http://hg.python.org/cpython/rev/5e456e1a9e8c changeset: 72466:5e456e1a9e8c user: Mark Dickinson <mdickinson@enthought.com> date: Sat Sep 24 19:11:53 2011 +0100 summary: Issue #1621: Fix undefined behaviour from signed overflow in get_integer (stringlib/formatter.h) files: Objects/stringlib/formatter.h | 16 +++++++--------- 1 files changed, 7 insertions(+), 9 deletions(-) diff --git a/Objects/stringlib/formatter.h b/Objects/stringlib/formatter.h --- a/Objects/stringlib/formatter.h +++ b/Objects/stringlib/formatter.h @@ -73,7 +73,7 @@ get_integer(STRINGLIB_CHAR **ptr, STRINGLIB_CHAR *end, Py_ssize_t *result) { - Py_ssize_t accumulator, digitval, oldaccumulator; + Py_ssize_t accumulator, digitval; int numdigits; accumulator = numdigits = 0; for (;;(*ptr)++, numdigits++) { @@ -83,19 +83,17 @@ if (digitval < 0) break; /* - This trick was copied from old Unicode format code. It's cute, - but would really suck on an old machine with a slow divide - implementation. Fortunately, in the normal case we do not - expect too many digits. + Detect possible overflow before it happens: + + accumulator * 10 + digitval > PY_SSIZE_T_MAX if and only if + accumulator > (PY_SSIZE_T_MAX - digitval) / 10. */ - oldaccumulator = accumulator; - accumulator *= 10; - if ((accumulator+10)/10 != oldaccumulator+1) { + if (accumulator > (PY_SSIZE_T_MAX - digitval) / 10) { PyErr_Format(PyExc_ValueError, "Too many decimal digits in format string"); return -1; } - accumulator += digitval; + accumulator = accumulator * 10 + digitval; } *result = accumulator; return numdigits; -- Repository URL: http://hg.python.org/cpython