linux-kernel - Re: drivers/s390/char/keyboard.c NULL pointer reference

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Message-Id: <20170804092608.GB3278@osiris>
Date:   Fri, 4 Aug 2017 11:26:08 +0200
From:   Heiko Carstens <heiko.carstens@...ibm.com>
To:     sohu0106 <sohu0106@....com>
Cc:     schwidefsky@...ibm.com, linux-s390@...r.kernel.org,
        torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: drivers/s390/char/keyboard.c NULL pointer reference

On Thu, Aug 03, 2017 at 09:57:38PM +0800, sohu0106 wrote:
> 
> 
> Local users able to send the NULL arg argument to kbd_ioctl(), which could cause kernel crash
> 
> 
> 
> 
> diff --git a/keyboard.c 
> b/keyboard.c
> index ba0e4f9..3ec16b1 100644
> --- a/keyboard.c
> +++ b/keyboard.c
> @@ -456,6 +456,8 @@ int kbd_ioctl(struct kbd_data *kbd, unsigned int cmd, unsigned long arg)
>         int perm;
>  
>         argp = (void __user *)arg;
> +       if( !argp )
> +               return -EFAULT;

This doesn't make sense as well. All uaccess functions are able to handle
NULL pointers within user space.