netdev - Re: [PATCH] net/sched: fix use-after-free in taprio_dev

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Message-ID: <aElna+n07/Jrfxlh@v4bel-B760M-AORUS-ELITE-AX>
Date: Wed, 11 Jun 2025 07:24:27 -0400
From: Hyunwoo Kim <imv4bel@...il.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: Vladimir Oltean <vladimir.oltean@....com>, vinicius.gomes@...el.com,
	jhs@...atatu.com, xiyou.wangcong@...il.com, jiri@...nulli.us,
	davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
	horms@...nel.org, netdev@...r.kernel.org, v4bel@...ori.io,
	imv4bel@...il.com
Subject: Re: [PATCH] net/sched: fix use-after-free in taprio_dev_notifier

On Wed, Jun 11, 2025 at 04:01:50AM -0700, Eric Dumazet wrote:
> On Wed, Jun 11, 2025 at 3:03 AM Hyunwoo Kim <imv4bel@...il.com> wrote:
> >
> > Since taprio’s taprio_dev_notifier() isn’t protected by an
> > RCU read-side critical section, a race with advance_sched()
> > can lead to a use-after-free.
> >
> > Adding rcu_read_lock() inside taprio_dev_notifier() prevents this.
> >
> > Signed-off-by: Hyunwoo Kim <imv4bel@...il.com>
> 
> Looks good to me, but we need a Fixes: tag and/or a CC: stable@ o make
> sure this patch reaches appropriate stable trees.

Understood. I will submit the v2 patch after adding the tags.

> 
> Also please CC the author of the  patch.

Does “CC” here refer to a patch tag, or to the email’s cc? And by 
“patch author” you mean the author of the patch 
fed87cc6718ad5f80aa739fee3c5979a8b09d3a6, right?

> 
> It seems bug came with
> 
> commit fed87cc6718ad5f80aa739fee3c5979a8b09d3a6
> Author: Vladimir Oltean <vladimir.oltean@....com>
> Date:   Tue Feb 7 15:54:38 2023 +0200
> 
>     net/sched: taprio: automatically calculate queueMaxSDU based on TC
> gate durations
> 
> 
> 
> 
> > ---
> >  net/sched/sch_taprio.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
> > index 14021b812329..bd2b02d1dc63 100644
> > --- a/net/sched/sch_taprio.c
> > +++ b/net/sched/sch_taprio.c
> > @@ -1320,6 +1320,7 @@ static int taprio_dev_notifier(struct notifier_block *nb, unsigned long event,
> >         if (event != NETDEV_UP && event != NETDEV_CHANGE)
> >                 return NOTIFY_DONE;
> >
> > +       rcu_read_lock();
> >         list_for_each_entry(q, &taprio_list, taprio_list) {
> >                 if (dev != qdisc_dev(q->root))
> >                         continue;
> > @@ -1328,16 +1329,17 @@ static int taprio_dev_notifier(struct notifier_block *nb, unsigned long event,
> >
> >                 stab = rtnl_dereference(q->root->stab);
> >
> > -               oper = rtnl_dereference(q->oper_sched);
> > +               oper = rcu_dereference(q->oper_sched);
> >                 if (oper)
> >                         taprio_update_queue_max_sdu(q, oper, stab);
> >
> > -               admin = rtnl_dereference(q->admin_sched);
> > +               admin = rcu_dereference(q->admin_sched);
> >                 if (admin)
> >                         taprio_update_queue_max_sdu(q, admin, stab);
> >
> >                 break;
> >         }
> > +       rcu_read_unlock();
> >
> >         return NOTIFY_DONE;
> >  }
> > --
> > 2.34.1
> >