netdev - Re: [PATCH net-next] virtio-net: fix possible unsigned integer overflow

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Date:   Tue, 31 Jan 2023 16:17:09 +0800
From:   Heng Qi <hengqi@...ux.alibaba.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        Jason Wang <jasowang@...hat.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Jakub Kicinski <kuba@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Subject: Re: [PATCH net-next] virtio-net: fix possible unsigned integer
 overflow



在 2023/1/31 下午3:50, Michael S. Tsirkin 写道:
> On Tue, Jan 31, 2023 at 03:40:32PM +0800, Heng Qi wrote:
>> On Tue, Jan 31, 2023 at 02:20:49AM -0500, Michael S. Tsirkin wrote:
>>> On Tue, Jan 31, 2023 at 11:43:37AM +0800, Heng Qi wrote:
>>>> When the single-buffer xdp is loaded and after xdp_linearize_page()
>>>> is called, *num_buf becomes 0 and (*num_buf - 1) may overflow into
>>>> a large integer in virtnet_build_xdp_buff_mrg(), resulting in
>>>> unexpected packet dropping.
>>>>
>>>> Fixes: ef75cb51f139 ("virtio-net: build xdp_buff with multi buffers")
>>>> Signed-off-by: Heng Qi <hengqi@...ux.alibaba.com>
>>>> Reviewed-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
>>> Given the confusion, just make num_buf an int?
>> In the structure virtio_net_hdr_mrg_rxbuf, \field{num_buffers} is unsigned int,
>> which matches each other.
> Because hardware buffers are all unsigned. Does not mean we need
> to do all math unsigned now.

Yes.

>
>> And num_buf is used in many different places, it seems
>> to be a lot of work to modify it to int.
> Are you sure?
>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>

I will also change to int in the next version.

>
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 18b3de854aeb..97f2e9bfc6f9 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -722,7 +722,7 @@ static unsigned int virtnet_get_headroom(struct virtnet_info *vi)
>    * have enough headroom.
>    */
>   static struct page *xdp_linearize_page(struct receive_queue *rq,
> -				       u16 *num_buf,
> +				       int *num_buf,
>   				       struct page *p,
>   				       int offset,
>   				       int page_off,
> @@ -822,7 +822,7 @@ static struct sk_buff *receive_small(struct net_device *dev,
>   		if (unlikely(xdp_headroom < virtnet_get_headroom(vi))) {
>   			int offset = buf - page_address(page) + header_offset;
>   			unsigned int tlen = len + vi->hdr_len;
> -			u16 num_buf = 1;
> +			int num_buf = 1;
>   
>   			xdp_headroom = virtnet_get_headroom(vi);
>   			header_offset = VIRTNET_RX_PAD + xdp_headroom;
> @@ -948,7 +948,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>   					 struct virtnet_rq_stats *stats)
>   {
>   	struct virtio_net_hdr_mrg_rxbuf *hdr = buf;
> -	u16 num_buf = virtio16_to_cpu(vi->vdev, hdr->num_buffers);
> +	int num_buf = virtio16_to_cpu(vi->vdev, hdr->num_buffers);
>   	struct page *page = virt_to_head_page(buf);
>   	int offset = buf - page_address(page);
>   	struct sk_buff *head_skb, *curr_skb;
>
> Feel free to reuse.
>
>
>>>> ---
>>>>   drivers/net/virtio_net.c | 7 +++++--
>>>>   1 file changed, 5 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>>>> index aaa6fe9b214a..a8e9462903fa 100644
>>>> --- a/drivers/net/virtio_net.c
>>>> +++ b/drivers/net/virtio_net.c
>>>> @@ -1007,6 +1007,9 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
>>>>   	xdp_prepare_buff(xdp, buf - VIRTIO_XDP_HEADROOM,
>>>>   			 VIRTIO_XDP_HEADROOM + vi->hdr_len, len - vi->hdr_len, true);
>>>>   
>>>> +	if (!*num_buf)
>>>> +		return 0;
>>>> +
>>>>   	if (*num_buf > 1) {
>>>>   		/* If we want to build multi-buffer xdp, we need
>>>>   		 * to specify that the flags of xdp_buff have the
>>>
>>> This means truesize won't be set.
>> Do you mean xdp_frags_truesize please? If yes, the answer is yes, this fix
>> is only for single-buffer xdp, which doesn't need xdp_frags_truesize, and
>> already set it to 0 in its wrapper receive_mergeable().
> It seems cleaner to always set the value not rely on caller to do so.

Yes, I'll try to separate them in other patches.

Thanks.

>>>> @@ -1020,10 +1023,10 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
>>>>   		shinfo->xdp_frags_size = 0;
>>>>   	}
>>>>   
>>>> -	if ((*num_buf - 1) > MAX_SKB_FRAGS)
>>>> +	if (*num_buf > MAX_SKB_FRAGS + 1)
>>>>   		return -EINVAL;
>>> Admittedly this is cleaner.
>>>
>>>>   
>>>> -	while ((--*num_buf) >= 1) {
>>>> +	while (--*num_buf) {
>>> A bit more fragile, > 0 would be better.
>> Sure.
>>
>> Thanks.
>>
>>>>   		buf = virtqueue_get_buf_ctx(rq->vq, &len, &ctx);
>>>>   		if (unlikely(!buf)) {
>>>>   			pr_debug("%s: rx error: %d buffers out of %d missing\n",
>>>> -- 
>>>> 2.19.1.6.gb485710b