[RFCv3 05/15] tcp: authopt: Add crypto initialization

[Leonard Crestez]

The crypto_shash API is used in order to compute packet signatures. The
API comes with several unfortunate limitations:

1) Allocating a crypto_shash can sleep and must be done in user context.
2) Packet signatures must be computed in softirq context
3) Packet signatures use dynamic "traffic keys" which require exclusive
access to crypto_shash for crypto_setkey.

The solution is to allocate one crypto_shash for each possible cpu for
each algorithm at setsockopt time. The per-cpu tfm is then borrowed from
softirq context, signatures are computed and the tfm is returned.

The pool for each algorithm is reference counted, initialized at
setsockopt time and released in tcp_authopt_key_info's rcu callback

Signed-off-by: Leonard Crestez <cdleonard@xxxxxxxxx>
---
 include/net/tcp_authopt.h |   3 +
 net/ipv4/tcp_authopt.c    | 177 +++++++++++++++++++++++++++++++++++++-
 2 files changed, 178 insertions(+), 2 deletions(-)

diff --git a/include/net/tcp_authopt.h b/include/net/tcp_authopt.h
index b4277112b506..c9ee2059b442 100644
--- a/include/net/tcp_authopt.h
+++ b/include/net/tcp_authopt.h
@@ -2,10 +2,12 @@
 #ifndef _LINUX_TCP_AUTHOPT_H
 #define _LINUX_TCP_AUTHOPT_H
 
 #include <uapi/linux/tcp.h>
 
+struct tcp_authopt_alg_imp;
+
 /**
  * struct tcp_authopt_key_info - Representation of a Master Key Tuple as per RFC5925
  *
  * Key structure lifetime is only protected by RCU so readers needs to hold a
  * single rcu_read_lock until they're done with the key.
@@ -20,10 +22,11 @@ struct tcp_authopt_key_info {
 	u8 send_id, recv_id;
 	u8 alg_id;
 	u8 keylen;
 	u8 key[TCP_AUTHOPT_MAXKEYLEN];
 	struct sockaddr_storage addr;
+	struct tcp_authopt_alg_imp *alg;
 };
 
 /**
  * struct tcp_authopt_info - Per-socket information regarding tcp_authopt
  *
diff --git a/net/ipv4/tcp_authopt.c b/net/ipv4/tcp_authopt.c
index f6dddc5775ff..ce560bd88903 100644
--- a/net/ipv4/tcp_authopt.c
+++ b/net/ipv4/tcp_authopt.c
@@ -4,10 +4,161 @@
 #include <net/tcp.h>
 #include <net/tcp_authopt.h>
 #include <crypto/hash.h>
 #include <trace/events/tcp.h>
 
