chain.__setstate__ Type Confusion

[JohnLeitch]

BPO	28322
Nosy	@rhettinger, @serhiy-storchaka
PRs	[Do Not Merge] Convert Misc/NEWS so that it is managed by towncrier #552
Files	itertools.patch: Patch Py35_itertools.py: Repro file itertools_setstate.patch

^{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 = 'https://github.com/serhiy-storchaka'
closed_at = <Date 2016-10-02.06:21:44.613>
created_at = <Date 2016-10-01.06:27:48.227>
labels = ['3.7', 'library', 'type-crash']
title = 'chain.__setstate__ Type Confusion'
updated_at = <Date 2017-03-31.16:36:22.966>
user = 'https://bugs.python.org/JohnLeitch'

bugs.python.org fields:

activity = <Date 2017-03-31.16:36:22.966>
actor = 'dstufft'
assignee = 'serhiy.storchaka'
closed = True
closed_date = <Date 2016-10-02.06:21:44.613>
closer = 'serhiy.storchaka'
components = ['Library (Lib)']
creation = <Date 2016-10-01.06:27:48.227>
creator = 'JohnLeitch'
dependencies = []
files = ['44899', '44900', '44905']
hgrepos = []
issue_num = 28322
keywords = ['patch']
message_count = 5.0
messages = ['277799', '277804', '277848', '277855', '277856']
nosy_count = 4.0
nosy_names = ['rhettinger', 'python-dev', 'serhiy.storchaka', 'JohnLeitch']
pr_nums = ['552']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'crash'
url = 'https://bugs.python.org/issue28322'
versions = ['Python 3.5', 'Python 3.6', 'Python 3.7']

[JohnLeitch]

Python 3.5.2 suffers from a type confusion vulnerability in the chain.__setstate__ method of the itertools module. The issue exists due to lack of argument validation in the chain_setstate() function:

static PyObject *
chain_setstate(chainobject *lz, PyObject *state)
{
    PyObject *source, *active=NULL;

if (! PyArg_ParseTuple(state, "O|O", &source, &active))
    return NULL;

    Py_INCREF(source);
    Py_XSETREF(lz->source, source);
    Py_XINCREF(active);
    Py_XSETREF(lz->active, active);
    Py_RETURN_NONE;
}

After parsing the argument tuple, source and active are set without validating that they are iterator objects. This causes issues elsewhere, where the values are passed PyIter_Next:

static PyObject *
chain_next(chainobject *lz)
{
    PyObject *item;

if (lz->source == NULL)
    return NULL;                                    /* already stopped */

    if (lz->active == NULL) {
        PyObject *iterable = PyIter_Next(lz->source);
        if (iterable == NULL) {
            Py_CLEAR(lz->source);
            return NULL;                                /* no more input sources */
        }
        lz->active = PyObject_GetIter(iterable);
        Py_DECREF(iterable);
        if (lz->active == NULL) {
            Py_CLEAR(lz->source);
            return NULL;                                /* input not iterable */
        }
    }
    item = PyIter_Next(lz->active);
    if (item != NULL)
        return item;
    if (PyErr_Occurred()) {
        if (PyErr_ExceptionMatches(PyExc_StopIteration))
            PyErr_Clear();
        else
            return NULL;                                /* input raised an exception */
    }
    Py_CLEAR(lz->active);
    return chain_next(lz);                      /* recurse and use next active */
}

In some cases, this can lead to a DEP access violation. It might be possible to exploit this to achieve code execution.

(4074.198c): Access violation - code c0000005 (first chance)
First chance exceptions are reported before any exception handling.
This exception may be expected and handled.
eax=00000000 ebx=0132fa10 ecx=5b547028 edx=00000002 esi=0132fa10 edi=5b37b3e0
eip=00000000 esp=009ef940 ebp=009ef94c iopl=0 nv up ei pl zr na pe nc
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010246
00000000 ?? ???
0:000> k6
ChildEBP RetAddr
WARNING: Frame IP not in any known module. Following frames may be wrong.
009ef93c 5b329ac0 0x0
009ef94c 5b2cb321 python35!PyIter_Next+0x10 [c:\build\cpython\objects\abstract.c @ 2778]
009ef960 5b37b42e python35!chain_next+0x21 [c:\build\cpython\modules\itertoolsmodule.c @ 1846]
009ef970 5b33fedd python35!wrap_next+0x4e [c:\build\cpython\objects\typeobject.c @ 5470]
009ef990 5b328b9d python35!wrapper_call+0x7d [c:\build\cpython\objects\descrobject.c @ 1195]
009ef9ac 5b3c463c python35!PyObject_Call+0x6d [c:\build\cpython\objects\abstract.c @ 2167]

To fix this issue, it is recommended that chain_setstate() be updated to validate its arguments. A proposed patch has been attached.

static PyObject *
chain_setstate(chainobject *lz, PyObject *state)
{
    PyObject *source, *active=NULL;

if (! PyArg_ParseTuple(state, "O|O", &source, &active))
    return NULL;

    if (!PyIter_Check(source) || (active != NULL && !PyIter_Check(active))) {
        PyErr_SetString(PyExc_ValueError, "Arguments must be iterators.");
        return NULL;
    }

    Py_INCREF(source);
    Py_XSETREF(lz->source, source);
    Py_XINCREF(active);
    Py_XSETREF(lz->active, active);
    Py_RETURN_NONE;
}

[serhiy-storchaka]

There is similar issue with itertools.cycle(). And leaking SystemError to user code should be considered as a bug.

Proposed patch fixes these issues.

[rhettinger]

The patch looks reasonable.

[python-dev]

New changeset 258ebc539b2e by Serhiy Storchaka in branch '3.5':
Issue bpo-28322: Fixed possible crashes when unpickle itertools objects from
https://hg.python.org/cpython/rev/258ebc539b2e

New changeset c4937d066a8e by Serhiy Storchaka in branch '3.6':
Issue bpo-28322: Fixed possible crashes when unpickle itertools objects from
https://hg.python.org/cpython/rev/c4937d066a8e

New changeset cb0755aa9f3d by Serhiy Storchaka in branch 'default':
Issue bpo-28322: Fixed possible crashes when unpickle itertools objects from
https://hg.python.org/cpython/rev/cb0755aa9f3d

[serhiy-storchaka]

Thank you for your contribution John.

cycle.__setstate__() was fixed in a4d5ef7fdec3 in 3.6, but the fix was not backported to 3.5. There is no pickle support in 2.7.