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

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 <redacted>
Signed-off-by: Thadeu Lima de Souza Cascardo <redacted>
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)

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 <redacted>
Signed-off-by: Thadeu Lima de Souza Cascardo <redacted>
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)

On 6/7/21 12:53 PM, Roopa Prabhu wrote:

On 6/7/21 10:35 AM, David Ahern wrote:

quoted

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 <redacted>
Signed-off-by: Thadeu Lima de Souza Cascardo <redacted>
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.

On 6/7/21 3:04 PM, David Ahern wrote:

On 6/7/21 12:53 PM, Roopa Prabhu wrote:

quoted

On 6/7/21 10:35 AM, David Ahern wrote:

quoted

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 <redacted>
Signed-off-by: Thadeu Lima de Souza Cascardo <redacted>
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.

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 <redacted>
Signed-off-by: Thadeu Lima de Souza Cascardo <redacted>
Signed-off-by: David Ahern <dsahern@kernel.org>
---
rebased to net tree

Applied, thanks.