Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
(for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

As found with Coccinelle[1], add __counted_by for struct 
mlxsw_sp_nexthop_group_info.

[1] 
https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci

Cc: Ido Schimmel <ido...@nvidia.com>
Cc: Petr Machata <pe...@nvidia.com>
Cc: "David S. Miller" <da...@davemloft.net>
Cc: Eric Dumazet <eduma...@google.com>
Cc: Jakub Kicinski <k...@kernel.org>
Cc: Paolo Abeni <pab...@redhat.com>
Cc: net...@vger.kernel.org
Signed-off-by: Kees Cook <keesc...@chromium.org>
---
 drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c 
b/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
index debd2c466f11..82a95125d9ca 100644
--- a/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
+++ b/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
@@ -3107,7 +3107,7 @@ struct mlxsw_sp_nexthop_group_info {
           gateway:1, /* routes using the group use a gateway */
           is_resilient:1;
        struct list_head list; /* member in nh_res_grp_list */
-       struct mlxsw_sp_nexthop nexthops[];
+       struct mlxsw_sp_nexthop nexthops[] __counted_by(count);
 };
 
 static struct mlxsw_sp_rif *
-- 
2.34.1


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