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 <[email protected]>
Signed-off-by: Tuo Li <[email protected]>
---
drivers/gpu/drm/exynos/exynos_drm_crtc.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/exynos/exynos_drm_crtc.c b/drivers/gpu/drm/exynos/exynos_drm_crtc.c
index 4153f302de7c..d19e796c2061 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_crtc.c
+++ b/drivers/gpu/drm/exynos/exynos_drm_crtc.c
@@ -39,13 +39,12 @@ static void exynos_drm_crtc_atomic_disable(struct drm_crtc *crtc,
if (exynos_crtc->ops->atomic_disable)
exynos_crtc->ops->atomic_disable(exynos_crtc);
+ spin_lock_irq(&crtc->dev->event_lock);
if (crtc->state->event && !crtc->state->active) {
- spin_lock_irq(&crtc->dev->event_lock);
drm_crtc_send_vblank_event(crtc, crtc->state->event);
- spin_unlock_irq(&crtc->dev->event_lock);
-
crtc->state->event = NULL;
}
+ spin_unlock_irq(&crtc->dev->event_lock);
}
static int exynos_crtc_atomic_check(struct drm_crtc *crtc,
--
2.34.1
On 30/06/2023 04:19, Tuo Li wrote:
> 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 <[email protected]>
I cannot find this report. This is an open source work and public
collaboration. The "Reported-by" usually means that the issue was
reported to us, in some way, usually in public. Can we see the report?
Otherwise adding non-public, non-verifiable reports is useless and
clutters our report-credit-system.
Best regards,
Krzysztof
On 30/06/2023 04:19, Tuo Li wrote:
> 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 <[email protected]>
> Signed-off-by: Tuo Li <[email protected]>
Reviewed-by: Krzysztof Kozlowski <[email protected]>
Best regards,
Krzysztof
On 03/07/2023 05:00, Tuo Li wrote:
> Hello,
>
> Thanks for your reply! The report is publicly available at
> https://sites.google.com/view/basscheck/home. And this
> patch is from the 8th report on this website.
Great, thank you!
Best regards,
Krzysztof
> -----Original Message-----
> From: Tuo Li <[email protected]>
> Sent: Friday, June 30, 2023 11:19 AM
> To: [email protected]; [email protected];
> [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]
> Cc: [email protected]; [email protected];
> [email protected]; [email protected];
> [email protected]; Tuo Li <[email protected]>; BassCheck
> <[email protected]>
> Subject: [PATCH] drm/exynos: fix a possible null-pointer dereference due
> to data race in exynos_drm_crtc_atomic_disable()
>
> 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 <[email protected]>
> Signed-off-by: Tuo Li <[email protected]>
Applied.
Thanks,
Inki Dae
> ---
> drivers/gpu/drm/exynos/exynos_drm_crtc.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/exynos/exynos_drm_crtc.c
> b/drivers/gpu/drm/exynos/exynos_drm_crtc.c
> index 4153f302de7c..d19e796c2061 100644
> --- a/drivers/gpu/drm/exynos/exynos_drm_crtc.c
> +++ b/drivers/gpu/drm/exynos/exynos_drm_crtc.c
> @@ -39,13 +39,12 @@ static void exynos_drm_crtc_atomic_disable(struct
> drm_crtc *crtc,
> if (exynos_crtc->ops->atomic_disable)
> exynos_crtc->ops->atomic_disable(exynos_crtc);
>
> + spin_lock_irq(&crtc->dev->event_lock);
> if (crtc->state->event && !crtc->state->active) {
> - spin_lock_irq(&crtc->dev->event_lock);
> drm_crtc_send_vblank_event(crtc, crtc->state->event);
> - spin_unlock_irq(&crtc->dev->event_lock);
> -
> crtc->state->event = NULL;
> }
> + spin_unlock_irq(&crtc->dev->event_lock);
> }
>
> static int exynos_crtc_atomic_check(struct drm_crtc *crtc,
> --
> 2.34.1