Re: [PATCH net] e100: Fix possible use after free in e100_xmit_prepare

[Alexander H Duyck]

On Wed, 2022-11-16 at 01:24 +0800, Wang Hai wrote:
> In e100_xmit_prepare(), if we can't map the skb, then return -ENOMEM, so
> e100_xmit_frame() will return NETDEV_TX_BUSY and the upper layer will
> resend the skb. But the skb is already freed, which will cause UAF bug
> when the upper layer resends the skb.
> 
> Remove the harmful free.
> 
> Fixes: 5e5d49422dfb ("e100: Release skb when DMA mapping is failed in e100_xmit_prepare")
> Signed-off-by: Wang Hai <wanghai38@xxxxxxxxxx>
> ---
>  drivers/net/ethernet/intel/e100.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/e100.c b/drivers/net/ethernet/intel/e100.c
> index 560d1d442232..d3fdc290937f 100644
> --- a/drivers/net/ethernet/intel/e100.c
> +++ b/drivers/net/ethernet/intel/e100.c
> @@ -1741,11 +1741,8 @@ static int e100_xmit_prepare(struct nic *nic, struct cb *cb,
>  	dma_addr = dma_map_single(&nic->pdev->dev, skb->data, skb->len,
>  				  DMA_TO_DEVICE);
>  	/* If we can't map the skb, have the upper layer try later */
> -	if (dma_mapping_error(&nic->pdev->dev, dma_addr)) {
> -		dev_kfree_skb_any(skb);
> -		skb = NULL;
> +	if (dma_mapping_error(&nic->pdev->dev, dma_addr))
>  		return -ENOMEM;
> -	}
>  
>  	/*
>  	 * Use the last 4 bytes of the SKB payload packet as the CRC, used for

I'm surprised the original patch that this essentially reverts was even
accepted.

Reviewed-by: Alexander Duyck <alexanderduyck@xxxxxx>