Message-ID: <5547A614.9020109@hurleysoftware.com>
Date: Mon, 04 May 2015 13:02:12 -0400
From: Peter Hurley <peter@hurleysoftware.com>
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To: Jan Kiszka <jan.kiszka@siemens.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
CC: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-serial@vger.kernel.org
Subject: Re: [PATCH] serial: 8250: Prevent kernel crash with nr_uarts=0
References: <554797D4.5080704@siemens.com>
In-Reply-To: <554797D4.5080704@siemens.com>
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Hi Jan,

On 05/04/2015 12:01 PM, Jan Kiszka wrote:
> When nr_uarts was set to 0 (via config or 8250_core.nr_uarts), we crash
> early on x86 because serial8250_isa_init_ports dereferences base_ops
> which remains NULL. In fact, there is nothing to do for that function if
> there are no uarts.

Thanks for finding this.

So nr_uarts == 0 effectively disables the 8250 driver. Is there any 
reason not to simply abort the driver init instead?

Regards,
Peter Hurley

> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> ---
>  drivers/tty/serial/8250/8250_core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
> index 4506e40..e1363a40 100644
> --- a/drivers/tty/serial/8250/8250_core.c
> +++ b/drivers/tty/serial/8250/8250_core.c
> @@ -3256,7 +3256,7 @@ static void __init serial8250_isa_init_ports(void)
>  	static int first = 1;
>  	int i, irqflag = 0;
>  
> -	if (!first)
> +	if (!first || nr_uarts == 0)
>  		return;
>  	first = 0;
>  
> 

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