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[3.7] bpo-35552: Fix reading past the end in PyUnicode_FromFormat() and PyBytes_FromFormat(). (GH-11276) #11533

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Merged
miss-islington merged 1 commit into from
Jan 12, 2019
Merged

[3.7] bpo-35552: Fix reading past the end in PyUnicode_FromFormat() and PyBytes_FromFormat(). (GH-11276) #11533

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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2018-12-21-13-29-30.bpo-35552.1DzQQc.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Format characters ``%s`` and ``%V`` in :c:func:`PyUnicode_FromFormat` and
``%s`` in :c:func:`PyBytes_FromFormat` no longer read memory past the
limit if *precision* is specified.
12 changes: 9 additions & 3 deletions Objects/bytesobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -311,9 +311,15 @@ PyBytes_FromFormatV(const char *format, va_list vargs)
Py_ssize_t i;

p = va_arg(vargs, const char*);
i = strlen(p);
if (prec > 0 && i > prec)
i = prec;
if (prec <= 0) {
i = strlen(p);
}
else {
i = 0;
while (i < prec && p[i]) {
i++;
}
}
s = _PyBytesWriter_WriteBytes(&writer, s, p, i);
if (s == NULL)
goto error;
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12 changes: 9 additions & 3 deletions Objects/unicodeobject.c
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Expand Up @@ -2579,9 +2579,15 @@ unicode_fromformat_write_cstr(_PyUnicodeWriter *writer, const char *str,
PyObject *unicode;
int res;

length = strlen(str);
if (precision != -1)
length = Py_MIN(length, precision);
if (precision == -1) {
length = strlen(str);
}
else {
length = 0;
while (length < precision && str[length]) {
length++;
}
}
unicode = PyUnicode_DecodeUTF8Stateful(str, length, "replace", NULL);
if (unicode == NULL)
return -1;
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