linux-kernel - Re: [PATCH] drivers: tty: vt: vt.c: fix NULL dereference crash

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Date:   Fri, 12 Mar 2021 09:33:37 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Hassan Shahbazi <h.shahbazi.git@...il.com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drivers: tty: vt: vt.c: fix NULL dereference crash

On Sun, Mar 07, 2021 at 12:56:43PM +0200, Hassan Shahbazi wrote:
> Fix a NULL deference crash on hiding the cursor.
> 
> Reported by: syzbot
> https://syzkaller.appspot.com/bug?id=defb47bf56e1c14d5687280c7bb91ce7b608b94b
> 
> Signed-off-by: Hassan Shahbazi <h.shahbazi.git@...il.com>
> ---
>  drivers/tty/vt/vt.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
> index 284b07224c55..8c3e83c81341 100644
> --- a/drivers/tty/vt/vt.c
> +++ b/drivers/tty/vt/vt.c
> @@ -904,7 +904,9 @@ static void hide_cursor(struct vc_data *vc)
>  	if (vc_is_sel(vc))
>  		clear_selection();
>  
> -	vc->vc_sw->con_cursor(vc, CM_ERASE);
> +	if (vc->vc_sw)
> +		vc->vc_sw->con_cursor(vc, CM_ERASE);
> +
>  	hide_softcursor(vc);
>  }
>  
> -- 
> 2.26.2
> 

Are you sure this actually fixes the problem?  How did you test it?  Did
syzbot test this?

I had a few reports of this patch _not_ solving the problem, so getting
confirmation of this would be good.

thanks,

greg k-h