3.16.60-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Matthew Auld <matthew.auld@intel.com>

commit 20943f984967477c906522112d2b6b5a29f94684 upstream.

Operating on a zero sized GEM userptr object will lead to explosions.

Fixes: 5cc9ed4b9a7a ("drm/i915: Introduce mapping of user pages into video memory (userptr) ioctl")
Testcase: igt/gem_userptr_blits/input-checking
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Chris Wilson <redacted>
Reviewed-by: Chris Wilson <redacted>
Signed-off-by: Chris Wilson <redacted>
Link: https://patchwork.freedesktop.org/patch/msgid/20180502195021.30900-1-matthew.auld@intel.com
(cherry picked from commit c11c7bfd213495784b22ef82a69b6489f8d0092f)
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Ben Hutchings <redacted>
---
 drivers/gpu/drm/i915/i915_gem_userptr.c | 3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/gpu/drm/i915/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/i915_gem_userptr.c

@@ -657,6 +657,9 @@ i915_gem_userptr_ioctl(struct drm_device
 			    I915_USERPTR_UNSYNCHRONIZED))
 		return -EINVAL;
 
+	if (!args->user_size)
+		return -EINVAL;
+
 	if (offset_in_page(args->user_ptr | args->user_size))
 		return -EINVAL;