[PATCH] drm/virtio: fix memory leak of fence event on execbuffer failure

virtio_gpu_execbuffer_ioctl() reserves a DRM event with
drm_event_reserve_init() when VIRTGPU_EXECBUF_RING_IDX selects a ring that
userspace has enabled polling for. virtio_gpu_init_submit() does this
before the BO handles, the command buffer, the syncobj arrays and the
in-fence are processed, so every later error path runs with the event
already pending, including plain argument validation failures such as an
invalid bo_handle or an in-syncobj that carries no fence.

On those paths, virtio_gpu_cleanup_submit() drops the out-fence without
cancelling the event. The fence is freed without ever having been emitted,
taking the only driver-side pointer to the event with it. Closing the DRM
file does not help. drm_events_release() unlinks pending events but
deliberately leaves the freeing to the driver's later drm_send_event(),
which never runs for an orphaned event, so the allocation is leaked
permanently.

Found when fuzzing the virtio driver with Syzkaller:

	BUG: memory leak
	unreferenced object 0xffff88802c176e80 (size 96):
	comm "syz.1.367", pid 10561, jiffies 4294960122
	hex dump (first 32 bytes):
		00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
		c8 6e 17 2c 80 88 ff ff 00 00 00 00 00 00 00 00  .n.,............
	backtrace (crc e1973c6b):
		kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
		slab_post_alloc_hook mm/slub.c:4597 [inline]
		slab_alloc_node mm/slub.c:4917 [inline]
		__kmalloc_cache_noprof+0x49d/0x6f0 mm/slub.c:5485
		_kmalloc_noprof include/linux/slab.h:988 [inline]
		_kzalloc_noprof include/linux/slab.h:1309 [inline]
		virtio_gpu_fence_event_create drivers/gpu/drm/virtio/virtgpu_submit.c:282 [inline]
		virtio_gpu_init_submit drivers/gpu/drm/virtio/virtgpu_submit.c:398 [inline]
		virtio_gpu_execbuffer_ioctl+0xbbf/0x1aa0 drivers/gpu/drm/virtio/virtgpu_submit.c:505
		drm_ioctl_kernel+0x1f4/0x3e0 drivers/gpu/drm/drm_ioctl.c:817
		drm_ioctl+0x5f4/0xc70 drivers/gpu/drm/drm_ioctl.c:914
		vfs_ioctl fs/ioctl.c:51 [inline]
		__do_sys_ioctl fs/ioctl.c:597 [inline]
		__se_sys_ioctl fs/ioctl.c:583 [inline]
		__x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
		do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
		do_syscall_64+0x116/0x800 arch/x86/entry/syscall_64.c:94
		entry_SYSCALL_64_after_hwframe+0x77/0x7f

Fix by cancelling and freeing the DRM event on the execbuffer error path
before dropping the fence. Clear the fence's event pointer after
cancellation so it does not retain a dangling pointer.

Fixes: cd7f5ca33585 ("drm/virtio: implement context init: add virtio_gpu_fence_event")
Cc: stable@vger.kernel.org
Signed-off-by: Peiyang He <redacted>
Assisted-by: Codex:gpt-5.6-luna
---
 drivers/gpu/drm/virtio/virtgpu_submit.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/virtio/virtgpu_submit.c b/drivers/gpu/drm/virtio/virtgpu_submit.c
index 32cb1e4aa425..734b1e976a75 100644
--- a/drivers/gpu/drm/virtio/virtgpu_submit.c
+++ b/drivers/gpu/drm/virtio/virtgpu_submit.c

@@ -538,6 +538,10 @@ int virtio_gpu_execbuffer_ioctl(struct drm_device *dev, void *data,
 	virtio_gpu_process_post_deps(&submit);
 	virtio_gpu_complete_submit(&submit);
 cleanup:
+	if (ret && submit.out_fence && submit.out_fence->e) {
+		drm_event_cancel_free(dev, &submit.out_fence->e->base);
+		submit.out_fence->e = NULL;
+	}
 	virtio_gpu_cleanup_submit(&submit);
 
 	return ret;

-- 
2.43.0