[RFC ovpn net-next v2 07/14] ovpn: make key contexts refcounted

Epoch key rotation needs to replace encrypt and decrypt key contexts
while packets may still hold references from the async AEAD path.

Publish key contexts through RCU, add a per-context kref, and let
encrypt and decrypt requests hold a context until their completion
callback runs. Direct-key behavior is otherwise unchanged.

Signed-off-by: Ralf Lici <[email protected]>
---
No functional changes since v1 https://lore.kernel.org/openvpn-devel/4ae05d37fc69c2c29d83f824616b1aee6315ab6b.1782919654.git.ralf@mandelbit.com/

 drivers/net/ovpn/crypto.h      | 34 ++++++++++++++++++++--
 drivers/net/ovpn/crypto_aead.c | 20 ++++++++++---
 drivers/net/ovpn/crypto_key.c  | 53 +++++++++++++++++++---------------
 drivers/net/ovpn/io.c          |  8 +++--
 drivers/net/ovpn/skb.h         |  2 ++
 5 files changed, 86 insertions(+), 31 deletions(-)

diff --git a/drivers/net/ovpn/crypto.h b/drivers/net/ovpn/crypto.h
index c36cd8299afd..1d62f2be23c9 100644
--- a/drivers/net/ovpn/crypto.h
+++ b/drivers/net/ovpn/crypto.h
@@ -10,6 +10,9 @@
 #ifndef _NET_OVPN_OVPNCRYPTO_H_
 #define _NET_OVPN_OVPNCRYPTO_H_
 
+#include <linux/kref.h>
+#include <linux/rcupdate.h>
+
 #include "crypto_limits.h"
 #include "pktid.h"
 #include "proto.h"
@@ -47,6 +50,8 @@ struct ovpn_key_ctx {
 	struct ovpn_key_usage usage;
 	atomic64_t decrypt_failures;
 	unsigned long decrypt_failure_flags;
+	struct kref refcount;
+	struct rcu_head rcu;
 };
 
 struct ovpn_crypto_key_slot {
@@ -54,8 +59,8 @@ struct ovpn_crypto_key_slot {
 	enum ovpn_cipher_alg cipher_alg;
 	struct ovpn_limit usage_limit;
 
-	struct ovpn_key_ctx *encrypt;
-	struct ovpn_key_ctx *decrypt;
+	struct ovpn_key_ctx __rcu *encrypt;
+	struct ovpn_key_ctx __rcu *decrypt;
 	struct kref refcount;
 	struct rcu_head rcu;
 };
@@ -137,6 +142,31 @@ static inline void ovpn_crypto_key_slot_put(struct ovpn_crypto_key_slot *ks)
 	kref_put(&ks->refcount, ovpn_crypto_key_slot_release);
 }
 
+void ovpn_key_ctx_release(struct kref *kref);
+
+static inline void ovpn_key_ctx_put(struct ovpn_key_ctx *key)
+{
+	if (key)
+		kref_put(&key->refcount, ovpn_key_ctx_release);
+}
+
+static inline int ovpn_key_ctx_get(struct ovpn_key_ctx **out,
+				   struct ovpn_key_ctx __rcu **rcu_ptr)
+{
+	struct ovpn_key_ctx *key;
+
+	rcu_read_lock();
+	key = rcu_dereference(*rcu_ptr);
+	if (unlikely(!key || !kref_get_unless_zero(&key->refcount))) {
+		rcu_read_unlock();
+		return -ENOKEY;
+	}
+	rcu_read_unlock();
+
+	*out = key;
+	return 0;
+}
+
 int ovpn_crypto_state_reset(struct ovpn_crypto_state *cs,
 			    const struct ovpn_peer_key_reset *pkr);
 
diff --git a/drivers/net/ovpn/crypto_aead.c b/drivers/net/ovpn/crypto_aead.c
index 31f5327694d2..39bd320169d3 100644
--- a/drivers/net/ovpn/crypto_aead.c
+++ b/drivers/net/ovpn/crypto_aead.c
@@ -150,8 +150,8 @@ static struct scatterlist *ovpn_aead_crypto_req_sg(struct crypto_aead *aead,
 int ovpn_aead_encrypt(struct ovpn_peer *peer, struct ovpn_crypto_key_slot *ks,
 		      struct sk_buff *skb)
 {
-	struct ovpn_key_ctx *key = ks->encrypt;
 	unsigned int plaintext_len, tag_size;
+	struct ovpn_key_ctx *key = NULL;
 	struct aead_request *req;
 	struct sk_buff *trailer;
 	struct scatterlist *sg;
@@ -164,6 +164,12 @@ int ovpn_aead_encrypt(struct ovpn_peer *peer, struct ovpn_crypto_key_slot *ks,
 	ovpn_skb_cb(skb)->peer = peer;
 	ovpn_skb_cb(skb)->ks = ks;
 	plaintext_len = skb->len;
+
+	ret = ovpn_key_ctx_get(&key, &ks->encrypt);
+	if (unlikely(ret))
+		return ret;
+	ovpn_skb_cb(skb)->key = key;
+
 	tag_size = crypto_aead_authsize(key->tfm);
 
