netdev - Re: Re: [PATCH] virtio-net: Add validation for used length

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Date:   Tue, 25 May 2021 16:45:56 +0800
From:   Yongji Xie <xieyongji@...edance.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        virtualization <virtualization@...ts.linux-foundation.org>,
        netdev@...r.kernel.org, linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Re: [PATCH] virtio-net: Add validation for used length

On Tue, May 25, 2021 at 2:30 PM Jason Wang <jasowang@...hat.com> wrote:
>
>
> 在 2021/5/25 下午12:58, Xie Yongji 写道:
> > This adds validation for used length (might come
> > from an untrusted device) to avoid data corruption
> > or loss.
> >
> > Signed-off-by: Xie Yongji <xieyongji@...edance.com>
> > ---
> >   drivers/net/virtio_net.c | 22 ++++++++++++++++++++++
> >   1 file changed, 22 insertions(+)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index c4711e23af88..2dcdc1a3c7e8 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -668,6 +668,13 @@ static struct sk_buff *receive_small(struct net_device *dev,
> >               void *orig_data;
> >               u32 act;
> >
> > +             if (unlikely(len > GOOD_PACKET_LEN)) {
> > +                     pr_debug("%s: rx error: len %u exceeds max size %lu\n",
> > +                              dev->name, len, GOOD_PACKET_LEN);
> > +                     dev->stats.rx_length_errors++;
> > +                     goto err_xdp;
> > +             }
>
>
> Need to count vi->hdr_len here?
>

We did len -= vi->hdr_len before.

>
> > +
> >               if (unlikely(hdr->hdr.gso_type))
> >                       goto err_xdp;
> >
> > @@ -739,6 +746,14 @@ static struct sk_buff *receive_small(struct net_device *dev,
> >       }
> >       rcu_read_unlock();
> >
> > +     if (unlikely(len > GOOD_PACKET_LEN)) {
> > +             pr_debug("%s: rx error: len %u exceeds max size %lu\n",
> > +                      dev->name, len, GOOD_PACKET_LEN);
> > +             dev->stats.rx_length_errors++;
> > +             put_page(page);
> > +             return NULL;
> > +     }
> > +
> >       skb = build_skb(buf, buflen);
> >       if (!skb) {
> >               put_page(page);
> > @@ -822,6 +837,13 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> >               void *data;
> >               u32 act;
> >
> > +             if (unlikely(len > truesize)) {
> > +                     pr_debug("%s: rx error: len %u exceeds truesize %lu\n",
> > +                              dev->name, len, (unsigned long)ctx);
> > +                     dev->stats.rx_length_errors++;
> > +                     goto err_xdp;
> > +             }
>
>
> There's a similar check after the XDP, let's simply move it here?

Do we still need that in non-XDP cases?

>
> And do we need similar check in receive_big()?
>

It seems that the check in page_to_skb() can do similar things.

Thanks,
Yongji