Message-Id: <20250227-b4-ovpn-v20-15-93f363310834@openvpn.net>
Date: Thu, 27 Feb 2025 02:21:40 +0100
From: Antonio Quartulli <antonio@...nvpn.net>
To: netdev@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
 Donald Hunter <donald.hunter@...il.com>, 
 Antonio Quartulli <antonio@...nvpn.net>, Shuah Khan <shuah@...nel.org>, 
 sd@...asysnail.net, ryazanov.s.a@...il.com, 
 Andrew Lunn <andrew+netdev@...n.ch>
Cc: Simon Horman <horms@...nel.org>, linux-kernel@...r.kernel.org, 
 linux-kselftest@...r.kernel.org, Xiao Liang <shaw.leon@...il.com>
Subject: [PATCH net-next v20 15/25] ovpn: implement multi-peer support

With this change an ovpn instance will be able to stay connected to
multiple remote endpoints.

This functionality is strictly required when running ovpn on an
OpenVPN server.

Signed-off-by: Antonio Quartulli <antonio@...nvpn.net>
---
 drivers/net/ovpn/main.c     |  68 ++++++++++++++++-
 drivers/net/ovpn/ovpnpriv.h |  19 +++++
 drivers/net/ovpn/peer.c     | 176 +++++++++++++++++++++++++++++++++++++++++++-
 drivers/net/ovpn/peer.h     |  10 +++
 drivers/net/ovpn/udp.c      |   9 ++-
 5 files changed, 275 insertions(+), 7 deletions(-)

diff --git a/drivers/net/ovpn/main.c b/drivers/net/ovpn/main.c
index 3498c0dafb1ee64b974a77dae882447e317352fd..bcbbc2200edd2e65190f5a7de07161321e16bb34 100644
--- a/drivers/net/ovpn/main.c
+++ b/drivers/net/ovpn/main.c
@@ -25,11 +25,66 @@
 #include "tcp.h"
 #include "udp.h"
 
+static void ovpn_priv_free(struct net_device *net)
+{
+	struct ovpn_priv *ovpn = netdev_priv(net);
+
+	kfree(ovpn->peers);
+}
+
+static int ovpn_mp_alloc(struct ovpn_priv *ovpn)
+{
+	struct in_device *dev_v4;
+	int i;
+
+	if (ovpn->mode != OVPN_MODE_MP)
+		return 0;
+
+	dev_v4 = __in_dev_get_rtnl(ovpn->dev);
+	if (dev_v4) {
+		/* disable redirects as Linux gets confused by ovpn
+		 * handling same-LAN routing.
+		 * This happens because a multipeer interface is used as
+		 * relay point between hosts in the same subnet, while
+		 * in a classic LAN this would not be needed because the
+		 * two hosts would be able to talk directly.
+		 */
+		IN_DEV_CONF_SET(dev_v4, SEND_REDIRECTS, false);
+		IPV4_DEVCONF_ALL(dev_net(ovpn->dev), SEND_REDIRECTS) = false;
+	}
+
+	/* the peer container is fairly large, therefore we allocate it only in
+	 * MP mode
+	 */
+	ovpn->peers = kzalloc(sizeof(*ovpn->peers), GFP_KERNEL);
+	if (!ovpn->peers)
+		return -ENOMEM;
+
+	for (i = 0; i < ARRAY_SIZE(ovpn->peers->by_id); i++) {
+		INIT_HLIST_HEAD(&ovpn->peers->by_id[i]);
+		INIT_HLIST_NULLS_HEAD(&ovpn->peers->by_vpn_addr4[i], i);
+		INIT_HLIST_NULLS_HEAD(&ovpn->peers->by_vpn_addr6[i], i);
+		INIT_HLIST_NULLS_HEAD(&ovpn->peers->by_transp_addr[i], i);
+	}
+
+	return 0;
+}
+
 static int ovpn_net_init(struct net_device *dev)
 {
 	struct ovpn_priv *ovpn = netdev_priv(dev);
+	int err = gro_cells_init(&ovpn->gro_cells, dev);
+
+	if (err < 0)
+		return err;
 
