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 <kasp...@gjkwv.06.feb.2021.kasperd.net>
> Signed-off-by: Thadeu Lima de Souza Cascardo <casca...@canonical.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.
Kind regards
Kasper
