pkt_sched: Fix sch_sfq vs tc_modify_qdisc oops

[ Upstream commit 41065fba ]

sch_sfq as a classful qdisc needs the .leaf handler. Otherwise, there
is an oops possible in tc_modify_qdisc()/check_loop().

Fixes commit 7d2681a6Signed-off-by: Jarek Poplawski <jarkao2@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

net/sched/sch_sfq.c

@@ -497,6 +497,11 @@ static int sfq_dump(struct Qdisc *sch, struct sk_buff *skb)
 	return -1;
 }
 
+static struct Qdisc *sfq_leaf(struct Qdisc *sch, unsigned long arg)
+{
+	return NULL;
+}
+
 static unsigned long sfq_get(struct Qdisc *sch, u32 classid)
 {
 	return 0;
@@ -560,6 +565,7 @@ static void sfq_walk(struct Qdisc *sch, struct qdisc_walker *arg)
 }
 
 static const struct Qdisc_class_ops sfq_class_ops = {
+	.leaf		=	sfq_leaf,
 	.get		=	sfq_get,
 	.tcf_chain	=	sfq_find_tcf,
 	.bind_tcf	=	sfq_bind,