[PATCH net] neighbour: allow NUD_NOARP entries to be forced GCed

[PATCH net] neighbour: allow NUD_NOARP entries to be forced GCed

[David Ahern]

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@gjkwv.06.feb.2021.kasperd.net>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: David Ahern <dsahern@kernel.org>
---
rebased to net tree

 net/core/neighbour.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 98f20efbfadf..bf774575ad71 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -238,6 +238,7 @@ 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))
-- 
2.24.3 (Apple Git-128)

Re: [PATCH net] neighbour: allow NUD_NOARP entries to be forced GCed

[Roopa Prabhu]

On 6/7/21 10:35 AM, David Ahern 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@gjkwv.06.feb.2021.kasperd.net>
> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
> Signed-off-by: David Ahern <dsahern@kernel.org>
> ---
> rebased to net tree


There are other use-cases  that use NUD_NOARP as static neighbour 
entries which should be exempt from forced gc.

for example when qualified by NTF_EXT_LEARNED for the E-VPN use-case.

The check in your patch below should exclude NTF_EXT_LEARNED entries.


(unrelated to the neighbour code ,  but bridge driver also uses 
NUD_NOARP for static entries)


>
>   net/core/neighbour.c | 1 +
>   1 file changed, 1 insertion(+)
>
> diff --git a/net/core/neighbour.c b/net/core/neighbour.c
> index 98f20efbfadf..bf774575ad71 100644
> --- a/net/core/neighbour.c
> +++ b/net/core/neighbour.c
> @@ -238,6 +238,7 @@ 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))

Re: [PATCH net] neighbour: allow NUD_NOARP entries to be forced GCed

[David Ahern]

On 6/7/21 12:53 PM, Roopa Prabhu wrote:
> 
> On 6/7/21 10:35 AM, David Ahern 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@gjkwv.06.feb.2021.kasperd.net>
>> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
>> Signed-off-by: David Ahern <dsahern@kernel.org>
>> ---
>> rebased to net tree
> 
> 
> There are other use-cases  that use NUD_NOARP as static neighbour
> entries which should be exempt from forced gc.
> 
> for example when qualified by NTF_EXT_LEARNED for the E-VPN use-case.
> 
> The check in your patch below should exclude NTF_EXT_LEARNED entries.
> 
> 
> (unrelated to the neighbour code ,  but bridge driver also uses
> NUD_NOARP for static entries)
> 
> 

Maybe I misunderstand your comment: forced_gc does not apply to static
entries; those were moved to a separate list to avoid walking them.

Re: [PATCH net] neighbour: allow NUD_NOARP entries to be forced GCed

[Roopa Prabhu]

On 6/7/21 3:04 PM, David Ahern wrote:
> On 6/7/21 12:53 PM, Roopa Prabhu wrote:
>> On 6/7/21 10:35 AM, David Ahern 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@gjkwv.06.feb.2021.kasperd.net>
>>> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
>>> Signed-off-by: David Ahern <dsahern@kernel.org>
>>> ---
>>> rebased to net tree
>>
>> There are other use-cases  that use NUD_NOARP as static neighbour
>> entries which should be exempt from forced gc.
>>
>> for example when qualified by NTF_EXT_LEARNED for the E-VPN use-case.
>>
>> The check in your patch below should exclude NTF_EXT_LEARNED entries.
>>
>>
>> (unrelated to the neighbour code ,  but bridge driver also uses
>> NUD_NOARP for static entries)
>>
>>
> Maybe I misunderstand your comment: forced_gc does not apply to static
> entries; those were moved to a separate list to avoid walking them.
>
I think you are right. so just to confirm, NUD_NOARP + NTF_EXT_LEARNED 
will never be included in the list for forced_gc and hence not affected 
by your patch ?

if yes, I am good.

Re: [PATCH net] neighbour: allow NUD_NOARP entries to be forced GCed

[David Miller]

From: David Ahern <dsahern@kernel.org>
Date: Mon,  7 Jun 2021 11:35:30 -0600

> 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@gjkwv.06.feb.2021.kasperd.net>
> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
> Signed-off-by: David Ahern <dsahern@kernel.org>
> ---
> rebased to net tree

Applied, thanks.