[PATCH] drm/fence: fix memory overwrite when setting out_fence fd

[Gustavo Padovan <gustavo@padovan.org>]

From: Gustavo Padovan <gustavo.padovan@collabora.com>

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>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Rafael Antognolli <rafael.antognolli@intel.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: stable@vger.kernel.org
---
 drivers/gpu/drm/drm_atomic.c  | 12 ++++++------
 include/drm/drm_atomic.h      |  2 +-
 include/drm/drm_mode_config.h |  2 +-
 3 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
index 6414bcf..723392f 100644
--- a/drivers/gpu/drm/drm_atomic.c
+++ b/drivers/gpu/drm/drm_atomic.c
@@ -286,15 +286,15 @@ 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;
@@ -507,7 +507,7 @@ 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;
@@ -1914,7 +1914,7 @@ 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;
 };
@@ -1951,7 +1951,7 @@ 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);
 
diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
index f96220e..f1cb2b0 100644
--- a/include/drm/drm_atomic.h
+++ b/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;
 	unsigned last_vblank_count;
 };
 
diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
index 17942c0..fe230f1 100644
--- a/include/drm/drm_mode_config.h
+++ b/include/drm/drm_mode_config.h
@@ -496,7 +496,7 @@ 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;
 	/**
-- 
2.5.5