[PATCH] drm/i915/gem: Fix NULL deref in I915_CONTEXT_PARAM_SSEU

[Joonas Lahtinen <joonas.lahtinen@linux.intel.com>]

Setting context engine slot N into I915_ENGINE_CLASS_INVALID /
I915_ENGINE_CLASS_INVALID_NONE and attempting to apply
I915_CONTEXT_PARAM_SSEU to the same slot N will deref NULL.
Fix that.

Discovered using AI-assisted static analysis confirmed by
Intel Product Security.

Reported-by: Martin Hodo <martin.hodo@intel.com>
Fixes: d4433c7600f7 ("drm/i915/gem: Use the proto-context to handle create parameters (v5)")
Cc: Faith Ekstrand <faith.ekstrand@collabora.com>
Cc: Simona Vetter <simona.vetter@ffwll.ch>
Cc: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: <stable@vger.kernel.org> # v5.15+
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
---
 drivers/gpu/drm/i915/gem/i915_gem_context.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
index aeafe1742d30..347d1f2c05f5 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
@@ -850,7 +850,7 @@ static int set_proto_ctx_sseu(struct drm_i915_file_private *fpriv,
 		pe = &pc->user_engines[idx];
 
 		/* Only render engine supports RPCS configuration. */
-		if (pe->engine->class != RENDER_CLASS)
+		if (!pe->engine || pe->engine->class != RENDER_CLASS)
 			return -EINVAL;
 
 		sseu = &pe->sseu;
-- 
2.54.0