Subject: Re: [PATCH] sysctl: fix min/max handling in __do_proc_doulongvec_minmax()

From: Robin Holt <[email-masked]>
Date: Mon, 4 Oct 2010 03:59:13 -0500

On Sat, Oct 02, 2010 at 03:17:49PM +0200, Eric Dumazet wrote:
> When proc_doulongvec_minmax() is used with an array of longs,
> and no min/max check requested (.extra1 or .extra2 being NULL), we
> dereference a NULL pointer for the second element of the array.
> 
> Noticed while doing some changes in network stack for the "16TB problem"
> 
> Signed-off-by: Eric Dumazet <[email-masked]>
> ---
>  kernel/sysctl.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index f88552c..4fba86d 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -2500,7 +2500,8 @@ static int __do_proc_doulongvec_minmax(void *data, struct ctl_table *table, int
>  				break;
>  			if (neg)
>  				continue;
> -			if ((min && val < *min) || (max && val > *max))
> +			if ((table->extra1 && val < *min) ||
> +			    (table->extra2 && val > *max))

How about changing:
        for (; left && vleft--; i++, min++, max++, first=0) {
into:
        for (; left && vleft--; i++, min = min ? min + 1 : NULL, max = max ? max + 1: NULL, first=0) {

That would make min and max correct and reduce the chances somebody in
the future overlooks the fact they are currently filled with garbage.

Robin