[PATCH v3] net/sched: fix use-after-free in taprio_dev_notifier

[Hyunwoo Kim <imv4bel@gmail.com>]

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.

Fixes: fed87cc6718a ("net/sched: taprio: automatically calculate queueMaxSDU based on TC gate durations")
Cc: stable@vger.kernel.org
Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
---
Changes in v3:
- Change so that taprio_set_picos_per_byte() is not included in the lock.
- v2: https://lore.kernel.org/all/aEq3J4ODxH7x+neT@v4bel-B760M-AORUS-ELITE-AX/

Changes in v2:
- Add the appropriate tags.
- v1: https://lore.kernel.org/all/aElUZyKy7x66X3SD@v4bel-B760M-AORUS-ELITE-AX/
---
 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..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;
 	}
-- 
2.34.1