[PATCH] fbcon: Check font dimension limits

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* [PATCH] fbcon: Check font dimension limits
       [not found] <20230126004911.869923511@ens-lyon.org>
@ 2023-01-26  0:49 ` Samuel Thibault
  2023-01-26  0:51   ` Samuel Thibault
                     ` (2 more replies)
  0 siblings, 3 replies; 7+ messages in thread
From: Samuel Thibault @ 2023-01-26  0:49 UTC (permalink / raw)
  To: gregkh, Daniel Vetter, Helge Deller
  Cc: linux-fbdev, dri-devel, linux-kernel, stable, Sanan Hasanov,
	Samuel Thibault

blit_x and blit_y are uint32_t, so fbcon currently cannot support fonts
larger than 32x32.

The 32x32 case also needs shifting an unsigned int, to properly set bit
31, otherwise we get "UBSAN: shift-out-of-bounds in fbcon_set_font",
as reported on

http://lore.kernel.org/all/IA1PR07MB98308653E259A6F2CE94A4AFABCE9@IA1PR07MB9830.namprd07.prod.outlook.com
Kernel Branch: 6.2.0-rc5-next-20230124
Kernel config: https://drive.google.com/file/d/1F-LszDAizEEH0ZX0HcSR06v5q8FPl2Uv/view?usp=sharing
Reproducer: https://drive.google.com/file/d/1mP1jcLBY7vWCNM60OMf-ogw-urQRjNrm/view?usp=sharing

Reported-by: Sanan Hasanov <sanan.hasanov@Knights.ucf.edu>
Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>

Index: linux-6.0/drivers/video/fbdev/core/fbcon.c
===================================================================
--- linux-6.0.orig/drivers/video/fbdev/core/fbcon.c
+++ linux-6.0/drivers/video/fbdev/core/fbcon.c
@@ -2489,9 +2489,12 @@ static int fbcon_set_font(struct vc_data
 	    h > FBCON_SWAP(info->var.rotate, info->var.yres, info->var.xres))
 		return -EINVAL;
 
+	if (font->width > 32 || font->height > 32)
+		return -EINVAL;
+
 	/* Make sure drawing engine can handle the font */
-	if (!(info->pixmap.blit_x & (1 << (font->width - 1))) ||
-	    !(info->pixmap.blit_y & (1 << (font->height - 1))))
+	if (!(info->pixmap.blit_x & (1U << (font->width - 1))) ||
+	    !(info->pixmap.blit_y & (1U << (font->height - 1))))
 		return -EINVAL;
 
 	/* Make sure driver can handle the font length */



^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: [PATCH] fbcon: Check font dimension limits
  2023-01-26  0:49 ` [PATCH] fbcon: Check font dimension limits Samuel Thibault
@ 2023-01-26  0:51   ` Samuel Thibault
  2023-01-26  7:43   ` Greg KH
  2023-01-26  9:02   ` Jiri Slaby
  2 siblings, 0 replies; 7+ messages in thread
From: Samuel Thibault @ 2023-01-26  0:51 UTC (permalink / raw)
  To: gregkh, Daniel Vetter, Helge Deller
  Cc: linux-fbdev, dri-devel, linux-kernel, stable, Sanan Hasanov

(FYI, the UB was already a problem before my big-font patch submission,
the checks I add here are already making sense in previous versions
anyway)

