Clip memory range to screen-buffer size to avoid out-of-bounds access in fbdev deferred I/O's damage handling. Fbdev's deferred I/O can only track pages. From the range of pages, the damage handler computes the clipping rectangle for the display update. If the fbdev screen buffer ends near the beginning of a page, that page could contain more scanlines. The damage handler would then track these non-existing scanlines as dirty and provoke an out-of-bounds access during the screen update. Hence, clip the maximum memory range to the size of the screen buffer. While at it, rename the variables min/max to min_off/max_off in drm_fb_helper_deferred_io(). This avoids confusion with the macros of the same name. Reported-by: Nuno Gonçalves <nunojpg@gmail.com> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de> Reviewed-by: Javier Martinez Canillas <javierm@redhat.com> Tested-by: Nuno Gonçalves <nunojpg@gmail.com> Fixes: 67b723f5b742 ("drm/fb-helper: Calculate damaged area in separate helper") Cc: Thomas Zimmermann <tzimmermann@suse.de> Cc: Javier Martinez Canillas <javierm@redhat.com> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com> Cc: Maxime Ripard <mripard@kernel.org> Cc: <stable@vger.kernel.org> # v5.18+ Link: https://patchwork.freedesktop.org/patch/msgid/20220621104617.8817-1-tzimmermann@suse.de