CVE-2026-99007: drm/fb-helper: defer setup when fbdev_probe() fails, not just on -EAGAIN

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

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

drm/fb-helper: defer setup when fbdev_probe() fails, not just on -EAGAIN

__drm_fb_helper_initial_config_and_unlock() calls
drm_client_modeset_probe() first, which already fills in each
mode_set->mode/num_connectors for every connected output, and only
afterwards calls drm_fb_helper_single_fb_probe() to create
fb_helper->fb and wire it into those mode_sets via
drm_setup_crtcs_fb().

If drm_fb_helper_single_fb_probe() fails with anything other than
-EAGAIN (e.g. dev->driver->fbdev_probe() itself fails), the function
bails out before drm_setup_crtcs_fb() runs and before setting
fb_helper->deferred_setup. The client is left with mode_sets that
have a mode and connectors but mode_set->fb == NULL, and nothing
marks this fb_helper as needing a retry.

__drm_fb_helper_restore_fbdev_mode_unlocked() only skips committing
when fb_helper->deferred_setup is set, so a later .restore() call
(drm_lastclose() on process exit, in this report) commits the stale
mode_set through drm_client_modeset_commit() ->
drm_client_modeset_commit_atomic() -> __drm_atomic_helper_set_config(),
which hits WARN_ON(!set->fb).

Mark fb_helper->deferred_setup on any drm_fb_helper_single_fb_probe()
failure, not just -EAGAIN, so restore keeps skipping the commit until
a later hotplug event successfully re-probes and re-populates
mode_set->fb. The real error code is still returned to the caller
unchanged.

The Linux kernel CVE team has assigned CVE-2026-99007 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 4.14 with commit ca91a2758fcef6635626993557dd51cfbb6dd134 and fixed in 6.6.160 with commit 4a2006c675758f0c765b36fec6b49d17e89159cf
	Issue introduced in 4.14 with commit ca91a2758fcef6635626993557dd51cfbb6dd134 and fixed in 6.12.113 with commit 3b303696f61461b3569019d7fcac6a646652b2b4
	Issue introduced in 4.14 with commit ca91a2758fcef6635626993557dd51cfbb6dd134 and fixed in 6.18.57 with commit 4e7b508c7c60dec7a86b7eb2a1b7e6d174afa457
	Issue introduced in 4.14 with commit ca91a2758fcef6635626993557dd51cfbb6dd134 and fixed in 7.2.11 with commit d510ed273854177f0a3ed330145858b2fe667f81
	Issue introduced in 4.14 with commit ca91a2758fcef6635626993557dd51cfbb6dd134 and fixed in 7.3 with commit 755c94d178b7e972bb766199d34e4ba4f63a89eb

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-99007
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/gpu/drm/drm_fb_helper.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/4a2006c675758f0c765b36fec6b49d17e89159cf
	https://git.kernel.org/stable/c/3b303696f61461b3569019d7fcac6a646652b2b4
	https://git.kernel.org/stable/c/4e7b508c7c60dec7a86b7eb2a1b7e6d174afa457
	https://git.kernel.org/stable/c/d510ed273854177f0a3ed330145858b2fe667f81
	https://git.kernel.org/stable/c/755c94d178b7e972bb766199d34e4ba4f63a89eb