From 8c3baf067791dd11bed9eeec3009da512a1b4ccc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alejandro=20Cabello=20Jim=C3=A9nez?=
 <alejandro.cabello89@gmail.com>
Date: Mon, 18 Aug 2025 23:25:59 +0200
Subject: [PATCH 1/2] gh-137928: Centralize size validation in
 multiprocessing.heap

---
 Lib/multiprocessing/heap.py | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/Lib/multiprocessing/heap.py b/Lib/multiprocessing/heap.py
index 6217dfe12689b3..5ef12959f89dda 100644
--- a/Lib/multiprocessing/heap.py
+++ b/Lib/multiprocessing/heap.py
@@ -155,6 +155,15 @@ def _roundup(n, alignment):
         mask = alignment - 1
         return (n + mask) & ~mask
 
+    @staticmethod
+    # Bind sys.maxsize once at function definition time to avoid global lookups.
+    def _validate_size(size, _maxsize=sys.maxsize):
+        """Validate requested size; raise ValueError if < 0, OverflowError if >= _maxsize."""
+        if size < 0:
+            raise ValueError("Size {0:n} out of range".format(size))
+        if _maxsize <= size:
+            raise OverflowError("Size {0:n} too large".format(size))
+
     def _new_arena(self, size):
         # Create a new arena with at least the given *size*
         length = self._roundup(max(self._size, size), mmap.PAGESIZE)
@@ -295,10 +304,7 @@ def free(self, block):
 
     def malloc(self, size):
         # return a block of right size (possibly rounded up)
-        if size < 0:
-            raise ValueError("Size {0:n} out of range".format(size))
-        if sys.maxsize <= size:
-            raise OverflowError("Size {0:n} too large".format(size))
+        Heap._validate_size(size)
         if os.getpid() != self._lastpid:
             self.__init__()                     # reinitialize after fork
         with self._lock:
@@ -324,10 +330,7 @@ class BufferWrapper(object):
     _heap = Heap()
 
     def __init__(self, size):
-        if size < 0:
-            raise ValueError("Size {0:n} out of range".format(size))
-        if sys.maxsize <= size:
-            raise OverflowError("Size {0:n} too large".format(size))
+        Heap._validate_size(size)
         block = BufferWrapper._heap.malloc(size)
         self._state = (block, size)
         util.Finalize(self, BufferWrapper._heap.free, args=(block,))

From 204d26466607295c7d601fb6969e477639f51878 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alejandro=20Cabello=20Jim=C3=A9nez?=
 <alejandro@travelperk.com>
Date: Thu, 21 Aug 2025 10:03:26 +0200
Subject: [PATCH 2/2] gh-137928: Move size validation helper to module level in
 multiprocessing.heap

---
 Lib/multiprocessing/heap.py | 30 +++++++++++++++++++-----------
 1 file changed, 19 insertions(+), 11 deletions(-)

diff --git a/Lib/multiprocessing/heap.py b/Lib/multiprocessing/heap.py
index 5ef12959f89dda..f1d74d245101c0 100644
--- a/Lib/multiprocessing/heap.py
+++ b/Lib/multiprocessing/heap.py
@@ -20,6 +20,12 @@
 
 __all__ = ['BufferWrapper']
 
+#
+# Module constants
+#
+
+_MAXSIZE = sys.maxsize
+
 #
 # Inheritable class which wraps an mmap, and from which blocks can be allocated
 #
@@ -108,6 +114,17 @@ def rebuild_arena(size, dupfd):
 
     reduction.register(Arena, reduce_arena)
 
+#
+# Validation helpers
+#
+
+def _validate_size(size):
+    """Validate requested size; raise ValueError if < 0, OverflowError if >= _MAXSIZE."""
+    if size < 0:
+        raise ValueError("Size {0:n} out of range".format(size))
+    if _MAXSIZE <= size:
+        raise OverflowError("Size {0:n} too large".format(size))
+
 #
 # Class allowing allocation of chunks of memory from arenas
 #
@@ -155,15 +172,6 @@ def _roundup(n, alignment):
         mask = alignment - 1
         return (n + mask) & ~mask
 
-    @staticmethod
-    # Bind sys.maxsize once at function definition time to avoid global lookups.
-    def _validate_size(size, _maxsize=sys.maxsize):
-        """Validate requested size; raise ValueError if < 0, OverflowError if >= _maxsize."""
-        if size < 0:
-            raise ValueError("Size {0:n} out of range".format(size))
-        if _maxsize <= size:
-            raise OverflowError("Size {0:n} too large".format(size))
-
     def _new_arena(self, size):
         # Create a new arena with at least the given *size*
         length = self._roundup(max(self._size, size), mmap.PAGESIZE)
@@ -304,7 +312,7 @@ def free(self, block):
 
     def malloc(self, size):
         # return a block of right size (possibly rounded up)
-        Heap._validate_size(size)
+        _validate_size(size)
         if os.getpid() != self._lastpid:
             self.__init__()                     # reinitialize after fork
         with self._lock:
@@ -330,7 +338,7 @@ class BufferWrapper(object):
     _heap = Heap()
 
     def __init__(self, size):
-        Heap._validate_size(size)
+        _validate_size(size)
         block = BufferWrapper._heap.malloc(size)
         self._state = (block, size)
         util.Finalize(self, BufferWrapper._heap.free, args=(block,))