linux-kernel - Re: [Bug] soft lockup in neigh_timer

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Message-ID: <da0f1340-34c5-4932-953e-25cad641db87@kernel.org>
Date: Wed, 9 Jul 2025 09:06:26 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Eric Dumazet <edumazet@...gle.com>, Luka <luka.2016.cs@...il.com>
Cc: "David S. Miller" <davem@...emloft.net>, Jakub Kicinski
 <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Simon Horman <horms@...nel.org>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [Bug] soft lockup in neigh_timer_handler in Linux kernel v6.12

On 08/07/2025 10:02, Eric Dumazet wrote:
> On Tue, Jul 8, 2025 at 12:54 AM Luka <luka.2016.cs@...il.com> wrote:
>>
>> Dear Linux Kernel Maintainers,
>>
>> I hope this message finds you well.
>>
>> I am writing to report a potential vulnerability I encountered during
>> testing of the Linux Kernel version v6.12.
>>
>> Git Commit: adc218676eef25575469234709c2d87185ca223a (tag: v6.12)
>>
>> Bug Location: neigh_timer_handler+0xc17/0xfe0 net/core/neighbour.c:1148
>>
>> Bug report: https://pastebin.com/06NiBtXm
>>
>> Entire kernel config: https://pastebin.com/MRWGr3nv
>>
>> Root Cause Analysis:
>>
>> A soft lockup occurs in the neighbor subsystem due to prolonged
>> execution within neigh_timer_handler(), where repeated neighbor entry
>> invalidation and associated routing operations (e.g.,
>> ipv4_link_failure() and arp_error_report()) lead to excessive CPU
>> occupation without yielding, triggering the kernel watchdog.
>>
>> At present, I have not yet obtained a minimal reproducer for this
>> issue. However, I am actively working on reproducing it, and I will
>> promptly share any additional findings or a working reproducer as soon
>> as it becomes available.
>>
>> Thank you very much for your time and attention to this matter. I
>> truly appreciate the efforts of the Linux kernel community.
> 
> Please stop sending duplicates, and 'analysis' AI generated.
> 
> If you really want to help, please provide a patch.

That's the same person which before was sending fake reports, based on
AI hallucination. Just in case - don't waste any time in reading the
reports.

Best regards,
Krzysztof