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Subject[PATCH 4.14 112/115] net: sched: fix crash when deleting secondary chains
Date
4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Roman Kapl <code@rkapl.cz>

commit d7aa04a5e82b4f254d306926c81eae8df69e5200 upstream.

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 f93e1cdcf42c ("net/sched: fix filter flushing"),
but unless you have KAsan or luck, you won't notice it until
commit 0dadc117ac8b ("cls_flower: use tcf_exts_get_net() before call_rcu()")

Fixes: f93e1cdcf42c ("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>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
net/sched/cls_api.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -197,14 +197,15 @@ static struct tcf_chain *tcf_chain_creat

static void tcf_chain_flush(struct tcf_chain *chain)
{
- struct tcf_proto *tp;
+ struct tcf_proto *tp = rtnl_dereference(chain->filter_chain);

if (chain->p_filter_chain)
RCU_INIT_POINTER(*chain->p_filter_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);
}
}


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