[PATCH] vt/fbcon: deinitialize resources in visual_init() after failed memory allocation

[PATCH] vt/fbcon: deinitialize resources in visual_init() after failed memory allocation

[Grzegorz Halat]

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@redhat.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

Re: [PATCH] vt/fbcon: deinitialize resources in visual_init() after failed memory allocation

[Grzegorz Halat]

On Fri, 26 Apr 2019 at 16:59, Grzegorz Halat <ghalat@redhat.com> 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.

Hi,
A gentle reminder. Could you please review my patch? I've seen two
crashes caused by this bug.

--
Grzegorz Halat

Re: [PATCH] vt/fbcon: deinitialize resources in visual_init() after failed memory allocation

[Greg Kroah-Hartman]

On Thu, May 16, 2019 at 04:33:40PM +0200, Grzegorz Halat wrote:
> On Fri, 26 Apr 2019 at 16:59, Grzegorz Halat <ghalat@redhat.com> 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.
> 
> Hi,
> A gentle reminder. Could you please review my patch? I've seen two
> crashes caused by this bug.

How?  How are you triggering a memory allocation failure in a "normal"
system?

Anyway, I'll queue this up, but it really does not seem like anything
anyone would see "in the wild".

thanks,

greg k-h

Re: [PATCH] vt/fbcon: deinitialize resources in visual_init() after failed memory allocation

[Grzegorz Halat]

On Fri, 24 May 2019 at 10:06, Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
> How?  How are you triggering a memory allocation failure in a "normal"
> system?
> Anyway, I'll queue this up, but it really does not seem like anything
> anyone would see "in the wild"

I've seen this crash twice in ours customer environment under low
memory conditions.
There is a report in Debian bug tracker:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug€4443
and LKML bug report:
https://lkml.org/lkml/2017/12/18/591

--
Grzegorz

Re: [PATCH] vt/fbcon: deinitialize resources in visual_init() after failed memory allocation

[Greg Kroah-Hartman]

On Fri, May 24, 2019 at 03:52:31PM +0200, Grzegorz Halat wrote:
> On Fri, 24 May 2019 at 10:06, Greg Kroah-Hartman
> <gregkh@linuxfoundation.org> wrote:
> > How?  How are you triggering a memory allocation failure in a "normal"
> > system?
> > Anyway, I'll queue this up, but it really does not seem like anything
> > anyone would see "in the wild"
> 
> I've seen this crash twice in ours customer environment under low
> memory conditions.
> There is a report in Debian bug tracker:
> https://bugs.debian.org/cgi-bin/bugreport.cgi?bug€4443
> and LKML bug report:
> https://lkml.org/lkml/2017/12/18/591

Ok, now queued up to go to Linus for 5.2-final.

thanks,

greg k-h

Re: [PATCH] vt/fbcon: deinitialize resources in visual_init() after failed memory allocation

[Bartlomiej Zolnierkiewicz]

On 4/26/19 4:59 PM, 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@redhat.com>

Acked-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics

Re: [PATCH] vt/fbcon: deinitialize resources in visual_init() after failed memory allocation

[Oleksandr Natalenko]

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@redhat.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@redhat.com>

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