CVE-2026-63826

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

fbdev: fix use-after-free in store_modes()

store_modes() replaces a framebuffer's modelist with modes from userspace.

On success it frees the old modelist with fb_destroy_modelist(). Two

fields still point into that freed list.

One pointer is fb_display[i].mode, the mode a console is using.

fbcon_new_modelist() moves these pointers to the new list. It only does so

for consoles still mapped to the framebuffer. An unmapped console is

skipped and keeps its stale pointer. Unbinding fbcon, for example, sets

con2fb_map[i] to -1 but leaves fb_display[i].mode set. An

FBIOPUT_VSCREENINFO ioctl with FB_ACTIVATE_INV_MODE later reaches

fbcon_mode_deleted(). That function reads the stale fb_display[i].mode

through fb_mode_is_equal(). The read is a use-after-free.

The other pointer is fb_info->mode, the current mode. It is set through

the mode sysfs attribute. store_modes() does not update fb_info->mode, so

it is left pointing into the freed list. show_mode(), the attribute's read

handler, dereferences the stale fb_info->mode through mode_string(). The

read is a use-after-free.

Clear both pointers before freeing the list. Commit a1f305893074 ("fbcon:

Set fb_display[i]->mode to NULL when the mode is released") added the

helper fbcon_delete_modelist(). It clears every fb_display[i].mode that

points into a given list. So far it is called only from the unregister

path. Call it from store_modes() too, and set fb_info->mode to NULL.