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

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Message-ID: <CANn89i+7m8koanZk=47FEhmTHUmOmu-yfViRPayjUct+voQiEQ@mail.gmail.com>
Date: Tue, 8 Jul 2025 01:02:48 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: 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 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.

Thank you.