Patch "net: sched: fix crash when deleting secondary chains" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

net: sched: fix crash when deleting secondary chains

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
net-sched-fix-crash-when-deleting-secondary-chains.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Roman Kapl <[email protected]>
Date: Mon, 20 Nov 2017 22:21:13 +0100
Subject: net: sched: fix crash when deleting secondary chains

From: Roman Kapl <[email protected]>

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()")

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

@@ -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);
 	}
 }
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/net-sched-crash-on-blocks-with-goto-chain-action.patch queue-4.14/net-sched-fix-crash-when-deleting-secondary-chains.patch