 	/* Sample AEAD header format:
@@ -263,8 +269,8 @@ int ovpn_aead_encrypt(struct ovpn_peer *peer, struct ovpn_crypto_key_slot *ks,
 int ovpn_aead_decrypt(struct ovpn_peer *peer, struct ovpn_crypto_key_slot *ks,
 		      struct sk_buff *skb)
 {
-	struct ovpn_key_ctx *key = ks->decrypt;
 	unsigned int payload_offset, tag_size;
+	struct ovpn_key_ctx *key = NULL;
 	int ret, payload_len, nfrags;
 	struct aead_request *req;
 	struct sk_buff *trailer;
@@ -272,13 +278,19 @@ int ovpn_aead_decrypt(struct ovpn_peer *peer, struct ovpn_crypto_key_slot *ks,
 	void *tmp;
 	u8 *iv;
 
+	ovpn_skb_cb(skb)->peer = peer;
+	ovpn_skb_cb(skb)->ks = ks;
+
+	ret = ovpn_key_ctx_get(&key, &ks->decrypt);
+	if (unlikely(ret))
+		return ret;
+	ovpn_skb_cb(skb)->key = key;
+
 	tag_size = crypto_aead_authsize(key->tfm);
 	payload_offset = ovpn_aead_direct_payload_offset(tag_size);
 	payload_len = skb->len - payload_offset;
 
 	ovpn_skb_cb(skb)->payload_offset = payload_offset;
-	ovpn_skb_cb(skb)->peer = peer;
-	ovpn_skb_cb(skb)->ks = ks;
 
 	/* sanity check on packet size, payload size must be >= 0 */
 	if (unlikely(payload_len < 0))
diff --git a/drivers/net/ovpn/crypto_key.c b/drivers/net/ovpn/crypto_key.c
index cdf35e2b241c..44110a0b38eb 100644
--- a/drivers/net/ovpn/crypto_key.c
+++ b/drivers/net/ovpn/crypto_key.c
@@ -82,6 +82,22 @@ static void ovpn_key_ctx_free(struct ovpn_key_ctx *key)
 	kfree(key);
 }
 
+static void ovpn_key_ctx_free_rcu(struct rcu_head *head)
+{
+	struct ovpn_key_ctx *key;
+
+	key = container_of(head, struct ovpn_key_ctx, rcu);
+	ovpn_key_ctx_free(key);
+}
+
+void ovpn_key_ctx_release(struct kref *kref)
+{
+	struct ovpn_key_ctx *key;
+
+	key = container_of(kref, struct ovpn_key_ctx, refcount);
+	call_rcu(&key->rcu, ovpn_key_ctx_free_rcu);
+}
+
 static struct ovpn_key_ctx *
 ovpn_key_ctx_new(const char *title, const char *alg_name,
 		 const struct ovpn_key_direction *dir, bool encrypt)
@@ -113,6 +129,7 @@ ovpn_key_ctx_new(const char *title, const char *alg_name,
 	ovpn_key_usage_init(&key->usage);
 	atomic64_set(&key->decrypt_failures, 0);
 	key->decrypt_failure_flags = 0;
+	kref_init(&key->refcount);
 
 	/* initialize only the packet ID direction this context owns */
 	if (encrypt)
@@ -128,8 +145,8 @@ void ovpn_crypto_key_slot_destroy(struct ovpn_crypto_key_slot *ks)
 	if (!ks)
 		return;
 
-	ovpn_key_ctx_free(ks->encrypt);
-	ovpn_key_ctx_free(ks->decrypt);
+	ovpn_key_ctx_put(rcu_access_pointer(ks->encrypt));
+	ovpn_key_ctx_put(rcu_access_pointer(ks->decrypt));
 	kfree(ks);
 }
 
@@ -137,6 +154,7 @@ struct ovpn_crypto_key_slot *
 ovpn_crypto_key_slot_new(const struct ovpn_key_config *kc)
 {
 	struct ovpn_crypto_key_slot *ks = NULL;
+	struct ovpn_key_ctx *key;
 	const char *alg_name;
 	int ret;
 
@@ -168,21 +186,19 @@ ovpn_crypto_key_slot_new(const struct ovpn_key_config *kc)
 	ks->cipher_alg = kc->cipher_alg;
 	ovpn_key_usage_limit_init(&ks->usage_limit, kc->cipher_alg);
 
-	ks->encrypt = ovpn_key_ctx_new("encrypt", alg_name, &kc->encrypt,
-				       true);
-	if (IS_ERR(ks->encrypt)) {
-		ret = PTR_ERR(ks->encrypt);
-		ks->encrypt = NULL;
+	key = ovpn_key_ctx_new("encrypt", alg_name, &kc->encrypt, true);
+	if (IS_ERR(key)) {
+		ret = PTR_ERR(key);
 		goto destroy_ks;
 	}
+	RCU_INIT_POINTER(ks->encrypt, key);
 
