Re: [PATCH net-next v18 20/25] ovpn: implement peer add/get/dump/delete via netlink

2025-01-13, 10:31:39 +0100, Antonio Quartulli wrote:

 int ovpn_nl_peer_new_doit(struct sk_buff *skb, struct genl_info *info)
 {
-	return -EOPNOTSUPP;
+	struct nlattr *attrs[OVPN_A_PEER_MAX + 1];
+	struct ovpn_priv *ovpn = info->user_ptr[0];
+	struct ovpn_socket *ovpn_sock;
+	struct socket *sock = NULL;
+	struct ovpn_peer *peer;
+	u32 sockfd, peer_id;
+	int ret;
+
+	/* peers can only be added when the interface is up and running */
+	if (!netif_running(ovpn->dev))
+		return -ENETDOWN;

Since we're not under rtnl_lock here, the device could go down while
we're creating this peer, and we may end up with a down device that
has a peer anyway.

I'm not sure what this (and the peer flushing on NETDEV_DOWN) is
trying to accomplish. Is it a problem to keep peers when the netdevice
is down?

+
+	if (GENL_REQ_ATTR_CHECK(info, OVPN_A_PEER))
+		return -EINVAL;
+
+	ret = nla_parse_nested(attrs, OVPN_A_PEER_MAX, info->attrs[OVPN_A_PEER],
+			       ovpn_peer_nl_policy, info->extack);
+	if (ret)
+		return ret;
+
+	ret = ovpn_nl_peer_precheck(ovpn, info, attrs);
+	if (ret < 0)
+		return ret;
+
+	if (NL_REQ_ATTR_CHECK(info->extack, info->attrs[OVPN_A_PEER], attrs,
+			      OVPN_A_PEER_SOCKET))
+		return -EINVAL;
+
+	peer_id = nla_get_u32(attrs[OVPN_A_PEER_ID]);
+	peer = ovpn_peer_new(ovpn, peer_id);
+	if (IS_ERR(peer)) {
+		NL_SET_ERR_MSG_FMT_MOD(info->extack,
+				       "cannot create new peer object for peer %u: %ld",
+				       peer_id, PTR_ERR(peer));
+		return PTR_ERR(peer);
+	}
+
+	/* lookup the fd in the kernel table and extract the socket object */
+	sockfd = nla_get_u32(attrs[OVPN_A_PEER_SOCKET]);
+	/* sockfd_lookup() increases sock's refcounter */
+	sock = sockfd_lookup(sockfd, &ret);
+	if (!sock) {
+		NL_SET_ERR_MSG_FMT_MOD(info->extack,
+				       "cannot lookup peer socket (fd=%u): %d",
+				       sockfd, ret);
+		return -ENOTSOCK;

All those returns should be "goto peer_release" (and setting ret) so
that we don't leak peer.

+	}
+
+	/* Only when using UDP as transport protocol the remote endpoint
+	 * can be configured so that ovpn knows where to send packets to.
+	 *
+	 * In case of TCP, the socket is connected to the peer and ovpn
+	 * will just send bytes over it, without the need to specify a
+	 * destination.
+	 */
+	if (sock->sk->sk_protocol != IPPROTO_UDP &&
+	    (attrs[OVPN_A_PEER_REMOTE_IPV4] ||
+	     attrs[OVPN_A_PEER_REMOTE_IPV6])) {
+		NL_SET_ERR_MSG_FMT_MOD(info->extack,
+				       "unexpected remote IP address for non UDP socket");
+		sockfd_put(sock);
+		return -EINVAL;

goto peer_release

+	}
+
+	ovpn_sock = ovpn_socket_new(sock, peer);
+	if (IS_ERR(ovpn_sock)) {
+		NL_SET_ERR_MSG_FMT_MOD(info->extack,
+				       "cannot encapsulate socket: %ld",
+				       PTR_ERR(ovpn_sock));
+		sockfd_put(sock);
+		return -ENOTSOCK;

goto peer_release

+	}
+
+	peer->sock = ovpn_sock;
+
+	ret = ovpn_nl_peer_modify(peer, info, attrs);
+	if (ret < 0)
+		goto peer_release;
+
+	ret = ovpn_peer_add(ovpn, peer);
+	if (ret < 0) {
+		NL_SET_ERR_MSG_FMT_MOD(info->extack,
+				       "cannot add new peer (id=%u) to hashtable: %d\n",
+				       peer->id, ret);
+		goto peer_release;
+	}
+
+	return 0;
+
+peer_release:
+	/* release right away because peer is not used in any context */
+	ovpn_peer_release(peer);
+
+	return ret;
 }

[...]

