From: Nguyen Ngoc Thang <ngocthang2710.1999@gmail.com> stable inclusion from stable-v6.6.160 commit 4a2006c675758f0c765b36fec6b49d17e89159cf category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/20885 CVE: CVE-2026-99007 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- commit 755c94d178b7e972bb766199d34e4ba4f63a89eb upstream. __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. Reported-by: syzbot+ca23c8570669ead78867@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=ca23c8570669ead78867 Fixes: ca91a2758fce ("drm/fb-helper: Support deferred setup") Cc: stable@vger.kernel.org Signed-off-by: Nguyen Ngoc Thang <ngocthang2710.1999@gmail.com> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de> Link: https://patch.msgid.link/20260927075434.72658-1-ngocthang2710.1999@gmail.com Link: https://patch.msgid.link/20260917154743.1621-1-shechenglong@xfusion.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Zhang Hongtao <zhanghongtao35@huawei.com> --- drivers/gpu/drm/drm_fb_helper.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c index 9691c93f19a0d..11dfd2b906c3c 100644 --- a/drivers/gpu/drm/drm_fb_helper.c +++ b/drivers/gpu/drm/drm_fb_helper.c @@ -1853,10 +1853,10 @@ __drm_fb_helper_initial_config_and_unlock(struct drm_fb_helper *fb_helper) drm_client_modeset_probe(&fb_helper->client, width, height); ret = drm_fb_helper_single_fb_probe(fb_helper); if (ret < 0) { - if (ret == -EAGAIN) { - fb_helper->deferred_setup = true; + /* modesets are probed but fb_helper->fb isn't; defer restore too */ + fb_helper->deferred_setup = true; + if (ret == -EAGAIN) ret = 0; - } mutex_unlock(&fb_helper->lock); return ret; -- 2.43.0