Patch "net_sched: close another race condition in tcf_mirred_release()" has been added to the 4.4-stable tree

Patch "net_sched: close another race condition in tcf_mirred_release()" has been added to the 4.4-stable tree

[gregkh]

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

    net_sched: close another race condition in tcf_mirred_release()

to the 4.4-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-close-another-race-condition-in-tcf_mirred_release.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From dc327f8931cb9d66191f489eb9a852fc04530546 Mon Sep 17 00:00:00 2001
From: WANG Cong <xiyou.wangcong@gmail.com>
Date: Mon, 16 May 2016 15:11:18 -0700
Subject: net_sched: close another race condition in tcf_mirred_release()

From: WANG Cong <xiyou.wangcong@gmail.com>

commit dc327f8931cb9d66191f489eb9a852fc04530546 upstream.

We saw the following extra refcount release on veth device:

  kernel: [7957821.463992] unregister_netdevice: waiting for mesos50284 to become free. Usage count = -1

Since we heavily use mirred action to redirect packets to veth, I think
this is caused by the following race condition:

CPU0:
tcf_mirred_release(): (in RCU callback)
	struct net_device *dev = rcu_dereference_protected(m->tcfm_dev, 1);

CPU1:
mirred_device_event():
        spin_lock_bh(&mirred_list_lock);
        list_for_each_entry(m, &mirred_list, tcfm_list) {
                if (rcu_access_pointer(m->tcfm_dev) == dev) {
                        dev_put(dev);
                        /* Note : no rcu grace period necessary, as
                         * net_device are already rcu protected.
                         */
                        RCU_INIT_POINTER(m->tcfm_dev, NULL);
                }
        }
        spin_unlock_bh(&mirred_list_lock);

CPU0:
tcf_mirred_release():
        spin_lock_bh(&mirred_list_lock);
        list_del(&m->tcfm_list);
        spin_unlock_bh(&mirred_list_lock);
        if (dev)               // <======== Stil refers to the old m->tcfm_dev
                dev_put(dev);  // <======== dev_put() is called on it again

The action init code path is good because it is impossible to modify
an action that is being removed.

So, fix this by moving everything under the spinlock.

Fixes: 2ee22a90c7af ("net_sched: act_mirred: remove spinlock in fast path")
Fixes: 6bd00b850635 ("act_mirred: fix a race condition on mirred_list")
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Cc: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 net/sched/act_mirred.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/net/sched/act_mirred.c
+++ b/net/sched/act_mirred.c
@@ -36,14 +36,15 @@ static DEFINE_SPINLOCK(mirred_list_lock)
 static void tcf_mirred_release(struct tc_action *a, int bind)
 {
 	struct tcf_mirred *m = to_mirred(a);
-	struct net_device *dev = rcu_dereference_protected(m->tcfm_dev, 1);
+	struct net_device *dev;
 
 	/* We could be called either in a RCU callback or with RTNL lock held. */
 	spin_lock_bh(&mirred_list_lock);
 	list_del(&m->tcfm_list);
-	spin_unlock_bh(&mirred_list_lock);
+	dev = rcu_dereference_protected(m->tcfm_dev, 1);
 	if (dev)
 		dev_put(dev);
+	spin_unlock_bh(&mirred_list_lock);
 }
 
 static const struct nla_policy mirred_policy[TCA_MIRRED_MAX + 1] = {


Patches currently in stable-queue which might be from xiyou.wangcong@gmail.com are

queue-4.4/net_sched-close-another-race-condition-in-tcf_mirred_release.patch