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bpo-36020: Require vsnprintf() to build Python (GH-20899)
The C99 functions snprintf() and vsnprintf() are now required to build Python. PyOS_snprintf() and PyOS_vsnprintf() no longer call Py_FatalError(). Previously, they called Py_FatalError() on a buffer overflow on platforms which don't provide vsnprintf().
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@ -27,12 +27,8 @@ not.
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The wrappers ensure that *str*[*size*-1] is always ``'\0'`` upon return. They
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never write more than *size* bytes (including the trailing ``'\0'``) into str.
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Both functions require that ``str != NULL``, ``size > 0`` and ``format !=
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NULL``.
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If the platform doesn't have :c:func:`vsnprintf` and the buffer size needed to
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avoid truncation exceeds *size* by more than 512 bytes, Python aborts with a
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:c:func:`Py_FatalError`.
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Both functions require that ``str != NULL``, ``size > 0``, ``format != NULL``
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and ``size < INT_MAX``.
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The return value (*rv*) for these functions should be interpreted as follows:
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@ -48,8 +44,8 @@ The return value (*rv*) for these functions should be interpreted as follows:
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this case too, but the rest of *str* is undefined. The exact cause of the error
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depends on the underlying platform.
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The following functions provide locale-independent string to number conversions.
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The following functions provide locale-independent string to number conversions.
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.. c:function:: double PyOS_string_to_double(const char *s, char **endptr, PyObject *overflow_exception)
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@ -123,6 +123,10 @@ that may require changes to your code.
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Build Changes
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=============
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* The C99 functions :c:func:`snprintf` and :c:func:`vsnprintf` are now required
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to build Python.
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(Contributed by Victor Stinner in :issue:`36020`.)
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C API Changes
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=============
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@ -0,0 +1,2 @@
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The C99 functions :c:func:`snprintf` and :c:func:`vsnprintf` are now required
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to build Python.
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@ -15,10 +15,6 @@
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PyOS_snprintf and PyOS_vsnprintf never write more than size bytes
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(including the trailing '\0') into str.
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If the platform doesn't have vsnprintf, and the buffer size needed to
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avoid truncation exceeds size by more than 512, Python aborts with a
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Py_FatalError.
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Return value (rv):
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When 0 <= rv < size, the output conversion was unexceptional, and
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@ -37,6 +33,7 @@
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PyMem_Malloc couldn't obtain space for a temp buffer.
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CAUTION: Unlike C99, str != NULL and size > 0 are required.
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Also, size must be smaller than INT_MAX.
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*/
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int
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@ -56,50 +53,22 @@ PyOS_vsnprintf(char *str, size_t size, const char *format, va_list va)
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{
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assert(str != NULL);
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assert(size > 0);
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assert(size <= (INT_MAX - 1));
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assert(format != NULL);
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int len; /* # bytes written, excluding \0 */
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#if defined(_MSC_VER) || defined(HAVE_SNPRINTF)
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# define _PyOS_vsnprintf_EXTRA_SPACE 1
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#else
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# define _PyOS_vsnprintf_EXTRA_SPACE 512
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char *buffer;
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#endif
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/* We take a size_t as input but return an int. Sanity check
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* our input so that it won't cause an overflow in the
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* vsnprintf return value or the buffer malloc size. */
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if (size > INT_MAX - _PyOS_vsnprintf_EXTRA_SPACE) {
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* vsnprintf return value. */
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if (size > INT_MAX - 1) {
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len = -666;
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goto Done;
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}
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#if defined(_MSC_VER)
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len = _vsnprintf(str, size, format, va);
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#elif defined(HAVE_SNPRINTF)
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len = vsnprintf(str, size, format, va);
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#else
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/* Emulate vsnprintf(). */
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buffer = PyMem_MALLOC(size + _PyOS_vsnprintf_EXTRA_SPACE);
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if (buffer == NULL) {
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len = -666;
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goto Done;
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}
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len = vsprintf(buffer, format, va);
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if (len < 0) {
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/* ignore the error */;
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}
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else if ((size_t)len >= size + _PyOS_vsnprintf_EXTRA_SPACE) {
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_Py_FatalErrorFunc(__func__, "Buffer overflow");
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}
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else {
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const size_t to_copy = (size_t)len < size ?
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(size_t)len : size - 1;
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assert(to_copy < size);
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memcpy(str, buffer, to_copy);
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str[to_copy] = '\0';
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}
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PyMem_FREE(buffer);
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len = vsnprintf(str, size, format, va);
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#endif
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Done:
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@ -107,5 +76,4 @@ PyOS_vsnprintf(char *str, size_t size, const char *format, va_list va)
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str[size-1] = '\0';
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}
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return len;
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#undef _PyOS_vsnprintf_EXTRA_SPACE
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}
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