[PATCH net] ieee802154: 6lowpan: only accept IPv6 packets in lowpan_xmit()

The aoe driver (or similar) generates a non-IPv6 packet
(e.g., ETH_P_AOE) and queues it for transmission via dev_queue_xmit()
on a 6LoWPAN interface (configured by the user or test case).

Since the packet is not IPv6, the 6LoWPAN header_ops->create function
(lowpan_header_create or header_create) returns early without initializing
the lowpan_addr_info structure in the skb headroom.

In the transmit function (lowpan_xmit), the driver calls lowpan_header
(or setup_header) which unconditionally copies and uses the lowpan_addr_info
from the headroom, which contains uninitialized data.

Fix this by dropping non IPv6 packets.

A similar fix is needed in net/bluetooth/6lowpan.c bt_xmit().

Fixes: 4dc315e267fe ("ieee802154: 6lowpan: move transmit functionality")
Reported-by: syzbot+f13c19f75e1097abd116@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/6a1fd763.278b5b03.2bcf39.0049.GAE@google.com/T/#u (local)
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
Cc: Alexander Aring <alex.aring@gmail.com>
Cc: Stefan Schmidt <stefan@datenfreihafen.org>
Cc: Miquel Raynal <miquel.raynal@bootlin.com>
---
 net/ieee802154/6lowpan/tx.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/ieee802154/6lowpan/tx.c b/net/ieee802154/6lowpan/tx.c
index 0c07662b44c0ca84e07c61309b6b46d37a7fdf6b..4df76ff50699ede5c187c9cca6f0cc10b19d2123 100644
--- a/net/ieee802154/6lowpan/tx.c
+++ b/net/ieee802154/6lowpan/tx.c

@@ -255,6 +255,11 @@ netdev_tx_t lowpan_xmit(struct sk_buff *skb, struct net_device *ldev)
 
 	pr_debug("package xmit\n");
 
+	if (skb->protocol != htons(ETH_P_IPV6)) {
+		kfree_skb(skb);
+		return NET_XMIT_DROP;
+	}
+
 	WARN_ON_ONCE(skb->len > IPV6_MIN_MTU);
 
 	/* We must take a copy of the skb before we modify/replace the ipv6

-- 
2.54.0.1013.g208068f2d8-goog