[PATCH 1/2] USB: serial: fix port tear down use-after-free

[Johan Hovold <johan@kernel.org>]

Some drivers for multiport devices access port driver data from
completion handlers of shared URBs submitted at attach() or first open()
and stopped at last close() or disconnect(), respectively.

A simple NULL check before accessing the driver data makes sure that a
port state container has at least been allocated, but a completion
handler can still race with port tear down.

Reorder the disconnect handling so that ports are not deregistered (and
their driver data freed) until after all ports have been hung up and the
driver disconnect() callback has run so that all I/O has been stopped.

Fixes: 2d93148ab698 ("USB: serial: fix lifetime and locking problems")
Reported-by: syzbot+e5e28c3e953b2eebb16e@syzkaller.appspotmail.com
Link: https://lore.kernel.org/all/6a7e6fb9.ec5dc6cc.21cb3f.00c0.GAE@google.com/
Cc: stable@vger.kernel.org	# 2.6.30
Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Johan Hovold <johan@kernel.org>
---
 drivers/usb/serial/usb-serial.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/serial/usb-serial.c b/drivers/usb/serial/usb-serial.c
index 17edc057a311..a4fbc849c0fa 100644
--- a/drivers/usb/serial/usb-serial.c
+++ b/drivers/usb/serial/usb-serial.c
@@ -1191,12 +1191,17 @@ static void usb_serial_disconnect(struct usb_interface *interface)
 		usb_serial_port_poison_urbs(port);
 		wake_up_interruptible(&port->port.delta_msr_wait);
 		cancel_work_sync(&port->work);
-		if (device_is_registered(&port->dev))
-			device_del(&port->dev);
 	}
+
 	if (serial->type->disconnect)
 		serial->type->disconnect(serial);
 
+	for (i = 0; i < serial->num_ports; ++i) {
+		port = serial->port[i];
+		if (device_is_registered(&port->dev))
+			device_del(&port->dev);
+	}
+
 	release_sibling(serial, interface);
 
 	/* let the last holder of this object cause it to be cleaned up */
-- 
2.54.0