[PATCH net-next 2/3] vsock: fix vsock_dequeue/enqueue_accept race

[Dexuan Cui]

With the current code, when vsock_dequeue_accept() is removing a sock
from the list, nothing prevents vsock_enqueue_accept() from adding a new
sock into the list concurrently. We should add a lock to protect the list.

Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
Cc: Andy King <acking@xxxxxxxxxx>
Cc: Dmitry Torokhov <dtor@xxxxxxxxxx>
Cc: George Zhang <georgezhang@xxxxxxxxxx>
Cc: Jorgen Hansen <jhansen@xxxxxxxxxx>
Cc: Reilly Grant <grantr@xxxxxxxxxx>
Cc: Asias He <asias@xxxxxxxxxx>
Cc: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
Cc: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
Cc: Cathy Avery <cavery@xxxxxxxxxx>
Cc: K. Y. Srinivasan <kys@xxxxxxxxxxxxx>
Cc: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
Cc: Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>
---
 net/vmw_vsock/af_vsock.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index dfc8c51e..b7b2c66 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -126,6 +126,7 @@ static struct proto vsock_proto = {
 
 static const struct vsock_transport *transport;
 static DEFINE_MUTEX(vsock_register_mutex);
+static DEFINE_SPINLOCK(vsock_accept_queue_lock);
 
 /**** EXPORTS ****/
 
@@ -406,7 +407,10 @@ void vsock_enqueue_accept(struct sock *listener, struct sock *connected)
 
 	sock_hold(connected);
 	sock_hold(listener);
+
+	spin_lock(&vsock_accept_queue_lock);
 	list_add_tail(&vconnected->accept_queue, &vlistener->accept_queue);
+	spin_unlock(&vsock_accept_queue_lock);
 }
 EXPORT_SYMBOL_GPL(vsock_enqueue_accept);
 
@@ -423,7 +427,10 @@ static struct sock *vsock_dequeue_accept(struct sock *listener)
 	vconnected = list_entry(vlistener->accept_queue.next,
 				struct vsock_sock, accept_queue);
 
+	spin_lock(&vsock_accept_queue_lock);
 	list_del_init(&vconnected->accept_queue);
+	spin_unlock(&vsock_accept_queue_lock);
+
 	sock_put(listener);
 	/* The caller will need a reference on the connected socket so we let
 	 * it call sock_put().
-- 
2.7.4