-	return gro_cells_init(&ovpn->gro_cells, dev);
+	err = ovpn_mp_alloc(ovpn);
+	if (err < 0) {
+		gro_cells_destroy(&ovpn->gro_cells);
+		return err;
+	}
+
+	return 0;
 }
 
 static void ovpn_net_uninit(struct net_device *dev)
@@ -100,6 +155,8 @@ static void ovpn_setup(struct net_device *dev)
 
 	dev->netdev_ops = &ovpn_netdev_ops;
 
+	dev->priv_destructor = ovpn_priv_free;
+
 	dev->hard_header_len = 0;
 	dev->addr_len = 0;
 	dev->mtu = ETH_DATA_LEN - OVPN_HEAD_ROOM;
@@ -197,9 +254,16 @@ static int ovpn_netdev_notifier_call(struct notifier_block *nb,
 		netif_carrier_off(dev);
 		ovpn->registered = false;
 
-		if (ovpn->mode == OVPN_MODE_P2P)
+		switch (ovpn->mode) {
+		case OVPN_MODE_P2P:
 			ovpn_peer_release_p2p(ovpn, NULL,
 					      OVPN_DEL_PEER_REASON_TEARDOWN);
+			break;
+		case OVPN_MODE_MP:
+			ovpn_peers_free(ovpn, NULL,
+					OVPN_DEL_PEER_REASON_TEARDOWN);
+			break;
+		}
 		break;
 	case NETDEV_POST_INIT:
 	case NETDEV_GOING_DOWN:
diff --git a/drivers/net/ovpn/ovpnpriv.h b/drivers/net/ovpn/ovpnpriv.h
index 2e3f4baf305f0b37b474d7b7d94751aa4af8a2ea..b26ad97215a3d42242ba349b348c2749f570797c 100644
--- a/drivers/net/ovpn/ovpnpriv.h
+++ b/drivers/net/ovpn/ovpnpriv.h
@@ -15,12 +15,30 @@
 #include <uapi/linux/if_link.h>
 #include <uapi/linux/ovpn.h>
 
+/**
+ * struct ovpn_peer_collection - container of peers for MultiPeer mode
+ * @by_id: table of peers index by ID
+ * @by_vpn_addr4: table of peers indexed by VPN IPv4 address (items can be
+ *		  rehashed on the fly due to peer IP change)
+ * @by_vpn_addr6: table of peers indexed by VPN IPv6 address (items can be
+ *		  rehashed on the fly due to peer IP change)
+ * @by_transp_addr: table of peers indexed by transport address (items can be
+ *		    rehashed on the fly due to peer IP change)
+ */
+struct ovpn_peer_collection {
+	DECLARE_HASHTABLE(by_id, 12);
+	struct hlist_nulls_head by_vpn_addr4[1 << 12];
+	struct hlist_nulls_head by_vpn_addr6[1 << 12];
+	struct hlist_nulls_head by_transp_addr[1 << 12];
+};
+
 /**
  * struct ovpn_priv - per ovpn interface state
  * @dev: the actual netdev representing the tunnel
  * @registered: whether dev is still registered with netdev or not
  * @mode: device operation mode (i.e. p2p, mp, ..)
  * @lock: protect this object
+ * @peers: data structures holding multi-peer references
  * @peer: in P2P mode, this is the only remote peer
  * @gro_cells: pointer to the Generic Receive Offload cell
  */
@@ -29,6 +47,7 @@ struct ovpn_priv {
 	bool registered;
 	enum ovpn_mode mode;
 	spinlock_t lock; /* protect writing to the ovpn_priv object */
+	struct ovpn_peer_collection *peers;
 	struct ovpn_peer __rcu *peer;
 	struct gro_cells gro_cells;
 };
diff --git a/drivers/net/ovpn/peer.c b/drivers/net/ovpn/peer.c
index 1f4148475c8b93aabc72694da5af97ae00a3a59d..b21ef6f10a7138e9f10c01b809df2cb0adf0abad 100644
--- a/drivers/net/ovpn/peer.c
+++ b/drivers/net/ovpn/peer.c
@@ -9,6 +9,7 @@
 
