Re: [PATCH] virtio_net: Remove BUG() to aviod machine dead

[Jason Wang]

在 2021/5/19 下午10:18, Xianting Tian 写道:
> thanks, I submit the patch as commented by Andrew 
> https://lkml.org/lkml/2021/5/18/256
>
> Actually, if xmit_skb() returns error, below code will give a warning 
> with error code.
>
>     /* Try to transmit */
>     err = xmit_skb(sq, skb);
>
>     /* This should not happen! */
>     if (unlikely(err)) {
>         dev->stats.tx_fifo_errors++;
>         if (net_ratelimit())
>             dev_warn(&dev->dev,
>                  "Unexpected TXQ (%d) queue failure: %d\n",
>                  qnum, err);
>         dev->stats.tx_dropped++;
>         dev_kfree_skb_any(skb);
>         return NETDEV_TX_OK;
>     }
>
>
>
>
>
> 在 2021/5/18 下午5:54, Michael S. Tsirkin 写道:
> > typo in subject
> >
> > On Tue, May 18, 2021 at 05:46:56PM +0800, Xianting Tian wrote:
> > > When met error, we output a print to avoid a BUG().


So you don't explain why you need to remove BUG(). I think it deserve a 
BUG().


> > > Signed-off-by: Xianting Tian <xianting.tian@xxxxxxxxxxxxxxxxx>
> > > ---
> > >   drivers/net/virtio_net.c | 5 ++---
> > >   1 file changed, 2 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > index c921ebf3ae82..a66174d13e81 100644
> > > --- a/drivers/net/virtio_net.c
> > > +++ b/drivers/net/virtio_net.c
> > > @@ -1647,9 +1647,8 @@ static int xmit_skb(struct send_queue *sq, struct
> > > sk_buff *skb)
> > >           hdr = skb_vnet_hdr(skb);
> > >
> > >       if (virtio_net_hdr_from_skb(skb, &hdr->hdr,
> > > -                    virtio_is_little_endian(vi->vdev), false,
> > > -                    0))
> > > -        BUG();
> > > +                virtio_is_little_endian(vi->vdev), false, 0))
> > > +        return -EPROTO;
> >
> > why EPROTO? can you add some comments to explain what is going on pls?
> >
> > is this related to a malicious hypervisor thing?


I think not if I was not wrong.

Each sources (either userspace or device), the skb should be built 
through virtio_net_hdr_to_skb() which means the validation has already 
been done.

If we it fails here, it's a real bug.

Thanks


> > don't we want at least a WARN_ON? Or _ONCE?
> >
> > >       if (vi->mergeable_rx_bufs)
> > >           hdr->num_buffers = 0;
> > > --
> > > 2.17.1