[PATCH v3] net: sched: tapr: prevent cycle_time == 0 in parse_taprio_schedule

[Du Cheng <ducheng2@gmail.com>]

There is a reproducible sequence from the userland that will trigger a WARN_ON()
condition in taprio_get_start_time, which causes kernel to panic if configured
as "panic_on_warn". Catch this during initialisation in parse_taprio_schedule to
prevent this condition.

Reported as bug on syzkaller:
https://syzkaller.appspot.com/bug?extid=d50710fd0873a9c6b40c

Reported-by: syzbot+d50710fd0873a9c6b40c@syzkaller.appspotmail.com
Signed-off-by: Du Cheng <ducheng2@gmail.com>
---
changelog
v1: Discussion https://lore.kernel.org/netdev/YHfwUmFODUHx8G5W@carbon/T/

v2: fix typo https://lore.kernel.org/netdev/20210415075953.83508-2-ducheng2@gmail.com/T/

v3: catch the condition in parse_taprio_schedule instead

 net/sched/sch_taprio.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index 8287894541e3..abd6b176383c 100644
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -901,6 +901,10 @@ static int parse_taprio_schedule(struct taprio_sched *q, struct nlattr **tb,
 
 		list_for_each_entry(entry, &new->entries, list)
 			cycle = ktime_add_ns(cycle, entry->interval);
+
+		if (!cycle)
+			return -EINVAL;
+
 		new->cycle_time = cycle;
 	}
 
-- 
2.30.2