# xmlparser_setevents(XMLParserObject *self, PyObject* args) # { # ... # /* clear out existing events */ # Py_CLEAR(target->start_event_obj); # 1 Py_CLEAR(target->end_event_obj); # Py_CLEAR(target->start_ns_event_obj); # Py_CLEAR(target->end_ns_event_obj); # # ... # # seqlen = PySequence_Size(events_seq); # for (i = 0; i < seqlen; ++i) { # 3 PyObject *event_name_obj = PySequence_Fast_GET_ITEM(events_seq, i); # ... # # if (event_name == NULL) { # ... # return NULL; # } else if (strcmp(event_name, "start") == 0) { # ... # } else if (strcmp(event_name, "end") == 0) { # Py_INCREF(event_name_obj); # 2 Py_XDECREF(target->end_event_obj); # target->end_event_obj = event_name_obj; # } # ... # } # ... # } # # This one leverages nested _setevents invocations. First invocation sets # target->end_event_obj to S1 instance. On seconds invocation, # target->end_event_obj has refcnt==1, so DECREF at line 1 triggers S1.__del__(). # Destructor invokes _setevents again and sets target->end_event_obj to a S3 # instance (with refcnt==1). After we return from nested call at line 1, # execution continues until it hits an "end" element. At line 2 S3.__del__() is # called and it deallocates "events_seq". This triggers a controlled OOB (we can # call it a use after free too) read at line 3. We can control a PyObject pointer. # # Program received signal SIGSEGV, Segmentation fault. # 0x4068563b in xmlparser_setevents (self=0x40669e4c, args=([], [])) at /home/p/Python-3.4.1/Modules/_elementtree.c:3560 # 3560 PyObject *event_name_obj = PySequence_Fast_GET_ITEM(events_seq, i); # (gdb) print i # $1 = 1337 # (gdb) print *(PyListObject*)events_seq # $2 = {ob_base = {ob_base = {_ob_next = 0x40669df4, _ob_prev = 0x4055f814, ob_refcnt = 3, ob_type = 0x830e1c0 <PyList_Type>}, # ob_size = 0}, ob_item = 0x0, allocated = 0} #

ping

ping

Proposed patch fixes both this issue and issue24104. With the special macro proposed in issue20440 it can be better.

New changeset deda5b5160d2 by Serhiy Storchaka in branch '2.7': Issue #24103: Fixed possible use after free in ElementTree.iterparse(). https://hg.python.org/cpython/rev/deda5b5160d2 New changeset ed62cf0cf256 by Serhiy Storchaka in branch '3.5': Issue #24103: Fixed possible use after free in ElementTree.XMLPullParser. https://hg.python.org/cpython/rev/ed62cf0cf256 New changeset 8a14af800f96 by Serhiy Storchaka in branch 'default': Issue #24103: Fixed possible use after free in ElementTree.XMLPullParser. https://hg.python.org/cpython/rev/8a14af800f96