Re: [PATCH] mlxsw: spectrum_router: Replace 0-length array with flexible array

Petr Machata
2023-01-06T10:50:28Z

Kees Cook <keescook@chromium.org> writes:

> Zero-length arrays are deprecated[1]. Replace struct
> mlxsw_sp_nexthop_group_info's "nexthops" 0-length array with a flexible
> array. Detected with GCC 13, using -fstrict-flex-arrays=3:
>
> drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c: In function 'mlxsw_sp_nexthop_group_hash_obj':
> drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c:3278:38: warning: array subscript i is outside array bounds of 'struct mlxsw_sp_nexthop[0]' [-Warray-bounds=]
> 3278 | val ^= jhash(&nh->ifindex, sizeof(nh->ifindex), seed);
> | ^~~~~~~~~~~~
> drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c:2954:33: note: while referencing 'nexthops'
> 2954 | struct mlxsw_sp_nexthop nexthops[0];
> | ^~~~~~~~
>
> [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#zero-length-and-one-element-arrays
>
> Cc: Ido Schimmel <idosch@nvidia.com>
> Cc: Petr Machata <petrm@nvidia.com>
> 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: "Gustavo A. R. Silva" <gustavoars@kernel.org>
> Cc: netdev@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@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 c22c3ac4e2a1..09e32778b012 100644
> --- a/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
> +++ b/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c
> @@ -2951,7 +2951,7 @@ 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[0];
> + struct mlxsw_sp_nexthop nexthops[];
> #define nh_rif nexthops[0].rif
> };

Thanks. I'll pass this through our nightly and report back.