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crash and refleaks when calling sqlite3.Cursor.__init__() more than once #75951

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orenmn mannequin opened this issue Oct 12, 2017 · 5 comments
Closed

crash and refleaks when calling sqlite3.Cursor.__init__() more than once #75951

orenmn mannequin opened this issue Oct 12, 2017 · 5 comments
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3.7 (EOL) end of life extension-modules C modules in the Modules dir type-crash A hard crash of the interpreter, possibly with a core dump

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@orenmn
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orenmn mannequin commented Oct 12, 2017

BPO 31770
Nosy @vstinner, @orenmn
PRs
  • bpo-31770: Prevent a crash and refleaks when calling sqlite3.Cursor.__init__() more than once #3968
  • [3.6] bpo-31770: Prevent a crash and refleaks when calling sqlite3.Cursor.__init__() more than once (GH-3968) #4301
  • [2.7] bpo-31770: Prevent a crash and refleaks when calling sqlite3.Cursor.__init__() more than once (GH-3968) #4302
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    Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.

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    GitHub fields:

    assignee = None
closed_at = <Date 2017-11-07.00:50:12.995>
created_at = <Date 2017-10-12.08:18:36.858>
labels = ['extension-modules', '3.7', 'type-crash']
title = 'crash and refleaks when calling sqlite3.Cursor.__init__() more than once'
updated_at = <Date 2017-11-07.00:50:12.994>
user = 'https://github.com/orenmn'

    bugs.python.org fields:

    activity = <Date 2017-11-07.00:50:12.994>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2017-11-07.00:50:12.995>
closer = 'vstinner'
components = ['Extension Modules']
creation = <Date 2017-10-12.08:18:36.858>
creator = 'Oren Milman'
dependencies = []
files = []
hgrepos = []
issue_num = 31770
keywords = ['patch']
message_count = 5.0
messages = ['304220', '305692', '305698', '305699', '305700']
nosy_count = 2.0
nosy_names = ['vstinner', 'Oren Milman']
pr_nums = ['3968', '4301', '4302']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'crash'
url = 'https://bugs.python.org/issue31770'
versions = ['Python 2.7', 'Python 3.6', 'Python 3.7']
    @orenmn
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    orenmn mannequin commented Oct 12, 2017

    The following code crashes:
    import sqlite3
    import weakref
    def callback(*args):
    pass

    connection = sqlite3.connect(":memory:")
cursor = sqlite3.Cursor(connection)
ref = weakref.ref(cursor, callback)
cursor.__init__(connection)
del cursor
del ref

    IIUC, this is because pysqlite_cursor_init() (in Modules/_sqlite/cursor.c) sets
    self->in_weakreflist to NULL, and thus corrupts the weakref list. Later,
    clear_weakref() (in Objects/weakrefobject.c) tries to remove a reference from
    the corrupted list, and crashes.

    In every other place (that i saw) where such a weakreflist field is used, it is
    set to NULL right after allocating the object (usually in new()), or just
    not set at all, e.g. in functools.partial.
    So since PyType_GenericNew() is the new() of sqlite3.Cursor, ISTM that the
    simplest solution is to not touch self->in_weakreflist at all in
    pysqlite_cursor_init().

    Also, the following code results in refleaks:
    import sys
    import sqlite3
    connection = sqlite3.connect(":memory:")
    cursor = sqlite3.Cursor(connection)
    refcount_before = sys.gettotalrefcount()
    cursor.__init__(connection)
    print(sys.gettotalrefcount() - refcount_before) # should be close to 0

    This is because pysqlite_cursor_init() doesn't decref before assigning to
    fields of self.

    I would open a PR to fix this soon.

    @orenmn orenmn mannequin added 3.7 (EOL) end of life extension-modules C modules in the Modules dir type-crash A hard crash of the interpreter, possibly with a core dump labels Oct 12, 2017
    @vstinner
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    vstinner commented Nov 7, 2017

    New changeset e56ab74 by Victor Stinner (Oren Milman) in branch 'master':
    bpo-31770: Prevent a crash and refleaks when calling sqlite3.Cursor.__init__() more than once (bpo-3968)
    e56ab74

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    vstinner commented Nov 7, 2017

    New changeset 4b544aa by Victor Stinner (Miss Islington (bot)) in branch '2.7':
    bpo-31770: Prevent a crash and refleaks when calling sqlite3.Cursor.__init__() more than once (GH-3968) (bpo-4302)
    4b544aa

    @vstinner
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    vstinner commented Nov 7, 2017

    New changeset 9684cf6 by Victor Stinner (Miss Islington (bot)) in branch '3.6':
    bpo-31770: Prevent a crash and refleaks when calling sqlite3.Cursor.__init__() more than once (GH-3968) (bpo-4301)
    9684cf6

    @vstinner
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    vstinner commented Nov 7, 2017

    Thank you Oren Milman for your bug report and the bug fix! I merged your PR and backported it Python 3.6 and 2.7.

    @vstinner vstinner closed this as completed Nov 7, 2017
    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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