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

[Dmitry Osipenko]

On 9/8/26 15:13, Peiyang He wrote:
> 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@xxxxxxxxxxxxxxx
> Signed-off-by: Peiyang He <peiyang_he@xxxxxxxxxxxxxxxx>
> 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;

Applied to misc-fixes, thanks!

-- 
Best regards,
Dmitry