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

[Jason Wang]

在 2021/5/25 下午4:45, Yongji Xie 写道:
> On Tue, May 25, 2021 at 2:30 PM Jason Wang <jasowang@xxxxxxxxxx> 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@xxxxxxxxxxxxx>
> > > ---
> > >    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.


Right.


> > > +
> > >                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?


I meant we check once for both XDP and non-XDP if we do it before if 
(xdp_prog)


> > And do we need similar check in receive_big()?
> It seems that the check in page_to_skb() can do similar things.


Right.

Thanks


> Thanks,
> Yongji