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commit e64242caef18b4a5840b0e7a9bff37abd4f4f933 upstream. We need to prevent that users configure a screen size which is smaller than the currently selected font size. Otherwise rendering chars on the screen will access memory outside the graphics memory region. This patch adds a new function fbcon_modechange_possible() which implements this check and which later may be extended with other checks if necessary. The new function is called from the FBIOPUT_VSCREENINFO ioctl handler in fbmem.c, which will return -EINVAL if userspace asked for a too small screen size. Signed-off-by: Helge Deller <deller@gmx.de> Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org> Cc: stable@vger.kernel.org # v5.4+ Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>