From: Eric Dumazet <edumazet@google.com>
Date: Mon, 5 Mar 2018 08:51:03 -0800
Subject: ieee802154: 6lowpan: fix possible NULL deref in lowpan_device_event()
Git-commit: ca0edb131bdf1e6beaeb2b8289fd6b374b74147d
Patch-mainline: v4.16-rc7
References: networking-stable-18_03_28

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 <edumazet@google.com>
Cc: Alexander Aring <alex.aring@gmail.com>
Cc: Stefan Schmidt <stefan@osg.samsung.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Acked-by: Stefan Schmidt <stefan@osg.samsung.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 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
@@ -205,9 +205,13 @@ 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)
 		return NOTIFY_DONE;
 
 	switch (event) {
@@ -216,8 +220,8 @@ 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:
 		return NOTIFY_DONE;