linux-kernel - Re: stack leak via uart_get

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Message-ID: <2023100517-washer-why-7513@gregkh>
Date:   Thu, 5 Oct 2023 19:55:34 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     Jiri Slaby <jirislaby@...nel.org>, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: stack leak via uart_get_info() ?

On Thu, Oct 05, 2023 at 07:34:21PM +0300, Alexey Dobriyan wrote:
> If this check ever triggers
> 
> 	static int uart_get_info(struct tty_port *port, struct serial_struct *retinfo)
> 	{
> 
> 		uport = uart_port_check(state);
> 	        if (!uport)
> 	                goto out;
> 
> then all those sysfs users will print stack contents to userspace.
> 
> Can it trigger while sysfs read is executing?

I don't think it can ever fail, we don't even check the result in other
places, so it should all be fine.

> Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
> ---
> 
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -775,6 +775,8 @@ static int uart_get_info(struct tty_port *port, struct serial_struct *retinfo)
>  	struct uart_port *uport;
>  	int ret = -ENODEV;
>  
> +	*retinfo = (struct serial_struct){};

This is good (although I hate the implied memcpy), a real memset would
be best to ensure that any holes are also filled.  Want to do that, or
want me to?

thanks,

greg k-h