ovpn: implement key add/get/del/swap via netlink

This change introduces the netlink commands needed to add, get, delete
and swap keys for a specific peer.

Userspace is expected to use these commands to create, inspect (non
sensitive data only), destroy and rotate session keys for a specific
peer.

Signed-off-by: Antonio Quartulli <antonio@openvpn.net>
Link: https://patch.msgid.link/20250415-b4-ovpn-v26-19-577f6097b964@openvpn.net
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/ovpn/crypto.c

@@ -146,3 +146,43 @@ void ovpn_crypto_key_slots_swap(struct ovpn_crypto_state *cs)
 
 	spin_unlock_bh(&cs->lock);
 }
+
+/**
+ * ovpn_crypto_config_get - populate keyconf object with non-sensible key data
+ * @cs: the crypto state to extract the key data from
+ * @slot: the specific slot to inspect
+ * @keyconf: the output object to populate
+ *
+ * Return: 0 on success or a negative error code otherwise
+ */
+int ovpn_crypto_config_get(struct ovpn_crypto_state *cs,
+			   enum ovpn_key_slot slot,
+			   struct ovpn_key_config *keyconf)
+{
+	struct ovpn_crypto_key_slot *ks;
+	int idx;
+
+	switch (slot) {
+	case OVPN_KEY_SLOT_PRIMARY:
+		idx = cs->primary_idx;
+		break;
+	case OVPN_KEY_SLOT_SECONDARY:
+		idx = !cs->primary_idx;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	rcu_read_lock();
+	ks = rcu_dereference(cs->slots[idx]);
+	if (!ks) {
+		rcu_read_unlock();
+		return -ENOENT;
+	}
+
+	keyconf->cipher_alg = ovpn_aead_crypto_alg(ks);
+	keyconf->key_id = ks->key_id;
+	rcu_read_unlock();
+
+	return 0;
+}

drivers/net/ovpn/crypto.h

@@ -136,4 +136,8 @@ void ovpn_crypto_state_release(struct ovpn_crypto_state *cs);
 
 void ovpn_crypto_key_slots_swap(struct ovpn_crypto_state *cs);
 
+int ovpn_crypto_config_get(struct ovpn_crypto_state *cs,
+			   enum ovpn_key_slot slot,
+			   struct ovpn_key_config *keyconf);
+
 #endif /* _NET_OVPN_OVPNCRYPTO_H_ */

drivers/net/ovpn/crypto_aead.c

@@ -364,3 +364,20 @@ ovpn_aead_crypto_key_slot_new(const struct ovpn_key_config *kc)
 	ovpn_aead_crypto_key_slot_destroy(ks);
 	return ERR_PTR(ret);
 }
+
+enum ovpn_cipher_alg ovpn_aead_crypto_alg(struct ovpn_crypto_key_slot *ks)
+{
+	const char *alg_name;
+
+	if (!ks->encrypt)
+		return OVPN_CIPHER_ALG_NONE;
+
+	alg_name = crypto_tfm_alg_name(crypto_aead_tfm(ks->encrypt));
+
+	if (!strcmp(alg_name, ALG_NAME_AES))
+		return OVPN_CIPHER_ALG_AES_GCM;
+	else if (!strcmp(alg_name, ALG_NAME_CHACHAPOLY))
+		return OVPN_CIPHER_ALG_CHACHA20_POLY1305;
+	else
+		return OVPN_CIPHER_ALG_NONE;
+}

drivers/net/ovpn/crypto_aead.h

@@ -24,4 +24,6 @@ struct ovpn_crypto_key_slot *
 ovpn_aead_crypto_key_slot_new(const struct ovpn_key_config *kc);
 void ovpn_aead_crypto_key_slot_destroy(struct ovpn_crypto_key_slot *ks);
 
+enum ovpn_cipher_alg ovpn_aead_crypto_alg(struct ovpn_crypto_key_slot *ks);
+
 #endif /* _NET_OVPN_OVPNAEAD_H_ */

drivers/net/ovpn/netlink.c

@@ -17,6 +17,7 @@
 #include "netlink.h"
 #include "netlink-gen.h"
 #include "bind.h"
+#include "crypto.h"
 #include "peer.h"
 #include "socket.h"
 
@@ -790,24 +791,316 @@ int ovpn_nl_peer_del_doit(struct sk_buff *skb, struct genl_info *info)
 	return ret;
 }
 
