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

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

在 2023/2/2 下午6:31, Michael S. Tsirkin 写道:
> On Thu, Feb 02, 2023 at 05:07:04PM +0800, Heng Qi wrote:
>>
>> 在 2023/2/2 下午4:16, Michael S. Tsirkin 写道:
>>> On Thu, Feb 02, 2023 at 04:14:51PM +0800, Heng Qi wrote:
>>>> 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.
>>> why do you want to exit early?
>> If num_buf is 0, we don't need to judge the subsequent process, because the
>> latter process
>> is used to build multi-buffer xdp, but this fix solves the possible problems
>> of single-buffer xdp.
>>
>> Thanks.
> An optimization then? As any optimization I'd like to see some numbers.
>
> Should have been documented as such not as part of a bugfix.

Sure, I'm going to remove this with a follow-up patch.😁

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