netdev - [PATCH net-next v3 21/24] ovpn: kill key and notify userspace in case of IV exhaustion

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Message-ID: <20240506011637.27272-22-antonio@openvpn.net>
Date: Mon,  6 May 2024 03:16:34 +0200
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>,
	Andrew Lunn <andrew@...n.ch>,
	Esben Haabendal <esben@...nix.com>,
	Antonio Quartulli <antonio@...nvpn.net>
Subject: [PATCH net-next v3 21/24] 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      | 16 +++++++++++++++
 drivers/net/ovpn/netlink.c | 42 ++++++++++++++++++++++++++++++++++++++
 drivers/net/ovpn/netlink.h |  8 ++++++++
 3 files changed, 66 insertions(+)

diff --git a/drivers/net/ovpn/io.c b/drivers/net/ovpn/io.c
index 19ebc0fbe2be..8806479ccae5 100644
--- a/drivers/net/ovpn/io.c
+++ b/drivers/net/ovpn/io.c
@@ -336,6 +336,22 @@ 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);
diff --git a/drivers/net/ovpn/netlink.c b/drivers/net/ovpn/netlink.c
index df14988c1f43..dc80004eadbb 100644
--- a/drivers/net/ovpn/netlink.c
+++ b/drivers/net/ovpn/netlink.c
@@ -862,6 +862,48 @@ int ovpn_nl_del_key_doit(struct sk_buff *skb, struct genl_info *info)
 	return 0;
 }
 
+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_NLGRP_PEERS, GFP_KERNEL);
+
+	return 0;
+
+err_free_msg:
+	nlmsg_free(msg);
+	return ret;
+}
+
 /**
  * ovpn_nl_init - perform any ovpn specific netlink initialization
  * @ovpn: the openvpn instance object
diff --git a/drivers/net/ovpn/netlink.h b/drivers/net/ovpn/netlink.h
index d79f3ca604b0..ccc49130a150 100644
--- a/drivers/net/ovpn/netlink.h
+++ b/drivers/net/ovpn/netlink.h
@@ -27,4 +27,12 @@ int ovpn_nl_register(void);
  */
 void ovpn_nl_unregister(void);
 
+/**
+ * ovpn_nl_notify_swap_keys - notify userspace peer's key must be renewed
+ * @peer: the peer whose key needs to be renewed
+ *
+ * Return: 0 on success or a negative error code otherwise
+ */
+int ovpn_nl_notify_swap_keys(struct ovpn_peer *peer);
+
 #endif /* _NET_OVPN_NETLINK_H_ */
-- 
2.43.2