[PATCH net-next v3 07/16] l2tp: hide sessions if they are closing

[James Chapman <jchapman@katalix.com>]

Replace the dead flag in the session context with a closing flag and
spinlock. Check it in session lookup functions such that we don't try
to access session data while it is being destroyed.

Signed-off-by: James Chapman <jchapman@katalix.com>
---
 net/l2tp/l2tp_core.c | 34 +++++++++++++++++++++++++++++++++-
 net/l2tp/l2tp_core.h |  2 ++
 2 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index 477b96cf8ab3..869dec89ff0f 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -198,7 +198,14 @@ struct l2tp_session *l2tp_session_get(const struct net *net,
 		rcu_read_lock_bh();
 		hlist_for_each_entry_rcu(session, session_list, global_hlist) {
 			if (session->session_id == session_id) {
+				spin_lock_bh(&session->lock);
+				if (session->closing) {
+					spin_unlock_bh(&session->lock);
+					rcu_read_unlock_bh();
+					return NULL;
+				}
 				l2tp_session_inc_refcount(session);
+				spin_unlock_bh(&session->lock);
 				rcu_read_unlock_bh();
 
 				return session;
@@ -213,7 +220,14 @@ struct l2tp_session *l2tp_session_get(const struct net *net,
 	read_lock_bh(&tunnel->hlist_lock);
 	hlist_for_each_entry(session, session_list, hlist) {
 		if (session->session_id == session_id) {
+			spin_lock_bh(&session->lock);
+			if (session->closing) {
+				spin_unlock_bh(&session->lock);
+				read_unlock_bh(&tunnel->hlist_lock);
+				return NULL;
+			}
 			l2tp_session_inc_refcount(session);
+			spin_unlock_bh(&session->lock);
 			read_unlock_bh(&tunnel->hlist_lock);
 
 			return session;
@@ -234,6 +248,12 @@ struct l2tp_session *l2tp_session_get_nth(struct l2tp_tunnel *tunnel, int nth)
 	read_lock_bh(&tunnel->hlist_lock);
 	for (hash = 0; hash < L2TP_HASH_SIZE; hash++) {
 		hlist_for_each_entry(session, &tunnel->session_hlist[hash], hlist) {
+			spin_lock_bh(&session->lock);
+			if (session->closing) {
+				spin_unlock_bh(&session->lock);
+				continue;
+			}
+			spin_unlock_bh(&session->lock);
 			if (++count > nth) {
 				l2tp_session_inc_refcount(session);
 				read_unlock_bh(&tunnel->hlist_lock);
@@ -261,6 +281,12 @@ struct l2tp_session *l2tp_session_get_by_ifname(const struct net *net,
 	rcu_read_lock_bh();
 	for (hash = 0; hash < L2TP_HASH_SIZE_2; hash++) {
 		hlist_for_each_entry_rcu(session, &pn->l2tp_session_hlist[hash], global_hlist) {
+			spin_lock_bh(&session->lock);
+			if (session->closing) {
+				spin_unlock_bh(&session->lock);
+				continue;
+			}
+			spin_unlock_bh(&session->lock);
 			if (!strcmp(session->ifname, ifname)) {
 				l2tp_session_inc_refcount(session);
 				rcu_read_unlock_bh();
@@ -1678,8 +1704,13 @@ void __l2tp_session_unhash(struct l2tp_session *session)
  */
 int l2tp_session_delete(struct l2tp_session *session)
 {
-	if (test_and_set_bit(0, &session->dead))
+	spin_lock_bh(&session->lock);
+	if (session->closing) {
+		spin_unlock_bh(&session->lock);
 		return 0;
+	}
+	session->closing = true;
+	spin_unlock_bh(&session->lock);
 
 	__l2tp_session_unhash(session);
 	l2tp_session_queue_purge(session);
@@ -1747,6 +1778,7 @@ struct l2tp_session *l2tp_session_create(int priv_size, struct l2tp_tunnel *tunn
 
 		INIT_HLIST_NODE(&session->hlist);
 		INIT_HLIST_NODE(&session->global_hlist);
+		spin_lock_init(&session->lock);
 
 		/* Inherit debug options from tunnel */
 		session->debug = tunnel->debug;
diff --git a/net/l2tp/l2tp_core.h b/net/l2tp/l2tp_core.h
index 4e098c822cd1..d28d91600ad5 100644
--- a/net/l2tp/l2tp_core.h
+++ b/net/l2tp/l2tp_core.h
@@ -75,6 +75,8 @@ struct l2tp_session {
 	int			magic;		/* should be
 						 * L2TP_SESSION_MAGIC */
 	long			dead;
+	bool                    closing;
+	spinlock_t              lock;		/* protect closing */
 
 	struct l2tp_tunnel	*tunnel;	/* back pointer to tunnel
 						 * context */
-- 
1.9.1