Re: [Patch net 1/2] net_sched: Prevent creation of classes with TC_H_ROOT

[Simon Horman <horms@kernel.org>]

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@theori.io>
> >> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.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")

Reviewed-by: Simon Horman <horms@kernel.org>