In order to prevent a potential NULL deference with hostile userspace,
we need to check whether the ioctl was passed an invalid args pointer.

Reported-by: Tommi Rantala <tt.rant...@gmail.com>
Link: 
http://lkml.kernel.org/r/ca+ydwtpubvbwxbt-tdgpuvj1eu7itmcho_2b3w13hkd5+jw...@mail.gmail.com
Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem_execbuffer.c |   11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c 
b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 365e41a..9f5602e 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -1103,7 +1103,11 @@ i915_gem_execbuffer(struct drm_device *dev, void *data,
        struct drm_i915_gem_exec_object2 *exec2_list = NULL;
        int ret, i;
 
-       if (args->buffer_count < 1) {
+       if (args == NULL)
+               return -EINVAL;
+
+       if (args->buffer_count < 1 ||
+           args->buffer_count > INT_MAX / sizeof(*exec2_list)) {
                DRM_DEBUG("execbuf with %d buffers\n", args->buffer_count);
                return -EINVAL;
        }
@@ -1182,8 +1186,11 @@ i915_gem_execbuffer2(struct drm_device *dev, void *data,
        struct drm_i915_gem_exec_object2 *exec2_list = NULL;
        int ret;
 
+       if (args == NULL)
+               return -EINVAL;
+
        if (args->buffer_count < 1 ||
-           args->buffer_count > UINT_MAX / sizeof(*exec2_list)) {
+           args->buffer_count > INT_MAX / sizeof(*exec2_list)) {
                DRM_DEBUG("execbuf2 with %d buffers\n", args->buffer_count);
                return -EINVAL;
        }
-- 
1.7.10.4

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