[PATCH 5.12 1/5] net: hso: fix NULL-deref on disconnect regression

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Johan Hovold <johan@kernel.org>

commit 2ad5692db72874f02b9ad551d26345437ea4f7f3 upstream.

Commit 8a12f8836145 ("net: hso: fix null-ptr-deref during tty device
unregistration") fixed the racy minor allocation reported by syzbot, but
introduced an unconditional NULL-pointer dereference on every disconnect
instead.

Specifically, the serial device table must no longer be accessed after
the minor has been released by hso_serial_tty_unregister().

Fixes: 8a12f8836145 ("net: hso: fix null-ptr-deref during tty device unregistration")
Cc: stable@vger.kernel.org
Cc: Anirudh Rayabharam <mail@anirudhrb.com>
Reported-by: Leonardo Antoniazzi <leoanto@aruba.it>
Signed-off-by: Johan Hovold <johan@kernel.org>
Reviewed-by: Anirudh Rayabharam <mail@anirudhrb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/net/usb/hso.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/net/usb/hso.c
+++ b/drivers/net/usb/hso.c
@@ -3104,7 +3104,7 @@ static void hso_free_interface(struct us
 			cancel_work_sync(&serial_table[i]->async_put_intf);
 			cancel_work_sync(&serial_table[i]->async_get_intf);
 			hso_serial_tty_unregister(serial);
-			kref_put(&serial_table[i]->ref, hso_serial_ref_free);
+			kref_put(&serial->parent->ref, hso_serial_ref_free);
 		}
 	}