+static int ovpn_nl_get_key_dir(struct genl_info *info, struct nlattr *key,
+			       enum ovpn_cipher_alg cipher,
+			       struct ovpn_key_direction *dir)
+{
+	struct nlattr *attrs[OVPN_A_KEYDIR_MAX + 1];
+	int ret;
+
+	ret = nla_parse_nested(attrs, OVPN_A_KEYDIR_MAX, key,
+			       ovpn_keydir_nl_policy, info->extack);
+	if (ret)
+		return ret;
+
+	switch (cipher) {
+	case OVPN_CIPHER_ALG_AES_GCM:
+	case OVPN_CIPHER_ALG_CHACHA20_POLY1305:
+		if (NL_REQ_ATTR_CHECK(info->extack, key, attrs,
+				      OVPN_A_KEYDIR_CIPHER_KEY) ||
+		    NL_REQ_ATTR_CHECK(info->extack, key, attrs,
+				      OVPN_A_KEYDIR_NONCE_TAIL))
+			return -EINVAL;
+
+		dir->cipher_key = nla_data(attrs[OVPN_A_KEYDIR_CIPHER_KEY]);
+		dir->cipher_key_size = nla_len(attrs[OVPN_A_KEYDIR_CIPHER_KEY]);
+
+		/* These algorithms require a 96bit nonce,
+		 * Construct it by combining 4-bytes packet id and
+		 * 8-bytes nonce-tail from userspace
+		 */
+		dir->nonce_tail = nla_data(attrs[OVPN_A_KEYDIR_NONCE_TAIL]);
+		dir->nonce_tail_size = nla_len(attrs[OVPN_A_KEYDIR_NONCE_TAIL]);
+		break;
+	default:
+		NL_SET_ERR_MSG_MOD(info->extack, "unsupported cipher");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+/**
+ * ovpn_nl_key_new_doit - configure a new key for the specified peer
+ * @skb: incoming netlink message
+ * @info: genetlink metadata
+ *
+ * This function allows the user to install a new key in the peer crypto
+ * state.
+ * Each peer has two 'slots', namely 'primary' and 'secondary', where
+ * keys can be installed. The key in the 'primary' slot is used for
+ * encryption, while both keys can be used for decryption by matching the
+ * key ID carried in the incoming packet.
+ *
+ * The user is responsible for rotating keys when necessary. The user
+ * may fetch peer traffic statistics via netlink in order to better
+ * identify the right time to rotate keys.
+ * The renegotiation follows these steps:
+ * 1. a new key is computed by the user and is installed in the 'secondary'
+ *    slot
+ * 2. at user discretion (usually after a predetermined time) 'primary' and
+ *    'secondary' contents are swapped and the new key starts being used for
+ *    encryption, while the old key is kept around for decryption of late
+ *    packets.
+ *
+ * Return: 0 on success or a negative error code otherwise.
+ */
 int ovpn_nl_key_new_doit(struct sk_buff *skb, struct genl_info *info)
 {
-	return -EOPNOTSUPP;
+	struct nlattr *attrs[OVPN_A_KEYCONF_MAX + 1];
+	struct ovpn_priv *ovpn = info->user_ptr[0];
+	struct ovpn_peer_key_reset pkr;
+	struct ovpn_peer *peer;
+	u32 peer_id;
+	int ret;
+
+	if (GENL_REQ_ATTR_CHECK(info, OVPN_A_KEYCONF))
+		return -EINVAL;
+
+	ret = nla_parse_nested(attrs, OVPN_A_KEYCONF_MAX,
+			       info->attrs[OVPN_A_KEYCONF],
+			       ovpn_keyconf_nl_policy, info->extack);
+	if (ret)
+		return ret;
+
+	if (NL_REQ_ATTR_CHECK(info->extack, info->attrs[OVPN_A_KEYCONF], attrs,
+			      OVPN_A_KEYCONF_PEER_ID))
+		return -EINVAL;
+
+	if (NL_REQ_ATTR_CHECK(info->extack, info->attrs[OVPN_A_KEYCONF], attrs,
+			      OVPN_A_KEYCONF_SLOT) ||
+	    NL_REQ_ATTR_CHECK(info->extack, info->attrs[OVPN_A_KEYCONF], attrs,
+			      OVPN_A_KEYCONF_KEY_ID) ||
+	    NL_REQ_ATTR_CHECK(info->extack, info->attrs[OVPN_A_KEYCONF], attrs,
+			      OVPN_A_KEYCONF_CIPHER_ALG) ||
+	    NL_REQ_ATTR_CHECK(info->extack, info->attrs[OVPN_A_KEYCONF], attrs,
+			      OVPN_A_KEYCONF_ENCRYPT_DIR) ||
+	    NL_REQ_ATTR_CHECK(info->extack, info->attrs[OVPN_A_KEYCONF], attrs,
+			      OVPN_A_KEYCONF_DECRYPT_DIR))
+		return -EINVAL;
+
+	pkr.slot = nla_get_u32(attrs[OVPN_A_KEYCONF_SLOT]);
+	pkr.key.key_id = nla_get_u32(attrs[OVPN_A_KEYCONF_KEY_ID]);
+	pkr.key.cipher_alg = nla_get_u32(attrs[OVPN_A_KEYCONF_CIPHER_ALG]);
+
+	ret = ovpn_nl_get_key_dir(info, attrs[OVPN_A_KEYCONF_ENCRYPT_DIR],
+				  pkr.key.cipher_alg, &pkr.key.encrypt);
+	if (ret < 0)
+		return ret;
+
+	ret = ovpn_nl_get_key_dir(info, attrs[OVPN_A_KEYCONF_DECRYPT_DIR],
+				  pkr.key.cipher_alg, &pkr.key.decrypt);
+	if (ret < 0)
+		return ret;
+
+	peer_id = nla_get_u32(attrs[OVPN_A_KEYCONF_PEER_ID]);
+	peer = ovpn_peer_get_by_id(ovpn, peer_id);
+	if (!peer) {
+		NL_SET_ERR_MSG_FMT_MOD(info->extack,
+				       "no peer with id %u to set key for",
+				       peer_id);
+		return -ENOENT;
+	}
+
+	ret = ovpn_crypto_state_reset(&peer->crypto, &pkr);
+	if (ret < 0) {
+		NL_SET_ERR_MSG_FMT_MOD(info->extack,
+				       "cannot install new key for peer %u",
+				       peer_id);
+		goto out;
+	}
+
+	netdev_dbg(ovpn->dev, "new key installed (id=%u) for peer %u\n",
+		   pkr.key.key_id, peer_id);
+out:
+	ovpn_peer_put(peer);
+	return ret;
+}
+
+static int ovpn_nl_send_key(struct sk_buff *skb, const struct genl_info *info,
+			    u32 peer_id, enum ovpn_key_slot slot,
+			    const struct ovpn_key_config *keyconf)
+{
+	struct nlattr *attr;
+	void *hdr;
+
+	hdr = genlmsg_put(skb, info->snd_portid, info->snd_seq, &ovpn_nl_family,
+			  0, OVPN_CMD_KEY_GET);
+	if (!hdr)
+		return -ENOBUFS;
+
+	attr = nla_nest_start(skb, OVPN_A_KEYCONF);
+	if (!attr)
+		goto err;
+
+	if (nla_put_u32(skb, OVPN_A_KEYCONF_PEER_ID, peer_id))
+		goto err;
+
+	if (nla_put_u32(skb, OVPN_A_KEYCONF_SLOT, slot) ||
+	    nla_put_u32(skb, OVPN_A_KEYCONF_KEY_ID, keyconf->key_id) ||
+	    nla_put_u32(skb, OVPN_A_KEYCONF_CIPHER_ALG, keyconf->cipher_alg))
+		goto err;
+
+	nla_nest_end(skb, attr);
+	genlmsg_end(skb, hdr);
+
+	return 0;
+err:
+	genlmsg_cancel(skb, hdr);
+	return -EMSGSIZE;
 }
 
