drm/fence: fix memory overwrite when setting out_fence fd

Currently if the userspace declares a int variable to store the out_fence
fd and pass it to OUT_FENCE_PTR the kernel will overwrite the 32 bits
above the int variable on 64 bits systems.

Fix this by making the internal storage of out_fence in the kernel a s32
pointer.

Reported-by: Chad Versace <chadversary@chromium.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
Fixes: beaf5af48034 ("drm/fence: add out-fences support")
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Rafael Antognolli <rafael.antognolli@intel.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-and-Tested-by: Chad Versace <chadversary@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1484317329-9293-1-git-send-email-gustavo@padovan.org

drivers/gpu/drm/drm_atomic.c

@@ -291,15 +291,15 @@ drm_atomic_get_crtc_state(struct drm_atomic_state *state,
 EXPORT_SYMBOL(drm_atomic_get_crtc_state);
 
 static void set_out_fence_for_crtc(struct drm_atomic_state *state,
-				   struct drm_crtc *crtc, s64 __user *fence_ptr)
+				   struct drm_crtc *crtc, s32 __user *fence_ptr)
 {
 	state->crtcs[drm_crtc_index(crtc)].out_fence_ptr = fence_ptr;
 }
 
-static s64 __user *get_out_fence_for_crtc(struct drm_atomic_state *state,
+static s32 __user *get_out_fence_for_crtc(struct drm_atomic_state *state,
 					  struct drm_crtc *crtc)
 {
-	s64 __user *fence_ptr;
+	s32 __user *fence_ptr;
 
 	fence_ptr = state->crtcs[drm_crtc_index(crtc)].out_fence_ptr;
 	state->crtcs[drm_crtc_index(crtc)].out_fence_ptr = NULL;
@@ -512,7 +512,7 @@ int drm_atomic_crtc_set_property(struct drm_crtc *crtc,
 		state->color_mgmt_changed |= replaced;
 		return ret;
 	} else if (property == config->prop_out_fence_ptr) {
-		s64 __user *fence_ptr = u64_to_user_ptr(val);
+		s32 __user *fence_ptr = u64_to_user_ptr(val);
 
 		if (!fence_ptr)
 			return 0;
@@ -1915,7 +1915,7 @@ EXPORT_SYMBOL(drm_atomic_clean_old_fb);
  */
 
 struct drm_out_fence_state {
-	s64 __user *out_fence_ptr;
+	s32 __user *out_fence_ptr;
 	struct sync_file *sync_file;
 	int fd;
 };
@@ -1952,7 +1952,7 @@ static int prepare_crtc_signaling(struct drm_device *dev,
 		return 0;
 
 	for_each_crtc_in_state(state, crtc, crtc_state, i) {
-		u64 __user *fence_ptr;
+		s32 __user *fence_ptr;
 
 		fence_ptr = get_out_fence_for_crtc(crtc_state->state, crtc);
 

include/drm/drm_atomic.h

@@ -144,7 +144,7 @@ struct __drm_crtcs_state {
 	struct drm_crtc *ptr;
 	struct drm_crtc_state *state;
 	struct drm_crtc_commit *commit;
-	s64 __user *out_fence_ptr;
+	s32 __user *out_fence_ptr;
 };
 
 struct __drm_connnectors_state {

include/drm/drm_mode_config.h

@@ -488,7 +488,7 @@ struct drm_mode_config {
 	/**
 	 * @prop_out_fence_ptr: Sync File fd pointer representing the
 	 * outgoing fences for a CRTC. Userspace should provide a pointer to a
-	 * value of type s64, and then cast that pointer to u64.
+	 * value of type s32, and then cast that pointer to u64.
 	 */
 	struct drm_property *prop_out_fence_ptr;
 	/**