gh-128916: Do not set SO_REUSEPORT on non-AF_INET* sockets (GH-128933)

* gh-128916: Do not set `SO_REUSEPORT` on non-`AF_INET*` sockets

Do not attempt to set ``SO_REUSEPORT`` on sockets of address familifies other
than ``AF_INET`` and ``AF_INET6``, as it is meaningless with these address
families, and the call with fail with Linux kernel 6.12.9 and newer.

* Apply suggestions from code review

Co-authored-by: Vinay Sajip <[email protected]>

---------
(cherry picked from commit 3829104)

Co-authored-by: Michał Górny <[email protected]>
Co-authored-by: Vinay Sajip <[email protected]>

Author: 2 people

Lib/asyncio/base_events.py

@@ -1550,7 +1550,9 @@ async def create_server(
                     if reuse_address:
                         sock.setsockopt(
                             socket.SOL_SOCKET, socket.SO_REUSEADDR, True)
-                    if reuse_port:
+                    # Since Linux 6.12.9, SO_REUSEPORT is not allowed
+                    # on other address families than AF_INET/AF_INET6.
+                    if reuse_port and af in (socket.AF_INET, socket.AF_INET6):
                         _set_reuseport(sock)
                     # Disable IPv4/IPv6 dual stack support (enabled by
                     # default on Linux) which makes a single socket

Lib/socket.py

@@ -932,7 +932,9 @@ def create_server(address, *, family=AF_INET, backlog=None, reuse_port=False,
                 # Fail later on bind(), for platforms which may not
                 # support this option.
                 pass
-        if reuse_port:
+        # Since Linux 6.12.9, SO_REUSEPORT is not allowed
+        # on other address families than AF_INET/AF_INET6.
+        if reuse_port and family in (AF_INET, AF_INET6):
             sock.setsockopt(SOL_SOCKET, SO_REUSEPORT, 1)
         if has_ipv6 and family == AF_INET6:
             if dualstack_ipv6:

Lib/socketserver.py

@@ -468,7 +468,12 @@ def server_bind(self):
         """
         if self.allow_reuse_address and hasattr(socket, "SO_REUSEADDR"):
             self.socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
-        if self.allow_reuse_port and hasattr(socket, "SO_REUSEPORT"):
+        # Since Linux 6.12.9, SO_REUSEPORT is not allowed
+        # on other address families than AF_INET/AF_INET6.
+        if (
+            self.allow_reuse_port and hasattr(socket, "SO_REUSEPORT")
+            and self.address_family in (socket.AF_INET, socket.AF_INET6)
+        ):
             self.socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, 1)
         self.socket.bind(self.server_address)
         self.server_address = self.socket.getsockname()

Misc/NEWS.d/next/Library/2025-01-17-11-46-16.gh-issue-128916.GEePbO.rst

@@ -0,0 +1,3 @@
+Do not attempt to set ``SO_REUSEPORT`` on sockets of address families
+other than ``AF_INET`` and ``AF_INET6``, as it is meaningless with these
+address families, and the call with fail with Linux kernel 6.12.9 and newer.