netdev - [Patch net] net_sched: close another race condition in tcf_mirred

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <1463436678-20254-1-git-send-email-xiyou.wangcong@gmail.com>
Date:	Mon, 16 May 2016 15:11:18 -0700
From:	Cong Wang <xiyou.wangcong@...il.com>
To:	netdev@...r.kernel.org
Cc:	Cong Wang <xiyou.wangcong@...il.com>,
	Jamal Hadi Salim <jhs@...atatu.com>
Subject: [Patch net] net_sched: close another race condition in tcf_mirred_release()

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@...atatu.com>
Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
---
 net/sched/act_mirred.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/sched/act_mirred.c b/net/sched/act_mirred.c
index 8f3948d..78db6d4 100644
--- 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] = {
-- 
2.1.0