[PATCH v2 4/4] ax.25: Remove the now superfluous sentinel elements from ctl_table array

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Joel Granados via B4 Relay <devnull+j.granados.samsung.com@kernel.org>
Date: Thu, 28 Mar 2024 16:40:05 +0100
> This commit comes at the tail end of a greater effort to remove the
> empty elements at the end of the ctl_table arrays (sentinels) which will
> reduce the overall build time size of the kernel and run time memory
> bloat by ~64 bytes per sentinel (further information Link :
> https://lore.kernel.org/all/ZO5Yx5JFogGi%2FcBo@bombadil.infradead.org/)
> 
> When we remove the sentinel from ax25_param_table a buffer overflow
> shows its ugly head. The sentinel's data element used to be changed when
> CONFIG_AX25_DAMA_SLAVE was not defined.

I think it's better to define the relation explicitly between the
enum and sysctl table by BUILD_BUG_ON() in ax25_register_dev_sysctl()

  BUILD_BUG_ON(AX25_MAX_VALUES != ARRAY_SIZE(ax25_param_table));

and guard AX25_VALUES_DS_TIMEOUT with #ifdef CONFIG_AX25_DAMA_SLAVE
as done for other enum.


> This did not have any adverse
> effects as we still stopped on the sentinel because of its null
> procname. But now that we do not have the sentinel element, we are
> careful to check ax25_param_table's size.
> 
> Signed-off-by: Joel Granados <j.granados@samsung.com>
> ---
>  net/ax25/sysctl_net_ax25.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/net/ax25/sysctl_net_ax25.c b/net/ax25/sysctl_net_ax25.c
> index db66e11e7fe8..e55be8817a1e 100644
> --- a/net/ax25/sysctl_net_ax25.c
> +++ b/net/ax25/sysctl_net_ax25.c
> @@ -141,8 +141,6 @@ static const struct ctl_table ax25_param_table[] = {
>  		.extra2		= &max_ds_timeout
>  	},
>  #endif
> -
> -	{ }	/* that's all, folks! */
>  };
>  
>  int ax25_register_dev_sysctl(ax25_dev *ax25_dev)
> @@ -155,7 +153,7 @@ int ax25_register_dev_sysctl(ax25_dev *ax25_dev)
>  	if (!table)
>  		return -ENOMEM;
>  
> -	for (k = 0; k < AX25_MAX_VALUES; k++)
> +	for (k = 0; k < AX25_MAX_VALUES && k < ARRAY_SIZE(ax25_param_table); k++)
>  		table[k].data = &ax25_dev->values[k];
>  
>  	snprintf(path, sizeof(path), "net/ax25/%s", ax25_dev->dev->name);
> 
> -- 
> 2.43.0