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

[Joel Granados]

On Thu, Mar 28, 2024 at 12:49:34PM -0700, Kuniyuki Iwashima wrote:
> From: Joel Granados via B4 Relay <devnull+j.granados.samsung.com@xxxxxxxxxx>
> 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@xxxxxxxxxxxxxxxxxxxxxx/)
> > 
> > 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 is a great idea. I'll also try to look and see where else I can add
the explicit relation check.

Thx for the review

> 
> 
> > 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@xxxxxxxxxxx>
> > ---
> >  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

-- 

Joel Granados

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