netdev - Re: [PATCH 2/2] neighbour: allow NUD_NOARP entries to be forced GCed

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Date:   Mon, 19 Apr 2021 10:10:12 -0700
From:   David Ahern <dsahern@...il.com>
To:     Kasper Dupont <kasperd@...fm.28.feb.2009.kasperd.net>,
        netdev@...r.kernel.org
Cc:     Thadeu Lima de Souza Cascardo <cascardo@...onical.com>,
        davem@...emloft.net, kuba@...nel.org, dsahern@...nel.org,
        Kasper Dupont <kasperd@...wv.06.feb.2021.kasperd.net>
Subject: Re: [PATCH 2/2] neighbour: allow NUD_NOARP entries to be forced GCed

On 4/19/21 9:44 AM, Kasper Dupont wrote:
> On 17/03/21 15.53, Thadeu Lima de Souza Cascardo wrote:
>> IFF_POINTOPOINT interfaces use NUD_NOARP entries for IPv6. It's possible to
>> fill up the neighbour table with enough entries that it will overflow for
>> valid connections after that.
>>
>> This behaviour is more prevalent after commit 58956317c8de ("neighbor:
>> Improve garbage collection") is applied, as it prevents removal from
>> entries that are not NUD_FAILED, unless they are more than 5s old.
>>
>> Fixes: 58956317c8de (neighbor: Improve garbage collection)
>> Reported-by: Kasper Dupont <kasperd@...wv.06.feb.2021.kasperd.net>
>> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@...onical.com>
>> ---
>>  net/core/neighbour.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/net/core/neighbour.c b/net/core/neighbour.c
>> index bbc89c7ffdfd..be5ca411b149 100644
>> --- a/net/core/neighbour.c
>> +++ b/net/core/neighbour.c
>> @@ -256,6 +256,7 @@ static int neigh_forced_gc(struct neigh_table *tbl)
>>  
>>  		write_lock(&n->lock);
>>  		if ((n->nud_state == NUD_FAILED) ||
>> +		    (n->nud_state == NUD_NOARP) ||
>>  		    (tbl->is_multicast &&
>>  		     tbl->is_multicast(n->primary_key)) ||
>>  		    time_after(tref, n->updated))
>> -- 
>> 2.27.0
>>
> 
> Is there any update regarding this change?
> 
> I noticed this regression when it was used in a DoS attack on one of
> my servers which I had upgraded from Ubuntu 18.04 to 20.04.
> 
> I have verified that Ubuntu 18.04 is not subject to this attack and
> Ubuntu 20.04 is vulnerable. I have also verified that the one-line
> change which Cascardo has provided fixes the vulnerability on Ubuntu
> 20.04.
> 

your testing included both patches or just this one?