netdev - [PATCH net-next] ovpn: properly deconfigure UDP-tunnel

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Message-ID: <20250514095842.12067-1-antonio@openvpn.net>
Date: Wed, 14 May 2025 11:58:42 +0200
From: Antonio Quartulli <antonio@...nvpn.net>
To: netdev@...r.kernel.org
Cc: Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Sabrina Dubroca <sd@...asysnail.net>,
	Antonio Quartulli <antonio@...nvpn.net>,
	David Ahern <dsahern@...nel.org>
Subject: [PATCH net-next] ovpn: properly deconfigure UDP-tunnel

When deconfiguring a UDP-tunnel from a socket, we cannot
call setup_udp_tunnel_sock(), as it is expected to be invoked
only during setup.

Implement a new function named cleanup_udp_tunnel_sock(),
that reverts was what done during setup, and invoke it.

This new function takes care of reverting everything that
was done by setup_udp_tunnel_sock() (i.e. unsetting various
sk members and cleaning up the encap state in the kernel).

Cc: David Ahern <dsahern@...nel.org>
Cc: Sabrina Dubroca <sd@...asysnail.net>
Reported-by: Paolo Abeni <pabeni@...hat.com>
Closes: https://lore.kernel.org/netdev/1a47ce02-fd42-4761-8697-f3f315011cc6@redhat.com
Signed-off-by: Antonio Quartulli <antonio@...nvpn.net>
---

@Jakub: I am sending this directly to net-next as it'd be better reviewed
by the broader audience on netdev right away.

@Paolo: I think this is the best way to handle the UDP tunnel cleanup.
Doing nothing is not truly an option because we leave all the encap
state enabled and this may lead to other issues.
cleanup_udp_tunnel_sock() will just undo anything that
setup_udp_tunnel_sock() had done during setup.

 drivers/net/ovpn/udp.c     |  5 +----
 include/net/udp_tunnel.h   |  1 +
 net/ipv4/udp_tunnel_core.c | 30 ++++++++++++++++++++++++++++++
 3 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ovpn/udp.c b/drivers/net/ovpn/udp.c
index aef8c0406ec9..137b58d49569 100644
--- a/drivers/net/ovpn/udp.c
+++ b/drivers/net/ovpn/udp.c
@@ -442,8 +442,5 @@ int ovpn_udp_socket_attach(struct ovpn_socket *ovpn_sock,
  */
 void ovpn_udp_socket_detach(struct ovpn_socket *ovpn_sock)
 {
-	struct udp_tunnel_sock_cfg cfg = { };
-
-	setup_udp_tunnel_sock(sock_net(ovpn_sock->sock->sk), ovpn_sock->sock,
-			      &cfg);
+	cleanup_udp_tunnel_sock(ovpn_sock->sock);
 }
diff --git a/include/net/udp_tunnel.h b/include/net/udp_tunnel.h
index 2df3b8344eb5..387445133eb7 100644
--- a/include/net/udp_tunnel.h
+++ b/include/net/udp_tunnel.h
@@ -92,6 +92,7 @@ struct udp_tunnel_sock_cfg {
 /* Setup the given (UDP) sock to receive UDP encapsulated packets */
 void setup_udp_tunnel_sock(struct net *net, struct socket *sock,
 			   struct udp_tunnel_sock_cfg *sock_cfg);
+void cleanup_udp_tunnel_sock(struct socket *sock);
 
 /* -- List of parsable UDP tunnel types --
  *
diff --git a/net/ipv4/udp_tunnel_core.c b/net/ipv4/udp_tunnel_core.c
index 2326548997d3..83e9fd2d499e 100644
--- a/net/ipv4/udp_tunnel_core.c
+++ b/net/ipv4/udp_tunnel_core.c
@@ -98,6 +98,36 @@ void setup_udp_tunnel_sock(struct net *net, struct socket *sock,
 }
 EXPORT_SYMBOL_GPL(setup_udp_tunnel_sock);
 
+void cleanup_udp_tunnel_sock(struct socket *sock)
+{
+	struct sock *sk = sock->sk;
+
+	/* Re-enable multicast loopback */
+	inet_set_bit(MC_LOOP, sk);
+
+	/* Disable CHECKSUM_UNNECESSARY to CHECKSUM_COMPLETE conversion */
+	inet_dec_convert_csum(sk);
+
+	rcu_assign_sk_user_data(sk, NULL);
+
+	udp_sk(sk)->encap_type = 0;
+	udp_sk(sk)->encap_rcv = NULL;
+	udp_sk(sk)->encap_err_rcv = NULL;
+	udp_sk(sk)->encap_err_lookup = NULL;
+	udp_sk(sk)->encap_destroy = NULL;
+	udp_sk(sk)->gro_receive = NULL;
+	udp_sk(sk)->gro_complete = NULL;
+
+	udp_clear_bit(ENCAP_ENABLED, sk);
+#if IS_ENABLED(CONFIG_IPV6)
+	if (READ_ONCE(sk->sk_family) == PF_INET6)
+		static_branch_dec(&udpv6_encap_needed_key);
+#endif
+	udp_encap_disable();
+	udp_tunnel_cleanup_gro(sk);
+}
+EXPORT_SYMBOL_GPL(cleanup_udp_tunnel_sock);
+
 void udp_tunnel_push_rx_port(struct net_device *dev, struct socket *sock,
 			     unsigned short type)
 {
-- 
2.49.0