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net: sched: fix crash when deleting secondary chains 

If you flush (delete) a filter chain other than chain 0 (such as when
deleting the device), the kernel may run into a use-after-free. The
chain refcount must not be decremented unless we are sure we are done
with the chain.

To reproduce the bug, run:
    ip link add dtest type dummy
    tc qdisc add dev dtest ingress
    tc filter add dev dtest chain 1  parent ffff: flower
    ip link del dtest

Introduced in: commit f93e1cdcf4 ("net/sched: fix filter flushing"),
but unless you have KAsan or luck, you won't notice it until
commit 0dadc117ac ("cls_flower: use tcf_exts_get_net() before call_rcu()")

Fixes: f93e1cdcf4 ("net/sched: fix filter flushing")
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Roman Kapl <code@rkapl.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>
hifive-unleashed-5.1
Roman Kapl 2017-11-20 22:21:13 +01:00 committed by David S. Miller
parent 0cc03504c9
commit d7aa04a5e8
1 changed files with 4 additions and 3 deletions
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7
net/sched/cls_api.c
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@ -205,13 +205,14 @@ static void tcf_chain_head_change(struct tcf_chain *chain,
static void tcf_chain_flush(struct tcf_chain *chain)
{
struct tcf_proto *tp;
struct tcf_proto *tp = rtnl_dereference(chain->filter_chain);
tcf_chain_head_change(chain, NULL);
while ((tp = rtnl_dereference(chain->filter_chain)) != NULL) {
while (tp) {
RCU_INIT_POINTER(chain->filter_chain, tp->next);
tcf_chain_put(chain);
tcf_proto_destroy(tp);
tp = rtnl_dereference(chain->filter_chain);
tcf_chain_put(chain);
}
}