 #include <linux/skbuff.h>
 #include <linux/list.h>
+#include <linux/hashtable.h>
 
 #include "ovpnpriv.h"
 #include "bind.h"
@@ -280,7 +281,19 @@ static void ovpn_peer_remove(struct ovpn_peer *peer,
 			     enum ovpn_del_peer_reason reason,
 			     struct llist_head *release_list)
 {
+	lockdep_assert_held(&peer->ovpn->lock);
+
 	switch (peer->ovpn->mode) {
+	case OVPN_MODE_MP:
+		/* prevent double remove */
+		if (hlist_unhashed(&peer->hash_entry_id))
+			return;
+
+		hlist_del_init_rcu(&peer->hash_entry_id);
+		hlist_nulls_del_init_rcu(&peer->hash_entry_addr4);
+		hlist_nulls_del_init_rcu(&peer->hash_entry_addr6);
+		hlist_nulls_del_init_rcu(&peer->hash_entry_transp_addr);
+		break;
 	case OVPN_MODE_P2P:
 		/* prevent double remove */
 		if (peer != rcu_access_pointer(peer->ovpn->peer))
@@ -292,8 +305,6 @@ static void ovpn_peer_remove(struct ovpn_peer *peer,
 		 */
 		netif_carrier_off(peer->ovpn->dev);
 		break;
-	default:
-		return;
 	}
 
 	peer->delete_reason = reason;
@@ -357,6 +368,89 @@ bool ovpn_peer_check_by_src(struct ovpn_priv *ovpn, struct sk_buff *skb,
 	return match;
 }
 
