[PATCH net-next v18 21/25] ovpn: implement key add/get/del/swap via netlink

Antonio Quartulli
2025-01-13T09:31:33Z

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>
---
drivers/net/ovpn/crypto.c | 40 ++++++
drivers/net/ovpn/crypto.h | 4 +
drivers/net/ovpn/crypto_aead.c | 17 +++
drivers/net/ovpn/crypto_aead.h | 2 +
drivers/net/ovpn/netlink.c | 301 ++++++++++++++++++++++++++++++++++++++++-
5 files changed, 360 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ovpn/crypto.c b/drivers/net/ovpn/crypto.c
index fabc19994ba34260753911ac7d3e50b643b9b89f..6fccd73c6cf7d2566d1b819cb6d5d7b2ea98e81d 100644
--- a/drivers/net/ovpn/crypto.c
+++ b/drivers/net/ovpn/crypto.c
@@ -150,3 +150,43 @@ 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;
+}
diff --git a/drivers/net/ovpn/crypto.h b/drivers/net/ovpn/crypto.h
index 33eb5bea59dc68110abfc5e940ffd841ac706388..87addc7bf07c02c3c23da7e6d1f86249d1d867c6 100644
--- a/drivers/net/ovpn/crypto.h
+++ b/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_ */
diff --git a/drivers/net/ovpn/crypto_aead.c b/drivers/net/ovpn/crypto_aead.c
index 03e35fa819e203efed4e79ac04f2be6040252312..7c56244af0750b8eafd9cf43f6daee4a57aaadf8 100644
--- a/drivers/net/ovpn/crypto_aead.c
+++ b/drivers/net/ovpn/crypto_aead.c
@@ -363,3 +363,20 @@ 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;
+}
diff --git a/drivers/net/ovpn/crypto_aead.h b/drivers/net/ovpn/crypto_aead.h
index 77ee8141599bc06b0dc664c5b0a4dae660a89238..fb65be82436edd7ff89b171f7a89c9103b617d1f 100644
--- a/drivers/net/ovpn/crypto_aead.h
+++ b/drivers/net/ovpn/crypto_aead.h
@@ -28,4 +28,6 @@ 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_ */
diff --git a/drivers/net/ovpn/netlink.c b/drivers/net/ovpn/netlink.c
index 9daa48c294b435f26aa099b28ec458a21de3a87a..4d46eb6d6f14bba8c3a8335d08922bb8f6d3149f 100644
--- a/drivers/net/ovpn/netlink.c
+++ b/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"

@@ -734,24 +735,316 @@ 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_u8(attrs[OVPN_A_KEYCONF_SLOT]);
+ pkr.key.key_id = nla_get_u16(attrs[OVPN_A_KEYCONF_KEY_ID]);
+ pkr.key.cipher_alg = nla_get_u16(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_u8(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;
}

/**

--
2.45.2