Re: [PATCH] serial: digicolor: fix use-after-free on driver unbind

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

On Mon, Dec 22, 2025 at 12:55:02PM +0800, Junrui Luo wrote:
> The digicolor_uart_console_write() function accesses the global
> digicolor_ports[] array to retrieve the uart port pointer, which
> can lead to a use-after-free if the console write occurs after
> the port has been removed via unbind.
> 
> digicolor_uart_remove() leaves a dangling pointer in the array.
> 
> Fix by clearing the array entry in digicolor_uart_remove() and
> adding a NULL check in digicolor_uart_console_write().
> 
> Reported-by: Yuhao Jiang <danisjiang@gmail.com>
> Reported-by: Junrui Luo <moonafterrain@outlook.com>
> Fixes: 5930cb3511df ("serial: driver for Conexant Digicolor USART")
> Signed-off-by: Junrui Luo <moonafterrain@outlook.com>
> ---
>  drivers/tty/serial/digicolor-usart.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/tty/serial/digicolor-usart.c b/drivers/tty/serial/digicolor-usart.c
> index d2482df5cb9b..5861be2072c4 100644
> --- a/drivers/tty/serial/digicolor-usart.c
> +++ b/drivers/tty/serial/digicolor-usart.c
> @@ -397,6 +397,9 @@ static void digicolor_uart_console_write(struct console *co, const char *c,
>  	unsigned long flags;
>  	int locked = 1;
>  
> +	if (!port)
> +		return;
> +

What prevents port from changing right after you tested this?

And who is calling unbind on a port?  Why?  That's a debuggging thing
that a developer could do, it should not be part of any normal system
operation.

thanks,

greg k-h