drm/i915: fix integer overflow in i915_gem_do_execbuffer()

BugLink: http://bugs.launchpad.net/bugs/996109

commit 44afb3a04391a74309d16180d1e4f8386fdfa745 upstream.

On 32-bit systems, a large args->num_cliprects from userspace via ioctl
may overflow the allocation size, leading to out-of-bounds access.

This vulnerability was introduced in commit 432e58ed ("drm/i915: Avoid
allocation for execbuffer object list").

Signed-off-by: Xi Wang <xi.wang@gmail.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 71215342724..bc927ae3164 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -1046,6 +1046,11 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
                         return -EINVAL;
                 }
 
+                if (args->num_cliprects > UINT_MAX / sizeof(*cliprects)) {
+                        DRM_DEBUG("execbuf with %u cliprects\n",
+                                  args->num_cliprects);
+                        return -EINVAL;
+                }
                 cliprects = kmalloc(args->num_cliprects * sizeof(*cliprects),
                                     GFP_KERNEL);
                 if (cliprects == NULL) {