Samuel Thibault, le jeu. 26 janv. 2023 01:49:12 +0100, a ecrit:
> blit_x and blit_y are uint32_t, so fbcon currently cannot support fonts
> larger than 32x32.
> 
> The 32x32 case also needs shifting an unsigned int, to properly set bit
> 31, otherwise we get "UBSAN: shift-out-of-bounds in fbcon_set_font",
> as reported on
> 
> http://lore.kernel.org/all/IA1PR07MB98308653E259A6F2CE94A4AFABCE9@IA1PR07MB9830.namprd07.prod.outlook.com
> Kernel Branch: 6.2.0-rc5-next-20230124
> Kernel config: https://drive.google.com/file/d/1F-LszDAizEEH0ZX0HcSR06v5q8FPl2Uv/view?usp=sharing
> Reproducer: https://drive.google.com/file/d/1mP1jcLBY7vWCNM60OMf-ogw-urQRjNrm/view?usp=sharing
> 
> Reported-by: Sanan Hasanov <sanan.hasanov@Knights.ucf.edu>
> Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
> 
> Index: linux-6.0/drivers/video/fbdev/core/fbcon.c
> ===================================================================
> --- linux-6.0.orig/drivers/video/fbdev/core/fbcon.c
> +++ linux-6.0/drivers/video/fbdev/core/fbcon.c
> @@ -2489,9 +2489,12 @@ static int fbcon_set_font(struct vc_data
>  	    h > FBCON_SWAP(info->var.rotate, info->var.yres, info->var.xres))
>  		return -EINVAL;
>  
> +	if (font->width > 32 || font->height > 32)
> +		return -EINVAL;
> +
>  	/* Make sure drawing engine can handle the font */
> -	if (!(info->pixmap.blit_x & (1 << (font->width - 1))) ||
> -	    !(info->pixmap.blit_y & (1 << (font->height - 1))))
> +	if (!(info->pixmap.blit_x & (1U << (font->width - 1))) ||
> +	    !(info->pixmap.blit_y & (1U << (font->height - 1))))
>  		return -EINVAL;
>  
>  	/* Make sure driver can handle the font length */
> 
> 

^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: [PATCH] fbcon: Check font dimension limits
  2023-01-26  0:49 ` [PATCH] fbcon: Check font dimension limits Samuel Thibault
  2023-01-26  0:51   ` Samuel Thibault
@ 2023-01-26  7:43   ` Greg KH
  2023-01-26  9:08     ` Jiri Slaby
  2023-01-29 15:13     ` Samuel Thibault
  2023-01-26  9:02   ` Jiri Slaby
  2 siblings, 2 replies; 7+ messages in thread
From: Greg KH @ 2023-01-26  7:43 UTC (permalink / raw)
  To: Samuel Thibault
  Cc: Daniel Vetter, Helge Deller, linux-fbdev, dri-devel,
	linux-kernel, stable, Sanan Hasanov

On Thu, Jan 26, 2023 at 01:49:12AM +0100, Samuel Thibault wrote:
> blit_x and blit_y are uint32_t, so fbcon currently cannot support fonts
> larger than 32x32.

"u32" you mean, right?

> The 32x32 case also needs shifting an unsigned int, to properly set bit
> 31, otherwise we get "UBSAN: shift-out-of-bounds in fbcon_set_font",
> as reported on
> 
> http://lore.kernel.org/all/IA1PR07MB98308653E259A6F2CE94A4AFABCE9@IA1PR07MB9830.namprd07.prod.outlook.com

Odd blank line?


> Kernel Branch: 6.2.0-rc5-next-20230124
> Kernel config: https://drive.google.com/file/d/1F-LszDAizEEH0ZX0HcSR06v5q8FPl2Uv/view?usp=sharing
> Reproducer: https://drive.google.com/file/d/1mP1jcLBY7vWCNM60OMf-ogw-urQRjNrm/view?usp=sharing

What are all of these lines for?

> 
> Reported-by: Sanan Hasanov <sanan.hasanov@Knights.ucf.edu>
> Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>

What commit id does this fix?  Should it go to stable kernels?

