Subject: Re: [PATCH v2 2/2] virtio-net: Prevent NULL dereference

From: "Michael S. Tsirkin" <[email-masked]>
Date: Mon, 3 Oct 2011 20:40:38 +0200

On Wed, Sep 28, 2011 at 05:40:55PM +0300, Sasha Levin wrote:
> This patch prevents a NULL dereference when the user has passed a length
> longer than an actual buffer to virtio-net.
> 
> Cc: Rusty Russell <[email-masked]>
> Cc: "Michael S. Tsirkin" <[email-masked]>
> Cc: [email-masked]
> Cc: [email-masked]
> Cc: [email-masked]
> Signed-off-by: Sasha Levin <[email-masked]>
> ---
>  drivers/net/virtio_net.c |   12 +++++++++++-
>  1 files changed, 11 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index bde0dec..4a53d2a 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -208,12 +208,22 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>  		return NULL;
>  	}
>  
> -	while (len) {
> +	while (len && page) {
>  		set_skb_frag(skb, page, offset, &len);
>  		page = (struct page *)page->private;
>  		offset = 0;
>  	}
>  
> +	/*
> +	 * This is the case where we ran out of pages in our linked list, but
> +	 * supposedly have more data to read.

Again, let's clarify that this only happens with broken devices.

> +	 */	
> +	if (len > 0) {
> +		pr_debug("%s: missing data to assemble skb\n", skb->dev->name);
> +		dev_kfree_skb(skb);
> +		return NULL;
> +	}
> +
>  	if (page)
>  		give_pages(vi, page);
>  
> -- 
> 1.7.6.1