Re: [PATCH] fbcon: Fix OOB access in font allocation

[Qianqiang Liu <qianqiang.liu@163.com>]

On Mon, Sep 22, 2025 at 03:45:54PM +0200, Thomas Zimmermann wrote:
> Commit 1a194e6c8e1e ("fbcon: fix integer overflow in fbcon_do_set_font")
> introduced an out-of-bounds access by storing data and allocation sizes
> in the same variable. Restore the old size calculation and use the new
> variable 'alloc_size' for the allocation.
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> Fixes: 1a194e6c8e1e ("fbcon: fix integer overflow in fbcon_do_set_font")
> Reported-by: Jani Nikula <jani.nikula@linux.intel.com>
> Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/15020
> Cc: Samasth Norway Ananda <samasth.norway.ananda@oracle.com>
> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: George Kennedy <george.kennedy@oracle.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Simona Vetter <simona@ffwll.ch>
> Cc: Helge Deller <deller@gmx.de>
> Cc: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
> Cc: Sam Ravnborg <sam@ravnborg.org>
> Cc: Qianqiang Liu <qianqiang.liu@163.com>
> Cc: Shixiong Ou <oushixiong@kylinos.cn>
> Cc: Kees Cook <kees@kernel.org>
> Cc: <stable@vger.kernel.org> # v5.9+
> Cc: Zsolt Kajtar <soci@c64.rulez.org>
> ---
>  drivers/video/fbdev/core/fbcon.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
> index 5fade44931b8..c1c0cdd7597c 100644
> --- a/drivers/video/fbdev/core/fbcon.c
> +++ b/drivers/video/fbdev/core/fbcon.c
> @@ -2518,7 +2518,7 @@ static int fbcon_set_font(struct vc_data *vc, const struct console_font *font,
>  	unsigned charcount = font->charcount;
>  	int w = font->width;
>  	int h = font->height;
> -	int size;
> +	int size, alloc_size;
>  	int i, csum;
>  	u8 *new_data, *data = font->data;
>  	int pitch = PITCH(font->width);
> @@ -2551,10 +2551,10 @@ static int fbcon_set_font(struct vc_data *vc, const struct console_font *font,
>  		return -EINVAL;
>  
>  	/* Check for overflow in allocation size calculation */
> -	if (check_add_overflow(FONT_EXTRA_WORDS * sizeof(int), size, &size))
> +	if (check_add_overflow(FONT_EXTRA_WORDS * sizeof(int), size, &alloc_size))
>  		return -EINVAL;
>  
> -	new_data = kmalloc(size, GFP_USER);
> +	new_data = kmalloc(alloc_size, GFP_USER);
>  
>  	if (!new_data)
>  		return -ENOMEM;
> -- 
> 2.51.0

Reviewed-by: Qianqiang Liu <qianqiang.liu@163.com>

-- 
Best,
Qianqiang Liu