Subject: Re: [PATCH iwl-next v2] ixgbe: Fix possible skb NULL pointer dereference

From: Maciej Fijalkowski <[email-masked]>
Date: Mon, 20 Jan 2025 15:45:19 +0100

On Fri, Jan 17, 2025 at 04:49:35PM +0100, Piotr Kwapulinski wrote:
> The commit c824125cbb18 ("ixgbe: Fix passing 0 to ERR_PTR in
> ixgbe_run_xdp()") stopped utilizing the ERR-like macros for xdp status
> encoding. Propagate this logic to the ixgbe_put_rx_buffer().
> 
> The commit also relaxed the skb NULL pointer check - caught by Smatch.
> Restore this check.
> 
> Fixes: c824125cbb18 ("ixgbe: Fix passing 0 to ERR_PTR in ixgbe_run_xdp()")
> Reported-by: Dan Carpenter <[email-masked]>
> Signed-off-by: Piotr Kwapulinski <[email-masked]>
> ---
>  drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> index 7236f20..c682c3d 100644
> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> @@ -2098,14 +2098,14 @@ static struct ixgbe_rx_buffer *ixgbe_get_rx_buffer(struct ixgbe_ring *rx_ring,
>  
>  static void ixgbe_put_rx_buffer(struct ixgbe_ring *rx_ring,
>  				struct ixgbe_rx_buffer *rx_buffer,
> -				struct sk_buff *skb,
> -				int rx_buffer_pgcnt)
> +				struct sk_buff *skb, int rx_buffer_pgcnt,
> +				int xdp_res)
>  {
>  	if (ixgbe_can_reuse_rx_page(rx_buffer, rx_buffer_pgcnt)) {
>  		/* hand second half of page back to the ring */
>  		ixgbe_reuse_rx_page(rx_ring, rx_buffer);
>  	} else {
> -		if (!IS_ERR(skb) && IXGBE_CB(skb)->dma == rx_buffer->dma) {
> +		if (skb && !xdp_res && IXGBE_CB(skb)->dma == rx_buffer->dma) {

xdp_res check is redundant here. skb ptr will be non-null only for xdp_res
== 0. so skb != NULL implies xdp_res == 0.

If I am not mistaken:D or ixgbe has some code path I missed.

Besides this, thanks for improving commit message!

>  			/* the page has been released from the ring */
>  			IXGBE_CB(skb)->page_released = true;
>  		} else {
> @@ -2415,7 +2415,8 @@ static int ixgbe_clean_rx_irq(struct ixgbe_q_vector *q_vector,
>  			break;
>  		}
>  
> -		ixgbe_put_rx_buffer(rx_ring, rx_buffer, skb, rx_buffer_pgcnt);
> +		ixgbe_put_rx_buffer(rx_ring, rx_buffer, skb, rx_buffer_pgcnt,
> +				    xdp_res);
>  		cleaned_count++;
>  
>  		/* place incomplete frames back on ring for completion */
> -- 
> v1 -> v2
>   Provide extra details in commit message for motivation of this patch.
> 
> 2.43.0
>