Messages in this thread Patch in this message | | | Date | Thu, 2 Jun 2022 23:42:02 +0300 | From | Ville Syrjälä <> | Subject | Re: [PATCH 2/3] drm/display/dp_mst: Fix drm_atomic_get_mst_topology_state() |
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On Thu, Jun 02, 2022 at 04:17:56PM -0400, Lyude Paul wrote: > I noticed a rather surprising issue here while working on removing all of > the non-atomic MST code: drm_atomic_get_mst_topology_state() doesn't check > the return value of drm_atomic_get_private_obj_state() and instead just > passes it directly to to_dp_mst_topology_state(). This means that if we > hit a deadlock or something else which would return an error code pointer, > we'll likely segfault the kernel. > > This is definitely another one of those fixes where I'm astonished we > somehow managed never to discover this issue until now…
It has been discussed before.
struct drm_dp_mst_topology_state { struct drm_private_state base; ... }
so offsetof(base)==0.
> > Signed-off-by: Lyude Paul <lyude@redhat.com> > Fixes: a4370c777406 ("drm/atomic: Make private objs proper objects") > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> > Cc: <stable@vger.kernel.org> # v4.14+ > --- > drivers/gpu/drm/display/drm_dp_mst_topology.c | 2 +- > include/drm/display/drm_dp_mst_helper.h | 2 ++ > 2 files changed, 3 insertions(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gpu/drm/display/drm_dp_mst_topology.c > index d84673b3294b..d6e595b95f07 100644 > --- a/drivers/gpu/drm/display/drm_dp_mst_topology.c > +++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c > @@ -5468,7 +5468,7 @@ EXPORT_SYMBOL(drm_dp_mst_topology_state_funcs); > struct drm_dp_mst_topology_state *drm_atomic_get_mst_topology_state(struct drm_atomic_state *state, > struct drm_dp_mst_topology_mgr *mgr) > { > - return to_dp_mst_topology_state(drm_atomic_get_private_obj_state(state, &mgr->base)); > + return to_dp_mst_topology_state_safe(drm_atomic_get_private_obj_state(state, &mgr->base)); > } > EXPORT_SYMBOL(drm_atomic_get_mst_topology_state); > > diff --git a/include/drm/display/drm_dp_mst_helper.h b/include/drm/display/drm_dp_mst_helper.h > index 10adec068b7f..fe7577e7f305 100644 > --- a/include/drm/display/drm_dp_mst_helper.h > +++ b/include/drm/display/drm_dp_mst_helper.h > @@ -541,6 +541,8 @@ struct drm_dp_payload { > }; > > #define to_dp_mst_topology_state(x) container_of(x, struct drm_dp_mst_topology_state, base) > +#define to_dp_mst_topology_state_safe(x) \ > + container_of_safe(x, struct drm_dp_mst_topology_state, base)
Wasn't aware of container_of_safe(). I suppose no real harm in using it. Not sure why we'd even keep the non-safe version around?
Though the use of container_of_safe() everywhere won't help when "casting" the other way (&foo->base, when foo==NULL/errptr). In order to make that work for non-zero offsets we'd have to introduce a casting macro for that direction as well.
> > struct drm_dp_vcpi_allocation { > struct drm_dp_mst_port *port; > -- > 2.35.3
-- Ville Syrjälä Intel
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