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# Bug
# ---
# 
# static PyObject*
# unicodedata_normalize(PyObject *self, PyObject *args)
# {
# ...
# if (strcmp(form, "NFKC") == 0) {
# if (is_normalized(self, input, 1, 1)) {
# Py_INCREF(input);
# return input;
# }
# return nfc_nfkc(self, input, 1);
# 
# We need to pass the is_normalized() check (repeated \xa0 char takes care of 
# that). nfc_nfkc calls:
# 
# static PyObject*
# nfd_nfkd(PyObject *self, PyObject *input, int k)
# {
# ...
# Py_ssize_t space, isize;
# ...
# isize = PyUnicode_GET_LENGTH(input);
# /* Overallocate at most 10 characters. */
# space = (isize > 10 ? 10 : isize) + isize;
# osize = space;
# 1 output = PyMem_Malloc(space * sizeof(Py_UCS4));
# 
# 1. if isize=2^30, then space=2^30+10, so space*sizeof(Py_UCS4)=(2^30+10)*4 ==
# 40 (modulo 2^32), so PyMem_Malloc allocates buffer too small to hold the
# result.
# 
# Crash
# -----
# 
# nfd_nfkd (self=<module at remote 0x4056e574>, input='...', k=1) at /home/p/Python-3.4.1/Modules/unicodedata.c:552
# 552 stackptr = 0;
# (gdb) n
# 553 isize = PyUnicode_GET_LENGTH(input);
# (gdb) n
# 555 space = (isize > 10 ? 10 : isize) + isize;
# (gdb) n
# 556 osize = space;
# (gdb) n
# 557 output = PyMem_Malloc(space * sizeof(Py_UCS4));
# (gdb) print space
# 9ドル = 1073741834
# (gdb) print space*4
# 10ドル = 40
# (gdb) c
# Continuing.
# 
# Program received signal SIGSEGV, Segmentation fault.
# 0x40579cbb in nfd_nfkd (self=<module at remote 0x4056e574>, input='', k=1) at /home/p/Python-3.4.1/Modules/unicodedata.c:614
# 614 output[o++] = code;
# 
# OS info
# -------
# 
# % ./python -V
# Python 3.4.1
# 
# % uname -a
# Linux ubuntu 3.8.0-29-generic #42~precise1-Ubuntu SMP Wed Aug 14 15:31:16 UTC 2013 i686 i686 i386 GNU/Linux
 
 
import unicodedata as ud
s="\xa0"*(2**30)
ud.normalize("NFKC", s)

New changeset 84025a32fa2b by Benjamin Peterson in branch '3.3':
fix possible overflow bugs in unicodedata (closes #23367)
https://hg.python.org/cpython/rev/84025a32fa2b
New changeset 90f960e79c9e by Benjamin Peterson in branch '3.4':
merge 3.3 (#23367)
https://hg.python.org/cpython/rev/90f960e79c9e
New changeset 93244000efea by Benjamin Peterson in branch 'default':
merge 3.4 (#23367)
https://hg.python.org/cpython/rev/93244000efea
New changeset 3019effc44f2 by Benjamin Peterson in branch '2.7':
fix possible overflow bugs in unicodedata (closes #23367)
https://hg.python.org/cpython/rev/3019effc44f2 

Actually integer overflow in the line
 space = (isize > 10 ? 10 : isize) + isize;
is not possible.
Integer overflows in PyMem_Malloc were fixed in issue23446.

Why can't (isize > 10 ? 10 : isize) + isize overflow?

Because isize is the size of real PyUnicode object. It's maximal value is PY_SSIZE_T_MAX - sizeof(PyASCIIObject) - 1.

Well, the test doesn't hurt.

True, but that could change and is not true in Python 2. I suppose we
could revert the change and add a static assertion.
On Mon, Mar 2, 2015, at 14:24, Serhiy Storchaka wrote:
> 
> Serhiy Storchaka added the comment:
> 
> Because isize is the size of real PyUnicode object. It's maximal value is
> PY_SSIZE_T_MAX - sizeof(PyASCIIObject) - 1.
> 
> ----------
> 
> _______________________________________
> Python tracker <report@bugs.python.org>
> <http://bugs.python.org/issue23367>
> _______________________________________

The test doesn't hurt.