Date:	Sat, 07 May 2011 15:54:10 +0200
From:	Gervais Arthur <arthur.gervais@...a-lyon.fr>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Jan Ceuleers <jan.ceuleers@...puter.org>, <netdev@...r.kernel.org>
Subject: Re: Fwd: PROBLEM: IPv6 Duplicate Address Detection with non RFC-conform
 ICMPv6 packets

On 05/07/2011 03:25 PM, Eric Dumazet wrote:
> Le samedi 07 mai 2011 à 15:17 +0200, Gervais Arthur a écrit :
>> On 05/07/2011 03:10 PM, Eric Dumazet wrote:
>>> Le samedi 07 mai 2011 à 14:55 +0200, Jan Ceuleers a écrit :
>>>> The networking folks are on netdev
>>>>
>>>> -------- Original Message --------
>>>> Subject: PROBLEM: IPv6 Duplicate Address Detection with non
RFC-conform
>>>> ICMPv6 packets
>>>> Date: Thu, 05 May 2011 11:52:05 +0200
>>>> From: Gervais Arthur<arthur.gervais@...a-lyon.fr>
>>>> To:<linux-kernel@...r.kernel.org>
>>>> CC:<arthur.gervais@...a-lyon.fr>
>>>>
>>>> [1.] One line summary of the problem:
>>>>
>>>> A specially crafted Ethernet ICMPv6 packet which is not conform to
the
>>>> RFC can perform a IPv6 Duplicate Address Detection Failure.
>>>>
>>>> [2.] Full description of the problem/report:
>>>>
>>>> If a new IPv6 node joins the local area network, the new node sends
an
>>>> ICMPv6 Neighbor Solicitation packet in order to check if the
>>>> self-generated local-link IPv6 address already occupied is.
>>>>
>>>> An attacker can answer to this Neighbor Solicitation packet with an
>>>> ICMPv6 Neighbor Advertisement packet, so that the new IPv6 node is
not
>>>> able to associate the just generated IPv6 address.
>>>> -- This problem is well known and IPv6 related.
>>>>
>>>> The new problem is that the attacker can modify the Ethernet Neighbor
>>>> Advertisement packets, so that they are not RFC conform and so that
it
>>>> is even more difficult to detect the attacker.
>>>>
>>>> If an attacker sends the following packet, duplicate address
detection
>>>> fails on Linux:
>>>>
>>>> Ethernet Layer: 	Victim MAC -->   Victim MAC
>>>> IPv6 Layer:		fe80::200:edff:feXX:XXXX -->   ff02::1
>>>> 			ICMPv6
>>>> 			  Type 136 (Neighbor Advertisement)
>>>> 			  Target: fe80::200:edff:feXX:XXXX
>>>> 			ICMPv6 Option
>>>> 			  Type 2 (Target link-layer address) Victim MAC
>>>>
>>>> Please find attached a drawing and a proof of concept.
>>>>
>>>> [3.] Keywords (i.e., modules, networking, kernel):
>>>>
>>>> Network, IPv6, Duplicate Address Detection
>>>>
>>>> [4.] Kernel version (from /proc/version):
>>>>
>>>> Latest tested:
>>>> Linux version 2.6.35-22-generic (buildd@...hera) (gcc version 4.4.5
>>>> (Ubuntu/Linaro 4.4.4-14ubuntu4) ) #33-Ubuntu SMP Sun Sep 19 20:34:50
>> UTC
>>>> 2010
>>>> (and before most probably)
>>>>
>>>> [6.] A small shell script or example program which triggers the
>>>>          problem (if possible)
>>>>
>>>> Please find attached a python script demonstrating the problem.
>>>>
>>>> [X.] Other notes, patches, fixes, workarounds:
>>>>
>>>> The Linux Kernel should not accept incoming Ethernet packets
>> originating
>>>> from an internal Ethernet card (identified by the MAC address)
>>>>
>>>
>>> I fail to understand the problem.
>>>
>>> The attacker might use any kind of source MAC address to fool 'Victim'
>>> or 'network admins'
>>>
>>> Why one particular address should be avoided ?
>>>
>>>
>>>
>>
>> Currently the IPv6 implementation says (from the victims view):
>> I send a Neighbor Solicitation for a given IPv6 address to check the
>> duplicate address detection.
>>
>> If I then receive a Neighbor Advertisement packet from my MAC address,
>> to my MAC address, with ICMPv6 target option my MAC address, then the
>> requested IPv6 address must already be used and I cannot take it.
>>
>> I think such a packet should never be allowed to be accepted, because
>> the victim just asked if the address is free.
>>
>> If such a packet is accepted, it is even more difficult to find the
>> attacker.
>>
>

If the network administrator is using some IDS like NDPMon 
(http://ndpmon.sourceforge.net/) to detect a DAD DoS attacks, and the 
attacker changes the MAC address like I described, it will not detect 
the DAD DoS attack anymore (because the victim itself claims already 
having the IPv6 address).

> What prevents the attacker to use random source Mac addresses,
> or using legit ones learnt from packet sniffing ?
>

Of course an attacker could use a random source Mac address, or any 
other already existing source Mac address from the network, but the IDS 
system will know (depending on how it works), that this Mac address has 
not this IPv6 address associated and therefore a DAD DoS is happening.

> Why only one given mac address is to be avoided, out of billions other ?
>

Why would the victim itself claim already having the IPv6 address?

> This would be a strange precedent. Practically nowhere we check incoming
> mac addresses from incoming packets. (only on netfilter it can be
> optionally done)
>

Yes I understand this point. But there is not only the source Mac 
address from the Ethernet frame, it is also the "target link-layer 
address" in the ICMPv6 Option which is related to this case.

> If you have a host with say one thousand NICS, should we make sure the
> packet we receive has not one of the thousand mac addresses we currently
> have on this host ?

I send the bug to this list, because I don't think this is a NDPMon 
specific problem. Windows for example does not accept the packets the 
way I described.

Maybe this is not an OS-specific problem, but attacks would be easier to 
detect, if those packets would not be accepted.

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