From d3a3bb94a50b93875d8b881b13f48886c944e08d Mon Sep 17 00:00:00 2001
From: Ma Lin <malincns@163.com>
Date: Wed, 17 Nov 2021 11:39:01 +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/2021-11-17-11-38-30.bpo-41735.2feh9v.rst | 1 +
 Modules/zlibmodule.c                                      | 8 +++++---
 2 files changed, 6 insertions(+), 3 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2021-11-17-11-38-30.bpo-41735.2feh9v.rst

diff --git a/Misc/NEWS.d/next/Library/2021-11-17-11-38-30.bpo-41735.2feh9v.rst b/Misc/NEWS.d/next/Library/2021-11-17-11-38-30.bpo-41735.2feh9v.rst
new file mode 100644
index 00000000000000..88970fbc1d3095
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2021-11-17-11-38-30.bpo-41735.2feh9v.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 8f8bcd85f2c16d..4dfd4ae6722002 100644
--- a/Modules/zlibmodule.c
+++ b/Modules/zlibmodule.c
@@ -1134,11 +1134,13 @@ zlib_Decompress_flush_impl(compobject *self, Py_ssize_t length)
         return NULL;
     }
 
-    if (PyObject_GetBuffer(self->unconsumed_tail, &data, PyBUF_SIMPLE) == -1)
-        return NULL;
-
     ENTER_ZLIB(self);
 
+    if (PyObject_GetBuffer(self->unconsumed_tail, &data, PyBUF_SIMPLE) == -1) {
+        LEAVE_ZLIB(self);
+        return NULL;
+    }
+
     self->zst.next_in = data.buf;
     ibuflen = data.len;
 

From 0803d3cd6e22fb96078393baa083ffb1c334dea2 Mon Sep 17 00:00:00 2001
From: "Gregory P. Smith" <greg@krypto.org>
Date: Fri, 26 Nov 2021 15:51:45 -0800
Subject: [PATCH 2/2] wording.

---
 .../next/Library/2021-11-17-11-38-30.bpo-41735.2feh9v.rst       | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Misc/NEWS.d/next/Library/2021-11-17-11-38-30.bpo-41735.2feh9v.rst b/Misc/NEWS.d/next/Library/2021-11-17-11-38-30.bpo-41735.2feh9v.rst
index 88970fbc1d3095..101da0e9ce6487 100644
--- a/Misc/NEWS.d/next/Library/2021-11-17-11-38-30.bpo-41735.2feh9v.rst
+++ b/Misc/NEWS.d/next/Library/2021-11-17-11-38-30.bpo-41735.2feh9v.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``.