Re: [PATCH net-next v2] virtio-net: fix possible unsigned integer overflow

[Heng Qi <hengqi@linux.alibaba.com>]

在 2023/2/2 下午4:07, Michael S. Tsirkin 写道:
> On Tue, Jan 31, 2023 at 04:50:04PM +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@linux.alibaba.com>
>> Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
>> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
>> ---
>> v1->v2:
>> - Change the type of num_buf from unsigned int to int. @Michael S . Tsirkin
>> - Some cleaner codes. @Michael S . Tsirkin
>>
>>   drivers/net/virtio_net.c | 15 +++++++++------
>>   1 file changed, 9 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index aaa6fe9b214a..8102861785a2 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -716,7 +716,7 @@ 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,
>> @@ -816,7 +816,7 @@ 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;
>> @@ -989,7 +989,7 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
>>   				      void *buf,
>>   				      unsigned int len,
>>   				      unsigned int frame_sz,
>> -				      u16 *num_buf,
>> +				      int *num_buf,
>>   				      unsigned int *xdp_frags_truesize,
>>   				      struct virtnet_rq_stats *stats)
>>   {
>> @@ -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
> Ouch. Why is this here? Merged so pls remove by a follow up patch, the
> rest of the code handles 0 fine. I'm not sure this introduces a bug by
> we don't want spaghetti code.

Yes it would work without this, but I was keeping this because I wanted 
it to handle 0 early and exit early.

Do you want to remove this?

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;
>>   
>> -	while ((--*num_buf) >= 1) {
>> +	while (--*num_buf > 0) {
>>   		buf = virtqueue_get_buf_ctx(rq->vq, &len, &ctx);
>>   		if (unlikely(!buf)) {
>>   			pr_debug("%s: rx error: %d buffers out of %d missing\n",
>> @@ -1076,7 +1079,7 @@ 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;
>> -- 
>> 2.19.1.6.gb485710b