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.

Userspace has two ways of deciding when the key has to be renewed before
exhausting the IV space:
1) time based approach:
   after X seconds/minutes userspace generates a new key and sends it
   to the kernel. This is based on guestimate and normally default
   timer value works well.

2) packet count based approach:
   after X packets/bytes userspace generates a new key and sends it to
   the kernel. Userspace keeps track of the amount of traffic by
   periodically polling GET_PEER and fetching the VPN/LINK stats.

Signed-off-by: Antonio Quartulli <antonio@openvpn.net>
Link: https://patch.msgid.link/20250415-b4-ovpn-v26-20-577f6097b964@openvpn.net
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/drivers/net/ovpn/crypto.c b/drivers/net/ovpn/crypto.c
index deeefffc098162b17ea53eb7a5de6b0f19a38022..90580e32052fb56c646a6df7816872366133bc75 100644 (file)
--- a/drivers/net/ovpn/crypto.c
+++ b/drivers/net/ovpn/crypto.c
@@ -54,6 +54,28 @@ void ovpn_crypto_state_release(struct ovpn_crypto_state *cs)
        }
 }
 
+/* removes the key matching the specified id from the crypto context */
+bool ovpn_crypto_kill_key(struct ovpn_crypto_state *cs, u8 key_id)
+{
+       struct ovpn_crypto_key_slot *ks = NULL;
+
+       spin_lock_bh(&cs->lock);
+       if (rcu_access_pointer(cs->slots[0])->key_id == key_id) {
+               ks = rcu_replace_pointer(cs->slots[0], NULL,
+                                        lockdep_is_held(&cs->lock));
+       } else if (rcu_access_pointer(cs->slots[1])->key_id == key_id) {
+               ks = rcu_replace_pointer(cs->slots[1], NULL,
+                                        lockdep_is_held(&cs->lock));
+       }
+       spin_unlock_bh(&cs->lock);
+
+       if (ks)
+               ovpn_crypto_key_slot_put(ks);
+
+       /* let the caller know if a key was actually killed */
+       return ks;
+}
+
 /* Reset the ovpn_crypto_state object in a way that is atomic
  * to RCU readers.
  */

diff --git a/drivers/net/ovpn/crypto.h b/drivers/net/ovpn/crypto.h
index 487d24a7d26635c9ca0fd66c75717502f60e7a0c..0e284fec3a75a0a5933978ea9d136f87a2e5c57a 100644 (file)
--- a/drivers/net/ovpn/crypto.h
+++ b/drivers/net/ovpn/crypto.h
@@ -140,4 +140,6 @@ int ovpn_crypto_config_get(struct ovpn_crypto_state *cs,
                           enum ovpn_key_slot slot,
                           struct ovpn_key_config *keyconf);
 
+bool ovpn_crypto_kill_key(struct ovpn_crypto_state *cs, u8 key_id);
+
 #endif /* _NET_OVPN_OVPNCRYPTO_H_ */

diff --git a/drivers/net/ovpn/io.c b/drivers/net/ovpn/io.c
index fd8820c7d133707b7ba52462218c428fdeca24d5..dd8a8055d9676e4b57cf9b5dc0ff1d082d231850 100644 (file)
--- a/drivers/net/ovpn/io.c
+++ b/drivers/net/ovpn/io.c
@@ -245,6 +245,20 @@ void ovpn_encrypt_post(void *data, int ret)
        kfree(ovpn_skb_cb(skb)->sg);
        aead_request_free(ovpn_skb_cb(skb)->req);
 
