vstinner', 'ned.deily', 'python-dev', 'Zach Riggle']
pr_nums = ['1757', '2405', '2410', '2411']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue29335'
versions = ['Python 2.7', 'Python 3.5', 'Python 3.6']
Activity
ZachRiggle commentedon Jan 20, 2017
The attached script hits some "This should never happen" code in the subprocess module.
These lines here:
https://github.com/python/cpython/blob/2.7/Lib/subprocess.py#L1036-L1038
The root cause is a lack of checking WIFSTOPPED and WSTOPSIG in the handler.
When a process elects into being ptraced via PTRACE_TRACEME, it is stopped on the SIGSEGV instead of terminating, allowing the user to attach a debugger before the kernel destroys the process.
This bug makes it impossible to wait on any process which crashes, which is set up to wait for a debugger.
ZachRiggle commentedon Jan 22, 2017
To further clarify the report:
When the attached proof-of-concept is executed, a RuntimeException is raised, which has a comment "Should never happen".
The issue isn't due to SIGCHLD, but rather following a waitpid() call. The code attempts to suss the exit code / reason for waitpid() returning, but does not check for WIFSTOPPED in its handler.
[-]Python 2.7 subprocess module does not check WIFSTOPPED on SIGCHLD[/-][+]subprocess module does not check WIFSTOPPED on SIGCHLD[/+]gpshead commentedon Jan 22, 2017
The attached patch should fix it.
I want to incorporate a bug.py like regression test into test_subprocess.py.
gpshead commentedon Jan 22, 2017
test added.
python-dev commentedon Jan 23, 2017
New changeset 269296b2a047 by Gregory P. Smith in branch '3.5':
Issue bpo-29335: Fix subprocess.Popen.wait() when the child process has
https://hg.python.org/cpython/rev/269296b2a047
New changeset ed5255a61648 by Gregory P. Smith in branch '3.6':
Issue bpo-29335: Fix subprocess.Popen.wait() when the child process has
https://hg.python.org/cpython/rev/ed5255a61648
New changeset 4f5e7d018195 by Gregory P. Smith in branch 'default':
Issue bpo-29335: Fix subprocess.Popen.wait() when the child process has
https://hg.python.org/cpython/rev/4f5e7d018195
ned-deily commentedon Jan 23, 2017
Among other buildbot failures:
http://buildbot.python.org/all/builders/x86%20Tiger%203.6/builds/142/steps/test/logs/stdio
======================================================================
ERROR: test_child_terminated_in_stopped_state (test.test_subprocess.POSIXProcessTestCase)
Test wait() behavior when waitpid returns WIFSTOPPED; bpo-29335.
----------------------------------------------------------------------
Ran 260 tests in 102.297s
Also, http://buildbot.python.org/all/builders/x86%20Ubuntu%20Shared%203.x/builds/240/steps/test/logs/stdio
python-dev commentedon Jan 23, 2017
New changeset 8e3d412f8e89 by Gregory P. Smith in branch '2.7':
Issue bpo-29335: Fix subprocess.Popen.wait() when the child process has
https://hg.python.org/cpython/rev/8e3d412f8e89
gpshead commentedon Jan 23, 2017
thanks Ned, I was awaiting interesting buildbot results. :)
fixed in 2.7 and 3.5 onwards. thanks for the report Zach.
not closing until I also apply the fix to the subprocess32 backport.
ZachRiggle commentedon Jan 23, 2017
Of note, there's no need to actually cause a SIGSEGV to generate the signal.
The tests might be more clear to replace:
with
vstinner commentedon Jan 23, 2017
If you want crashes, look at the portable faulthandler._sigsegv() :-)
ZachRiggle commentedon Jan 23, 2017
Neat, though that's not in the standard library.
The current logic for getting a handle to libc could also be simplified via ctypes.util.find_library (https://docs.python.org/3/library/ctypes.html#finding-shared-libraries).
Darwin:
>>> import ctypes.util >>> ctypes.util.find_library('c') '/usr/lib/libc.dylib' Linux: >>> import ctypes.util >>> ctypes.util.find_library('c') 'libc.so.6'gpshead commentedon May 23, 2017
New changeset 56bc3b7 by Gregory P. Smith in branch 'master':
bpo-29335 - apply suggested test_subprocess simplifications from haypo and Zach: (bpo-1757)
56bc3b7
gpshead commentedon May 24, 2017
Fixed applied to subprocess32 in google/python-subprocess32@0f1958e
vstinner commentedon Jun 26, 2017
New changeset cdee3f1 by Victor Stinner in branch 'master':
bpo-30764: test_subprocess uses SuppressCrashReport (bpo-2405)
cdee3f1
vstinner commentedon Jun 26, 2017
New changeset 849b062 by Victor Stinner in branch '3.5':
bpo-30764: test_subprocess uses SuppressCrashReport (bpo-2405) (bpo-2411)
849b062
vstinner commentedon Jun 26, 2017
New changeset 9ad50d9 by Victor Stinner in branch '3.6':
bpo-30764: test_subprocess uses SuppressCrashReport (bpo-2405) (bpo-2410)
9ad50d9
vstinner commentedon Jun 26, 2017
New changeset 2097b9e by Victor Stinner in branch '2.7':
[2.7] bpo-30764: test_subprocess uses SuppressCrashReport (bpo-2405) (bpo-2412)
2097b9e