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Fri, 13 Jun 2025 17:46:21 -0700 (PDT) Date: Fri, 13 Jun 2025 20:46:16 -0400 From: Hyunwoo Kim To: Vladimir Oltean Cc: Cong Wang , vinicius.gomes@intel.com, jhs@mojatatu.com, jiri@resnulli.us, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, netdev@vger.kernel.org, v4bel@theori.io, imv4bel@gmail.com Subject: Re: [PATCH v2] net/sched: fix use-after-free in taprio_dev_notifier Message-ID: References: <20250613205206.fssf4bi4wjgyy53x@skbuf> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20250613205206.fssf4bi4wjgyy53x@skbuf> On Fri, Jun 13, 2025 at 11:52:06PM +0300, Vladimir Oltean wrote: > On Thu, Jun 12, 2025 at 11:36:12PM -0400, Hyunwoo Kim wrote: > > On Thu, Jun 12, 2025 at 01:23:38PM -0700, Cong Wang wrote: > > > On Thu, Jun 12, 2025 at 07:16:55AM -0400, Hyunwoo Kim wrote: > > > > 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, > > > > > > There is a taprio_set_picos_per_byte() call here, it calls > > > __ethtool_get_link_ksettings() which could be blocking. > > > > > > For instance, gve_get_link_ksettings() calls > > > gve_adminq_report_link_speed() which is a blocking function. > > > > > > So I am afraid we can't enforce an atomic context here. > > > > In that case, how about moving the lock as follows so that > > taprio_set_picos_per_byte() isn’t included within it? > > > > ``` > > diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c > > index 14021b812329..2b14c81a87e5 100644 > > --- a/net/sched/sch_taprio.c > > +++ b/net/sched/sch_taprio.c > > @@ -1328,13 +1328,15 @@ static int taprio_dev_notifier(struct notifier_block *nb, unsigned long event, > > > > stab = rtnl_dereference(q->root->stab); > > > > - oper = rtnl_dereference(q->oper_sched); > > + rcu_read_lock(); > > + 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); > > + rcu_read_unlock(); > > > > break; > > } > > ``` > > > > This change still prevents the race condition with advance_sched(). > > This should work. OK, I’ll submit the v3 patch. > > And I'm sorry for the bug introduced here, and elsewhere, by assuming > rtnl_dereference() will be fine. > I mostly use taprio with offload, where switch_schedules() runs in > process context with rtnl_lock() held, not the software emulation that > changes the schedules from the advance_sched() hrtimer. Somehow the > different locking requirements for the 2 cases eluded me.