From: Hsin-Yi Wang hsinyi@chromium.org

mainline inclusion from mainline-v6.9-rc1 commit c958e86e9cc1b48cac004a6e245154dfba8e163b category: bugfix bugzilla: https://gitee.com/src-openeuler/kernel/issues/I9HK5V CVE: CVE-2024-26874

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id...

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It's possible that mtk_crtc->event is NULL in mtk_drm_crtc_finish_page_flip().

pending_needs_vblank value is set by mtk_crtc->event, but in mtk_drm_crtc_atomic_flush(), it's is not guarded by the same lock in mtk_drm_finish_page_flip(), thus a race condition happens.

Consider the following case:

CPU1 CPU2 step 1: mtk_drm_crtc_atomic_begin() mtk_crtc->event is not null, step 1: mtk_drm_crtc_atomic_flush: mtk_drm_crtc_update_config( !!mtk_crtc->event) step 2: mtk_crtc_ddp_irq -> mtk_drm_finish_page_flip: lock mtk_crtc->event set to null, pending_needs_vblank set to false unlock pending_needs_vblank set to true,

step 2: mtk_crtc_ddp_irq -> mtk_drm_finish_page_flip called again, pending_needs_vblank is still true //null pointer

Instead of guarding the entire mtk_drm_crtc_atomic_flush(), it's more efficient to just check if mtk_crtc->event is null before use.

Fixes: 119f5173628a ("drm/mediatek: Add DRM Driver for Mediatek SoC MT8173.") Signed-off-by: Hsin-Yi Wang hsinyi@chromium.org Reviewed-by: CK Hu ck.hu@mediatek.com Link: https://patchwork.kernel.org/project/dri-devel/patch/20240223212404.3709690-... Signed-off-by: Chun-Kuang Hu chunkuang.hu@kernel.org Signed-off-by: Xiongfeng Wang wangxiongfeng2@huawei.com --- drivers/gpu/drm/mediatek/mtk_drm_crtc.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_drm_crtc.c b/drivers/gpu/drm/mediatek/mtk_drm_crtc.c index 92ecb9bf982c..42da8bb4b7c3 100644 --- a/drivers/gpu/drm/mediatek/mtk_drm_crtc.c +++ b/drivers/gpu/drm/mediatek/mtk_drm_crtc.c @@ -79,11 +79,13 @@ static void mtk_drm_crtc_finish_page_flip(struct mtk_drm_crtc *mtk_crtc) struct drm_crtc *crtc = &mtk_crtc->base; unsigned long flags;

- spin_lock_irqsave(&crtc->dev->event_lock, flags); - drm_crtc_send_vblank_event(crtc, mtk_crtc->event); - drm_crtc_vblank_put(crtc); - mtk_crtc->event = NULL; - spin_unlock_irqrestore(&crtc->dev->event_lock, flags); + if (mtk_crtc->event) { + spin_lock_irqsave(&crtc->dev->event_lock, flags); + drm_crtc_send_vblank_event(crtc, mtk_crtc->event); + drm_crtc_vblank_put(crtc); + mtk_crtc->event = NULL; + spin_unlock_irqrestore(&crtc->dev->event_lock, flags); + } }

static void mtk_drm_finish_page_flip(struct mtk_drm_crtc *mtk_crtc)