Subject: Re: [PATCH 1/3 v2] ipv6: do not disable temp_address when reaching max_address

From: Ding Tianhong <[email-masked]>
Date: Wed, 14 Aug 2013 09:34:22 +0800

On 2013/8/13 19:05, Hannes Frederic Sowa wrote:
> 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
> 
Reference:
  -> http://seclists.org/oss-sec/2012/q4/292
  -> http://seclists.org/oss-sec/2013/q1/92

I think the point is after the ./flood_route26 attack, 
the proc/sys/net/ipv6/conf/iface/use_tempaddr will change from 2 to -1,
whether is correct? :)

regards
Ding Tianhong

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