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

Michael S. Tsirkin
2022-03-02T14:51:26Z

On Wed, Mar 02, 2022 at 01:56:35PM +0000, Lee Jones wrote:
> 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?

Can be a separate patch.

> Just before the first lock I assume?

I guess so, yes.

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