From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: "Miss Islington (bot)"
 <31488909+miss-islington@users.noreply.github.com>
Date: Fri, 6 Dec 2024 06:12:40 +0100
Subject: [PATCH] 00445: CVE-2024-12254: Ensure
 _SelectorSocketTransport.writelines pauses the protocol if needed

Ensure _SelectorSocketTransport.writelines pauses the protocol if it reaches the high water mark as needed.

Resolved upstream: https://github.com/python/cpython/issues/127655

Co-authored-by: J. Nick Koston <nick@koston.org>
Co-authored-by: Kumar Aditya <kumaraditya@python.org>
---
 Lib/asyncio/selector_events.py                       |  1 +
 Lib/test/test_asyncio/test_selector_events.py        | 12 ++++++++++++
 .../2024-12-05-21-35-19.gh-issue-127655.xpPoOf.rst   |  1 +
 3 files changed, 14 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Security/2024-12-05-21-35-19.gh-issue-127655.xpPoOf.rst

diff --git a/Lib/asyncio/selector_events.py b/Lib/asyncio/selector_events.py
index 790711f834..dd79ad18df 100644
--- a/Lib/asyncio/selector_events.py
+++ b/Lib/asyncio/selector_events.py
@@ -1183,6 +1183,7 @@ def writelines(self, list_of_data):
         # If the entire buffer couldn't be written, register a write handler
         if self._buffer:
             self._loop._add_writer(self._sock_fd, self._write_ready)
+            self._maybe_pause_protocol()
 
     def can_write_eof(self):
         return True
diff --git a/Lib/test/test_asyncio/test_selector_events.py b/Lib/test/test_asyncio/test_selector_events.py
index 47693ea4d3..736c19796e 100644
--- a/Lib/test/test_asyncio/test_selector_events.py
+++ b/Lib/test/test_asyncio/test_selector_events.py
@@ -805,6 +805,18 @@ def test_writelines_send_partial(self):
         self.assertTrue(self.sock.send.called)
         self.assertTrue(self.loop.writers)
 
+    def test_writelines_pauses_protocol(self):
+        data = memoryview(b'data')
+        self.sock.send.return_value = 2
+        self.sock.send.fileno.return_value = 7
+
+        transport = self.socket_transport()
+        transport._high_water = 1
+        transport.writelines([data])
+        self.assertTrue(self.protocol.pause_writing.called)
+        self.assertTrue(self.sock.send.called)
+        self.assertTrue(self.loop.writers)
+
     @unittest.skipUnless(selector_events._HAS_SENDMSG, 'no sendmsg')
     def test_write_sendmsg_full(self):
         data = memoryview(b'data')
diff --git a/Misc/NEWS.d/next/Security/2024-12-05-21-35-19.gh-issue-127655.xpPoOf.rst b/Misc/NEWS.d/next/Security/2024-12-05-21-35-19.gh-issue-127655.xpPoOf.rst
new file mode 100644
index 0000000000..76cfc58121
--- /dev/null
+++ b/Misc/NEWS.d/next/Security/2024-12-05-21-35-19.gh-issue-127655.xpPoOf.rst
@@ -0,0 +1 @@
+Fixed the :class:`!asyncio.selector_events._SelectorSocketTransport` transport not pausing writes for the protocol when the buffer reaches the high water mark when using :meth:`asyncio.WriteTransport.writelines`.