nouveau: fix fence waiting logic in screen destroy

nouveau_fence_wait has the expectation that an external entity is
holding onto the fence being waited on, not that it is merely held onto
by the current pointer. Fixes a use-after-free in nouveau_fence_wait
when used on the screen's current fence.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=75279
Signed-off-by: Ilia Mirkin <[email protected]>
Reviewed-by: Christoph Bumiller <[email protected]>
Cc: "9.2 10.0 10.1" <[email protected]>

1 files changed, 9 insertions, 2 deletions

diff --git a/src/gallium/drivers/nouveau/nv50/nv50_screen.c b/src/gallium/drivers/nouveau/nv50/nv50_screen.c
index ab0d63ea5f3..e8c7fe3cc24 100644
--- a/src/gallium/drivers/nouveau/nv50/nv50_screen.c
+++ b/src/gallium/drivers/nouveau/nv50/nv50_screen.c
@@ -294,8 +294,15 @@ nv50_screen_destroy(struct pipe_screen *pscreen)
       return;
 
    if (screen->base.fence.current) {
-      nouveau_fence_wait(screen->base.fence.current);
-      nouveau_fence_ref (NULL, &screen->base.fence.current);
+      struct nouveau_fence *current = NULL;
+
+      /* nouveau_fence_wait will create a new current fence, so wait on the
+       * _current_ one, and remove both.
+       */
+      nouveau_fence_ref(screen->base.fence.current, &current);
+      nouveau_fence_wait(current);
+      nouveau_fence_ref(NULL, &current);
+      nouveau_fence_ref(NULL, &screen->base.fence.current);
    }
    if (screen->base.pushbuf)
       screen->base.pushbuf->user_priv = NULL;