When allocating a `qxl_release` structure with `kmalloc()`, the underlying memory contained uninitialized garbage. Specifically, `release->base.flags` (part of the embedded `dma_fence`) was not cleared. This garbage in `base.flags` caused helper functions such as `dma_fence_was_initialized()` to return true even for releases where the fence was never actually initialized (e.g. via `dma_fence_init()`). Consequently, during release cleanup in `qxl_release_free()`, the driver attempted to put/free an uninitialized `dma_fence`, leading to refcount underflows (`refcount_t: underflow; use-after-free`) and subsequent NULL pointer dereferences in `dma_fence_signal_timestamp_locked()`. Fix this by switching from `kmalloc()` to `kzalloc_obj()` in `qxl_release_alloc()`, ensuring all fields (including embedded fence flags) are properly zero-initialized upon allocation, and remove redundant explicit zero-initializations. The dumps in question: refcount_t: underflow; use-after-free. WARNING: lib/refcount.c:28 at refcount_warn_saturate+0x59/0x90, CPU#0: kworker/0:0/1534 Modules linked in: af_packet nft_fib_inet ... CPU: 0 UID: 0 PID: 1534 Comm: kworker/0:0 Not tainted 7.1.3-1-default #1 PREEMPT(full) openSUSE Tumbleweed b041a6527f6e58424f4cd3de0fade8d408b378fd ... RIP: 0010:refcount_warn_saturate+0x59/0x90 ... Call Trace: <TASK> qxl_release_free+0xee/0xf0 [qxl d93e9381353e619799d56790f5f8dda6cce491f6] qxl_garbage_collect+0xd1/0x1b0 [qxl d93e9381353e619799d56790f5f8dda6cce491f6] process_one_work+0x19e/0x3a0 ... And then of course: BUG: kernel NULL pointer dereference, address: 0000000000000028 ... RIP: 0010:dma_fence_signal_timestamp_locked+0x32/0x120 Signed-off-by: Jiri Slaby (SUSE) <jirislaby(a)kernel.org&gt; Assisted-by: Gemini <gemini(a)google.com&gt; # only commit log Fixes: 2bcbc706dfa0 ("dma-buf: add dma_fence_was_initialized function v2") Closes: https://bugzilla.suse.com/show_bug.cgi?id=1271081 Cc: Christian König <christian.koenig(a)amd.com&gt; Cc: Tvrtko Ursulin <tvrtko.ursulin(a)igalia.com&gt; Cc: Dave Airlie <airlied(a)redhat.com&gt; Cc: Gerd Hoffmann <kraxel(a)redhat.com&gt; Cc: Maarten Lankhorst <maarten.lankhorst(a)linux.intel.com&gt; Cc: Maxime Ripard <mripard(a)kernel.org&gt; Cc: Thomas Zimmermann <tzimmermann(a)suse.de&gt; Cc: David Airlie <airlied(a)gmail.com&gt; Cc: Simona Vetter <simona(a)ffwll.ch&gt; Cc: stable(a)vger.kernel.org --- Cc: virtualization(a)lists.linux.dev Cc: spice-devel(a)lists.freedesktop.org Cc: dri-devel(a)lists.freedesktop.org [v2] use kzalloc_obj() instead of bare kzalloc() --- drivers/gpu/drm/qxl/qxl_release.c | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-) diff --git a/drivers/gpu/drm/qxl/qxl_release.c b/drivers/gpu/drm/qxl/qxl_release.c index 06979d0e8a9f..07dc6eafe6f7 100644 --- a/drivers/gpu/drm/qxl/qxl_release.c +++ b/drivers/gpu/drm/qxl/qxl_release.c @@ -89,17 +89,13 @@ qxl_release_alloc(struct qxl_device *qdev, int type, { struct qxl_release *release; int handle; - size_t size = sizeof(*release); - release = kmalloc(size, GFP_KERNEL); + release = kzalloc_obj(*release); if (!release) { DRM_ERROR("Out of memory\n"); return -ENOMEM; } - release->base.ops = NULL; release->type = type; - release->release_offset = 0; - release->surface_release_id = 0; INIT_LIST_HEAD(&release->bos); idr_preload(GFP_KERNEL); -- 2.55.0