4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jason Wang <jasow...@redhat.com>


[ Upstream commit dc6455a71c7fc5117977e197f67f71b49f27baba ]

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 switching to use vhost_poll_stop() which zeros poll->wqh after
removing poll from waitqueue to make sure it won't be freed twice.

Cc: Darren Kenny <darren.ke...@oracle.com>
Reported-by: syzbot+c0272972b01b872e6...@syzkaller.appspotmail.com
Fixes: 2b8b328b61c79 ("vhost_net: handle polling errors when setting backend")
Signed-off-by: Jason Wang <jasow...@redhat.com>
Reviewed-by: Darren Kenny <darren.ke...@oracle.com>
Acked-by: Michael S. Tsirkin <m...@redhat.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 drivers/vhost/vhost.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -173,8 +173,7 @@ int vhost_poll_start(struct vhost_poll *
        if (mask)
                vhost_poll_wakeup(&poll->wait, 0, 0, (void *)mask);
        if (mask & POLLERR) {
-               if (poll->wqh)
-                       remove_wait_queue(poll->wqh, &poll->wait);
+               vhost_poll_stop(poll);
                ret = -EINVAL;
        }
 


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