-	ks->decrypt = ovpn_key_ctx_new("decrypt", alg_name, &kc->decrypt,
-				       false);
-	if (IS_ERR(ks->decrypt)) {
-		ret = PTR_ERR(ks->decrypt);
-		ks->decrypt = NULL;
+	key = ovpn_key_ctx_new("decrypt", alg_name, &kc->decrypt, false);
+	if (IS_ERR(key)) {
+		ret = PTR_ERR(key);
 		goto destroy_ks;
 	}
+	RCU_INIT_POINTER(ks->decrypt, key);
 
 	return ks;
 
@@ -193,17 +209,8 @@ ovpn_crypto_key_slot_new(const struct ovpn_key_config *kc)
 
 enum ovpn_cipher_alg ovpn_crypto_key_slot_alg(struct ovpn_crypto_key_slot *ks)
 {
-	const char *alg_name;
-
-	if (!ks->encrypt || !ks->encrypt->tfm)
+	if (!ks)
 		return OVPN_CIPHER_ALG_NONE;
 
-	alg_name = crypto_tfm_alg_name(crypto_aead_tfm(ks->encrypt->tfm));
-
-	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;
+	return ks->cipher_alg;
 }
diff --git a/drivers/net/ovpn/io.c b/drivers/net/ovpn/io.c
index 2b1df68a1b1e..006d83fe3e2a 100644
--- a/drivers/net/ovpn/io.c
+++ b/drivers/net/ovpn/io.c
@@ -125,14 +125,14 @@ void ovpn_decrypt_post(void *data, int ret)
 
 	payload_offset = ovpn_skb_cb(skb)->payload_offset;
 	ks = ovpn_skb_cb(skb)->ks;
-	key = ks->decrypt;
+	key = ovpn_skb_cb(skb)->key;
 	peer = ovpn_skb_cb(skb)->peer;
 
 	/* crypto is done, cleanup skb CB and its members */
 	kfree(ovpn_skb_cb(skb)->crypto_tmp);
 
 	if (unlikely(ret == -EBADMSG)) {
-		if (unlikely(ovpn_aead_decrypt_failure_record(key)))
+		if (key && unlikely(ovpn_aead_decrypt_failure_record(key)))
 			ovpn_nl_key_swap_notify(peer, ks->key_id);
 		goto drop;
 	}
@@ -224,6 +224,7 @@ void ovpn_decrypt_post(void *data, int ret)
 		ovpn_peer_put(peer);
 	if (likely(ks))
 		ovpn_crypto_key_slot_put(ks);
+	ovpn_key_ctx_put(key);
 }
 
 /* RX path entry point: decrypt packet and forward it to the device */
@@ -256,6 +257,7 @@ void ovpn_encrypt_post(void *data, int ret)
 	struct ovpn_crypto_key_slot *ks;
 	struct sk_buff *skb = data;
 	struct ovpn_socket *sock;
+	struct ovpn_key_ctx *key;
 	struct ovpn_peer *peer;
 	unsigned int orig_len;
 
@@ -267,6 +269,7 @@ void ovpn_encrypt_post(void *data, int ret)
 
 	ks = ovpn_skb_cb(skb)->ks;
 	peer = ovpn_skb_cb(skb)->peer;
+	key = ovpn_skb_cb(skb)->key;
 
 	/* crypto is done, cleanup skb CB and its members */
 	kfree(ovpn_skb_cb(skb)->crypto_tmp);
@@ -322,6 +325,7 @@ void ovpn_encrypt_post(void *data, int ret)
 		ovpn_peer_put(peer);
 	if (likely(ks))
 		ovpn_crypto_key_slot_put(ks);
+	ovpn_key_ctx_put(key);
 	kfree_skb(skb);
 }
 
diff --git a/drivers/net/ovpn/skb.h b/drivers/net/ovpn/skb.h
index 4fb7ea025426..75d64161d774 100644
--- a/drivers/net/ovpn/skb.h
+++ b/drivers/net/ovpn/skb.h
@@ -22,6 +22,7 @@
  * struct ovpn_cb - ovpn skb control block
  * @peer: the peer this skb was received from/sent to
  * @ks: the crypto key slot used to encrypt/decrypt this skb
+ * @key: the key context used to encrypt/decrypt this skb
  * @crypto_tmp: pointer to temporary memory used for crypto operations
  *		containing the IV, the scatter gather list and the aead request
  * @payload_offset: offset in the skb where the payload starts
@@ -30,6 +31,7 @@
 struct ovpn_cb {
 	struct ovpn_peer *peer;
 	struct ovpn_crypto_key_slot *ks;
+	struct ovpn_key_ctx *key;
 	void *crypto_tmp;
 	unsigned int payload_offset;
 	bool nosignal;
-- 
2.54.0