Vulnerability CVE-2024-26874
Published: 2024-04-17

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

drm/mediatek: Fix a null pointer crash in mtk_drm_crtc_finish_page_flip

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.

 References:
https://git.kernel.org/stable/c/accdac6b71d5a2b84040c3d2234f53a60edc398e
https://git.kernel.org/stable/c/dfde84cc6c589f2a9f820f12426d97365670b731
https://git.kernel.org/stable/c/4688be96d20ffa49d2186523ee84f475f316fd49
https://git.kernel.org/stable/c/9beec711a17245b853d64488fd5b739031612340
https://git.kernel.org/stable/c/d2bd30c710475b2e29288827d2c91f9e6e2b91d7
https://git.kernel.org/stable/c/a3dd12b64ae8373a41a216a0b621df224210860a
https://git.kernel.org/stable/c/9acee29a38b4d4b70f1f583e5ef9a245db4db710
https://git.kernel.org/stable/c/3fc88b246a2fc16014e374040fc15af1d3752535
https://git.kernel.org/stable/c/c958e86e9cc1b48cac004a6e245154dfba8e163b
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