Re: [PATCH v3 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: Fri, 12 Apr 2024 16:48:32 +0200
> From: Joel Granados <j.granados@samsung.com>
> 
> 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/)
> 
> Avoid a buffer overflow when traversing the ctl_table by ensuring that
> AX25_MAX_VALUES is the same as the size of ax25_param_table. This is
> done with a BUILD_BUG_ON where ax25_param_table is defined and a
> CONFIG_AX25_DAMA_SLAVE guard in the unnamed enum definition as well as
> in the ax25_dev_device_up and ax25_ds_set_timer functions.
> 
> The overflow happened when the sentinel was removed from
> ax25_param_table. The sentinel's data element was changed when
> CONFIG_AX25_DAMA_SLAVE was undefined. This had no adverse effects as it
> still stopped on the sentinel's null procname but needed to be addressed
> once the sentinel was removed.
> 
> Signed-off-by: Joel Granados <j.granados@samsung.com>

Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>


> ---
>  include/net/ax25.h         | 2 ++
>  net/ax25/ax25_dev.c        | 3 +++
>  net/ax25/ax25_ds_timer.c   | 4 ++++
>  net/ax25/sysctl_net_ax25.c | 3 +--
>  4 files changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/include/net/ax25.h b/include/net/ax25.h
> index 0d939e5aee4e..eb9cee8252c8 100644
> --- a/include/net/ax25.h
> +++ b/include/net/ax25.h
> @@ -139,7 +139,9 @@ enum {
>  	AX25_VALUES_N2,		/* Default N2 value */
>  	AX25_VALUES_PACLEN,	/* AX.25 MTU */
>  	AX25_VALUES_PROTOCOL,	/* Std AX.25, DAMA Slave, DAMA Master */
> +#ifdef CONFIG_AX25_DAMA_SLAVE
>  	AX25_VALUES_DS_TIMEOUT,	/* DAMA Slave timeout */
> +#endif
>  	AX25_MAX_VALUES		/* THIS MUST REMAIN THE LAST ENTRY OF THIS LIST */
>  };
>  
> diff --git a/net/ax25/ax25_dev.c b/net/ax25/ax25_dev.c
> index c5462486dbca..af547e185a94 100644
> --- a/net/ax25/ax25_dev.c
> +++ b/net/ax25/ax25_dev.c
> @@ -78,7 +78,10 @@ void ax25_dev_device_up(struct net_device *dev)
>  	ax25_dev->values[AX25_VALUES_N2]        = AX25_DEF_N2;
>  	ax25_dev->values[AX25_VALUES_PACLEN]	= AX25_DEF_PACLEN;
>  	ax25_dev->values[AX25_VALUES_PROTOCOL]  = AX25_DEF_PROTOCOL;
> +
> +#ifdef CONFIG_AX25_DAMA_SLAVE
>  	ax25_dev->values[AX25_VALUES_DS_TIMEOUT]= AX25_DEF_DS_TIMEOUT;
> +#endif
>  
>  #if defined(CONFIG_AX25_DAMA_SLAVE) || defined(CONFIG_AX25_DAMA_MASTER)
>  	ax25_ds_setup_timer(ax25_dev);
> diff --git a/net/ax25/ax25_ds_timer.c b/net/ax25/ax25_ds_timer.c
> index c4f8adbf8144..8f385d2a7628 100644
> --- a/net/ax25/ax25_ds_timer.c
> +++ b/net/ax25/ax25_ds_timer.c
> @@ -49,12 +49,16 @@ void ax25_ds_del_timer(ax25_dev *ax25_dev)
>  
>  void ax25_ds_set_timer(ax25_dev *ax25_dev)
>  {
> +#ifdef CONFIG_AX25_DAMA_SLAVE
>  	if (ax25_dev == NULL)		/* paranoia */
>  		return;
>  
>  	ax25_dev->dama.slave_timeout =
>  		msecs_to_jiffies(ax25_dev->values[AX25_VALUES_DS_TIMEOUT]) / 10;
>  	mod_timer(&ax25_dev->dama.slave_timer, jiffies + HZ);
> +#else
> +	return;
> +#endif
>  }
>  
>  /*
> diff --git a/net/ax25/sysctl_net_ax25.c b/net/ax25/sysctl_net_ax25.c
> index db66e11e7fe8..fb9966926e90 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)
> @@ -155,6 +153,7 @@ int ax25_register_dev_sysctl(ax25_dev *ax25_dev)
>  	if (!table)
>  		return -ENOMEM;
>  
> +	BUILD_BUG_ON(AX25_MAX_VALUES != ARRAY_SIZE(ax25_param_table));
>  	for (k = 0; k < AX25_MAX_VALUES; k++)
>  		table[k].data = &ax25_dev->values[k];
>  
> 
> -- 
> 2.43.0