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

[Jason Wang <jasowang@redhat.com>]

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@bytedance.com>
> ---
>   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.

Thanks


>   	if (xdp_prog) {
>   		struct xdp_frame *xdpf;
>   		struct page *xdp_page;
> @@ -1012,13 +1033,6 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>   	}
>   	rcu_read_unlock();
>   
> -	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_skb;
> -	}
> -
>   	head_skb = page_to_skb(vi, rq, page, offset, len, truesize, !xdp_prog,
>   			       metasize, !!headroom);
>   	curr_skb = head_skb;