Re: [PATCH nf 2/3] netfilter: nfnetlink: relax strict multicast group from netlink_bind

[Patrick McHardy <kaber@trash.net>]

On 05.01, Pablo Neira Ayuso wrote:
> Relax the checking that was introduced in 97840cb ("netfilter:
> nfnetlink: fix insufficient validation in nfnetlink_bind") when the
> subscription bitmask is used. Existing userspace code code may request
> to listen to all of the existing netlink groups by setting an all to one
> subscription group bitmask. Netlink already validates subscription via
> setsockopt() for us.

What is the point of doing this? I don't think its particulary
reasonable to subscribe to ~0 unless you're implementing some kind of
monitor.

We also don't know whether a bitmask or an invalid group number was
used, so the comment below is at least misleading.

And, unrelated, but since it went in via netfilter asking anyway, why
is the group number signed? That doesn't make any sense, it is treated
as unsigned everywhere else.

> diff --git a/net/netfilter/nfnetlink.c b/net/netfilter/nfnetlink.c
> index c6619d4..5082d81 100644
> --- a/net/netfilter/nfnetlink.c
> +++ b/net/netfilter/nfnetlink.c
> @@ -469,8 +469,11 @@ static int nfnetlink_bind(int group)
>  	const struct nfnetlink_subsystem *ss;
>  	int type;
>  
> +	/* No strict check for groups when subscription bitmask is used, group
> +	 * binding via setsockopt() already rejects this from netlink.
> +	 */
>  	if (group <= NFNLGRP_NONE || group > NFNLGRP_MAX)
> -		return -EINVAL;
> +		return 0;
>  
>  	type = nfnl_group2type[group];
>  
> -- 
> 1.7.10.4
>