Re: [PATCH v2] sky2: Make sure there is at least one frag_addr available

["Gustavo A. R. Silva" <gustavo@embeddedor.com>]

On 9/22/23 10:50, Kees Cook wrote:
> In the pathological case of building sky2 with 16k PAGE_SIZE, the
> frag_addr[] array would never be used, so the original code was correct
> that size should be 0. But the compiler now gets upset with 0 size arrays
> in places where it hasn't eliminated the code that might access such an
> array (it can't figure out that in this case an rx skb with fragments
> would never be created). To keep the compiler happy, 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/
> Reviewed-by: Alexander Lobakin <aleksander.lobakin@intel.com>
> Signed-off-by: Kees Cook <keescook@chromium.org>

Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Thanks
--
Gustavo

> ---
> v2 - improve commit message, add Ack
> v1 - https://lore.kernel.org/netdev/20230920202509.never.299-kees@kernel.org/
> ---
>   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 {