> 
> Index: linux-6.0/drivers/video/fbdev/core/fbcon.c
> ===================================================================
> --- linux-6.0.orig/drivers/video/fbdev/core/fbcon.c
> +++ linux-6.0/drivers/video/fbdev/core/fbcon.c
> @@ -2489,9 +2489,12 @@ static int fbcon_set_font(struct vc_data
>  	    h > FBCON_SWAP(info->var.rotate, info->var.yres, info->var.xres))
>  		return -EINVAL;
>  
> +	if (font->width > 32 || font->height > 32)
> +		return -EINVAL;
> +
>  	/* Make sure drawing engine can handle the font */
> -	if (!(info->pixmap.blit_x & (1 << (font->width - 1))) ||
> -	    !(info->pixmap.blit_y & (1 << (font->height - 1))))
> +	if (!(info->pixmap.blit_x & (1U << (font->width - 1))) ||
> +	    !(info->pixmap.blit_y & (1U << (font->height - 1))))

Are you sure this is still needed with the above check added?  If so,
why?  What is the difference in the compiled code?

thanks,

greg k-h

^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: [PATCH] fbcon: Check font dimension limits
  2023-01-26  7:43   ` Greg KH
@ 2023-01-26  9:08     ` Jiri Slaby
  2023-01-29 15:13     ` Samuel Thibault
  1 sibling, 0 replies; 7+ messages in thread
From: Jiri Slaby @ 2023-01-26  9:08 UTC (permalink / raw)
  To: Greg KH, Samuel Thibault
  Cc: Daniel Vetter, Helge Deller, linux-fbdev, dri-devel,
	linux-kernel, stable, Sanan Hasanov

On 26. 01. 23, 8:43, Greg KH wrote:
>> --- linux-6.0.orig/drivers/video/fbdev/core/fbcon.c
>> +++ linux-6.0/drivers/video/fbdev/core/fbcon.c
>> @@ -2489,9 +2489,12 @@ static int fbcon_set_font(struct vc_data
>>   	    h > FBCON_SWAP(info->var.rotate, info->var.yres, info->var.xres))
>>   		return -EINVAL;
>>   
>> +	if (font->width > 32 || font->height > 32)
>> +		return -EINVAL;
>> +
>>   	/* Make sure drawing engine can handle the font */
>> -	if (!(info->pixmap.blit_x & (1 << (font->width - 1))) ||
>> -	    !(info->pixmap.blit_y & (1 << (font->height - 1))))
>> +	if (!(info->pixmap.blit_x & (1U << (font->width - 1))) ||
>> +	    !(info->pixmap.blit_y & (1U << (font->height - 1))))
> 
> Are you sure this is still needed with the above check added?  If so,
> why?  What is the difference in the compiled code?

For font->{width,height} == 32, definitely. IMO, 1 << 31 is undefined as 
1 << 31 cannot be represented by an (signed) int.

-- 
js
suse labs


^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: [PATCH] fbcon: Check font dimension limits
  2023-01-26  7:43   ` Greg KH
  2023-01-26  9:08     ` Jiri Slaby
@ 2023-01-29 15:13     ` Samuel Thibault
  1 sibling, 0 replies; 7+ messages in thread
From: Samuel Thibault @ 2023-01-29 15:13 UTC (permalink / raw)
  To: Greg KH
  Cc: Daniel Vetter, Helge Deller, linux-fbdev, dri-devel,
	linux-kernel, stable, Sanan Hasanov

Greg KH, le jeu. 26 janv. 2023 08:43:02 +0100, a ecrit:
> On Thu, Jan 26, 2023 at 01:49:12AM +0100, Samuel Thibault wrote:
> > blit_x and blit_y are uint32_t, so fbcon currently cannot support fonts
> > larger than 32x32.
> 
> "u32" you mean, right?

Right :)

> > The 32x32 case also needs shifting an unsigned int, to properly set bit
> > 31, otherwise we get "UBSAN: shift-out-of-bounds in fbcon_set_font",
> > as reported on
> > 
> > http://lore.kernel.org/all/IA1PR07MB98308653E259A6F2CE94A4AFABCE9@IA1PR07MB9830.namprd07.prod.outlook.com
> 
> Odd blank line?

