Fix undefined behavior in parsetok()

ZackerySpytz · ZackerySpytz · commit 11da66a855fb · 2018-07-24T10:04:07.000-06:00
diff --git 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;

Original file line number	Diff line number	Diff line change
`@@ -225,7 +225,7 @@ parsetok(struct tok_state tok, grammar g, int start, perrdetail *err_ret,`
`225`	`225`	`}`
`226`	`226`	`else`
`227`	`227`	`started = 1;`
`228`		`- len = b - a; /* XXX this may compute NULL - NULL */`
	`228`	`+ len = a != NULL && b != NULL ? b - a : 0;`
`229`	`229`	`str = (char *) PyObject_MALLOC(len + 1);`
`230`	`230`	`if (str == NULL) {`
`231`	`231`	`err_ret->error = E_NOMEM;`