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

[Yongji Xie]

On Mon, May 31, 2021 at 3:51 PM Jason Wang <jasowang@xxxxxxxxxx> wrote:
>
>
> 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.
>

OK, will send v4 soon.

Thanks,
Yongji