linux-kernel - Re: [RFC 1/2] virtio_net: timeout control virtqueue commands

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Message-ID: <CACGkMEvJwcTFmDTXyXvMM1dP0OginF-FKZsksFO1DamRQJP1TQ@mail.gmail.com>
Date: Sat, 11 Oct 2025 15:44:57 +0800
From: Jason Wang <jasowang@...hat.com>
To: Eugenio Pérez <eperezma@...hat.com>
Cc: mst@...hat.com, Yongji Xie <xieyongji@...edance.com>, virtualization@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, Maxime Coquelin <mcoqueli@...hat.com>, 
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Dragos Tatulea DE <dtatulea@...dia.com>
Subject: Re: [RFC 1/2] virtio_net: timeout control virtqueue commands

On Tue, Oct 7, 2025 at 9:06 PM Eugenio Pérez <eperezma@...hat.com> wrote:
>
> An userland device implemented through VDUSE could take rtnl forever if
> the virtio-net driver is running on top of virtio_vdpa.  Let's break the
> device if it does not return the buffer in a longer-than-assumible
> timeout.
>
> A less agressive path can be taken to recover the device, like only
> resetting the control virtqueue.  However, the state of the device after
> this action is taken races, as the vq could be reset after the device
> writes the OK.  Leaving TODO anyway.
>
> Signed-off-by: Eugenio Pérez <eperezma@...hat.com>
> ---
>  drivers/net/virtio_net.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 31bd32bdecaf..ed68ad69a019 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -3576,6 +3576,7 @@ static bool virtnet_send_command_reply(struct virtnet_info *vi, u8 class, u8 cmd
>  {
>         struct scatterlist *sgs[5], hdr, stat;
>         u32 out_num = 0, tmp, in_num = 0;
> +       unsigned long end_time;
>         bool ok;
>         int ret;
>
> @@ -3614,11 +3615,20 @@ static bool virtnet_send_command_reply(struct virtnet_info *vi, u8 class, u8 cmd
>
>         /* Spin for a response, the kick causes an ioport write, trapping
>          * into the hypervisor, so the request should be handled immediately.
> +        *
> +        * Long timeout so a malicious device is not able to lock rtnl forever.
>          */
> +       end_time = jiffies + 30 * HZ;

The problem that 30 * HZ is probably long enough to trigger the
warnings like hungtask?


>         while (!virtqueue_get_buf(vi->cvq, &tmp) &&
>                !virtqueue_is_broken(vi->cvq)) {
>                 cond_resched();
>                 cpu_relax();
> +
> +               if (time_after(end_time, jiffies)) {
> +                       /* TODO Reset vq if possible? */
> +                       virtio_break_device(vi->vdev);
> +                       break;
> +               }
>         }
>
>  unlock:
> --
> 2.51.0
>

Thansk