netdev - Re: [syzbot] [batman?] BUG: soft lockup in sys

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Date: Mon, 12 Feb 2024 12:23:51 +0100
From: Sven Eckelmann <sven@...fation.org>
To: syzbot <syzbot+a6a4b5bb3da165594cff@...kaller.appspotmail.com>,
 Eric Dumazet <edumazet@...gle.com>
Cc: a@...table.cc, b.a.t.m.a.n@...ts.open-mesh.org, davem@...emloft.net,
 kuba@...nel.org, linux-kernel@...r.kernel.org, mareklindner@...mailbox.ch,
 netdev@...r.kernel.org, pabeni@...hat.com, sw@...onwunderlich.de,
 syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [batman?] BUG: soft lockup in sys_sendmsg

On Monday, 12 February 2024 11:41:38 CET Eric Dumazet wrote:
> This patch [1] looks suspicious

Shouldn't be caused by this - but this might be another way to trigger the 
problem. The problem would be visible even without it when a mtu is explicitly 
set. But the reproducer is not available so I can't actually check what is 
going on.

> I think batman-adv should reject too small MTU values.

You are refering to the size calculated by 
batadv_tt_local_table_transmit_size(), right? And yes, I would agree that it 
looks suspicious and might not have been correctly integrated in 
batadv_max_header_len() when commit a19d3d85e1b8 ("batman-adv: limit local 
translation table max size") introduced the code. But I think we also need to 
remove interfaces again when receiving NETDEV_CHANGEMTU and an interface is 
not having the correctly sized anymore. So have to check how to do this the 
best way.

Kind regards,
	Sven
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