net-sched: sch_cbq: avoid infinite loop

Its possible to setup a bad cbq configuration leading to
an infinite loop in cbq_classify()

DEV_OUT=eth0
ICMP="match ip protocol 1 0xff"
U32="protocol ip u32"
DST="match ip dst"
tc qdisc add dev $DEV_OUT root handle 1: cbq avpkt 1000 \
	bandwidth 100mbit
tc class add dev $DEV_OUT parent 1: classid 1:1 cbq \
	rate 512kbit allot 1500 prio 5 bounded isolated
tc filter add dev $DEV_OUT parent 1: prio 3 $U32 \
	$ICMP $DST 192.168.3.234 flowid 1:

Reported-by: Denys Fedoryschenko <denys@visp.net.lb>
Tested-by: Denys Fedoryschenko <denys@visp.net.lb>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
index 6aabd77d1cfdd5cddd34b55dc69699cae9956e57..564b9fc8efd3c8778ef8ba155cf17f79d92a9a80 100644 (file)
--- a/net/sched/sch_cbq.c
+++ b/net/sched/sch_cbq.c
@@ -250,10 +250,11 @@ cbq_classify(struct sk_buff *skb, struct Qdisc *sch, int *qerr)
                        else if ((cl = defmap[res.classid & TC_PRIO_MAX]) == NULL)
                                cl = defmap[TC_PRIO_BESTEFFORT];
 
-                       if (cl == NULL || cl->level >= head->level)
+                       if (cl == NULL)
                                goto fallback;
                }
-
+               if (cl->level >= head->level)
+                       goto fallback;
 #ifdef CONFIG_NET_CLS_ACT
                switch (result) {
                case TC_ACT_QUEUED: