[PATCH 4.8 20/35] drm/i915: Dont touch NULL sg on i915_gem_object_get_pages_gtt() error

[Greg Kroah-Hartman]

4.8-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>

commit 2420489bcb8910188578acc0c11c75445c2e4b92 upstream.

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@xxxxxxxxxx>
Fixes: e227330223a7 ("drm/i915: avoid leaking DMA mappings")
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Imre Deak <imre.deak@xxxxxxxxx>
Link: http://patchwork.freedesktop.org/patch/msgid/20161114112930.2033-1-chris@xxxxxxxxxxxxxxxxxx
Reviewed-by: Matthew Auld <matthew.auld@xxxxxxxxx>
(cherry picked from commit b17993b7b29612369270567643bcff814f4b3d7f)
Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/gpu/drm/i915/i915_gem.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2540,7 +2540,7 @@ i915_gem_object_get_pages_gtt(struct drm
 			page = shmem_read_mapping_page(mapping, i);
 			if (IS_ERR(page)) {
 				ret = PTR_ERR(page);
-				goto err_pages;
+				goto err_sg;
 			}
 		}
 #ifdef CONFIG_SWIOTLB
@@ -2583,8 +2583,9 @@ i915_gem_object_get_pages_gtt(struct drm
 
 	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);