 int ovpn_nl_key_get_doit(struct sk_buff *skb, struct genl_info *info)
 {
-	return -EOPNOTSUPP;
+	struct nlattr *attrs[OVPN_A_KEYCONF_MAX + 1];
+	struct ovpn_priv *ovpn = info->user_ptr[0];
+	struct ovpn_key_config keyconf = { 0 };
+	enum ovpn_key_slot slot;
+	struct ovpn_peer *peer;
+	struct sk_buff *msg;
+	u32 peer_id;
+	int ret;
+
+	if (GENL_REQ_ATTR_CHECK(info, OVPN_A_KEYCONF))
+		return -EINVAL;
+
+	ret = nla_parse_nested(attrs, OVPN_A_KEYCONF_MAX,
+			       info->attrs[OVPN_A_KEYCONF],
+			       ovpn_keyconf_nl_policy, info->extack);
+	if (ret)
+		return ret;
+
+	if (NL_REQ_ATTR_CHECK(info->extack, info->attrs[OVPN_A_KEYCONF], attrs,
+			      OVPN_A_KEYCONF_PEER_ID))
+		return -EINVAL;
+
+	if (NL_REQ_ATTR_CHECK(info->extack, info->attrs[OVPN_A_KEYCONF], attrs,
+			      OVPN_A_KEYCONF_SLOT))
+		return -EINVAL;
+
+	peer_id = nla_get_u32(attrs[OVPN_A_KEYCONF_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;
+	}
+
+	slot = nla_get_u32(attrs[OVPN_A_KEYCONF_SLOT]);
+
+	ret = ovpn_crypto_config_get(&peer->crypto, slot, &keyconf);
+	if (ret < 0) {
+		NL_SET_ERR_MSG_FMT_MOD(info->extack,
+				       "cannot extract key from slot %u for peer %u",
+				       slot, peer_id);
+		goto err;
+	}
+
+	msg = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
+	if (!msg) {
+		ret = -ENOMEM;
+		goto err;
+	}
+
+	ret = ovpn_nl_send_key(msg, info, peer->id, slot, &keyconf);
+	if (ret < 0) {
+		nlmsg_free(msg);
+		goto err;
+	}
+
+	ret = genlmsg_reply(msg, info);
+err:
+	ovpn_peer_put(peer);
+	return ret;
 }
 
