Subject: Re: [PATCH] liquidio: avoid NULL pointer dereference in lio_vf_rep_copy_packet()

From: Jakub Kicinski <[email-masked]>
Date: Tue, 29 Nov 2022 21:23:07 -0800

On Mon, 28 Nov 2022 13:26:59 +0300 Aleksandr Burakov wrote:
> --- a/drivers/net/ethernet/cavium/liquidio/lio_vf_rep.c
> +++ b/drivers/net/ethernet/cavium/liquidio/lio_vf_rep.c
> @@ -272,13 +272,12 @@ lio_vf_rep_copy_packet(struct octeon_device *oct,
>  				pg_info->page_offset;
>  			memcpy(skb->data, va, MIN_SKB_SIZE);
>  			skb_put(skb, MIN_SKB_SIZE);
> +			skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags,
> +					pg_info->page,
> +					pg_info->page_offset + MIN_SKB_SIZE,
> +					len - MIN_SKB_SIZE,
> +					LIO_RXBUFFER_SZ);
>  		}
> -
> -		skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags,
> -				pg_info->page,
> -				pg_info->page_offset + MIN_SKB_SIZE,
> -				len - MIN_SKB_SIZE,
> -				LIO_RXBUFFER_SZ);
>  	} else {
>  		struct octeon_skb_page_info *pg_info =
>  			((struct octeon_skb_page_info *)(skb->cb));

The else branch also looks at pg_info and derefs page like there's 
no tomorrow. You need to put a bit more effort into the analysis.

Marvell people please chime in and tell us what the intention is here.
Whether page can be NULL here or this is defensive programming and can
be dropped.