netdev - [PATCH net-next v2 02/12] net: sched: cls_u32: disallow linking to root hnode

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Message-Id: <20181008102244.22212-3-jhs@emojatatu.com>
Date:   Mon,  8 Oct 2018 06:22:34 -0400
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     davem@...emloft.net
Cc:     xiyou.wangcong@...il.com, jiri@...nulli.us, netdev@...r.kernel.org,
        viro@...iv.linux.org.uk, Jamal Hadi Salim <jhs@...atatu.com>
Subject: [PATCH net-next v2 02/12] net: sched: cls_u32: disallow linking to root hnode

From: Al Viro <viro@...iv.linux.org.uk>

Operation makes no sense.  Nothing will actually break if we do so
(depth limit in u32_classify() will prevent infinite loops), but
according to maintainers it's best prohibited outright.

NOTE: doing so guarantees that u32_destroy() will trigger the call
of u32_destroy_hnode(); we might want to make that unconditional.

Test:
tc qdisc add dev eth0 ingress
tc filter add dev eth0 parent ffff: protocol ip prio 100 u32 \
link 800: offset at 0 mask 0f00 shift 6 plus 0 eat match ip protocol 6 ff
should fail with
Error: cls_u32: Not linking to root node

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Jamal Hadi Salim <jhs@...atatu.com>
---
 net/sched/cls_u32.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index 622f4657da94..3357331a80a2 100644
--- a/net/sched/cls_u32.c
+++ b/net/sched/cls_u32.c
@@ -797,6 +797,10 @@ static int u32_set_parms(struct net *net, struct tcf_proto *tp,
 				NL_SET_ERR_MSG_MOD(extack, "Link hash table not found");
 				return -EINVAL;
 			}
+			if (ht_down->is_root) {
+				NL_SET_ERR_MSG_MOD(extack, "Not linking to root node");
+				return -EINVAL;
+			}
 			ht_down->refcnt++;
 		}
 
-- 
2.11.0