netdev - Re: [PATCH net-next 1/5] virtio_net: Fix an unsafe reference to the page chain

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Date: Sun, 28 May 2023 02:16:33 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Liang Chen <liangchen.linux@...il.com>
Cc: jasowang@...hat.com, virtualization@...ts.linux-foundation.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	xuanzhuo@...ux.alibaba.com, kuba@...nel.org, edumazet@...gle.com,
	davem@...emloft.net, pabeni@...hat.com, alexander.duyck@...il.com
Subject: Re: [PATCH net-next 1/5] virtio_net: Fix an unsafe reference to the
 page chain

On Fri, May 26, 2023 at 01:46:17PM +0800, Liang Chen wrote:
> "private" of buffer page is currently used for big mode to chain pages.
> But in mergeable mode, that offset of page could mean something else,
> e.g. when page_pool page is used instead. So excluding mergeable mode to
> avoid such a problem.
> 
> Signed-off-by: Liang Chen <liangchen.linux@...il.com>

Ugh the subject makes it looks like current code has a problem
but I don't think so because I don't think anything besides
big packets uses page->private.

The reason patch is needed is because follow up patches
use page_pool.
pls adjust commit log and subject to make all this clear.


> ---
>  drivers/net/virtio_net.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 5a7f7a76b920..c5dca0d92e64 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -497,7 +497,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>  			return NULL;
>  
>  		page = (struct page *)page->private;
> -		if (page)
> +		if (!vi->mergeable_rx_bufs && page)

To be safe let's limit to big packets too:

	if (!vi->mergeable_rx_bufs && vi->big_packets && page)



>  			give_pages(rq, page);
>  		goto ok;
>  	}
> -- 
> 2.31.1