Subject: Re: iproute u32 filter - server hang

From: Patrick McHardy <[email-masked]>
Date: Wed, 31 Mar 2010 11:34:41 +0200

Paweł Staszewski wrote:
> I find some problem with iproute2 and u32 filters
> 
> To reproduce the problem (need to make one mistake in filter parent
> declaration 1:101):
> 
> ...
> tc filter add dev eth0 protocol ip parent 1:101 u32 match ip protocol 1
> 0xff flowid 1:101
> 
> ping 212.77.100.101
> And after this server will stop responding to anything - without any
> error (hang).

This is caused by hfsc_classify() looping endlessly since the filter
points to the originating class. hfsc_bind_tcf() is actually supposed
to prevent this, but it only prevents resolving the filter immediately
and we still run into the loop at runtime.

This patch (based on how CBQ handles this) should abort classification
and fall back to the default class. It would be better to simply catch
this at configuration time, but that looks a bit more involved. I'll try
to look into it this weekend.

diff --git a/net/sched/sch_hfsc.c b/net/sched/sch_hfsc.c
index b38b39c..a435cf1 100644
--- a/net/sched/sch_hfsc.c
+++ b/net/sched/sch_hfsc.c
@@ -1155,7 +1155,7 @@ static struct hfsc_class *
 hfsc_classify(struct sk_buff *skb, struct Qdisc *sch, int *qerr)
 {
 	struct hfsc_sched *q = qdisc_priv(sch);
-	struct hfsc_class *cl;
+	struct hfsc_class *head, *cl;
 	struct tcf_result res;
 	struct tcf_proto *tcf;
 	int result;
@@ -1166,6 +1166,7 @@ hfsc_classify(struct sk_buff *skb, struct Qdisc *sch, int *qerr)
 			return cl;
 
 	*qerr = NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
+	head = &q->root;
 	tcf = q->root.filter_list;
 	while (tcf && (result = tc_classify(skb, tcf, &res)) >= 0) {
 #ifdef CONFIG_NET_CLS_ACT
@@ -1180,6 +1181,8 @@ hfsc_classify(struct sk_buff *skb, struct Qdisc *sch, int *qerr)
 		if ((cl = (struct hfsc_class *)res.class) == NULL) {
 			if ((cl = hfsc_find_class(res.classid, sch)) == NULL)
 				break; /* filter selected invalid classid */
+			if (cl->level >= head->level)
+				break; /* filter may only point downwards */
 		}
 
 		if (cl->level == 0)
@@ -1187,6 +1190,7 @@ hfsc_classify(struct sk_buff *skb, struct Qdisc *sch, int *qerr)
 
 		/* apply inner filter chain */
 		tcf = cl->filter_list;
+		head = cl;
 	}
 
 	/* classification failed, try default class */