Re: [PATCH 1/1] vhost: Protect the virtqueue from being cleared whilst still in use

Lee Jones
2022-03-02T13:56:46Z

On Wed, 02 Mar 2022, Michael S. Tsirkin wrote:

> On Wed, Mar 02, 2022 at 07:54:21AM +0000, Lee Jones wrote:
> > vhost_vsock_handle_tx_kick() already holds the mutex during its call
> > to vhost_get_vq_desc(). All we have to do is take the same lock
> > during virtqueue clean-up and we mitigate the reported issues.
> >
> > Link: https://syzkaller.appspot.com/bug?extid=279432d30d825e63ba00
> >
> > Cc: <stable@vger.kernel.org>
> > Reported-by: syzbot+adc3cb32385586bec859@syzkaller.appspotmail.com
> > Signed-off-by: Lee Jones <lee.jones@linaro.org>
> > ---
> > drivers/vhost/vhost.c | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > index 59edb5a1ffe28..bbaff6a5e21b8 100644
> > --- a/drivers/vhost/vhost.c
> > +++ b/drivers/vhost/vhost.c
> > @@ -693,6 +693,7 @@ void vhost_dev_cleanup(struct vhost_dev *dev)
> > int i;
> >
> > for (i = 0; i < dev->nvqs; ++i) {
> > + mutex_lock(&dev->vqs[i]->mutex);
> > if (dev->vqs[i]->error_ctx)
> > eventfd_ctx_put(dev->vqs[i]->error_ctx);
> > if (dev->vqs[i]->kick)
> > @@ -700,6 +701,7 @@ void vhost_dev_cleanup(struct vhost_dev *dev)
> > if (dev->vqs[i]->call_ctx.ctx)
> > eventfd_ctx_put(dev->vqs[i]->call_ctx.ctx);
> > vhost_vq_reset(dev, dev->vqs[i]);
> > + mutex_unlock(&dev->vqs[i]->mutex);
> > }
>
> So this is a mitigation plan but the bug is still there though
> we don't know exactly what it is. I would prefer adding something like
> WARN_ON(mutex_is_locked(vqs[i]->mutex) here - does this make sense?

As a rework to this, or as a subsequent patch?

Just before the first lock I assume?

--
Lee Jones [李琼斯]
Principal Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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