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* [PATCH 0/1] pull request for net: batman-adv 2024-04-05
@ 2024-04-05  8:31 Simon Wunderlich
  2024-04-05  8:31 ` [PATCH 1/1] batman-adv: Avoid infinite loop trying to resize local TT Simon Wunderlich
  0 siblings, 1 reply; 2+ messages in thread
From: Simon Wunderlich @ 2024-04-05  8:31 UTC (permalink / raw)
  To: davem, kuba; +Cc: netdev, b.a.t.m.a.n, Simon Wunderlich

Hi David, hi Jakub,

here is a bugfix for batman-adv which we would like to have integrated into net.

Please pull or let me know of any problem!

Thank you,
      Simon

The following changes since commit 4cece764965020c22cff7665b18a012006359095:

  Linux 6.9-rc1 (2024-03-24 14:10:05 -0700)

are available in the Git repository at:

  git://git.open-mesh.org/linux-merge.git tags/batadv-net-pullrequest-20240405

for you to fetch changes up to b1f532a3b1e6d2e5559c7ace49322922637a28aa:

  batman-adv: Avoid infinite loop trying to resize local TT (2024-03-29 20:18:43 +0100)

----------------------------------------------------------------
Here is a batman-adv bugfix:

 - void infinite loop trying to resize local TT, by Sven Eckelmann

----------------------------------------------------------------
Sven Eckelmann (1):
      batman-adv: Avoid infinite loop trying to resize local TT

 net/batman-adv/translation-table.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

^ permalink raw reply	[flat|nested] 2+ messages in thread

* [PATCH 1/1] batman-adv: Avoid infinite loop trying to resize local TT
  2024-04-05  8:31 [PATCH 0/1] pull request for net: batman-adv 2024-04-05 Simon Wunderlich
@ 2024-04-05  8:31 ` Simon Wunderlich
  0 siblings, 0 replies; 2+ messages in thread
From: Simon Wunderlich @ 2024-04-05  8:31 UTC (permalink / raw)
  To: davem, kuba
  Cc: netdev, b.a.t.m.a.n, Sven Eckelmann, stable,
	syzbot+a6a4b5bb3da165594cff, Simon Wunderlich

From: Sven Eckelmann <sven@narfation.org>

If the MTU of one of an attached interface becomes too small to transmit
the local translation table then it must be resized to fit inside all
fragments (when enabled) or a single packet.

But if the MTU becomes too low to transmit even the header + the VLAN
specific part then the resizing of the local TT will never succeed. This
can for example happen when the usable space is 110 bytes and 11 VLANs are
on top of batman-adv. In this case, at least 116 byte would be needed.
There will just be an endless spam of

   batman_adv: batadv0: Forced to purge local tt entries to fit new maximum fragment MTU (110)

in the log but the function will never finish. Problem here is that the
timeout will be halved all the time and will then stagnate at 0 and
therefore never be able to reduce the table even more.

There are other scenarios possible with a similar result. The number of
BATADV_TT_CLIENT_NOPURGE entries in the local TT can for example be too
high to fit inside a packet. Such a scenario can therefore happen also with
only a single VLAN + 7 non-purgable addresses - requiring at least 120
bytes.

While this should be handled proactively when:

* interface with too low MTU is added
* VLAN is added
* non-purgeable local mac is added
* MTU of an attached interface is reduced
* fragmentation setting gets disabled (which most likely requires dropping
  attached interfaces)

not all of these scenarios can be prevented because batman-adv is only
consuming events without the the possibility to prevent these actions
(non-purgable MAC address added, MTU of an attached interface is reduced).
It is therefore necessary to also make sure that the code is able to handle
also the situations when there were already incompatible system
configuration are present.

Cc: stable@vger.kernel.org
Fixes: a19d3d85e1b8 ("batman-adv: limit local translation table max size")
Reported-by: syzbot+a6a4b5bb3da165594cff@syzkaller.appspotmail.com
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
---
 net/batman-adv/translation-table.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/batman-adv/translation-table.c b/net/batman-adv/translation-table.c
index b95c36765d04..2243cec18ecc 100644
--- a/net/batman-adv/translation-table.c
+++ b/net/batman-adv/translation-table.c
@@ -3948,7 +3948,7 @@ void batadv_tt_local_resize_to_mtu(struct net_device *soft_iface)
 
 	spin_lock_bh(&bat_priv->tt.commit_lock);
 
-	while (true) {
+	while (timeout) {
 		table_size = batadv_tt_local_table_transmit_size(bat_priv);
 		if (packet_size_max >= table_size)
 			break;
-- 
2.39.2


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