netdev - Re: [PATCH 1/3 v2] ipv6: do not disable temp_address when reaching max

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Date:	Tue, 13 Aug 2013 13:05:21 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Ding Tianhong <dingtianhong@...wei.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>,
	Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH 1/3 v2] ipv6: do not disable temp_address when reaching max_address

On Tue, Aug 13, 2013 at 03:57:14PM +0800, Ding Tianhong wrote:
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index da4241c..72911fd 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -1134,10 +1134,27 @@ retry:
>  	if (IS_ERR_OR_NULL(ift)) {
>  		in6_ifa_put(ifp);
>  		in6_dev_put(idev);
> -		pr_info("%s: retry temporary address regeneration\n", __func__);
> -		tmpaddr = &addr;
> -		write_lock(&idev->lock);
> -		goto retry;
> +
> +		/* According RFC4941 3.3.7:
> +		 * If DAD indicates the address is already in use,
> +		 * the node must generate a new randomized interface
> +		 * identifier as described in section 3.2 above, and
> +		 * repeat the previous steps as appropriate up to
> +		 * TEMP_IDGEN_RETRIES times.
> +		 * If after TEMP_IDGEN_RETRIES consecutive attempts no
> +		 * non-unique address was generated, the node must log
> +		 * a system error and must not attempt to generate
> +		 * temporary address for that interface.
> +		 * So we have to check the return err and distinguish
> +		 * the correct retry path.
> +		 */
> +		if (PTR_ERR(ift) == -EEXIST) {
> +			pr_info("%s: retry temporary address regeneration\n", __func__);
> +			tmpaddr = &addr;
> +			write_lock(&idev->lock);
> +			goto retry;
> +		} else
> +			goto out;

Correct me if I am wrong, but the RFC referes by mentioning "in use" to
allocated on the subnet and not in use by this host. I don't see how this
fixes the CVE then. dad is triggered by ipv6_add_addr.

Greetings,

  Hannes

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