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net: sched: cls_u32: disallow linking to root hnode

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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@zeniv.linux.org.uk>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Al Viro 2018-10-08 06:22:34 -04:00 committed by David S. Miller
parent b44ef84542
commit 27594ec4b6
1 changed files with 4 additions and 0 deletions
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4
net/sched/cls_u32.c
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@ -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++;
}