[PATCH 3/5] cachefiles: flush ondemand_object_worker during clean object

[Jia Zhu]

Thanks for catching this. How about adding a Fixes tag.

Reviewed-by: Jia Zhu <zhujia.zj at bytedance.com>


在 2024/4/24 11:34, libaokun at huaweicloud.com 写道:
> 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 complete.
> 
> Signed-off-by: Hou Tao <houtao1 at huawei.com>
> Signed-off-by: Baokun Li <libaokun1 at huawei.com>
> ---
>   fs/cachefiles/ondemand.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/fs/cachefiles/ondemand.c b/fs/cachefiles/ondemand.c
> index d24bff43499b..f6440b3e7368 100644
> --- a/fs/cachefiles/ondemand.c
> +++ b/fs/cachefiles/ondemand.c
> @@ -589,6 +589,9 @@ void cachefiles_ondemand_clean_object(struct cachefiles_object *object)
>   		}
>   	}
>   	xa_unlock(&cache->reqs);
> +
> +	/* Wait for ondemand_object_worker() to finish to avoid UAF. */
> +	cancel_work_sync(&object->ondemand->ondemand_work);
>   }
>   
>   int cachefiles_ondemand_init_obj_info(struct cachefiles_object *object,