Not sure what you mean? I found it easier to read to put a blank line
between the text and the references.

> > Kernel Branch: 6.2.0-rc5-next-20230124
> > Kernel config: https://drive.google.com/file/d/1F-LszDAizEEH0ZX0HcSR06v5q8FPl2Uv/view?usp=sharing
> > Reproducer: https://drive.google.com/file/d/1mP1jcLBY7vWCNM60OMf-ogw-urQRjNrm/view?usp=sharing
> 
> What are all of these lines for?

They provide the references that were set in the original report

http://lore.kernel.org/all/IA1PR07MB98308653E259A6F2CE94A4AFABCE9@IA1PR07MB9830.namprd07.prod.outlook.com

Arguably the "branch" and "config" are not that useful since the bug has
been there for more than a dozen years, but notably the "Reproducer" is
useful to provide a userland program that triggers the UB.

> > Reported-by: Sanan Hasanov <sanan.hasanov@Knights.ucf.edu>
> > Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
> 
> What commit id does this fix?

I though it was there forever, but it seems the check was added in 2007,
so I'll add it in next version.

> Should it go to stable kernels?

Yes. I added stable in Cc of the mail but missed adding it in the text,
I will add it.

> > Index: linux-6.0/drivers/video/fbdev/core/fbcon.c
> > ===================================================================
> > --- linux-6.0.orig/drivers/video/fbdev/core/fbcon.c
> > +++ linux-6.0/drivers/video/fbdev/core/fbcon.c
> > @@ -2489,9 +2489,12 @@ static int fbcon_set_font(struct vc_data
> >  	    h > FBCON_SWAP(info->var.rotate, info->var.yres, info->var.xres))
> >  		return -EINVAL;
> >  
> > +	if (font->width > 32 || font->height > 32)
> > +		return -EINVAL;
> > +
> >  	/* Make sure drawing engine can handle the font */
> > -	if (!(info->pixmap.blit_x & (1 << (font->width - 1))) ||
> > -	    !(info->pixmap.blit_y & (1 << (font->height - 1))))
> > +	if (!(info->pixmap.blit_x & (1U << (font->width - 1))) ||
> > +	    !(info->pixmap.blit_y & (1U << (font->height - 1))))
> 
> Are you sure this is still needed with the above check added?  If so,
> why?  What is the difference in the compiled code?

As mentioned by Jiri, yes in the 32 case it's needed otherwise it's UB.

Samuel

^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: [PATCH] fbcon: Check font dimension limits
  2023-01-26  0:49 ` [PATCH] fbcon: Check font dimension limits Samuel Thibault
  2023-01-26  0:51   ` Samuel Thibault
  2023-01-26  7:43   ` Greg KH
@ 2023-01-26  9:02   ` Jiri Slaby
  2023-01-29 15:04     ` Samuel Thibault
  2 siblings, 1 reply; 7+ messages in thread
From: Jiri Slaby @ 2023-01-26  9:02 UTC (permalink / raw)
  To: Samuel Thibault, gregkh, Daniel Vetter, Helge Deller
  Cc: linux-fbdev, dri-devel, linux-kernel, stable, Sanan Hasanov

