linux-kernel - Re: [PATCH] vt/fbcon: deinitialize resources in visual

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Date:   Tue, 21 May 2019 08:27:51 +0200
From:   Oleksandr Natalenko <oleksandr@...hat.com>
To:     Grzegorz Halat <ghalat@...hat.com>
Cc:     Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, linux-fbdev@...r.kernel.org
Subject: Re: [PATCH] vt/fbcon: deinitialize resources in visual_init() after
 failed memory allocation

Hi.

On Fri, Apr 26, 2019 at 04:43:57PM +0200, Grzegorz Halat wrote:
> After memory allocation failure vc_allocate() doesn't clean up data
> which has been initialized in visual_init(). In case of fbcon this
> leads to divide-by-0 in fbcon_init() on next open of the same tty.
> 
> memory allocation in vc_allocate() may fail here:
> 1097:     vc->vc_screenbuf = kzalloc(vc->vc_screenbuf_size, GFP_KERNEL);
> 
> on next open() fbcon_init() skips vc_font.data initialization:
> 1088:     if (!p->fontdata) {
> 
> division by zero in fbcon_init() happens here:
> 1149:     new_cols /= vc->vc_font.width;
> 
> Additional check is needed in fbcon_deinit() to prevent
> usage of uninitialized vc_screenbuf:
> 
> 1251:        if (vc->vc_hi_font_mask && vc->vc_screenbuf)
> 1252:                set_vc_hi_font(vc, false);
> 
> Crash:
> 
>  #6 [ffffc90001eafa60] divide_error at ffffffff81a00be4
>     [exception RIP: fbcon_init+463]
>     RIP: ffffffff814b860f  RSP: ffffc90001eafb18  RFLAGS: 00010246
> ...
>  #7 [ffffc90001eafb60] visual_init at ffffffff8154c36e
>  #8 [ffffc90001eafb80] vc_allocate at ffffffff8154f53c
>  #9 [ffffc90001eafbc8] con_install at ffffffff8154f624
> ...
> 
> Signed-off-by: Grzegorz Halat <ghalat@...hat.com>
> ---
>  drivers/tty/vt/vt.c              | 11 +++++++++--
>  drivers/video/fbdev/core/fbcon.c |  2 +-
>  2 files changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
> index 650c66886c80..ec85d195678f 100644
> --- a/drivers/tty/vt/vt.c
> +++ b/drivers/tty/vt/vt.c
> @@ -1056,6 +1056,13 @@ static void visual_init(struct vc_data *vc, int num, int init)
>  	vc->vc_screenbuf_size = vc->vc_rows * vc->vc_size_row;
>  }
>  
> +
> +static void visual_deinit(struct vc_data *vc)
> +{
> +	vc->vc_sw->con_deinit(vc);
> +	module_put(vc->vc_sw->owner);
> +}
> +
>  int vc_allocate(unsigned int currcons)	/* return 0 on success */
>  {
>  	struct vt_notifier_param param;
> @@ -1103,6 +1110,7 @@ int vc_allocate(unsigned int currcons)	/* return 0 on success */
>  
>  	return 0;
>  err_free:
> +	visual_deinit(vc);
>  	kfree(vc);
>  	vc_cons[currcons].d = NULL;
>  	return -ENOMEM;
> @@ -1331,9 +1339,8 @@ struct vc_data *vc_deallocate(unsigned int currcons)
>  		param.vc = vc = vc_cons[currcons].d;
>  		atomic_notifier_call_chain(&vt_notifier_list, VT_DEALLOCATE, &param);
>  		vcs_remove_sysfs(currcons);
> -		vc->vc_sw->con_deinit(vc);
> +		visual_deinit(vc);
>  		put_pid(vc->vt_pid);
> -		module_put(vc->vc_sw->owner);
>  		vc_uniscr_set(vc, NULL);
>  		kfree(vc->vc_screenbuf);
>  		vc_cons[currcons].d = NULL;
> diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
> index cd059a801662..c59b23f6e9ba 100644
> --- a/drivers/video/fbdev/core/fbcon.c
> +++ b/drivers/video/fbdev/core/fbcon.c
> @@ -1248,7 +1248,7 @@ static void fbcon_deinit(struct vc_data *vc)
>  	if (free_font)
>  		vc->vc_font.data = NULL;
>  
> -	if (vc->vc_hi_font_mask)
> +	if (vc->vc_hi_font_mask && vc->vc_screenbuf)
>  		set_vc_hi_font(vc, false);
>  
>  	if (!con_is_bound(&fb_con))
> -- 
> 2.20.1
> 

LGTM.

Reviewed-by: Oleksandr Natalenko <oleksandr@...hat.com>

-- 
  Best regards,
    Oleksandr Natalenko (post-factum)
    Senior Software Maintenance Engineer