Subject: Re: [PATCH] net/qlcnic: fix possible use-after-free bugs in qlcnic_alloc_rx_skb()

From: Simon Horman <[email-masked]>
Date: Fri, 15 Sep 2023 07:45:41 +0200

On Wed, Sep 13, 2023 at 06:41:19PM +0800, Ma Ke wrote:
> In qlcnic_alloc_rx_skb(), when dma_map_single() fails, skb is freed
> immediately. And skb could be freed again. This issue could allow a
> local attacker to crash the system due to a use-after-free flaw.
> 
> Signed-off-by: Ma Ke <[email-masked]>
> ---
>  drivers/net/ethernet/qlogic/qlcnic/qlcnic_io.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/net/ethernet/qlogic/qlcnic/qlcnic_io.c b/drivers/net/ethernet/qlogic/qlcnic/qlcnic_io.c
> index 41894d154013..6501aaf2b5ce 100644
> --- a/drivers/net/ethernet/qlogic/qlcnic/qlcnic_io.c
> +++ b/drivers/net/ethernet/qlogic/qlcnic/qlcnic_io.c
> @@ -832,6 +832,7 @@ static int qlcnic_alloc_rx_skb(struct qlcnic_adapter *adapter,
>  	if (dma_mapping_error(&pdev->dev, dma)) {
>  		adapter->stats.rx_dma_map_error++;
>  		dev_kfree_skb_any(skb);
> +		skb = NULL;
>  		return -ENOMEM;

Hi Ma Ke,

I am a unclear on how skb could be freed a second time.
skb is a local variable which goes out of scope when
the function returns.