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

Heng Qi
2023-01-31T08:17:21Z

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@linux.alibaba.com>
>>>> Reviewed-by: Xuan Zhuo <xuanzhuo@linux.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@redhat.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