[PATCH net] net/hsr: Fix NULL pointer dereference and refcnt bugs when deleting a HSR interface.

[PATCH net] net/hsr: Fix NULL pointer dereference and refcnt bugs when deleting a HSR interface.

[Arvid Brodin]

How to repeat:

$ sudo ip link add hsr0 type hsr slave1 <if1> slave2 <if2>
$ sudo ip link del hsr0
BUG: unable to handle kernel NULL pointer dereference at 0000000000000018
IP: [<ffffffff8187f495>] hsr_del_port+0x15/0xa0
etc...

Reported-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Fixes: 51f3c605318b056a ("net/hsr: Move slave init to hsr_slave.c.")
Signed-off-by: Arvid Brodin <arvid.brodin@alten.se>
---
 net/hsr/hsr_device.c |  3 +++
 net/hsr/hsr_main.c   |  4 ++++
 net/hsr/hsr_slave.c  | 10 +++++++---
 3 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/net/hsr/hsr_device.c b/net/hsr/hsr_device.c
index a138d75..44d2746 100644
--- a/net/hsr/hsr_device.c
+++ b/net/hsr/hsr_device.c
@@ -359,8 +359,11 @@ static void hsr_dev_destroy(struct net_device *hsr_dev)
 	struct hsr_port *port;
 
 	hsr = netdev_priv(hsr_dev);
+
+	rtnl_lock();
 	hsr_for_each_port(hsr, port)
 		hsr_del_port(port);
+	rtnl_unlock();
 
 	del_timer_sync(&hsr->prune_timer);
 	del_timer_sync(&hsr->announce_timer);
diff --git a/net/hsr/hsr_main.c b/net/hsr/hsr_main.c
index 779d28b..cd37d00 100644
--- a/net/hsr/hsr_main.c
+++ b/net/hsr/hsr_main.c
@@ -36,6 +36,10 @@ static int hsr_netdev_notify(struct notifier_block *nb, unsigned long event,
 			return NOTIFY_DONE;	/* Not an HSR device */
 		hsr = netdev_priv(dev);
 		port = hsr_port_get_hsr(hsr, HSR_PT_MASTER);
+		if (port == NULL) {
+			/* Resend of notification concerning removed device? */
+			return NOTIFY_DONE;
+		}
 	} else {
 		hsr = port->hsr;
 	}
diff --git a/net/hsr/hsr_slave.c b/net/hsr/hsr_slave.c
index a348dcb..7d37366 100644
--- a/net/hsr/hsr_slave.c
+++ b/net/hsr/hsr_slave.c
@@ -181,8 +181,10 @@ void hsr_del_port(struct hsr_port *port)
 	list_del_rcu(&port->port_list);
 
 	if (port != master) {
-		netdev_update_features(master->dev);
-		dev_set_mtu(master->dev, hsr_get_max_mtu(hsr));
+		if (master != NULL) {
+			netdev_update_features(master->dev);
+			dev_set_mtu(master->dev, hsr_get_max_mtu(hsr));
+		}
 		netdev_rx_handler_unregister(port->dev);
 		dev_set_promiscuity(port->dev, -1);
 	}
@@ -192,5 +194,7 @@ void hsr_del_port(struct hsr_port *port)
 	 */
 
 	synchronize_rcu();
-	dev_put(port->dev);
+
+	if (port != master)
+		dev_put(port->dev);
 }
-- 
2.0.4

-- 
Arvid Brodin | Consultant (Linux)
ALTEN | Knarrarnäsgatan 7 | SE-164 40 Kista | Sweden
arvid.brodin@alten.se | www.alten.se/en/

Re: [PATCH net] net/hsr: Fix NULL pointer dereference and refcnt bugs when deleting a HSR interface.

[David Miller]

From: Arvid Brodin <arvid.brodin@alten.se>
Date: Thu, 19 Feb 2015 20:22:38 +0100

> How to repeat:
> 
> $ sudo ip link add hsr0 type hsr slave1 <if1> slave2 <if2>
> $ sudo ip link del hsr0
> BUG: unable to handle kernel NULL pointer dereference at 0000000000000018
> IP: [<ffffffff8187f495>] hsr_del_port+0x15/0xa0
> etc...
> 
> Reported-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
> Fixes: 51f3c605318b056a ("net/hsr: Move slave init to hsr_slave.c.")
> Signed-off-by: Arvid Brodin <arvid.brodin@alten.se>

You're going to have to write a better commit log message than
this.

For example, wouldn't it be better to restructure the code or
rearrange things slightly rather than just sticking NULL pointer
checks all over the place?

If this were structures properly, you wouldn't get notifications
for devices which lack a device private.

A spackling of NULL pointer checks to fix a bug is always a huge
red flag.