6.1-stable review patch. If anyone has any objections, please let me know.
------------------
From: Andrew Jeffery andrew@codeconstruct.com.au
[ Upstream commit e4f349bd6e58051df698b82f94721f18a02a293d ]
mctp_flow_prepare_output() is called in mctp_route_output(), which places outbound packets onto a given interface. The packet may represent a message fragment, in which case we provoke an unbalanced reference count to the underlying device. This causes trouble if we ever attempt to remove the interface:
[ 48.702195] usb 1-1: USB disconnect, device number 2 [ 58.883056] unregister_netdevice: waiting for mctpusb0 to become free. Usage count = 2 [ 69.022548] unregister_netdevice: waiting for mctpusb0 to become free. Usage count = 2 [ 79.172568] unregister_netdevice: waiting for mctpusb0 to become free. Usage count = 2 ...
Predicate the invocation of mctp_dev_set_key() in mctp_flow_prepare_output() on not already having associated the device with the key. It's not yet realistic to uphold the property that the key maintains only one device reference earlier in the transmission sequence as the route (and therefore the device) may not be known at the time the key is associated with the socket.
Fixes: 67737c457281 ("mctp: Pass flow data & flow release events to drivers") Acked-by: Jeremy Kerr jk@codeconstruct.com.au Signed-off-by: Andrew Jeffery andrew@codeconstruct.com.au Link: https://patch.msgid.link/20250508-mctp-dev-refcount-v1-1-d4f965c67bb5@codeco... Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/mctp/route.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/net/mctp/route.c b/net/mctp/route.c index e72cdd4ce588f..62952ad5cb636 100644 --- a/net/mctp/route.c +++ b/net/mctp/route.c @@ -274,8 +274,10 @@ static void mctp_flow_prepare_output(struct sk_buff *skb, struct mctp_dev *dev)
key = flow->key;
- if (WARN_ON(key->dev && key->dev != dev)) + if (key->dev) { + WARN_ON(key->dev != dev); return; + }
mctp_dev_set_key(dev, key); }