mctp: Implement a timeout for tags

Currently, a MCTP (local-eid,remote-eid,tag) tuple is allocated to a
socket on send, and only expires when the socket is closed.

This change introduces a tag timeout, freeing the tuple after a fixed
expiry - currently six seconds. This is greater than (but close to) the
max response timeout in upper-layer bindings.
Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/mctp.h

@@ -62,6 +62,11 @@ struct mctp_sock {
 	 * by sk->net->keys_lock
 	 */
 	struct hlist_head keys;
+
+	/* mechanism for expiring allocated keys; will release an allocated
+	 * tag, and any netdev state for a request/response pairing
+	 */
+	struct timer_list key_expiry;
 };
 
 /* Key for matching incoming packets to sockets or reassembly contexts.
@@ -107,6 +112,8 @@ struct mctp_sock {
  *      the (complete) reply, or during reassembly errors. Here, we clean up
  *      the reassembly context (marking reasm_dead, to prevent another from
  *      starting), and remove the socket from the netns & socket lists.
+ *
+ *    - through an expiry timeout, on a per-socket timer
  */
 struct mctp_sk_key {
 	mctp_eid_t	peer_addr;
@@ -138,6 +145,9 @@ struct mctp_sk_key {
 
 	/* key validity */
 	bool		valid;
+
+	/* expiry timeout; valid (above) cleared on expiry */
+	unsigned long	expiry;
 };
 
 struct mctp_skb_cb {

net/mctp/af_mctp.c

@@ -223,16 +223,60 @@ static const struct proto_ops mctp_dgram_ops = {
 	.sendpage	= sock_no_sendpage,
 };
 
+static void mctp_sk_expire_keys(struct timer_list *timer)
+{
+	struct mctp_sock *msk = container_of(timer, struct mctp_sock,
+					     key_expiry);
+	struct net *net = sock_net(&msk->sk);
+	unsigned long next_expiry, flags;
+	struct mctp_sk_key *key;
+	struct hlist_node *tmp;
+	bool next_expiry_valid = false;
+
+	spin_lock_irqsave(&net->mctp.keys_lock, flags);
+
+	hlist_for_each_entry_safe(key, tmp, &msk->keys, sklist) {
+		spin_lock(&key->lock);
+
+		if (!time_after_eq(key->expiry, jiffies)) {
+			key->valid = false;
+			hlist_del_rcu(&key->hlist);
+			hlist_del_rcu(&key->sklist);
+			spin_unlock(&key->lock);
+			mctp_key_unref(key);
+			continue;
+		}
+
+		if (next_expiry_valid) {
+			if (time_before(key->expiry, next_expiry))
+				next_expiry = key->expiry;
+		} else {
+			next_expiry = key->expiry;
+			next_expiry_valid = true;
+		}
+		spin_unlock(&key->lock);
+	}
+
+	spin_unlock_irqrestore(&net->mctp.keys_lock, flags);
+
+	if (next_expiry_valid)
+		mod_timer(timer, next_expiry);
+}
+
 static int mctp_sk_init(struct sock *sk)
 {
 	struct mctp_sock *msk = container_of(sk, struct mctp_sock, sk);
 
 	INIT_HLIST_HEAD(&msk->keys);
+	timer_setup(&msk->key_expiry, mctp_sk_expire_keys, 0);
 	return 0;
 }
 
 static void mctp_sk_close(struct sock *sk, long timeout)
 {
+	struct mctp_sock *msk = container_of(sk, struct mctp_sock, sk);
+
+	del_timer_sync(&msk->key_expiry);
 	sk_common_release(sk);
 }
 

net/mctp/route.c

@@ -24,6 +24,8 @@
 #include <net/sock.h>
 
 static const unsigned int mctp_message_maxlen = 64 * 1024;
+static const unsigned long mctp_key_lifetime = 6 * CONFIG_HZ;
+
 
 /* route output callbacks */
 static int mctp_route_discard(struct mctp_route *route, struct sk_buff *skb)
@@ -175,6 +177,9 @@ static int mctp_key_add(struct mctp_sk_key *key, struct mctp_sock *msk)
 
 	if (!rc) {
 		refcount_inc(&key->refs);
+		key->expiry = jiffies + mctp_key_lifetime;
+		timer_reduce(&msk->key_expiry, key->expiry);
+
 		hlist_add_head(&key->hlist, &net->mctp.keys);
 		hlist_add_head(&key->sklist, &msk->keys);
 	}
@@ -497,6 +502,9 @@ static void mctp_reserve_tag(struct net *net, struct mctp_sk_key *key,
 
 	lockdep_assert_held(&mns->keys_lock);
 
+	key->expiry = jiffies + mctp_key_lifetime;
+	timer_reduce(&msk->key_expiry, key->expiry);
+
 	/* we hold the net->key_lock here, allowing updates to both
 	 * then net and sk
 	 */