From: Cong Wang <xiyou.wangcong@gmail.com>
Date: Thu, 27 Sep 2018 13:42:19 -0700
Subject: net_sched: fix a crash in tc_new_tfilter()
Patch-mainline: v4.20-rc1
Git-commit: 460b360104d51552a57f39e54b2589c9fd7fa0b3
References: bsc#1109837

When tcf_block_find() fails, it already rollbacks the qdisc refcnt,
so its caller doesn't need to clean up this again. Avoid calling
qdisc_put() again by resetting qdisc to NULL for callers.

Reported-by: syzbot+37b8770e6d5a8220a039@syzkaller.appspotmail.com
Fixes: e368fdb61d8e ("net: sched: use Qdisc rcu API instead of relying on rtnl lock")
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 net/sched/cls_api.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -720,8 +720,10 @@ static struct tcf_block *tcf_block_find(
 errout_rcu:
 	rcu_read_unlock();
 errout_qdisc:
-	if (*q)
+	if (*q) {
 		qdisc_put(*q);
+		*q = NULL;
+	}
 	return ERR_PTR(err);
 }