From a76f96c951fd24843d2e9df88002f60c044fbcfc Mon Sep 17 00:00:00 2001
From: Gyanu Mayank <gyanumayank0@gmail.com>
Date: Tue, 22 Sep 2026 21:19:04 +0530
Subject: [PATCH] Reject a bad subprocess pipe protocol owner with TypeError.

The constructor only checked proc and fd under UVLOOP_DEBUG, then cast proc and segfaulted. That check now always runs.

Fixes #765.
---
 tests/test_subprocess_pipe_proto.py | 16 ++++++++++++++++
 uvloop/handles/process.pyx          | 17 ++++++++++++-----
 2 files changed, 28 insertions(+), 5 deletions(-)
 create mode 100644 tests/test_subprocess_pipe_proto.py

diff --git a/tests/test_subprocess_pipe_proto.py b/tests/test_subprocess_pipe_proto.py
new file mode 100644
index 000000000..d39ceb241
--- /dev/null
+++ b/tests/test_subprocess_pipe_proto.py
@@ -0,0 +1,16 @@
+import unittest
+
+from uvloop.loop import ReadSubprocessPipeProto, WriteSubprocessPipeProto
+
+
+class TestSubprocessPipeProto(unittest.TestCase):
+    def test_rejects_non_process_owner(self):
+        with self.assertRaises(TypeError):
+            ReadSubprocessPipeProto(1, 7)
+        with self.assertRaises(TypeError):
+            WriteSubprocessPipeProto(1, 7)
+
+    def test_rejects_non_int_fd(self):
+        # Owner is checked first. A non-process still must not segfault.
+        with self.assertRaises(TypeError):
+            WriteSubprocessPipeProto(object(), 'nope')
diff --git a/uvloop/handles/process.pyx b/uvloop/handles/process.pyx
index 63b982ae5..391390b2d 100644
--- a/uvloop/handles/process.pyx
+++ b/uvloop/handles/process.pyx
@@ -706,11 +706,18 @@ cdef class UVProcessTransport(UVProcess):
 class WriteSubprocessPipeProto(aio_BaseProtocol):
 
     def __init__(self, proc, fd):
-        if UVLOOP_DEBUG:
-            if type(proc) is not UVProcessTransport:
-                raise TypeError
-            if not isinstance(fd, int):
-                raise TypeError
+        # Release builds used to cast `proc` and segfault. Reject a bad owner
+        # here so a mistaken constructor argument is a TypeError.
+        if type(proc) is not UVProcessTransport:
+            raise TypeError(
+                'proc must be a UVProcessTransport, not {!r}'.format(
+                    type(proc).__name__,
+                ),
+            )
+        if not isinstance(fd, int):
+            raise TypeError(
+                'fd must be an int, not {!r}'.format(type(fd).__name__),
+            )
         self.proc = proc
         self.fd = fd
         self.pipe = None