From 0bee1972ede66db2e52849b21effe66bcaf84bc0 Mon Sep 17 00:00:00 2001
From: Ma Lin <malincns@163.com>
Date: Tue, 16 Nov 2021 18:12:25 +0800
Subject: [PATCH 1/2] Fix thread lock in zlib.Decompress.flush() may go wrong

Getting `.unconsumed_tail` before acquiring the thread lock may mix up decompress state.
---
 .../next/Library/2021-11-16-18-13-49.bpo-41735.D72UY1.rst    | 1 +
 Modules/zlibmodule.c                                         | 5 +++--
 2 files changed, 4 insertions(+), 2 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2021-11-16-18-13-49.bpo-41735.D72UY1.rst

diff --git a/Misc/NEWS.d/next/Library/2021-11-16-18-13-49.bpo-41735.D72UY1.rst b/Misc/NEWS.d/next/Library/2021-11-16-18-13-49.bpo-41735.D72UY1.rst
new file mode 100644
index 00000000000000..88970fbc1d3095
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2021-11-16-18-13-49.bpo-41735.D72UY1.rst
@@ -0,0 +1 @@
+Fix thread lock in zlib.Decompress.flush() method may go wrong.
diff --git a/Modules/zlibmodule.c b/Modules/zlibmodule.c
index 67bde701fa608b..f9646568d7e01d 100644
--- a/Modules/zlibmodule.c
+++ b/Modules/zlibmodule.c
@@ -1269,12 +1269,13 @@ zlib_Decompress_flush_impl(compobject *self, PyTypeObject *cls,
         return NULL;
     }
 
+    ENTER_ZLIB(self);
+
     if (PyObject_GetBuffer(self->unconsumed_tail, &data, PyBUF_SIMPLE) == -1) {
+        LEAVE_ZLIB(self);
         return NULL;
     }
 
-    ENTER_ZLIB(self);
-
     self->zst.next_in = data.buf;
     ibuflen = data.len;
 

From dd72e4b28b4e9e09861a3e4a2d3ac7f4f72d73ee Mon Sep 17 00:00:00 2001
From: "Gregory P. Smith" <greg@krypto.org>
Date: Fri, 26 Nov 2021 15:50:09 -0800
Subject: [PATCH 2/2] wording.

---
 .../next/Library/2021-11-16-18-13-49.bpo-41735.D72UY1.rst       | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Misc/NEWS.d/next/Library/2021-11-16-18-13-49.bpo-41735.D72UY1.rst b/Misc/NEWS.d/next/Library/2021-11-16-18-13-49.bpo-41735.D72UY1.rst
index 88970fbc1d3095..101da0e9ce6487 100644
--- a/Misc/NEWS.d/next/Library/2021-11-16-18-13-49.bpo-41735.D72UY1.rst
+++ b/Misc/NEWS.d/next/Library/2021-11-16-18-13-49.bpo-41735.D72UY1.rst
@@ -1 +1 @@
-Fix thread lock in zlib.Decompress.flush() method may go wrong.
+Fix thread lock in ``zlib.Decompress.flush()`` method before ``PyObject_GetBuffer``.