[PATCH 6.2 128/211] drm/ttm: Fix a NULL pointer dereference

[Greg Kroah-Hartman]

From: Thomas Hellström <thomas.hellstrom at linux.intel.com>

commit 9a9a8fe26751334b7739193a94eba741073b8a55 upstream.

The LRU mechanism may look up a resource in the process of being removed
from an object. The locking rules here are a bit unclear but it looks
currently like res->bo assignment is protected by the LRU lock, whereas
bo->resource is protected by the object lock, while *clearing* of
bo->resource is also protected by the LRU lock. This means that if
we check that bo->resource points to the LRU resource under the LRU
lock we should be safe.
So perform that check before deciding to swap out a bo. That avoids
dereferencing a NULL bo->resource in ttm_bo_swapout().

Fixes: 6a9b02899402 ("drm/ttm: move the LRU into resource handling v4")
Cc: Christian König <christian.koenig at amd.com>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Christian Koenig <christian.koenig at amd.com>
Cc: Huang Rui <ray.huang at amd.com>
Cc: Alex Deucher <alexander.deucher at amd.com>
Cc: Felix Kuehling <Felix.Kuehling at amd.com>
Cc: Philip Yang <Philip.Yang at amd.com>
Cc: Qiang Yu <qiang.yu at amd.com>
Cc: Matthew Auld <matthew.auld at intel.com>
Cc: Nirmoy Das <nirmoy.das at intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Cc: "Thomas Hellström" <thomas.hellstrom at linux.intel.com>
Cc: Anshuman Gupta <anshuman.gupta at intel.com>
Cc: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam at amd.com>
Cc: dri-devel at lists.freedesktop.org
Cc: <stable at vger.kernel.org> # v5.19+
Signed-off-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
Reviewed-by: Christian König <christian.koenig at amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230307144621.10748-2-thomas.hellstrom@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
---
 drivers/gpu/drm/ttm/ttm_device.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/gpu/drm/ttm/ttm_device.c
+++ b/drivers/gpu/drm/ttm/ttm_device.c
@@ -158,7 +158,7 @@ int ttm_device_swapout(struct ttm_device
 			struct ttm_buffer_object *bo = res->bo;
 			uint32_t num_pages;
 
-			if (!bo)
+			if (!bo || bo->resource != res)
 				continue;
 
 			num_pages = PFN_UP(bo->base.size);