netdev - Re: [Patch net 1/2] net_sched: Prevent creation of classes with TC_H

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Message-ID: <Z9CX6IKX9pL+NPYU@pop-os.localdomain>
Date: Tue, 11 Mar 2025 13:07:04 -0700
From: Cong Wang <xiyou.wangcong@...il.com>
To: Simon Horman <horms@...nel.org>
Cc: Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
	jhs@...atatu.com, jiri@...nulli.us, mincho@...ori.io
Subject: Re: [Patch net 1/2] net_sched: Prevent creation of classes with
 TC_H_ROOT

On Tue, Mar 11, 2025 at 05:04:49PM +0100, Simon Horman wrote:
> On Tue, Mar 11, 2025 at 01:47:32PM +0100, Paolo Abeni wrote:
> > 
> > 
> > On 3/11/25 11:48 AM, Simon Horman wrote:
> > > On Thu, Mar 06, 2025 at 03:23:54PM -0800, Cong Wang wrote:
> > >> The function qdisc_tree_reduce_backlog() uses TC_H_ROOT as a termination
> > >> condition when traversing up the qdisc tree to update parent backlog
> > >> counters. However, if a class is created with classid TC_H_ROOT, the
> > >> traversal terminates prematurely at this class instead of reaching the
> > >> actual root qdisc, causing parent statistics to be incorrectly maintained.
> > >> In case of DRR, this could lead to a crash as reported by Mingi Cho.
> > >>
> > >> Prevent the creation of any Qdisc class with classid TC_H_ROOT
> > >> (0xFFFFFFFF) across all qdisc types, as suggested by Jamal.
> > >>
> > >> Reported-by: Mingi Cho <mincho@...ori.io>
> > >> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
> > > 
> > > Hi Cong,
> > > 
> > > This change looks good to me.
> > > But could we get a fixes tag?`
> > > 
> > > ...
> > 
> > Should be:
> > 
> > Fixes: 066a3b5b2346 ("[NET_SCHED] sch_api: fix
> > qdisc_tree_decrease_qlen() loop")
> 
> Thanks.
> 
> Looking at that, I might have gone for the following commit,
> which is a fix for the above one. But either way is fine by me.
> 
> commit 2e95c4384438 ("net/sched: stop qdisc_tree_reduce_backlog on TC_H_ROOT")

Indeed it is. Sorry for forgetting about it.

Thanks a lot!