CVE-2026-53403

In the Linux kernel, the following vulnerability has been resolved:

fbdev: Fix fb_new_modelist to prevent null-ptr-deref in fb_videomode_to_var

info->var, a framebuffer's current mode, is expected to have a matching

entry in info->modelist. var_to_display() relies on this and treats a

failed fb_match_mode() as "This should not happen". fb_set_var() keeps it

true by adding the mode to the list on every change, and

do_register_framebuffer() does the same at registration.

store_modes() replaces the modelist from userspace. fb_new_modelist()

validates the new modes but does not check that info->var still has a

match. It relies on fbcon_new_modelist() to re-point consoles, but that

only handles consoles mapped to the framebuffer. With fbcon unbound there

are none, so info->var is left describing a mode that is no longer in the

list.

A later console takeover runs var_to_display(), where fb_match_mode()

returns NULL and leaves fb_display[i].mode NULL. fbcon_switch() passes it

to display_to_var(), and fb_videomode_to_var() dereferences the NULL mode.

Keep the current mode in the list in fb_new_modelist(), the same way

fb_set_var() does.