+#define ovpn_get_hash_head(_tbl, _key, _key_len) ({		\
+	typeof(_tbl) *__tbl = &(_tbl);				\
+	(&(*__tbl)[jhash(_key, _key_len, 0) % HASH_SIZE(*__tbl)]); }) \
+
+/**
+ * ovpn_peer_add_mp - add peer to related tables in a MP instance
+ * @ovpn: the instance to add the peer to
+ * @peer: the peer to add
+ *
+ * Return: 0 on success or a negative error code otherwise
+ */
+static int ovpn_peer_add_mp(struct ovpn_priv *ovpn, struct ovpn_peer *peer)
+{
+	struct sockaddr_storage sa = { 0 };
+	struct hlist_nulls_head *nhead;
+	struct sockaddr_in6 *sa6;
+	struct sockaddr_in *sa4;
+	struct ovpn_bind *bind;
+	struct ovpn_peer *tmp;
+	size_t salen;
+	int ret = 0;
+
+	spin_lock_bh(&ovpn->lock);
+	/* do not add duplicates */
+	tmp = ovpn_peer_get_by_id(ovpn, peer->id);
+	if (tmp) {
+		ovpn_peer_put(tmp);
+		ret = -EEXIST;
+		goto out;
+	}
+
+	bind = rcu_dereference_protected(peer->bind, true);
+	/* peers connected via TCP have bind == NULL */
+	if (bind) {
+		switch (bind->remote.in4.sin_family) {
+		case AF_INET:
+			sa4 = (struct sockaddr_in *)&sa;
+
+			sa4->sin_family = AF_INET;
+			sa4->sin_addr.s_addr = bind->remote.in4.sin_addr.s_addr;
+			sa4->sin_port = bind->remote.in4.sin_port;
+			salen = sizeof(*sa4);
+			break;
+		case AF_INET6:
+			sa6 = (struct sockaddr_in6 *)&sa;
+
+			sa6->sin6_family = AF_INET6;
+			sa6->sin6_addr = bind->remote.in6.sin6_addr;
+			sa6->sin6_port = bind->remote.in6.sin6_port;
+			salen = sizeof(*sa6);
+			break;
+		default:
+			ret = -EPROTONOSUPPORT;
+			goto out;
+		}
+
+		nhead = ovpn_get_hash_head(ovpn->peers->by_transp_addr, &sa,
+					   salen);
+		hlist_nulls_add_head_rcu(&peer->hash_entry_transp_addr, nhead);
+	}
+
+	hlist_add_head_rcu(&peer->hash_entry_id,
+			   ovpn_get_hash_head(ovpn->peers->by_id, &peer->id,
+					      sizeof(peer->id)));
+
+	if (peer->vpn_addrs.ipv4.s_addr != htonl(INADDR_ANY)) {
+		nhead = ovpn_get_hash_head(ovpn->peers->by_vpn_addr4,
+					   &peer->vpn_addrs.ipv4,
+					   sizeof(peer->vpn_addrs.ipv4));
+		hlist_nulls_add_head_rcu(&peer->hash_entry_addr4, nhead);
+	}
+
+	if (!ipv6_addr_any(&peer->vpn_addrs.ipv6)) {
+		nhead = ovpn_get_hash_head(ovpn->peers->by_vpn_addr6,
+					   &peer->vpn_addrs.ipv6,
+					   sizeof(peer->vpn_addrs.ipv6));
+		hlist_nulls_add_head_rcu(&peer->hash_entry_addr6, nhead);
+	}
+out:
+	spin_unlock_bh(&ovpn->lock);
+	return ret;
+}
+
 /**
  * ovpn_peer_add_p2p - add peer to related tables in a P2P instance
  * @ovpn: the instance to add the peer to
@@ -399,11 +493,42 @@ static int ovpn_peer_add_p2p(struct ovpn_priv *ovpn, struct ovpn_peer *peer)
 int ovpn_peer_add(struct ovpn_priv *ovpn, struct ovpn_peer *peer)
 {
 	switch (ovpn->mode) {
+	case OVPN_MODE_MP:
+		return ovpn_peer_add_mp(ovpn, peer);
 	case OVPN_MODE_P2P:
 		return ovpn_peer_add_p2p(ovpn, peer);
-	default:
-		return -EOPNOTSUPP;
 	}
+
+	return -EOPNOTSUPP;
+}
+
+/**
+ * ovpn_peer_del_mp - delete peer from related tables in a MP instance
+ * @peer: the peer to delete
+ * @reason: reason why the peer was deleted (sent to userspace)
+ * @release_list: list where delete peer should be appended
+ *
+ * Return: 0 on success or a negative error code otherwise
+ */
+static int ovpn_peer_del_mp(struct ovpn_peer *peer,
+			    enum ovpn_del_peer_reason reason,
+			    struct llist_head *release_list)
+{
+	struct ovpn_peer *tmp;
+	int ret = -ENOENT;
+
+	lockdep_assert_held(&peer->ovpn->lock);
+
+	tmp = ovpn_peer_get_by_id(peer->ovpn, peer->id);
+	if (tmp == peer) {
+		ovpn_peer_remove(peer, reason, release_list);
+		ret = 0;
+	}
+
+	if (tmp)
+		ovpn_peer_put(tmp);
+
+	return ret;
 }
 
 /**
@@ -480,6 +605,9 @@ int ovpn_peer_del(struct ovpn_peer *peer, enum ovpn_del_peer_reason reason)
 
 	spin_lock_bh(&peer->ovpn->lock);
 	switch (peer->ovpn->mode) {
+	case OVPN_MODE_MP:
+		ret = ovpn_peer_del_mp(peer, reason, &release_list);
+		break;
 	case OVPN_MODE_P2P:
 		ret = ovpn_peer_del_p2p(peer, reason, &release_list);
 		break;
@@ -490,3 +618,43 @@ int ovpn_peer_del(struct ovpn_peer *peer, enum ovpn_del_peer_reason reason)
 
