[Intel-gfx] [PATCH] drm/i915: Fix use after free in logical_render_ring_init

[Tvrtko Ursulin]

From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

Commit 3b3f1650b1ca ("drm/i915: Allocate intel_engine_cs
structure only for the enabled engines") introduced the
dynanically allocated engine instances and created an
potential use after free scenario in logical_render_ring_init
where lrc_destroy_wa_ctx_obj could be called after the engine
instance has been freed.

This can only happen during engine setup/init error handling
which luckily does not happen ever in practice.

Fix is to not call lrc_destroy_wa_ctx_obj since it would have
already been executed from the preceding engine cleanup.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Reported-by: Dan Carpenter <dan.carpenter at oracle.com>
Fixes: 3b3f1650b1ca ("drm/i915: Allocate intel_engine_cs structure only for the enabled engines")
Cc: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Cc: Daniel Vetter <daniel.vetter at intel.com>
Cc: Jani Nikula <jani.nikula at linux.intel.com>
---
 drivers/gpu/drm/i915/intel_lrc.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 8b412880e88c..877adedbf833 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1965,12 +1965,7 @@ int logical_render_ring_init(struct intel_engine_cs *engine)
 			  ret);
 	}
 
-	ret = logical_ring_init(engine);
-	if (ret) {
-		lrc_destroy_wa_ctx_obj(engine);
-	}
-
-	return ret;
+	return logical_ring_init(engine);
 }
 
 int logical_xcs_ring_init(struct intel_engine_cs *engine)
-- 
2.7.4