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

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Date:   Thu, 2 Feb 2023 17:07:04 +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 v2] virtio-net: fix possible unsigned integer
 overflow



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@...ux.alibaba.com>
>>>> Reviewed-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
>>>> Signed-off-by: Michael S. Tsirkin <mst@...hat.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.

>
>>>> @@ -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