Bug 2502208 (CVE-2026-53403)

Summary: CVE-2026-53403 kernel: fbdev: Fix fb_new_modelist to prevent null-ptr-deref in fb_videomode_to_var
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
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OS: Linux   
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A flaw was found in the Linux kernel's framebuffer device (fbdev) subsystem. When a new modelist is set from userspace, the fb_new_modelist function fails to ensure that the current framebuffer mode remains valid within the updated list. This can lead to a null-pointer dereference if a console attempts to take over, resulting in a system crash and a Denial of Service (DoS).
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Description OSIDB Bzimport 2026-07-19 13:01:56 UTC 
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.
Comment 1 Keith Grant 2026-07-20 14:28:41 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026071959-CVE-2026-53403-6dc1@gregkh/T