[New-bugs-announce] [issue22520] integer overflow in computing unicode's object representation

[paul]

New submission from paul:

# unicode_repr(PyObject *unicode)
# {
#     ...
# 1   isize = PyUnicode_GET_LENGTH(unicode);
#     idata = PyUnicode_DATA(unicode);
# 
#     /* Compute length of output, quote characters, and
#        maximum character */
#     osize = 0;
#     ...
#     for (i = 0; i < isize; i++) {
#         Py_UCS4 ch = PyUnicode_READ(ikind, idata, i);
#         switch (ch) {
#         ...
#         default:
#             /* Fast-path ASCII */
#             if (ch < ' ' || ch == 0x7f)
# 2               osize += 4; /* \xHH */ 
#             ...
#         }
#     }
# 
#     ...
# 3   repr = PyUnicode_New(osize, max);
#     ...
#         for (i = 0, o = 1; i < isize; i++) {
#             Py_UCS4 ch = PyUnicode_READ(ikind, idata, i);
#             ...
#                 else {
# 4                   PyUnicode_WRITE(okind, odata, o++, ch);
#                 }
#             }
#         }
#     }
#     /* Closing quote already added at the beginning */
# 5   assert(_PyUnicode_CheckConsistency(repr, 1));
#     return repr;
# }
# 
# 1. isize=2^30+1
# 2. osize=isize*4=4
# 3. allocated buffer is too small
# 4. heap overflow
# 5. this assert will likely fail, since there is a good chance the allocated
#    buffer is just before the huge one, so the huge one will overwrite itself.

----------
files: poc_repr_unicode.py
messages: 227839
nosy: pkt
priority: normal
severity: normal
status: open
title: integer overflow in computing unicode's object representation
type: crash
versions: Python 3.4
Added file: http://bugs.python.org/file36756/poc_repr_unicode.py

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue22520>
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