netdev - [PATCH net-next v2 20/22] ovpn: kill key and notify userspace in case of IV exhaustion

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Message-ID: <20240304150914.11444-21-antonio@openvpn.net>
Date: Mon,  4 Mar 2024 16:09:11 +0100
From: Antonio Quartulli <antonio@...nvpn.net>
To: netdev@...r.kernel.org
Cc: Jakub Kicinski <kuba@...nel.org>,
	Sergey Ryazanov <ryazanov.s.a@...il.com>,
	Paolo Abeni <pabeni@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Antonio Quartulli <antonio@...nvpn.net>
Subject: [PATCH net-next v2 20/22] ovpn: kill key and notify userspace in case of IV exhaustion

IV wrap-around is cryptographically dangerous for a number of ciphers,
therefore kill the key and inform userspace (via netlink) should the
IV space go exhausted.

Signed-off-by: Antonio Quartulli <antonio@...nvpn.net>
---
 drivers/net/ovpn/io.c      | 14 +++++++++++++
 drivers/net/ovpn/netlink.c | 42 ++++++++++++++++++++++++++++++++++++++
 drivers/net/ovpn/netlink.h |  3 +++
 3 files changed, 59 insertions(+)

diff --git a/drivers/net/ovpn/io.c b/drivers/net/ovpn/io.c
index cb2a355f8766..ea8367c3da08 100644
--- a/drivers/net/ovpn/io.c
+++ b/drivers/net/ovpn/io.c
@@ -318,6 +318,20 @@ static bool ovpn_encrypt_one(struct ovpn_peer *peer, struct sk_buff *skb)
 	/* encrypt */
 	ret = ovpn_aead_encrypt(ks, skb, peer->id);
 	if (unlikely(ret < 0)) {
+		/* if we ran out of IVs we must kill the key as it can't be used anymore */
+		if (ret == -ERANGE) {
+			netdev_warn(peer->ovpn->dev,
+				    "killing primary key as we ran out of IVs for peer %u\n",
+				    peer->id);
+			ovpn_crypto_kill_primary(&peer->crypto);
+			ret = ovpn_nl_notify_swap_keys(peer);
+			if (ret < 0)
+				netdev_warn(peer->ovpn->dev,
+					    "couldn't send key killing notification to userspace for peer %u\n",
+					    peer->id);
+			goto err;
+		}
+
 		net_err_ratelimited("%s: error during encryption for peer %u, key-id %u: %d\n",
 				    peer->ovpn->dev->name, peer->id, ks->key_id, ret);
 		goto err;
diff --git a/drivers/net/ovpn/netlink.c b/drivers/net/ovpn/netlink.c
index dbe1dfddba4c..e8b55c0a15e9 100644
--- a/drivers/net/ovpn/netlink.c
+++ b/drivers/net/ovpn/netlink.c
@@ -891,6 +891,48 @@ static struct genl_family ovpn_nl_family __ro_after_init = {
 	.n_mcgrps = ARRAY_SIZE(ovpn_nl_mcgrps),
 };
 
+int ovpn_nl_notify_swap_keys(struct ovpn_peer *peer)
+{
+	struct sk_buff *msg;
+	void *hdr;
+	int ret;
+
+	netdev_info(peer->ovpn->dev, "peer with id %u must rekey - primary key unusable.\n",
+		    peer->id);
+
+	msg = nlmsg_new(100, GFP_KERNEL);
+	if (!msg)
+		return -ENOMEM;
+
+	hdr = genlmsg_put(msg, 0, 0, &ovpn_nl_family, 0,
+			  OVPN_CMD_SWAP_KEYS);
+	if (!hdr) {
+		ret = -ENOBUFS;
+		goto err_free_msg;
+	}
+
+	if (nla_put_u32(msg, OVPN_A_IFINDEX, peer->ovpn->dev->ifindex)) {
+		ret = -EMSGSIZE;
+		goto err_free_msg;
+	}
+
+	if (nla_put_u32(msg, OVPN_A_PEER_ID, peer->id)) {
+		ret = -EMSGSIZE;
+		goto err_free_msg;
+	}
+
+	genlmsg_end(msg, hdr);
+
+	genlmsg_multicast_netns(&ovpn_nl_family, dev_net(peer->ovpn->dev),
+				msg, 0, OVPN_MCGRP_PEERS, GFP_KERNEL);
+
+	return 0;
+
+err_free_msg:
+	nlmsg_free(msg);
+	return ret;
+}
+
 /**
  * ovpn_nl_notify() - react to openvpn userspace process exit
  */
diff --git a/drivers/net/ovpn/netlink.h b/drivers/net/ovpn/netlink.h
index eb7f234842ef..17ca69761440 100644
--- a/drivers/net/ovpn/netlink.h
+++ b/drivers/net/ovpn/netlink.h
@@ -9,10 +9,13 @@
 #ifndef _NET_OVPN_NETLINK_H_
 #define _NET_OVPN_NETLINK_H_
 
+struct ovpn_peer;
 struct ovpn_struct;
 
 int ovpn_nl_init(struct ovpn_struct *ovpn);
 int ovpn_nl_register(void);
 void ovpn_nl_unregister(void);
 
+int ovpn_nl_notify_swap_keys(struct ovpn_peer *peer);
+
 #endif /* _NET_OVPN_NETLINK_H_ */
-- 
2.43.0