[PATCH net] net/sched: sch_taprio: reset child qdiscs before freeing them

[Davide Caratti]

syzkaller shows that packets can still be dequeued while taprio_destroy()
is running. Let sch_taprio use the reset() function to cancel the advance
timer and drop all skbs from the child qdiscs.

Fixes: 5a781ccbd19e ("tc: Add support for configuring the taprio scheduler")
Link: 
https://syzkaller.appspot.com/bug?id=f362872379bf8f0017fb667c1ab158f2d1e764ae
Reported-by: syzbot+8971da381fb5a31f5...@syzkaller.appspotmail.com
Signed-off-by: Davide Caratti <dcara...@redhat.com>
---
 net/sched/sch_taprio.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index 26fb8a62996b..c74817ec9964 100644
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -1597,6 +1597,21 @@ static int taprio_change(struct Qdisc *sch, struct 
nlattr *opt,
        return err;
 }
 
+static void taprio_reset(struct Qdisc *sch)
+{
+       struct taprio_sched *q = qdisc_priv(sch);
+       struct net_device *dev = qdisc_dev(sch);
+       int i;
+
+       hrtimer_cancel(&q->advance_timer);
+       if (q->qdiscs) {
+               for (i = 0; i < dev->num_tx_queues && q->qdiscs[i]; i++)
+                       qdisc_reset(q->qdiscs[i]);
+       }
+       sch->qstats.backlog = 0;
+       sch->q.qlen = 0;
+}
+
 static void taprio_destroy(struct Qdisc *sch)
 {
        struct taprio_sched *q = qdisc_priv(sch);
@@ -1607,7 +1622,6 @@ static void taprio_destroy(struct Qdisc *sch)
        list_del(&q->taprio_list);
        spin_unlock(&taprio_list_lock);
 
-       hrtimer_cancel(&q->advance_timer);
 
        taprio_disable_offload(dev, q, NULL);
 
@@ -1954,6 +1968,7 @@ static struct Qdisc_ops taprio_qdisc_ops __read_mostly = {
        .init           = taprio_init,
        .change         = taprio_change,
        .destroy        = taprio_destroy,
+       .reset          = taprio_reset,
        .peek           = taprio_peek,
        .dequeue        = taprio_dequeue,
        .enqueue        = taprio_enqueue,
-- 
2.29.2