drm/exynos: fix a possible null-pointer dereference due to data race in...

drm/exynos: fix a possible null-pointer dereference due to data race in exynos_drm_crtc_atomic_disable()

mainline inclusion
from mainline-v6.6-rc1
commit 2e63972a
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I917IV
CVE: CVE-2024-22386

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=2e63972a2de14482d0eae1a03a73e379f1c3f44c



-----------------------------------

The variable crtc->state->event is often protected by the lock
crtc->dev->event_lock when is accessed. However, it is accessed as a
condition of an if statement in exynos_drm_crtc_atomic_disable() without
holding the lock:

  if (crtc->state->event && !crtc->state->active)

However, if crtc->state->event is changed to NULL by another thread right
after the conditions of the if statement is checked to be true, a
null-pointer dereference can occur in drm_crtc_send_vblank_event():

  e->pipe = pipe;

To fix this possible null-pointer dereference caused by data race, the
spin lock coverage is extended to protect the if statement as well as the
function call to drm_crtc_send_vblank_event().

Reported-by: BassCheck <bass@buaa.edu.cn>
Link: https://sites.google.com/view/basscheck/home


Signed-off-by: Tuo Li <islituo@gmail.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Added relevant link.
Signed-off-by: Inki Dae <inki.dae@samsung.com>
Signed-off-by: Hui Tang <tanghui20@huawei.com>