Re: [PATCH] sky2: Make sure there is at least one frag_addr available

[Alexander Lobakin <aleksander.lobakin@intel.com>]

From: Kees Cook <keescook@chromium.org>
Date: Wed, 20 Sep 2023 13:25:13 -0700

> In the likely pathological case of building sky2 with 16k PAGE_SIZE,
> make sure there is at least 1 frag_addr in struct rx_ring_info:
> 
>    In file included from include/linux/skbuff.h:28,
>                     from include/net/net_namespace.h:43,
>                     from include/linux/netdevice.h:38,
>                     from drivers/net/ethernet/marvell/sky2.c:18:
>    drivers/net/ethernet/marvell/sky2.c: In function 'sky2_rx_unmap_skb':
>    include/linux/dma-mapping.h:416:36: warning: array subscript i is outside array bounds of 'dma_addr_t[0]' {aka 'long long unsigned int[]'} [-Warray-bounds=]
>      416 | #define dma_unmap_page(d, a, s, r) dma_unmap_page_attrs(d, a, s, r, 0)
>          |                                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    drivers/net/ethernet/marvell/sky2.c:1257:17: note: in expansion of macro 'dma_unmap_page'
>     1257 |                 dma_unmap_page(&pdev->dev, re->frag_addr[i],
>          |                 ^~~~~~~~~~~~~~
>    In file included from drivers/net/ethernet/marvell/sky2.c:41:
>    drivers/net/ethernet/marvell/sky2.h:2198:25: note: while referencing 'frag_addr'
>     2198 |         dma_addr_t      frag_addr[ETH_JUMBO_MTU >> PAGE_SHIFT];
>          |                         ^~~~~~~~~
> 
> With CONFIG_PAGE_SIZE_16KB=y, PAGE_SHIFT == 14, so:
> 
>   #define ETH_JUMBO_MTU   9000
> 
> causes "ETH_JUMBO_MTU >> PAGE_SHIFT" to be 0. Use "?: 1" to solve this build warning.
> 
> Cc: Mirko Lindner <mlindner@marvell.com>
> Cc: Stephen Hemminger <stephen@networkplumber.org>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: Eric Dumazet <edumazet@google.com>
> Cc: Jakub Kicinski <kuba@kernel.org>
> Cc: Paolo Abeni <pabeni@redhat.com>
> Cc: netdev@vger.kernel.org
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202309191958.UBw1cjXk-lkp@intel.com/
> Signed-off-by: Kees Cook <keescook@chromium.org>

Reviewed-by: Alexander Lobakin <aleksander.lobakin@intel.com>

That "nobody uses this HW on non-x86 systems, why bother" is fun each time.

> ---
>  drivers/net/ethernet/marvell/sky2.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/marvell/sky2.h b/drivers/net/ethernet/marvell/sky2.h
> index ddec1627f1a7..8d0bacf4e49c 100644
> --- a/drivers/net/ethernet/marvell/sky2.h
> +++ b/drivers/net/ethernet/marvell/sky2.h
> @@ -2195,7 +2195,7 @@ struct rx_ring_info {
>  	struct sk_buff	*skb;
>  	dma_addr_t	data_addr;
>  	DEFINE_DMA_UNMAP_LEN(data_size);
> -	dma_addr_t	frag_addr[ETH_JUMBO_MTU >> PAGE_SHIFT];
> +	dma_addr_t	frag_addr[ETH_JUMBO_MTU >> PAGE_SHIFT ?: 1];
>  };
>  
>  enum flow_control {

Thanks,
Olek