linux-kernel - Re: [Discuss] KASAN: null-ptr-deference in qdisc_tree_reduce

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Message-ID: <aIO/ESEgsCzBv/hX@pop-os.localdomain>
Date: Fri, 25 Jul 2025 10:29:53 -0700
From: Cong Wang <xiyou.wangcong@...il.com>
To: huyizhen2024@....com
Cc: jhs@...atatu.com, jiri@...nulli.us, davem@...emloft.net,
	edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
	horms@...nel.org, andy@...yhouse.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [Discuss] KASAN: null-ptr-deference in qdisc_tree_reduce_backlog

On Wed, Jul 23, 2025 at 10:48:27PM +0800, huyizhen2024@....com wrote:
> Hello.
> 
> KASAN found a null ptr deference in qdisc_tree_reduce_backlog.
> If cops->find cannot find a qdisc, it returns NULL.
> And if cops->qlen_notify doesn't valid arg, it will deference the NULL ptr, resulting in a kernel crash.
> Should we add a check for the argument in cops->qlen_notify?
> 
> Looking forward to your reply, thank you!
> 
> net\sched\sch_hfsc.c:1237 hfsc_qlen_notify-null-ptr-deref
> 
> other info that might help debug this:
> 

Thanks for your report.

May we know which kernel version you are testing? Because recently we
fixed quite some qlen_notify related issues, testing the latest -net is
highly recommended.

And, if you have a reproducer, please provide it too.

Regards,
Cong Wang