netdev - Re: [PATCHv2] net/ipv6: add sysctl option accept_ra_hop

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Date:	Wed, 29 Jul 2015 10:00:35 +0800
From:	Hangbin Liu <liuhangbin@...il.com>
To:	YOSHIFUJI Hideaki <hideaki.yoshifuji@...aclelinux.com>
Cc:	network dev <netdev@...r.kernel.org>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>
Subject: Re: [PATCHv2] net/ipv6: add sysctl option accept_ra_hop_limit

2015-07-28 11:58 GMT+08:00 YOSHIFUJI Hideaki
<hideaki.yoshifuji@...aclelinux.com>:
> Hi,
>
> Hangbin Liu wrote:
>> 2015-07-28 7:50 GMT+08:00 YOSHIFUJI Hideaki/吉藤英明
>> <hideaki.yoshifuji@...aclelinux.com>:
>>> Hi,
>>>
>>> Hangbin Liu wrote:
>>>> Commit 6fd99094de2b ("ipv6: Don't reduce hop limit for an interface")
>>>> disabled accept hop limit from RA if it is higher than the current hop
>>>> limit for security stuff. But this behavior kind of break the RFC definition.
>>>>
>>>> RFC 4861, 6.3.4.  Processing Received Router Advertisements
>>>>    If the received Cur Hop Limit value is non-zero, the host SHOULD set
>>>>    its CurHopLimit variable to the received value.
>>>>
>>>> So add sysctl option accept_ra_hop_limit to let user choose whether accept
>>>> hop limit info in RA.
>>>>
>>>
>>> How about introducing "minimum hop limit", instead?
>>
>> Hi Yoshifuji,
>>
>> This is a good idea. Maybe this can be another sysctl option?
>>
>> The minimum hop limit can be an enhancement of the security issue, then we will
>> not only increase the hop limit, but also could decrease it in the
>> range of values we
>> accept.
>>
>> On the other hand, with this patch, we can enable, disable or partly
>> enable accept
>> hop limit. If we only use "minimum hop limit", people could not use a static hop
>> limit value.
>>
>> May be we use a “hop limit range" instead? How do you think?
>
> I think name of sysctl is the same as you suggested and change the
> semantics.  default value is 0 to accept all hotlimit value
> as before and people can set it to 32 (for example) to reject
> too-small hoplimit (0-31).

OK, then I will try submit a "minimum hop limit", thanks for your suggestion :)

Regards
Hangbin
>
> --yoshfuji
>
>>
>> Thanks
>> Hangbin
>>
>>>
>>> |commit 6fd99094de2b83d1d4c8457f2c83483b2828e75a
>>> |Author: D.S. Ljungmark <ljungmark@...io.se>
>>> |Date:   Wed Mar 25 09:28:15 2015 +0100
>>> |
>>> |    ipv6: Don't reduce hop limit for an interface
>>> :
>>> |    RFC 3756, Section 4.2.7, "Parameter Spoofing"
>>> |
>>> :
>>> |   >   As an example, one possible approach to mitigate this threat is to
>>> |    >   ignore very small hop limits.  The nodes could implement a
>>> |    >   configurable minimum hop limit, and ignore attempts to set it below
>>> |    >   said limit.
>
> --
> Hideaki Yoshifuji <hideaki.yoshifuji@...aclelinux.com>
> Technical Division, MIRACLE LINUX CORPORATION
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