+/* All current algorithms have a mac length of 12 but crypto API digestsize can be larger */
+#define TCP_AUTHOPT_MAXMACBUF	20
+#define TCP_AUTHOPT_MAX_TRAFFIC_KEY_LEN	20
+
+struct tcp_authopt_alg_imp {
+	/* Name of algorithm in crypto-api */
+	const char *alg_name;
+	/* One of the TCP_AUTHOPT_ALG_* constants from uapi */
+	u8 alg_id;
+	/* Length of traffic key */
+	u8 traffic_key_len;
+	/* Length of mac in TCP option */
+	u8 maclen;
+
+	/* shared crypto_shash */
+	spinlock_t lock;
+	int ref_cnt;
+	struct crypto_shash *tfm;
+};
+
+static struct tcp_authopt_alg_imp tcp_authopt_alg_list[] = {
+	{
+		.alg_id = TCP_AUTHOPT_ALG_HMAC_SHA_1_96,
+		.alg_name = "hmac(sha1)",
+		.traffic_key_len = 20,
+		.maclen = 12,
+		.lock = __SPIN_LOCK_UNLOCKED(tcp_authopt_alg_list[0].lock),
+	},
+	{
+		.alg_id = TCP_AUTHOPT_ALG_AES_128_CMAC_96,
+		.alg_name = "cmac(aes)",
+		.traffic_key_len = 16,
+		.maclen = 12,
+		.lock = __SPIN_LOCK_UNLOCKED(tcp_authopt_alg_list[1].lock),
+	},
+};
+
+/* get a pointer to the tcp_authopt_alg instance or NULL if id invalid */
+static inline struct tcp_authopt_alg_imp *tcp_authopt_alg_get(int alg_num)
+{
+	if (alg_num <= 0 || alg_num > 2)
+		return NULL;
+	return &tcp_authopt_alg_list[alg_num - 1];
+}
+
+/* Mark an algorithm as in-use from user context */
+static int tcp_authopt_alg_require(struct tcp_authopt_alg_imp *alg)
+{
+	struct crypto_shash *tfm = NULL;
+	bool need_init = false;
+
+	might_sleep();
+
+	/* If we're the first user then we need to initialize shash but we might lose the race. */
+	spin_lock_bh(&alg->lock);
+	WARN_ON(alg->ref_cnt < 0);
+	if (alg->ref_cnt == 0)
+		need_init = true;
+	else
+		++alg->ref_cnt;
+	spin_unlock_bh(&alg->lock);
+
+	/* Already initialized */
+	if (!need_init)
+		return 0;
+
+	tfm = crypto_alloc_shash(alg->alg_name, 0, 0);
+	if (IS_ERR(tfm))
+		return PTR_ERR(tfm);
+
+	spin_lock_bh(&alg->lock);
+	if (alg->ref_cnt == 0)
+		/* race won */
+		alg->tfm = tfm;
+	else
+		/* race lost, free tfm later */
+		need_init = false;
+	++alg->ref_cnt;
+	spin_unlock_bh(&alg->lock);
+
+	if (!need_init)
+		crypto_free_shash(tfm);
+	else
+		pr_info("initialized tcp-ao %s", alg->alg_name);
+
+	return 0;
+}
+
+static void tcp_authopt_alg_release(struct tcp_authopt_alg_imp *alg)
+{
+	struct crypto_shash *tfm_to_free = NULL;
+
+	spin_lock_bh(&alg->lock);
+	--alg->ref_cnt;
+	WARN_ON(alg->ref_cnt < 0);
+	if (alg->ref_cnt == 0) {
+		tfm_to_free = alg->tfm;
+		alg->tfm = NULL;
+	}
+	spin_unlock_bh(&alg->lock);
+
+	if (tfm_to_free) {
+		pr_info("released tcp-ao %s", alg->alg_name);
+		crypto_free_shash(tfm_to_free);
+	}
+}
+
+/* increase reference count on an algorithm that is already in use */
+static void tcp_authopt_alg_incref(struct tcp_authopt_alg_imp *alg)
+{
+	spin_lock_bh(&alg->lock);
+	WARN_ON(alg->ref_cnt <= 0);
+	++alg->ref_cnt;
+	spin_unlock_bh(&alg->lock);
+}
+
+static struct crypto_shash *tcp_authopt_alg_get_tfm(struct tcp_authopt_alg_imp *alg)
+{
+	spin_lock_bh(&alg->lock);
+	WARN_ON(alg->ref_cnt < 0);
+	return alg->tfm;
+}
+
+static void tcp_authopt_alg_put_tfm(struct tcp_authopt_alg_imp *alg, struct crypto_shash *tfm)
+{
+	WARN_ON(tfm != alg->tfm);
+	spin_unlock_bh(&alg->lock);
+}
+
+static struct crypto_shash *tcp_authopt_get_kdf_shash(struct tcp_authopt_key_info *key)
+{
+	return tcp_authopt_alg_get_tfm(key->alg);
+}
+
+static void tcp_authopt_put_kdf_shash(struct tcp_authopt_key_info *key,
+				      struct crypto_shash *tfm)
+{
+	return tcp_authopt_alg_put_tfm(key->alg, tfm);
+}
+
+static struct crypto_shash *tcp_authopt_get_mac_shash(struct tcp_authopt_key_info *key)
+{
+	return tcp_authopt_alg_get_tfm(key->alg);
+}
+
+static void tcp_authopt_put_mac_shash(struct tcp_authopt_key_info *key,
+				      struct crypto_shash *tfm)
+{
+	return tcp_authopt_alg_put_tfm(key->alg, tfm);
+}
+
 /* checks that ipv4 or ipv6 addr matches. */
 static bool ipvx_addr_match(struct sockaddr_storage *a1,
 			    struct sockaddr_storage *a2)
 {
 	if (a1->ss_family != a2->ss_family)
@@ -118,17 +269,25 @@ int tcp_get_authopt_val(struct sock *sk, struct tcp_authopt *opt)
 	opt->flags = info->flags & TCP_AUTHOPT_KNOWN_FLAGS;
 
