fbcon: Fix OOB access in font allocation

Commit 1a194e6 ("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: 1a194e6 ("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
Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/6201
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>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Qianqiang Liu <qianqiang.liu@163.com>
Link: https://lore.kernel.org/r/20250922134619.257684-1-tzimmermann@suse.de

Author: tdz

drivers/video/fbdev/core/fbcon.c

@@ -2504,7 +2504,7 @@ 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);
@@ -2537,10 +2537,10 @@ 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;