Re: [PATCH nf] ebtables: arpreply: Add the standard target sanity check

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Fri, May 12, 2017 at 05:44:10PM +0800, gfree.wind@vip.163.com wrote:
> From: Gao Feng <gfree.wind@vip.163.com>
> 
> The info->target is from userspace and it would be used directly.
> So we need to add the sanity check to make sure it is a valid standard
> target, although the ebtables tool has already checked it. Kernel need
> to check anything from userspace.
> 
> If the target was set as an evil value, it would break the ebtables
> and cause a panic. Because the non-standard target is treated as one
> offset.
> 
> Signed-off-by: Gao Feng <gfree.wind@vip.163.com>
> ---
>  net/bridge/netfilter/ebt_arpreply.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/net/bridge/netfilter/ebt_arpreply.c b/net/bridge/netfilter/ebt_arpreply.c
> index 5929309..c4886d9 100644
> --- a/net/bridge/netfilter/ebt_arpreply.c
> +++ b/net/bridge/netfilter/ebt_arpreply.c
> @@ -68,6 +68,9 @@ static int ebt_arpreply_tg_check(const struct xt_tgchk_param *par)
>  	if (e->ethproto != htons(ETH_P_ARP) ||
>  	    e->invflags & EBT_IPROTO)
>  		return -EINVAL;
> +	if (INVALID_TARGET)

Please, add:

static inline bool ebt_invalid_target(int target)
{
        return (target < -NUM_STANDARD_TARGETS || target >= 0);
}

and use it in this fix.

So we can get rid of this obscure INVALID_TARGET macro.

Thanks.