[Bug] soft lockup in neigh_timer_handler in Linux kernel v6.12

[Bug] soft lockup in neigh_timer_handler in Linux kernel v6.12

[Luka]

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.

Best regards,
Luka

Re: [Bug] soft lockup in neigh_timer_handler in Linux kernel v6.12

[Eric Dumazet]

On Tue, Jul 8, 2025 at 12:54 AM Luka <luka.2016.cs@gmail.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.

Re: [Bug] soft lockup in neigh_timer_handler in Linux kernel v6.12

[Krzysztof Kozlowski]

On 08/07/2025 10:02, Eric Dumazet wrote:
> On Tue, Jul 8, 2025 at 12:54 AM Luka <luka.2016.cs@gmail.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