Re: [PATCH v3] virtio-net: Add validation for used length

[Jason Wang]

在 2021/5/31 下午3:19, Yongji Xie 写道:
> On Mon, May 31, 2021 at 2:49 PM Jason Wang <jasowang@xxxxxxxxxx> wrote:
> > 在 2021/5/28 下午8:11, 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 | 28 +++++++++++++++++++++-------
> > >    1 file changed, 21 insertions(+), 7 deletions(-)
> > >
> > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > index 073fec4c0df1..01f15b65824c 100644
> > > --- a/drivers/net/virtio_net.c
> > > +++ b/drivers/net/virtio_net.c
> > > @@ -732,6 +732,17 @@ static struct sk_buff *receive_small(struct net_device *dev,
> > >
> > >        rcu_read_lock();
> > >        xdp_prog = rcu_dereference(rq->xdp_prog);
> > > +     if (unlikely(len > GOOD_PACKET_LEN)) {
> > > +             pr_debug("%s: rx error: len %u exceeds max size %d\n",
> > > +                      dev->name, len, GOOD_PACKET_LEN);
> > > +             dev->stats.rx_length_errors++;
> > > +             if (xdp_prog)
> > > +                     goto err_xdp;
> > > +
> > > +             rcu_read_unlock();
> > > +             put_page(page);
> > > +             return NULL;
> > > +     }
> > >        if (xdp_prog) {
> > >                struct virtio_net_hdr_mrg_rxbuf *hdr = buf + header_offset;
> > >                struct xdp_frame *xdpf;
> > > @@ -888,6 +899,16 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> > >
> > >        rcu_read_lock();
> > >        xdp_prog = rcu_dereference(rq->xdp_prog);
> > > +     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++;
> > > +             if (xdp_prog)
> > > +                     goto err_xdp;
> > > +
> > > +             rcu_read_unlock();
> > > +             goto err_skb;
> > > +     }
> >
> > Patch looks correct but I'd rather not bother XDP here. It would be
> > better if we just do the check before rcu_read_lock() and use err_skb
> > directly() to avoid RCU/XDP stuffs.
> If so, we will miss the statistics of xdp_drops. Is it OK?


It should be ok, we still had drops and it was dropped before dealing 
with XDP.

The motivation is to have simple codes.

Thanks


> Thanks,
> Yongji