[issue24427] subclass of multiprocessing Connection segfault upon attribute acces

[Irit Katriel]

Change by Irit Katriel :


--
resolution:  -> out of date
stage: needs patch -> resolved
status: open -> closed

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[issue24427] subclass of multiprocessing Connection segfault upon attribute acces

[Irit Katriel]

Irit Katriel  added the comment:

The fact that a bug was discovered a long time ago doesn't say anything about 
its relevance (hence old issues are not automatically closed). 

In this case I believe the bug is no longer relevant and therefore the issue 
can be closed.

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[issue24427] subclass of multiprocessing Connection segfault upon attribute acces

[William Pickard]

William Pickard  added the comment:

You did just necro a 5 year old bug report...

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nosy: +WildCard65

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[issue24427] subclass of multiprocessing Connection segfault upon attribute acces

[William Pickard]

Change by William Pickard :


--
nosy:  -WildCard65

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[issue24427] subclass of multiprocessing Connection segfault upon attribute acces

[Irit Katriel]

Irit Katriel  added the comment:

I think this issue is out of date. 

1. I replaced the import statement in the script by "from 
multiprocessing.connection import Connection" and it gave "AttributeError: 
'Crash' object has no attribute 'bar'" rather than a segfault. 

2.  I can't find "ConnectionObject" in the current codebase.

--
components: +Interpreter Core
nosy: +iritkatriel
type:  -> crash

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[issue24427] subclass of multiprocessing Connection segfault upon attribute acces

[Davin Potts]

Changes by Davin Potts :


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nosy: +davin

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[issue24427] subclass of multiprocessing Connection segfault upon attribute acces

[Rose Ames]

Rose Ames added the comment:

Reproduced - the crash exists and the patch fixes it.

--
nosy: +superluser
versions: +Python 2.7

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[issue24427] subclass of multiprocessing Connection segfault upon attribute acces

[Charles-François Natali]

New submission from Charles-François Natali:

The following segfaults in _PyObject_GenericGetAttrWithDict:


from socket import socketpair
from _multiprocessing import Connection


class Crash(Connection):
pass

_, w = socketpair()

Crash(w.fileno()).bar


#0  _PyObject_GenericGetAttrWithDict (dict=0xa6b001c, name=0xb7281020, 
obj=0x8c12478) at Objects/object.c:1427
#1  PyObject_GenericGetAttr (obj=0x8c12478, name=0xb7281020) at 
Objects/object.c:1461

(gdb) p *(obj + obj-ob_type-tp_dictoffset)
$8 = {ob_refcnt = 0, ob_type = 0x0}

It's probably not specific to this example, but I'm not familiar enough with 
object construction/descriptors to know what's going on here.

Note that the following atch fixes the crash, but I don't know why:

--- a/Modules/_multiprocessing/connection.h Wed Apr 15 19:30:38 2015 +0100
+++ b/Modules/_multiprocessing/connection.h Wed Jun 10 20:25:15 2015 +0100
@@ -58,7 +58,7 @@
 return NULL;
 }
 
-self = PyObject_New(ConnectionObject, type);
+self = type-tp_alloc(type, 0);
 if (self == NULL)
 return NULL;
 
@@ -86,7 +86,7 @@
 CLOSE(self-handle);
 Py_END_ALLOW_THREADS
 }
-PyObject_Del(self);
+Py_TYPE(self)-tp_free((PyObject*)self);
 }
 
 /*


--
messages: 245140
nosy: neologix, pitrou
priority: normal
severity: normal
stage: needs patch
status: open
title: subclass of multiprocessing Connection segfault upon attribute acces

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