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

From: Kees Cook <[email-masked]>
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 <[email-masked]>
Cc: Stephen Hemminger <[email-masked]>
Cc: "David S. Miller" <[email-masked]>
Cc: Eric Dumazet <[email-masked]>
Cc: Jakub Kicinski <[email-masked]>
Cc: Paolo Abeni <[email-masked]>
Cc: [email-masked]
Reported-by: kernel test robot <[email-masked]>
Closes: https://lore.kernel.org/oe-kbuild-all/[email-masked]/
Signed-off-by: Kees Cook <[email-masked]>
---
 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 {
-- 
2.34.1