 	return 0;
 }
 
+static void tcp_authopt_key_free_rcu(struct rcu_head *rcu)
+{
+	struct tcp_authopt_key_info *key = container_of(rcu, struct tcp_authopt_key_info, rcu);
+
+	tcp_authopt_alg_release(key->alg);
+	kfree(key);
+}
+
 static void tcp_authopt_key_del(struct sock *sk,
 				struct tcp_authopt_info *info,
 				struct tcp_authopt_key_info *key)
 {
 	hlist_del_rcu(&key->node);
 	atomic_sub(sizeof(*key), &sk->sk_omem_alloc);
-	kfree_rcu(key, rcu);
+	call_rcu(&key->rcu, tcp_authopt_key_free_rcu);
 }
 
 /* free info and keys but don't touch tp->authopt_info */
 static void __tcp_authopt_info_free(struct sock *sk, struct tcp_authopt_info *info)
 {
@@ -160,10 +319,12 @@ void tcp_authopt_clear(struct sock *sk)
 int tcp_set_authopt_key(struct sock *sk, sockptr_t optval, unsigned int optlen)
 {
 	struct tcp_authopt_key opt;
 	struct tcp_authopt_info *info;
 	struct tcp_authopt_key_info *key_info;
+	struct tcp_authopt_alg_imp *alg;
+	int err;
 
 	sock_owned_by_me(sk);
 
 	/* If userspace optlen is too short fill the rest with zeros */
 	if (optlen > sizeof(opt))
@@ -199,23 +360,35 @@ int tcp_set_authopt_key(struct sock *sk, sockptr_t optval, unsigned int optlen)
 	/* Initialize tcp_authopt_info if not already set */
 	info = __tcp_authopt_info_get_or_create(sk);
 	if (IS_ERR(info))
 		return PTR_ERR(info);
 
+	/* check the algorithm */
+	alg = tcp_authopt_alg_get(opt.alg);
+	if (!alg)
+		return -EINVAL;
+	WARN_ON(alg->alg_id != opt.alg);
+	err = tcp_authopt_alg_require(alg);
+	if (err)
+		return err;
+
 	/* If an old key exists with exact ID then remove and replace.
 	 * RCU-protected readers might observe both and pick any.
 	 */
 	key_info = tcp_authopt_key_lookup_exact(sk, info, &opt);
 	if (key_info)
 		tcp_authopt_key_del(sk, info, key_info);
 	key_info = sock_kmalloc(sk, sizeof(*key_info), GFP_KERNEL | __GFP_ZERO);
-	if (!key_info)
+	if (!key_info) {
+		tcp_authopt_alg_release(alg);
 		return -ENOMEM;
+	}
 	key_info->flags = opt.flags & TCP_AUTHOPT_KEY_KNOWN_FLAGS;
 	key_info->send_id = opt.send_id;
 	key_info->recv_id = opt.recv_id;
 	key_info->alg_id = opt.alg;
+	key_info->alg = alg;
 	key_info->keylen = opt.keylen;
 	memcpy(key_info->key, opt.key, opt.keylen);
 	memcpy(&key_info->addr, &opt.addr, sizeof(key_info->addr));
 	hlist_add_head_rcu(&key_info->node, &info->head);
 
-- 
2.25.1