 	return ret;
 }
+
+/**
+ * ovpn_peers_free - free all peers in the instance
+ * @ovpn: the instance whose peers should be released
+ * @sk: if not NULL, only peers using this socket are removed and the socket
+ *      is released immediately
+ * @reason: the reason for releasing all peers
+ */
+void ovpn_peers_free(struct ovpn_priv *ovpn, struct sock *sk,
+		     enum ovpn_del_peer_reason reason)
+{
+	struct ovpn_socket *ovpn_sock;
+	LLIST_HEAD(release_list);
+	struct ovpn_peer *peer;
+	struct hlist_node *tmp;
+	bool skip;
+	int bkt;
+
+	spin_lock_bh(&ovpn->lock);
+	hash_for_each_safe(ovpn->peers->by_id, bkt, tmp, peer, hash_entry_id) {
+		/* if a socket was passed as argument, skip all peers except
+		 * those using it
+		 */
+		if (sk) {
+			skip = true;
+
+			rcu_read_lock();
+			ovpn_sock = rcu_access_pointer(peer->sock);
+			if (ovpn_sock && ovpn_sock->sock->sk == sk)
+				skip = false;
+			rcu_read_unlock();
+
+			if (skip)
+				continue;
+		}
+
+		ovpn_peer_remove(peer, reason, &release_list);
+	}
+	unlock_ovpn(ovpn, &release_list);
+}
diff --git a/drivers/net/ovpn/peer.h b/drivers/net/ovpn/peer.h
index 777a0b24843ed03e83ae8821837103a979e2c6de..e88f1e695bd7a4cb0827f8d552ee900a2b3f722e 100644
--- a/drivers/net/ovpn/peer.h
+++ b/drivers/net/ovpn/peer.h
@@ -25,6 +25,10 @@
  * @vpn_addrs: IP addresses assigned over the tunnel
  * @vpn_addrs.ipv4: IPv4 assigned to peer on the tunnel
  * @vpn_addrs.ipv6: IPv6 assigned to peer on the tunnel
+ * @hash_entry_id: entry in the peer ID hashtable
+ * @hash_entry_addr4: entry in the peer IPv4 hashtable
+ * @hash_entry_addr6: entry in the peer IPv6 hashtable
+ * @hash_entry_transp_addr: entry in the peer transport address hashtable
  * @sock: the socket being used to talk to this peer
  * @tcp: keeps track of TCP specific state
  * @tcp.strp: stream parser context (TCP only)
@@ -57,6 +61,10 @@ struct ovpn_peer {
 		struct in_addr ipv4;
 		struct in6_addr ipv6;
 	} vpn_addrs;
+	struct hlist_node hash_entry_id;
+	struct hlist_nulls_node hash_entry_addr4;
+	struct hlist_nulls_node hash_entry_addr6;
+	struct hlist_nulls_node hash_entry_transp_addr;
 	struct ovpn_socket __rcu *sock;
 
 	struct {
@@ -117,6 +125,8 @@ int ovpn_peer_add(struct ovpn_priv *ovpn, struct ovpn_peer *peer);
 int ovpn_peer_del(struct ovpn_peer *peer, enum ovpn_del_peer_reason reason);
 void ovpn_peer_release_p2p(struct ovpn_priv *ovpn, struct sock *sk,
 			   enum ovpn_del_peer_reason reason);
+void ovpn_peers_free(struct ovpn_priv *ovpn, struct sock *sock,
+		     enum ovpn_del_peer_reason reason);
 
 struct ovpn_peer *ovpn_peer_get_by_transp_addr(struct ovpn_priv *ovpn,
 					       struct sk_buff *skb);
diff --git a/drivers/net/ovpn/udp.c b/drivers/net/ovpn/udp.c
index 81f0ec332fc885d53e5a357512628f245ef3774f..4201ccf00bfb50a768eaf2d6e28a2fd4470e8644 100644
--- a/drivers/net/ovpn/udp.c
+++ b/drivers/net/ovpn/udp.c
@@ -448,9 +448,16 @@ static void ovpn_udp_close(struct sock *sk, long timeout)
 	ovpn = sock->ovpn;
 	rcu_read_unlock();
 
-	if (ovpn->mode == OVPN_MODE_P2P)
+	switch (ovpn->mode) {
+	case OVPN_MODE_MP:
+		ovpn_peers_free(ovpn, sk,
+				OVPN_DEL_PEER_REASON_TRANSPORT_DISCONNECT);
+		break;
+	case OVPN_MODE_P2P:
 		ovpn_peer_release_p2p(ovpn, sk,
 				      OVPN_DEL_PEER_REASON_TRANSPORT_DISCONNECT);
+		break;
+	}
 	sock->udp_prot->close(sk, timeout);
 }
 

-- 
2.45.3

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