[PATCH net] 6lowpan: fix netdev_priv() type confusion in lowpan_event()

[Roman Gushchin <roman.gushchin@linux.dev>]

lowpan_event() assumes any netdevice with dev->type == ARPHRD_6LOWPAN
has a struct lowpan_dev in netdev_priv(dev). However, non-6LoWPAN
devices can also have ARPHRD_6LOWPAN, e.g. a TUN device via TUNSETLINK
or a bonding device inheriting dev->type from its lower device.

Bringing such a device up or down causes lowpan_event() to read and
overwrite unrelated netdev_priv() memory. Since unprivileged users can
create TUN and bonding devices in a user and network namespace, they
can corrupt struct bonding and trigger a slab use-after-free.

Also check dev->ndisc_ops == &lowpan_ndisc_ops, which is set only by
lowpan_register_netdevice() on genuine 6LoWPAN devices.

Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
Fixes: 5609c185f24d ("6lowpan: iphc: add support for stateful compression")
Fixes: 2ad3ed59198c ("6lowpan: add 802.15.4 short addr slaac")
Cc: stable@vger.kernel.org
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://sashiko.dev/#/bug/linux-97b284e0-576e-4373-b62f-eb132f482b91
---
 net/6lowpan/6lowpan_i.h | 13 ++++++++++---
 net/6lowpan/core.c      |  2 +-
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/net/6lowpan/6lowpan_i.h b/net/6lowpan/6lowpan_i.h
index 01853cec0209..07f11d4dde6e 100644
--- a/net/6lowpan/6lowpan_i.h
+++ b/net/6lowpan/6lowpan_i.h
@@ -2,19 +2,26 @@
 #ifndef __6LOWPAN_I_H
 #define __6LOWPAN_I_H
 
+#include <linux/if_arp.h>
 #include <linux/netdevice.h>
 
 #include <net/6lowpan.h>
 
-/* caller need to be sure it's dev->type is ARPHRD_6LOWPAN */
+extern const struct ndisc_ops lowpan_ndisc_ops;
+
+static inline bool lowpan_is_dev(const struct net_device *dev)
+{
+	return dev->type == ARPHRD_6LOWPAN &&
+	       dev->ndisc_ops == &lowpan_ndisc_ops;
+}
+
+/* caller must ensure lowpan_is_dev(dev) is true */
 static inline bool lowpan_is_ll(const struct net_device *dev,
 				enum lowpan_lltypes lltype)
 {
 	return lowpan_dev(dev)->lltype == lltype;
 }
 
-extern const struct ndisc_ops lowpan_ndisc_ops;
-
 int addrconf_ifid_802154_6lowpan(u8 *eui, struct net_device *dev);
 
 #ifdef CONFIG_6LOWPAN_DEBUGFS
diff --git a/net/6lowpan/core.c b/net/6lowpan/core.c
index 850d4a185f55..748103d37e31 100644
--- a/net/6lowpan/core.c
+++ b/net/6lowpan/core.c
@@ -113,7 +113,7 @@ static int lowpan_event(struct notifier_block *unused,
 	struct in6_addr addr;
 	int i;
 
-	if (dev->type != ARPHRD_6LOWPAN)
+	if (!lowpan_is_dev(dev))
 		return NOTIFY_DONE;
 
 	idev = __in6_dev_get(dev);
-- 
2.56.0.455.g6c5a503b38-goog