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

Tony Solomonik webhook-mailer at python.org
Sun Aug 30 00:53:17 EDT 2020

commit: 75c80b0bda89debf312f075716b8c467d411f90e
branch: master
author: Tony Solomonik <tony.solomonik at gmail.com>
committer: GitHub <noreply at github.com>
date: 2020-08-29T23:53:08-05:00

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

Free the stack allocated in va_build_stack if do_mkstack fails
and the stack is not a small_stack

A Misc/NEWS.d/next/Core and Builtins/2020-08-12-20-29-57.bpo-41533.4pcVAc.rst
M Python/modsupport.c

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
new file mode 100644
index 0000000000000..e166f0c0b621a
--- /dev/null
+++ 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
index 2637039d4a151..2dabcf383409e 100644
--- a/Python/modsupport.c
+++ b/Python/modsupport.c
@@ -622,6 +622,9 @@ va_build_stack(PyObject **small_stack, Py_ssize_t small_stack_len,
     if (res < 0) {
+        if (stack != small_stack) {
+            PyMem_Free(stack);
+        }
         return NULL;

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