[PATCH 4.9 57/92] serial: uartlite: fix exit path null pointer

[Greg Kroah-Hartman]

From: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>

commit a553add0846f355a28ed4e81134012e4a1e280c2 upstream.

Call uart_unregister_driver() conditionally instead of
unconditionally, only if it has been previously registered.

This uses driver.state, just as the sh-sci.c driver does.

Fixes this null pointer dereference in tty_unregister_driver(),
since the 'driver' argument is null:

  general protection fault: 0000 [#1] PREEMPT SMP KASAN PTI
  RIP: 0010:tty_unregister_driver+0x25/0x1d0

Fixes: 238b8721a554 ("[PATCH] serial uartlite driver")
Signed-off-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Cc: stable <stable@xxxxxxxxxxxxxxx>
Cc: Peter Korsgaard <jacmet@xxxxxxxxxx>
Link: https://lore.kernel.org/r/9c8e6581-6fcc-a595-0897-4d90f5d710df@xxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/tty/serial/uartlite.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/tty/serial/uartlite.c
+++ b/drivers/tty/serial/uartlite.c
@@ -746,7 +746,8 @@ err_uart:
 static void __exit ulite_exit(void)
 {
 	platform_driver_unregister(&ulite_platform_driver);
-	uart_unregister_driver(&ulite_uart_driver);
+	if (ulite_uart_driver.state)
+		uart_unregister_driver(&ulite_uart_driver);
 }
 
 module_init(ulite_init);