[Patch net] net_sched: fix tcm_parent in tc filter dump

[Cong Wang]

When we tell kernel to dump filters from root (ffff:ffff),
those filters on ingress (ffff:0000) are matched, but their
true parents must be dumped as they are. However, kernel
dumps just whatever we tell it, that is either ffff:ffff
or ffff:0000:

 $ nl-cls-list --dev=dummy0 --parent=root
 cls basic dev dummy0 id none parent root prio 49152 protocol ip match-all
 cls basic dev dummy0 id :1 parent root prio 49152 protocol ip match-all
 $ nl-cls-list --dev=dummy0 --parent=ffff:
 cls basic dev dummy0 id none parent ffff: prio 49152 protocol ip match-all
 cls basic dev dummy0 id :1 parent ffff: prio 49152 protocol ip match-all

This is confusing and misleading, more importantly this is
a regression since 4.15, so the old behavior must be restored.

Steps to reproduce this:
 ip li set dev dummy0 up
 tc qd add dev dummy0 ingress
 tc filter add dev dummy0 parent ffff: protocol arp basic action pass
 tc filter show dev dummy0 root

Before this patch:
 filter protocol arp pref 49152 basic
 filter protocol arp pref 49152 basic handle 0x1
        action order 1: gact action pass
         random type none pass val 0
         index 1 ref 1 bind 1

After this patch:
 filter parent ffff: protocol arp pref 49152 basic
 filter parent ffff: protocol arp pref 49152 basic handle 0x1
        action order 1: gact action pass
         random type none pass val 0
         index 1 ref 1 bind 1

Fixes: a10fa20101ae ("net: sched: propagate q and parent from caller down to 
tcf_fill_node")
Cc: Jamal Hadi Salim <j...@mojatatu.com>
Cc: Jiri Pirko <j...@resnulli.us>
Signed-off-by: Cong Wang <xiyou.wangc...@gmail.com>
---
 net/sched/cls_api.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
index 55bd1429678f..80e93c96d2b2 100644
--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -2612,12 +2612,10 @@ static int tc_dump_tfilter(struct sk_buff *skb, struct 
netlink_callback *cb)
                        return skb->len;
 
                parent = tcm->tcm_parent;
-               if (!parent) {
+               if (!parent)
                        q = dev->qdisc;
-                       parent = q->handle;
-               } else {
+               else
                        q = qdisc_lookup(dev, TC_H_MAJ(tcm->tcm_parent));
-               }
                if (!q)
                        goto out;
                cops = q->ops->cl_ops;
@@ -2633,6 +2631,7 @@ static int tc_dump_tfilter(struct sk_buff *skb, struct 
netlink_callback *cb)
                block = cops->tcf_block(q, cl, NULL);
                if (!block)
                        goto out;
+               parent = block->q->handle;
                if (tcf_block_shared(block))
                        q = NULL;
        }
-- 
2.26.1