High [CVE-2026-63826] fix use-after-free in store_modes
This high-severity Red Hat Linux advisory covers CVE-2026-63826 affecting Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Red Hat package: kernel-rt.
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Summary
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 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(). 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.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative. Check it before change work.
Official advisory · medium-confidence parse· fetched 7 days ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists. Confirm against the vendor advisory.
Official advisory · medium-confidence parse· fetched 7 days ago·verify at source
Mitigation
The source record does not include mitigation steps. That does not mean no fix exists. Read the vendor advisory below for the authoritative guidance.
Official advisory · medium-confidence parse· fetched 7 days ago·verify at source
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