We tried to remove vq poll from wait queue, but do not check whether
or not it was in a list before. This will lead double free. Fixing
this by checking poll->wqh to make sure it was in a list.

Reported-by: syzbot+c0272972b01b872e604a@syzkaller.appspotmail.com
Fixes: 2b8b328b61c79 ("vhost_net: handle polling errors when setting backend")
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 drivers/vhost/vhost.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 1b3e8d2d..5d5a9d9 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c

@@ -212,8 +212,7 @@ int vhost_poll_start(struct vhost_poll *poll, struct file *file)
 	if (mask)
 		vhost_poll_wakeup(&poll->wait, 0, 0, poll_to_key(mask));
 	if (mask & EPOLLERR) {
-		if (poll->wqh)
-			remove_wait_queue(poll->wqh, &poll->wait);
+		vhost_poll_stop(poll);
 		ret = -EINVAL;
 	}
 

-- 
2.7.4