closes bpo-41533: Fix a potential memory leak when allocating a stack (GH-21847)

miss-islington · tontinton · web-flow · commit 106c1df736d3 · 2020-09-04T15:56:04.000-07:00
Free the stack allocated in va_build_stack if do_mkstack fails and the stack is not a small_stack (cherry picked from commit 75c80b0) Co-authored-by: Tony Solomonik <tony.solomonik@gmail.com>
diff --git a/Misc/NEWS.d/next/Core and Builtins/2020-08-12-20-29-57.bpo-41533.4pcVAc.rst b/Misc/NEWS.d/next/Core and Builtins/2020-08-12-20-29-57.bpo-41533.4pcVAc.rst
@@ -0,0 +1,2 @@
+Free the stack allocated in ``va_build_stack`` if ``do_mkstack`` fails and
+the stack is not a ``small_stack``.
diff --git a/Python/modsupport.c b/Python/modsupport.c
@@ -619,6 +619,9 @@ va_build_stack(PyObject **small_stack, Py_ssize_t small_stack_len,
     va_end(lva);
 
     if (res < 0) {
+        if (stack != small_stack) {
+            PyMem_Free(stack);
+        }
         return NULL;
     }
 

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	+Free the stack allocated in ``va_build_stack`` if ``do_mkstack`` fails and
	`2`	+the stack is not a ``small_stack``.
Original file line number	Diff line number	Diff line change
`@@ -619,6 +619,9 @@ va_build_stack(PyObject **small_stack, Py_ssize_t small_stack_len,`
`619`	`619`	`va_end(lva);`
`620`	`620`
`621`	`621`	`if (res < 0) {`
	`622`	`+ if (stack != small_stack) {`
	`623`	`+ PyMem_Free(stack);`
	`624`	`+ }`
`622`	`625`	`return NULL;`
`623`	`626`	`}`
`624`	`627`