[PATCH 4.4 18/20] ieee802154: 6lowpan: fix possible NULL deref in lowpan_device_event()

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <eduma...@google.com>


[ Upstream commit ca0edb131bdf1e6beaeb2b8289fd6b374b74147d ]

A tun device type can trivially be set to arbitrary value using
TUNSETLINK ioctl().

Therefore, lowpan_device_event() must really check that ieee802154_ptr
is not NULL.

Fixes: 2c88b5283f60d ("ieee802154: 6lowpan: remove check on null")
Signed-off-by: Eric Dumazet <eduma...@google.com>
Cc: Alexander Aring <alex.ar...@gmail.com>
Cc: Stefan Schmidt <ste...@osg.samsung.com>
Reported-by: syzbot <syzkal...@googlegroups.com>
Acked-by: Stefan Schmidt <ste...@osg.samsung.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 net/ieee802154/6lowpan/core.c |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

--- a/net/ieee802154/6lowpan/core.c
+++ b/net/ieee802154/6lowpan/core.c
@@ -206,9 +206,13 @@ static inline void lowpan_netlink_fini(v
 static int lowpan_device_event(struct notifier_block *unused,
                               unsigned long event, void *ptr)
 {
-       struct net_device *wdev = netdev_notifier_info_to_dev(ptr);
+       struct net_device *ndev = netdev_notifier_info_to_dev(ptr);
+       struct wpan_dev *wpan_dev;
 
-       if (wdev->type != ARPHRD_IEEE802154)
+       if (ndev->type != ARPHRD_IEEE802154)
+               return NOTIFY_DONE;
+       wpan_dev = ndev->ieee802154_ptr;
+       if (!wpan_dev)
                goto out;
 
        switch (event) {
@@ -217,8 +221,8 @@ static int lowpan_device_event(struct no
                 * also delete possible lowpan interfaces which belongs
                 * to the wpan interface.
                 */
-               if (wdev->ieee802154_ptr->lowpan_dev)
-                       lowpan_dellink(wdev->ieee802154_ptr->lowpan_dev, NULL);
+               if (wpan_dev->lowpan_dev)
+                       lowpan_dellink(wpan_dev->lowpan_dev, NULL);
                break;
        default:
                break;