closes bpo-34400: Fix undefined behavior in parsetok(). (GH-4439)

Avoid undefined pointer arithmetic with NULL.

closes bpo-34400: Fix undefined behavior in parsetok(). (GH-4439)
Avoid undefined pointer arithmetic with NULL.
7c4ab2af · Zackery Spytz · Benjamin Peterson · 88bfd0bc · 7c4ab2af · 7c4ab2af
Kaydet (Commit) 7c4ab2af authored Agu 15, 2018 tarafından Zackery Spytz Kaydeden (comit) Benjamin Peterson Agu 15, 2018
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2018-08-14-03-52-43.bpo-34400.AJD0bz.rst ...ore and Builtins/2018-08-14-03-52-43.bpo-34400.AJD0bz.rst +1 -0

parsetok.c Parser/parsetok.c +1 -1

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--- a/Misc/NEWS.d/next/Core and Builtins/2018-08-14-03-52-43.bpo-34400.AJD0bz.rst
+++ b/Misc/NEWS.d/next/Core and Builtins/2018-08-14-03-52-43.bpo-34400.AJD0bz.rst
+Fix undefined behavior in parsetok.c.  Patch by Zackery Spytz.
--- a/Parser/parsetok.c
+++ b/Parser/parsetok.c
@@ -225,7 +225,7 @@ parsetok(struct tok_state *tok, grammar *g, int start, perrdetail *err_ret,
        }
        else
            started = 1;
-        len = b - a; /* XXX this may compute NULL - NULL */
+        len = (a != NULL && b != NULL) ? b - a : 0;
        str = (char *) PyObject_MALLOC(len + 1);
        if (str == NULL) {
            err_ret->error = E_NOMEM;