[PATCH v3 7/9] cachefiles: wait for ondemand_object_worker to finish when dropping object

[Gao Xiang]

On 2024/6/28 14:29, libaokun at huaweicloud.com wrote:
> From: Hou Tao <houtao1 at huawei.com>
> 
> When queuing ondemand_object_worker() to re-open the object,
> cachefiles_object is not pinned. The cachefiles_object may be freed when
> the pending read request is completed intentionally and the related
> erofs is umounted. If ondemand_object_worker() runs after the object is
> freed, it will incur use-after-free problem as shown below.
> 
> process A  processs B  process C  process D
> 
> cachefiles_ondemand_send_req()
> // send a read req X
> // wait for its completion
> 
>             // close ondemand fd
>             cachefiles_ondemand_fd_release()
>             // set object as CLOSE
> 
>                         cachefiles_ondemand_daemon_read()
>                         // set object as REOPENING
>                         queue_work(fscache_wq, &info->ondemand_work)
> 
>                                  // close /dev/cachefiles
>                                  cachefiles_daemon_release
>                                  cachefiles_flush_reqs
>                                  complete(&req->done)
> 
> // read req X is completed
> // umount the erofs fs
> cachefiles_put_object()
> // object will be freed
> cachefiles_ondemand_deinit_obj_info()
> kmem_cache_free(object)
>                         // both info and object are freed
>                         ondemand_object_worker()
> 
> When dropping an object, it is no longer necessary to reopen the object,
> so use cancel_work_sync() to cancel or wait for ondemand_object_worker()
> to finish.
> 
> Fixes: 0a7e54c1959c ("cachefiles: resend an open request if the read request's object is closed")
> Signed-off-by: Hou Tao <houtao1 at huawei.com>
> Signed-off-by: Baokun Li <libaokun1 at huawei.com>
> Reviewed-by: Jia Zhu <zhujia.zj at bytedance.com>
> Acked-by: Jeff Layton <jlayton at kernel.org>

Reviewed-by: Gao Xiang <hsiangkao at linux.alibaba.com>

Thanks,
Gao Xiang