Subject: [PATCH 3/7] net_sched: let qdisc_put() accept NULL pointer

From: Cong Wang <[email-masked]>
Date: Thu, 12 Sep 2019 10:22:30 -0700

[ Upstream commit 6efb971ba8edfbd80b666f29de12882852f095ae ]

When tcf_block_get() fails in sfb_init(), q->qdisc is still a NULL
pointer which leads to a crash in sfb_destroy(). Similar for
sch_dsmark.

Instead of fixing each separately, Linus suggested to just accept
NULL pointer in qdisc_put(), which would make callers easier.

(For sch_dsmark, the bug probably exists long before commit
6529eaba33f0.)

Fixes: 6529eaba33f0 ("net: sched: introduce tcf block infractructure")
Reported-by: [email-masked]
Suggested-by: Linus Torvalds <[email-masked]>
Cc: Jamal Hadi Salim <[email-masked]>
Cc: Jiri Pirko <[email-masked]>
Signed-off-by: Cong Wang <[email-masked]>
Acked-by: Jiri Pirko <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 net/sched/sch_generic.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index ac28f6a5d70e..17bd8f539bc7 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -985,6 +985,9 @@ static void qdisc_destroy(struct Qdisc *qdisc)
 
 void qdisc_put(struct Qdisc *qdisc)
 {
+	if (!qdisc)
+		return;
+
 	if (qdisc->flags & TCQ_F_BUILTIN ||
 	    !refcount_dec_and_test(&qdisc->refcnt))
 		return;
-- 
2.21.0