[issue24407] Use after free in PyDict_merge

[paul]

New submission from paul:

# PyDict_Merge:
# 
# 1       for (i = 0, n = DK_SIZE(other->ma_keys); i < n; i++) {
#             ...
# 3           entry = &other->ma_keys->dk_entries[i];
#             ...
# 2               if (insertdict(mp, entry->me_key,
#                                entry->me_hash,
#                                value) != 0)
#                     return -1;
#             ...
#         }
# 
# 1. n is set once 
# 2. it's possible to run a custom __eq__ method from inside the insertdict. 
#    __eq__ clears the "other" dict. "n" variables is now out of date
# 3. out of bounds read
# 
# CRASH:
# ------
#
# * thread #1: tid = 27715, 0x080d1c1d python`insertdict(mp=0xb71d66f4, key=0x61682044, hash=543582496, value=0xb71d6664) + 132 at dictobject.c:819, name = 'python', stop reason = invalid address (fault address: 0x61682050)
#     frame #0: 0x080d1c1d python`insertdict(mp=0xb71d66f4, key=0x61682044, hash=543582496, value=0xb71d6664) + 132 at dictobject.c:819
#    816      if (ep == NULL) {
#    817          return -1;
#    818      }
# -> 819      assert(PyUnicode_CheckExact(key) || mp->ma_keys->dk_lookup == lookdict);
#    820      Py_INCREF(value);
#    821      MAINTAIN_TRACKING(mp, key, value);
#    822      old_value = *value_addr;
#

----------
files: dict_merge.py
messages: 245001
nosy: pkt
priority: normal
severity: normal
status: open
title: Use after free in PyDict_merge
type: crash
versions: Python 3.5
Added file: http://bugs.python.org/file39659/dict_merge.py

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue24407>
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