Messages in this thread | | | Date | Wed, 7 Dec 2022 13:59:04 +0000 | Subject | Re: [PATCH] drm: mali-dp: Add check for kzalloc | From | Robin Murphy <> |
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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@iscas.ac.cn> > --- > 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
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