[Patch net] net_sched: check cops->tcf_block in tc_bind_tclass()

[Cong Wang]

At least sch_red and sch_tbf don't implement ->tcf_block()
while still have a non-zero tc "class".

Instead of adding nop implementations to each of such qdisc's,
we can just relax the check of cops->tcf_block() in
tc_bind_tclass(). They don't support TC filter anyway.

Reported-by: syzbot+21b29db13c065852f...@syzkaller.appspotmail.com
Cc: Jamal Hadi Salim <j...@mojatatu.com>
Cc: Jiri Pirko <j...@resnulli.us>
Signed-off-by: Cong Wang <xiyou.wangc...@gmail.com>
---
 net/sched/sch_api.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index 04faee7ccbce..1047825d9f48 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -1920,6 +1920,8 @@ static void tc_bind_tclass(struct Qdisc *q, u32 portid, 
u32 clid,
        cl = cops->find(q, portid);
        if (!cl)
                return;
+       if (!cops->tcf_block)
+               return;
        block = cops->tcf_block(q, cl, NULL);
        if (!block)
                return;
-- 
2.21.0