[PATCH] serial-uartlite: Fix null-ptr-deref in ulite_exit

[YueHaibing]

If ulite_probe is not called or failed to registed
uart_register_driver, unload the module will call
uart_unregister_driver, which will tigger NULL
pointer dereference like this:

BUG: KASAN: null-ptr-deref in tty_unregister_driver+0x19/0x100
Read of size 4 at addr 0000000000000034 by task syz-executor.0/4246

CPU: 0 PID: 4246 Comm: syz-executor.0 Tainted: G         C        5.1.0+ #26
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014
Call Trace:
 dump_stack+0xa9/0x10e
 ? tty_unregister_driver+0x19/0x100
 ? tty_unregister_driver+0x19/0x100
 __kasan_report+0x171/0x18d
 ? tty_unregister_driver+0x19/0x100
 kasan_report+0xe/0x20
 tty_unregister_driver+0x19/0x100
 uart_unregister_driver+0x30/0xc0
 __x64_sys_delete_module+0x244/0x330
 ? __ia32_sys_delete_module+0x330/0x330
 ? __x64_sys_clock_gettime+0xe3/0x160
 ? trace_hardirqs_on_thunk+0x1a/0x1c
 ? trace_hardirqs_off_caller+0x3e/0x130
 ? lockdep_hardirqs_off+0xb5/0x100
 ? mark_held_locks+0x1a/0x90
 ? do_syscall_64+0x14/0x2a0
 do_syscall_64+0x72/0x2a0
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

This patch fix this by moving uart_unregister_driver
to ulite_remove.

Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
Fixes: 415b43bdb008 ("tty: serial: uartlite: Move uart register to probe")
Signed-off-by: YueHaibing <yuehaibing@xxxxxxxxxx>
---
 drivers/tty/serial/uartlite.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/serial/uartlite.c b/drivers/tty/serial/uartlite.c
index b8b912b..2e49fb6 100644
--- a/drivers/tty/serial/uartlite.c
+++ b/drivers/tty/serial/uartlite.c
@@ -867,6 +867,7 @@ static int ulite_remove(struct platform_device *pdev)
 	pm_runtime_disable(&pdev->dev);
 	pm_runtime_set_suspended(&pdev->dev);
 	pm_runtime_dont_use_autosuspend(&pdev->dev);
+	uart_unregister_driver(&ulite_uart_driver);
 	return rc;
 }
 
@@ -897,7 +898,6 @@ static int __init ulite_init(void)
 static void __exit ulite_exit(void)
 {
 	platform_driver_unregister(&ulite_platform_driver);
-	uart_unregister_driver(&ulite_uart_driver);
 }
 
 module_init(ulite_init);
-- 
1.8.3.1