On 26. 01. 23, 1:49, Samuel Thibault wrote:
> blit_x and blit_y are uint32_t, so fbcon currently cannot support fonts
> larger than 32x32.
> 
> The 32x32 case also needs shifting an unsigned int, to properly set bit
> 31, otherwise we get "UBSAN: shift-out-of-bounds in fbcon_set_font",
> as reported on
> 
> http://lore.kernel.org/all/IA1PR07MB98308653E259A6F2CE94A4AFABCE9@IA1PR07MB9830.namprd07.prod.outlook.com
> Kernel Branch: 6.2.0-rc5-next-20230124
> Kernel config: https://drive.google.com/file/d/1F-LszDAizEEH0ZX0HcSR06v5q8FPl2Uv/view?usp=sharing
> Reproducer: https://drive.google.com/file/d/1mP1jcLBY7vWCNM60OMf-ogw-urQRjNrm/view?usp=sharing
> 
> Reported-by: Sanan Hasanov <sanan.hasanov@Knights.ucf.edu>
> Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
> 
> Index: linux-6.0/drivers/video/fbdev/core/fbcon.c
> ===================================================================
> --- linux-6.0.orig/drivers/video/fbdev/core/fbcon.c
> +++ linux-6.0/drivers/video/fbdev/core/fbcon.c
> @@ -2489,9 +2489,12 @@ static int fbcon_set_font(struct vc_data
>   	    h > FBCON_SWAP(info->var.rotate, info->var.yres, info->var.xres))
>   		return -EINVAL;
>   
> +	if (font->width > 32 || font->height > 32)
> +		return -EINVAL;
> +
>   	/* Make sure drawing engine can handle the font */
> -	if (!(info->pixmap.blit_x & (1 << (font->width - 1))) ||
> -	    !(info->pixmap.blit_y & (1 << (font->height - 1))))
> +	if (!(info->pixmap.blit_x & (1U << (font->width - 1))) ||
> +	    !(info->pixmap.blit_y & (1U << (font->height - 1))))

So use BIT() properly then? That should be used in all these shifts 
anyway. Exactly to avoid UB.

thanks,
-- 
js
suse labs


^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: [PATCH] fbcon: Check font dimension limits
  2023-01-26  9:02   ` Jiri Slaby
@ 2023-01-29 15:04     ` Samuel Thibault
  0 siblings, 0 replies; 7+ messages in thread
From: Samuel Thibault @ 2023-01-29 15:04 UTC (permalink / raw)
  To: Jiri Slaby
  Cc: gregkh, Daniel Vetter, Helge Deller, linux-fbdev, dri-devel,
	linux-kernel, stable, Sanan Hasanov

Jiri Slaby, le jeu. 26 janv. 2023 10:02:55 +0100, a ecrit:
> On 26. 01. 23, 1:49, Samuel Thibault wrote:
> > Index: linux-6.0/drivers/video/fbdev/core/fbcon.c
> > ===================================================================
> > --- linux-6.0.orig/drivers/video/fbdev/core/fbcon.c
> > +++ linux-6.0/drivers/video/fbdev/core/fbcon.c
> > @@ -2489,9 +2489,12 @@ static int fbcon_set_font(struct vc_data
> >   	    h > FBCON_SWAP(info->var.rotate, info->var.yres, info->var.xres))
> >   		return -EINVAL;
> > +	if (font->width > 32 || font->height > 32)
> > +		return -EINVAL;
> > +
> >   	/* Make sure drawing engine can handle the font */
> > -	if (!(info->pixmap.blit_x & (1 << (font->width - 1))) ||
> > -	    !(info->pixmap.blit_y & (1 << (font->height - 1))))
> > +	if (!(info->pixmap.blit_x & (1U << (font->width - 1))) ||
> > +	    !(info->pixmap.blit_y & (1U << (font->height - 1))))
> 
> So use BIT() properly then? That should be used in all these shifts anyway.
> Exactly to avoid UB.

Right, I'll use that in next version.

Samuel

^ permalink raw reply	[flat|nested] 7+ messages in thread

end of thread, other threads:[~2023-01-29 15:13 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
     [not found] <20230126004911.869923511@ens-lyon.org>
2023-01-26  0:49 ` [PATCH] fbcon: Check font dimension limits Samuel Thibault
2023-01-26  0:51   ` Samuel Thibault
2023-01-26  7:43   ` Greg KH
2023-01-26  9:08     ` Jiri Slaby
2023-01-29 15:13     ` Samuel Thibault
2023-01-26  9:02   ` Jiri Slaby
2023-01-29 15:04     ` Samuel Thibault

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