 int ovpn_nl_peer_del_doit(struct sk_buff *skb, struct genl_info *info)
 {
-	return -EOPNOTSUPP;
+	struct nlattr *attrs[OVPN_A_PEER_MAX + 1];
+	struct ovpn_priv *ovpn = info->user_ptr[0];
+	struct ovpn_peer *peer;
+	u32 peer_id;
+	int ret;
+
+	if (GENL_REQ_ATTR_CHECK(info, OVPN_A_PEER))
+		return -EINVAL;
+
+	ret = nla_parse_nested(attrs, OVPN_A_PEER_MAX, info->attrs[OVPN_A_PEER],
+			       ovpn_peer_nl_policy, info->extack);
+	if (ret)
+		return ret;
+
+	if (NL_REQ_ATTR_CHECK(info->extack, info->attrs[OVPN_A_PEER], attrs,
+			      OVPN_A_PEER_ID))
+		return -EINVAL;
+
+	peer_id = nla_get_u32(attrs[OVPN_A_PEER_ID]);
+	peer = ovpn_peer_get_by_id(ovpn, peer_id);
+	if (!peer) {
+		NL_SET_ERR_MSG_FMT_MOD(info->extack,
+				       "cannot find peer with id %u", peer_id);
+		return -ENOENT;
+	}
+
+	netdev_dbg(ovpn->dev, "del peer %u\n", peer->id);
+	ret = ovpn_peer_del(peer, OVPN_DEL_PEER_REASON_USERSPACE);

With the delayed socket release (which is similar to what was in v11,
but now with refcounting on the netdevice which should make
rtnl_link_unregister in ovpn_cleanup wait [*]), we may return to
userspace as if the peer was gone, but the socket hasn't been detached
yet.

A userspace application that tries to remove the peer and immediately
re-create it with the same socket could get EBUSY if the workqueue
hasn't done its job yet. That would be quite confusing to the
application.

So I would add a completion to wait here until the socket has been
fully detached. Something like below.

[*] I don't think the current refcounting fully protects against that,
I'll comment on 05/25


-------- 8< --------

diff --git a/drivers/net/ovpn/netlink.c b/drivers/net/ovpn/netlink.c
index 72357bb5f30b..19aa4ee6d468 100644
--- a/drivers/net/ovpn/netlink.c
+++ b/drivers/net/ovpn/netlink.c

@@ -733,6 +733,9 @@ int ovpn_nl_peer_del_doit(struct sk_buff *skb, struct genl_info *info)
 
 	netdev_dbg(ovpn->dev, "del peer %u\n", peer->id);
 	ret = ovpn_peer_del(peer, OVPN_DEL_PEER_REASON_USERSPACE);
+	if (ret >= 0 && peer->sock)
+		wait_for_completion(&peer->sock_detach);
+
 	ovpn_peer_put(peer);
 
 	return ret;

diff --git a/drivers/net/ovpn/peer.c b/drivers/net/ovpn/peer.c
index b032390047fe..6120521d0c32 100644
--- a/drivers/net/ovpn/peer.c
+++ b/drivers/net/ovpn/peer.c

@@ -92,6 +92,7 @@ struct ovpn_peer *ovpn_peer_new(struct ovpn_priv *ovpn, u32 id)
 	ovpn_peer_stats_init(&peer->vpn_stats);
 	ovpn_peer_stats_init(&peer->link_stats);
 	INIT_WORK(&peer->keepalive_work, ovpn_peer_keepalive_send);
+	init_completion(&peer->sock_detach);
 
 	ret = dst_cache_init(&peer->dst_cache, GFP_KERNEL);
 	if (ret < 0) {

diff --git a/drivers/net/ovpn/peer.h b/drivers/net/ovpn/peer.h
index 7a062cc5a5a4..8c54bf5709ef 100644
--- a/drivers/net/ovpn/peer.h
+++ b/drivers/net/ovpn/peer.h

@@ -112,6 +112,7 @@ struct ovpn_peer {
 	struct rcu_head rcu;
 	struct work_struct remove_work;
 	struct work_struct keepalive_work;
+	struct completion sock_detach;
 };
 
 /**

diff --git a/drivers/net/ovpn/socket.c b/drivers/net/ovpn/socket.c
index a5c3bc834a35..7cefac42c3be 100644
--- a/drivers/net/ovpn/socket.c
+++ b/drivers/net/ovpn/socket.c

@@ -31,6 +31,8 @@ static void ovpn_socket_release_kref(struct kref *kref)
 
 	sockfd_put(sock->sock);
 	kfree_rcu(sock, rcu);
+
+	complete(&sock->peer->sock_detach);
 }
 
 /**

@@ -181,12 +183,12 @@ struct ovpn_socket *ovpn_socket_new(struct socket *sock, struct ovpn_peer *peer)
 
 	ovpn_sock->sock = sock;
 	kref_init(&ovpn_sock->refcount);
+	ovpn_sock->peer = peer;
 
 	/* TCP sockets are per-peer, therefore they are linked to their unique
 	 * peer
 	 */
 	if (sock->sk->sk_protocol == IPPROTO_TCP) {
-		ovpn_sock->peer = peer;
 		ovpn_peer_hold(peer);
 	} else if (sock->sk->sk_protocol == IPPROTO_UDP) {
 		/* in UDP we only link the ovpn instance since the socket is

diff --git a/drivers/net/ovpn/socket.h b/drivers/net/ovpn/socket.h
index 15827e347f53..3f5a35fd9048 100644
--- a/drivers/net/ovpn/socket.h
+++ b/drivers/net/ovpn/socket.h

@@ -28,12 +28,12 @@ struct ovpn_peer;
  * @rcu: member used to schedule RCU destructor callback
  */
 struct ovpn_socket {
+	struct ovpn_peer *peer;
 	union {
 		struct {
 			struct ovpn_priv *ovpn;
 			netdevice_tracker dev_tracker;
 		};
-		struct ovpn_peer *peer;
 	};
 
 	struct socket *sock;

-- 
Sabrina