 int ovpn_nl_key_swap_doit(struct sk_buff *skb, struct genl_info *info)
 {
-	return -EOPNOTSUPP;
+	struct ovpn_priv *ovpn = info->user_ptr[0];
+	struct nlattr *attrs[OVPN_A_PEER_MAX + 1];
+	struct ovpn_peer *peer;
+	u32 peer_id;
+	int ret;
+
+	if (GENL_REQ_ATTR_CHECK(info, OVPN_A_KEYCONF))
+		return -EINVAL;
+
+	ret = nla_parse_nested(attrs, OVPN_A_KEYCONF_MAX,
+			       info->attrs[OVPN_A_KEYCONF],
+			       ovpn_keyconf_nl_policy, info->extack);
+	if (ret)
+		return ret;
+
+	if (NL_REQ_ATTR_CHECK(info->extack, info->attrs[OVPN_A_KEYCONF], attrs,
+			      OVPN_A_KEYCONF_PEER_ID))
+		return -EINVAL;
+
+	peer_id = nla_get_u32(attrs[OVPN_A_KEYCONF_PEER_ID]);
+	peer = ovpn_peer_get_by_id(ovpn, peer_id);
+	if (!peer) {
+		NL_SET_ERR_MSG_FMT_MOD(info->extack,
+				       "no peer with id %u to swap keys for",
+				       peer_id);
+		return -ENOENT;
+	}
+
+	ovpn_crypto_key_slots_swap(&peer->crypto);
+	ovpn_peer_put(peer);
+
+	return 0;
 }
 
 int ovpn_nl_key_del_doit(struct sk_buff *skb, struct genl_info *info)
 {
-	return -EOPNOTSUPP;
+	struct nlattr *attrs[OVPN_A_KEYCONF_MAX + 1];
+	struct ovpn_priv *ovpn = info->user_ptr[0];
+	enum ovpn_key_slot slot;
+	struct ovpn_peer *peer;
+	u32 peer_id;
+	int ret;
+
+	if (GENL_REQ_ATTR_CHECK(info, OVPN_A_KEYCONF))
+		return -EINVAL;
+
+	ret = nla_parse_nested(attrs, OVPN_A_KEYCONF_MAX,
+			       info->attrs[OVPN_A_KEYCONF],
+			       ovpn_keyconf_nl_policy, info->extack);
+	if (ret)
+		return ret;
+
+	if (NL_REQ_ATTR_CHECK(info->extack, info->attrs[OVPN_A_KEYCONF], attrs,
+			      OVPN_A_KEYCONF_PEER_ID))
+		return -EINVAL;
+
+	if (NL_REQ_ATTR_CHECK(info->extack, info->attrs[OVPN_A_KEYCONF], attrs,
+			      OVPN_A_KEYCONF_SLOT))
+		return -EINVAL;
+
+	peer_id = nla_get_u32(attrs[OVPN_A_KEYCONF_PEER_ID]);
+	slot = nla_get_u32(attrs[OVPN_A_KEYCONF_SLOT]);
+
+	peer = ovpn_peer_get_by_id(ovpn, peer_id);
+	if (!peer) {
+		NL_SET_ERR_MSG_FMT_MOD(info->extack,
+				       "no peer with id %u to delete key for",
+				       peer_id);
+		return -ENOENT;
+	}
+
+	ovpn_crypto_key_slot_delete(&peer->crypto, slot);
+	ovpn_peer_put(peer);
+
+	return 0;
 }
 
 /**