[PATCH 1/2] drm/sched: memset() 'job' in drm_sched_job_init()

[Philipp Stanner]

drm_sched_job_init() has no control over how users allocate struct
drm_sched_job. Unfortunately, the function can also not set some struct
members such as job->sched.

This could theoretically lead to UB by users dereferencing the struct's
pointer members too early.

It is easier to debug such issues if these pointers are initialized to
NULL, so dereferencing them causes a NULL pointer exception.
Accordingly, drm_sched_entity_init() does precisely that and initializes
its struct with memset().

Initialize parameter "job" to 0 in drm_sched_job_init().

Signed-off-by: Philipp Stanner <pstanner at redhat.com>
---
No changes in v2.

+CC Christian and Tvrtko in this thread.
Would be cool if someone can do a review.
---
 drivers/gpu/drm/scheduler/sched_main.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
index dab8cca79eb7..2e0e5a9577d1 100644
--- a/drivers/gpu/drm/scheduler/sched_main.c
+++ b/drivers/gpu/drm/scheduler/sched_main.c
@@ -796,6 +796,14 @@ int drm_sched_job_init(struct drm_sched_job *job,
 		return -EINVAL;
 	}
 
+	/*
+	 * We don't know for sure how the user has allocated. Thus, zero the
+	 * struct so that unallowed (i.e., too early) usage of pointers that
+	 * this function does not set is guaranteed to lead to a NULL pointer
+	 * exception instead of UB.
+	 */
+	memset(job, 0, sizeof(*job));
+
 	job->entity = entity;
 	job->credits = credits;
 	job->s_fence = drm_sched_fence_alloc(entity, owner);
-- 
2.47.0