[PATCH 6.18 071/198] net: lapbether: handle NETDEV_PRE_TYPE_CHANGE

Greg Kroah-Hartman
2026-04-20T15:59:24Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit b120e4432f9f56c7103133d6a11245e617695adb ]

lapbeth_data_transmit() expects the underlying device type
to be ARPHRD_ETHER.

Returning NOTIFY_BAD from lapbeth_device_event() makes sure
bonding driver can not break this expectation.

Fixes: 872254dd6b1f ("net/bonding: Enable bonding to enslave non ARPHRD_ETHER")
Reported-by: syzbot+d8c285748fa7292580a9@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/69cd22a1.050a0220.70c3a.0002.GAE@google.com/T/#u
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Martin Schiller <ms@dev.tdt.de>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20260402103519.1201565-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/net/wan/lapbether.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/net/wan/lapbether.c b/drivers/net/wan/lapbether.c
index f357a7ac70ac4..9861c99ea56c4 100644
--- a/drivers/net/wan/lapbether.c
+++ b/drivers/net/wan/lapbether.c
@@ -446,33 +446,36 @@ static void lapbeth_free_device(struct lapbethdev *lapbeth)
static int lapbeth_device_event(struct notifier_block *this,
unsigned long event, void *ptr)
{
- struct lapbethdev *lapbeth;
struct net_device *dev = netdev_notifier_info_to_dev(ptr);
+ struct lapbethdev *lapbeth;

if (dev_net(dev) != &init_net)
return NOTIFY_DONE;

- if (!dev_is_ethdev(dev) && !lapbeth_get_x25_dev(dev))
+ lapbeth = lapbeth_get_x25_dev(dev);
+ if (!dev_is_ethdev(dev) && !lapbeth)
return NOTIFY_DONE;

switch (event) {
case NETDEV_UP:
/* New ethernet device -> new LAPB interface */
- if (!lapbeth_get_x25_dev(dev))
+ if (!lapbeth)
lapbeth_new_device(dev);
break;
case NETDEV_GOING_DOWN:
/* ethernet device closes -> close LAPB interface */
- lapbeth = lapbeth_get_x25_dev(dev);
if (lapbeth)
dev_close(lapbeth->axdev);
break;
case NETDEV_UNREGISTER:
/* ethernet device disappears -> remove LAPB interface */
- lapbeth = lapbeth_get_x25_dev(dev);
if (lapbeth)
lapbeth_free_device(lapbeth);
break;
+ case NETDEV_PRE_TYPE_CHANGE:
+ /* Our underlying device type must not change. */
+ if (lapbeth)
+ return NOTIFY_BAD;
}

return NOTIFY_DONE;
--
2.53.0