drm/i915: Don't touch NULL sg on i915_gem_object_get_pages_gtt() error

On the DMA mapping error path, sg may be NULL (it has already been
marked as the last scatterlist entry), and we should avoid dereferencing
it again.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: e227330223a7 ("drm/i915: avoid leaking DMA mappings")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Imre Deak <imre.deak@intel.com>
Cc: stable@vger.kernel.org
Link: http://patchwork.freedesktop.org/patch/msgid/20161114112930.2033-1-chris@chris-wilson.co.uk
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
(cherry picked from commit b17993b7b29612369270567643bcff814f4b3d7f)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 91ab7e9d6d2ead0827c0b452f119062d8be50a0a..00eb4814b9131655b4ac441d7dbabed02c6ccc8e 100644 (file)
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2268,7 +2268,7 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
                        page = shmem_read_mapping_page(mapping, i);
                        if (IS_ERR(page)) {
                                ret = PTR_ERR(page);
-                               goto err_pages;
+                               goto err_sg;
                        }
                }
 #ifdef CONFIG_SWIOTLB
@@ -2311,8 +2311,9 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
 
        return 0;
 
-err_pages:
+err_sg:
        sg_mark_end(sg);
+err_pages:
        for_each_sgt_page(page, sgt_iter, st)
                put_page(page);
        sg_free_table(st);