On 2022-12-07 09:21, Jiasheng Jiang wrote:
As kzalloc may fail and return NULL pointer, it should be better to check
the return value in order to avoid the NULL pointer dereference in
__drm_atomic_helper_connector_reset.
This commit message is nonsense; if
__drm_atomic_helper_connector_reset() would dereference the NULL implied
by &mw_state->base, it would equally still dereference the explicit NULL
pointer passed after this patch.
The current code works out OK because "base" is the first member of
struct malidp_mw_connector_state, thus if mw_state is NULL then
&mw_state->base == NULL + 0 == NULL. Now you *could* argue that this
isn't robust if the layout of struct malidp_mw_connector_state ever
changes, and that could be a valid justification for making this change,
but the reason given certainly isn't.
Arithmetic on a (potentially) NULL pointer may well be a sign that it's
worth a closer look to check whether it really is what the code intended
to do, but don't automatically assume it has to be a bug. Otherwise,
good luck with "fixing" every user of container_of() throughout the
entire kernel.
Thanks,
Robin.
Fixes: 8cbc5caf36ef ("drm: mali-dp: Add writeback connector")
Signed-off-by: Jiasheng Jiang <jiasheng@xxxxxxxxxxx>
---
drivers/gpu/drm/arm/malidp_mw.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/arm/malidp_mw.c b/drivers/gpu/drm/arm/malidp_mw.c
index ef76d0e6ee2f..fe4474c2ddcf 100644
--- a/drivers/gpu/drm/arm/malidp_mw.c
+++ b/drivers/gpu/drm/arm/malidp_mw.c
@@ -72,7 +72,11 @@ static void malidp_mw_connector_reset(struct drm_connector *connector)
__drm_atomic_helper_connector_destroy_state(connector->state);
kfree(connector->state);
- __drm_atomic_helper_connector_reset(connector, &mw_state->base);
+
+ if (mw_state)
+ __drm_atomic_helper_connector_reset(connector, &mw_state->base);
+ else
+ __drm_atomic_helper_connector_reset(connector, NULL);
}
static enum drm_connector_status
