Re: [PATCH net] vhost: correctly remove wait queue during poll failure

[Jason Wang]

On 2018å03æ27æ 17:28, Darren Kenny wrote:
> Hi Jason,
>
> On Tue, Mar 27, 2018 at 11:47:22AM +0800, Jason Wang wrote:
> > 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.
>
> This text seems at odds with the code below, instead of checking
> poll-whq, you are removing that check...
>
> Maybe the text needs rewording?

Yes, I admit it's bad, thanks for pointing out.

How about:

"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."

Thanks

> Thanks,
>
> Darren.
>
> > Reported-by: syzbot+c0272972b01b872e604a@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Fixes: 2b8b328b61c79 ("vhost_net: handle polling errors when setting 
> > backend")
> > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> > ---
> > 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)
> > ÂÂÂÂif (mask)
> > ÂÂÂÂÂÂÂ vhost_poll_wakeup(&poll->wait, 0, 0, poll_to_key(mask));
> > ÂÂÂÂif (mask & EPOLLERR) {
> > -ÂÂÂÂÂÂÂ if (poll->wqh)
> > -ÂÂÂÂÂÂÂÂÂÂÂ remove_wait_queue(poll->wqh, &poll->wait);
> > +ÂÂÂÂÂÂÂ vhost_poll_stop(poll);
> > ÂÂÂÂÂÂÂ ret = -EINVAL;
> > ÂÂÂÂ}
> >
> > --
> > 2.7.4