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batman-adv/patches/0011-batman-adv-Avoid-infinite-loop-trying-to-resize-loca.patch
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From: Sven Eckelmann <[email protected]> | ||
Date: Mon, 12 Feb 2024 14:32:13 +0100 | ||
Subject: batman-adv: Avoid infinite loop trying to resize local TT | ||
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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. | ||
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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 | ||
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batman_adv: batadv0: Forced to purge local tt entries to fit new maximum fragment MTU (110) | ||
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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. | ||
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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. | ||
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While this should be handled proactively when: | ||
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* 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) | ||
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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. | ||
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Cc: [email protected] | ||
Fixes: f7f2fe494388 ("batman-adv: limit local translation table max size") | ||
Reported-by: [email protected] | ||
Signed-off-by: Sven Eckelmann <[email protected]> | ||
Origin: upstream, https://git.open-mesh.org/batman-adv.git/commit/05f6eadbbddc834669249ae204026c383445b571 | ||
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--- 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(struc | ||
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spin_lock_bh(&bat_priv->tt.commit_lock); | ||
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- while (true) { | ||
+ while (timeout) { | ||
table_size = batadv_tt_local_table_transmit_size(bat_priv); | ||
if (packet_size_max >= table_size) | ||
break; |