From: Ma Lin <animalize@users.noreply.github.com>
Date: Sat, 27 Nov 2021 00:21:22 +0000 (+0800)
Subject: [3.9] bpo-41735: Fix thread lock in zlib.Decompress.flush() may go wrong (GH-29588)
X-Git-Tag: v3.9.10~98
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=86c1265cdc64030c8921e0da5fcae2ac64299c26;p=thirdparty%2FPython%2Fcpython.git

[3.9] bpo-41735: Fix thread lock in zlib.Decompress.flush() may go wrong (GH-29588)

* Fix thread lock in zlib.Decompress.flush() may go wrong
Getting `.unconsumed_tail` before acquiring the thread lock may mix up decompress state.

backport of https://github.com/python/cpython/pull/29587 to 3.9/3.8.
---

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 000000000000..101da0e9ce64
--- /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 before ``PyObject_GetBuffer``.
diff --git a/Modules/zlibmodule.c b/Modules/zlibmodule.c
index 8f8bcd85f2c1..4dfd4ae67220 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;