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, 8 insertions, 1 deletions

diff --git a/src/gallium/drivers/nouveau/nvc0/nvc0_screen.c b/src/gallium/drivers/nouveau/nvc0/nvc0_screen.c
index 044847dfd27..04f30886a09 100644
--- a/src/gallium/drivers/nouveau/nvc0/nvc0_screen.c
+++ b/src/gallium/drivers/nouveau/nvc0/nvc0_screen.c
@@ -340,7 +340,14 @@ nvc0_screen_destroy(struct pipe_screen *pscreen)
       return;
 
    if (screen->base.fence.current) {
-      nouveau_fence_wait(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)