From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Miller <davem@davemloft.net>
Subject: Re: [PATCH net] ipv6: do not overwrite inetpeer metrics prematurely
Date: Wed, 12 Mar 2014 16:54:43 -0400 (EDT)
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From: Michal Kubecek <mkubecek@suse.cz>
Date: Tue, 11 Mar 2014 16:08:14 +0100

> +	nla_for_each_attr(nla, mx, mx_len, remaining) {
> +		int type = nla_type(nla);
> +
> +		if (type) {
> +			if (type > RTAX_MAX)
> +				return -EINVAL;
> +
> +			mp[type - 1] = nla_get_u32(nla);
> +		}
> +	}

It was surprising to me that nla_for_each_attr() works with a second
argument of NULL.

It only does so when the length is zero, due to how the test in nla_ok()
is codified.

I know it's a minor nit, but can you only execute this loop if mx is
non-NULL?

Perhaps you can put this into (yet another) helper function:

int __fib6_commit_metrics(u32 *mp, struct nlattr *mx, int mx_len)

Otherwise looks good to me.