Re: [PATCH net-next v1 1/4] virtio-net: fix overflow inside virtnet_rq_alloc

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Oct 29, 2024 at 04:46:12PM +0800, Xuan Zhuo wrote:
> When the frag just got a page, then may lead to regression on VM.
> Specially if the sysctl net.core.high_order_alloc_disable value is 1,
> then the frag always get a page when do refill.
> 
> Which could see reliable crashes or scp failure (scp a file 100M in size
> to VM).
> 
> The issue is that the virtnet_rq_dma takes up 16 bytes at the beginning
> of a new frag. When the frag size is larger than PAGE_SIZE,
> everything is fine. However, if the frag is only one page and the
> total size of the buffer and virtnet_rq_dma is larger than one page, an
> overflow may occur.
> 
> The commit f9dac92ba908 ("virtio_ring: enable premapped mode whatever
> use_dma_api") introduced this problem. And we reverted some commits to
> fix this in last linux version. Now we try to enable it and fix this
> bug directly.
> 
> Here, when the frag size is not enough, we reduce the buffer len to fix
> this problem.
> 
> Reported-by: "Si-Wei Liu" <si-wei.liu@oracle.com>
> Tested-by: Darren Kenny <darren.kenny@oracle.com>
> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>


This one belongs in net I feel. However, patches 2 and on
depend on it not to cause regressions. So I suggest merging it
on both branches, git will figure out the conflict I think.


> ---
>  drivers/net/virtio_net.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 792e9eadbfc3..d50c1940eb23 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -926,9 +926,6 @@ static void *virtnet_rq_alloc(struct receive_queue *rq, u32 size, gfp_t gfp)
>  	void *buf, *head;
>  	dma_addr_t addr;
>  
> -	if (unlikely(!skb_page_frag_refill(size, alloc_frag, gfp)))
> -		return NULL;
> -
>  	head = page_address(alloc_frag->page);
>  
>  	if (rq->do_dma) {
> @@ -2423,6 +2420,9 @@ static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
>  	len = SKB_DATA_ALIGN(len) +
>  	      SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
>  
> +	if (unlikely(!skb_page_frag_refill(len, &rq->alloc_frag, gfp)))
> +		return -ENOMEM;
> +
>  	buf = virtnet_rq_alloc(rq, len, gfp);
>  	if (unlikely(!buf))
>  		return -ENOMEM;
> @@ -2525,6 +2525,12 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
>  	 */
>  	len = get_mergeable_buf_len(rq, &rq->mrg_avg_pkt_len, room);
>  
> +	if (unlikely(!skb_page_frag_refill(len + room, alloc_frag, gfp)))
> +		return -ENOMEM;
> +
> +	if (!alloc_frag->offset && len + room + sizeof(struct virtnet_rq_dma) > alloc_frag->size)
> +		len -= sizeof(struct virtnet_rq_dma);
> +
>  	buf = virtnet_rq_alloc(rq, len + room, gfp);
>  	if (unlikely(!buf))
>  		return -ENOMEM;
> -- 
> 2.32.0.3.g01195cf9f