+       if (unlikely(ret == -ERANGE)) {
+               /* we ran out of IVs and we must kill the key as it can't be
+                * use anymore
+                */
+               netdev_warn(peer->ovpn->dev,
+                           "killing key %u for peer %u\n", ks->key_id,
+                           peer->id);
+               if (ovpn_crypto_kill_key(&peer->crypto, ks->key_id))
+                       /* let userspace know so that a new key must be negotiated */
+                       ovpn_nl_key_swap_notify(peer, ks->key_id);
+
+               goto err;
+       }
+
        if (unlikely(ret < 0))
                goto err;
 

diff --git a/drivers/net/ovpn/netlink.c b/drivers/net/ovpn/netlink.c
index 1f4220021df3a6e74d6e8946a58882bf5d66e444..f0b5716059364a1deee1c7d4da1d5341b53dffca 100644 (file)
--- a/drivers/net/ovpn/netlink.c
+++ b/drivers/net/ovpn/netlink.c
@@ -1103,6 +1103,70 @@ int ovpn_nl_key_del_doit(struct sk_buff *skb, struct genl_info *info)
        return 0;
 }
 
+/**
+ * ovpn_nl_key_swap_notify - notify userspace peer's key must be renewed
+ * @peer: the peer whose key needs to be renewed
+ * @key_id: the ID of the key that needs to be renewed
+ *
+ * Return: 0 on success or a negative error code otherwise
+ */
+int ovpn_nl_key_swap_notify(struct ovpn_peer *peer, u8 key_id)
+{
+       struct ovpn_socket *sock;
+       struct nlattr *k_attr;
+       struct sk_buff *msg;
+       int ret = -EMSGSIZE;
+       void *hdr;
+
+       netdev_info(peer->ovpn->dev, "peer with id %u must rekey - primary key unusable.\n",
+                   peer->id);
+
+       msg = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_ATOMIC);
+       if (!msg)
+               return -ENOMEM;
+
+       hdr = genlmsg_put(msg, 0, 0, &ovpn_nl_family, 0, OVPN_CMD_KEY_SWAP_NTF);
+       if (!hdr) {
+               ret = -ENOBUFS;
+               goto err_free_msg;
+       }
+
+       if (nla_put_u32(msg, OVPN_A_IFINDEX, peer->ovpn->dev->ifindex))
+               goto err_cancel_msg;
+
+       k_attr = nla_nest_start(msg, OVPN_A_KEYCONF);
+       if (!k_attr)
+               goto err_cancel_msg;
+
+       if (nla_put_u32(msg, OVPN_A_KEYCONF_PEER_ID, peer->id))
+               goto err_cancel_msg;
+
+       if (nla_put_u16(msg, OVPN_A_KEYCONF_KEY_ID, key_id))
+               goto err_cancel_msg;
+
+       nla_nest_end(msg, k_attr);
+       genlmsg_end(msg, hdr);
+
+       rcu_read_lock();
+       sock = rcu_dereference(peer->sock);
+       if (!sock) {
+               ret = -EINVAL;
+               goto err_unlock;
+       }
+       genlmsg_multicast_netns(&ovpn_nl_family, sock_net(sock->sock->sk),
+                               msg, 0, OVPN_NLGRP_PEERS, GFP_ATOMIC);
+       rcu_read_unlock();
+
+       return 0;
+err_unlock:
+       rcu_read_unlock();
+err_cancel_msg:
+       genlmsg_cancel(msg, hdr);
+err_free_msg:
+       nlmsg_free(msg);
+       return ret;
+}
+
 /**
  * ovpn_nl_register - perform any needed registration in the NL subsustem
  *

diff --git a/drivers/net/ovpn/netlink.h b/drivers/net/ovpn/netlink.h
index 0d6c34e17082cc7c52dd9c5d5ed1e964925b3f4b..5dc84c8e5e803014053faa0d892fc3a7259d40e5 100644 (file)
--- a/drivers/net/ovpn/netlink.h
+++ b/drivers/net/ovpn/netlink.h
@@ -12,4 +12,6 @@
 int ovpn_nl_register(void);
 void ovpn_nl_unregister(void);
 
+int ovpn_nl_key_swap_notify(struct ovpn_peer *peer, u8 key_id);
+
 #endif /* _NET_OVPN_NETLINK_H_ */