drm/syncobj: Fix use-after-free

commit a37eef63bc9e16e06361b539e528058146af80ab upstream.

While reviewing Christian's annotation patch I noticed that we have a
user-after-free for the WAIT_FOR_SUBMIT case: We drop the syncobj
reference before we've completed the waiting.

Of course usually there's nothing bad happening here since userspace
keeps the reference, but we can't rely on userspace to play nice here!

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Fixes: bc9c80fe01a2 ("drm/syncobj: use the timeline point in drm_syncobj_find_fence v4")
Reviewed-by: Christian König <christian.koenig@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Cc: <stable@vger.kernel.org> # v5.2+
Link: https://patchwork.freedesktop.org/patch/msgid/20210119130318.615145-1-daniel.vetter@ffwll.ch
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
index 4b5c7b0ed714831a22a0a30e95af9b3929f8154e..8fdb271354061c667715affcd4704c4c64aaaf71 100644 (file)
--- a/drivers/gpu/drm/drm_syncobj.c
+++ b/drivers/gpu/drm/drm_syncobj.c
@@ -326,19 +326,18 @@ int drm_syncobj_find_fence(struct drm_file *file_private,
                return -ENOENT;
 
        *fence = drm_syncobj_fence_get(syncobj);
-       drm_syncobj_put(syncobj);
 
        if (*fence) {
                ret = dma_fence_chain_find_seqno(fence, point);
                if (!ret)
-                       return 0;
+                       goto out;
                dma_fence_put(*fence);
        } else {
                ret = -EINVAL;
        }
 
        if (!(flags & DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT))
-               return ret;
+               goto out;
 
        memset(&wait, 0, sizeof(wait));
        wait.task = current;
@@ -370,6 +369,9 @@ int drm_syncobj_find_fence(struct drm_file *file_private,
        if (wait.node.next)
                drm_syncobj_remove_wait(syncobj, &wait);
 
+out:
+       drm_syncobj_put(syncobj);
+
        return ret;
 }
 EXPORT_SYMBOL(drm_syncobj_find_fence);