[PATCH 3.14 06/19] wext: fix message delay/ordering

Greg Kroah-Hartman
2016-03-14T18:08:32Z

From: Johannes Berg <johannes.berg@intel.com>

commit 8bf862739a7786ae72409220914df960a0aa80d8 upstream.

Beniamino reported that he was getting an RTM_NEWLINK message for a
given interface, after the RTM_DELLINK for it. It turns out that the
message is a wireless extensions message, which was sent because the
interface had been connected and disconnection while it was deleted
caused a wext message.

For its netlink messages, wext uses RTM_NEWLINK, but the message is
without all the regular rtnetlink attributes, so "ip monitor link"
prints just rudimentary information:

5: wlan1: <BROADCAST,MULTICAST> mtu 1500 qdisc mq state DOWN group default
link/ether 02:00:00:00:01:00 brd ff:ff:ff:ff:ff:ff
Deleted 5: wlan1: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default
link/ether 02:00:00:00:01:00 brd ff:ff:ff:ff:ff:ff
5: wlan1: <BROADCAST,MULTICAST,UP>
link/ether
(from my hwsim reproduction)

This can cause userspace to get confused since it doesn't expect an
RTM_NEWLINK message after RTM_DELLINK.

The reason for this is that wext schedules a worker to send out the
messages, and the scheduling delay can cause the messages to get out
to userspace in different order.

To fix this, have wext register a netdevice notifier and flush out
any pending messages when netdevice state changes. This fixes any
ordering whenever the original message wasn't sent by a notifier
itself.

Reported-by: Beniamino Galvani <bgalvani@redhat.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
net/wireless/wext-core.c | 51 ++++++++++++++++++++++++++++++++++++-----------
1 file changed, 40 insertions(+), 11 deletions(-)

--- a/net/wireless/wext-core.c
+++ b/net/wireless/wext-core.c
@@ -342,6 +342,39 @@ static const int compat_event_type_size[

/* IW event code */

+static void wireless_nlevent_flush(void)
+{
+ struct sk_buff *skb;
+ struct net *net;
+
+ ASSERT_RTNL();
+
+ for_each_net(net) {
+ while ((skb = skb_dequeue(&net->wext_nlevents)))
+ rtnl_notify(skb, net, 0, RTNLGRP_LINK, NULL,
+ GFP_KERNEL);
+ }
+}
+
+static int wext_netdev_notifier_call(struct notifier_block *nb,
+ unsigned long state, void *ptr)
+{
+ /*
+ * When a netdev changes state in any way, flush all pending messages
+ * to avoid them going out in a strange order, e.g. RTM_NEWLINK after
+ * RTM_DELLINK, or with IFF_UP after without IFF_UP during dev_close()
+ * or similar - all of which could otherwise happen due to delays from
+ * schedule_work().
+ */
+ wireless_nlevent_flush();
+
+ return NOTIFY_OK;
+}
+
+static struct notifier_block wext_netdev_notifier = {
+ .notifier_call = wext_netdev_notifier_call,
+};
+
static int __net_init wext_pernet_init(struct net *net)
{
skb_queue_head_init(&net->wext_nlevents);
@@ -360,7 +393,12 @@ static struct pernet_operations wext_per

static int __init wireless_nlevent_init(void)
{
- return register_pernet_subsys(&wext_pernet_ops);
+ int err = register_pernet_subsys(&wext_pernet_ops);
+
+ if (err)
+ return err;
+
+ return register_netdevice_notifier(&wext_netdev_notifier);
}

subsys_initcall(wireless_nlevent_init);
@@ -368,17 +406,8 @@ subsys_initcall(wireless_nlevent_init);
/* Process events generated by the wireless layer or the driver. */
static void wireless_nlevent_process(struct work_struct *work)
{
- struct sk_buff *skb;
- struct net *net;
-
rtnl_lock();
-
- for_each_net(net) {
- while ((skb = skb_dequeue(&net->wext_nlevents)))
- rtnl_notify(skb, net, 0, RTNLGRP_LINK, NULL,
- GFP_KERNEL);
- }
-
+ wireless_nlevent_flush();
rtnl_unlock();
}