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

[Johan Hovold <johan@kernel.org>]

On Thu, May 16, 2019 at 12:09:31PM +0800, YueHaibing wrote:
> 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

> This patch fix this by moving uart_unregister_driver
> to ulite_remove.
> 
> Reported-by: Hulk Robot <hulkci@huawei.com>
> Fixes: 415b43bdb008 ("tty: serial: uartlite: Move uart register to probe")
> Signed-off-by: YueHaibing <yuehaibing@huawei.com>
> ---
>  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);

This broken. Consider what happens if you have tho ports registered and
you unbind the first.

Someone else sent a fix for this here

	https://lkml.kernel.org/r/20190514033219.169947-1-wangkefeng.wang@huawei.com

That fix also has some issues, but is still better given the current
state this driver is in.

>  	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);

Johan