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Message-ID: <8572a732-ca12-48d7-817c-d8218d536c0c@bytedance.com>
Date: Thu, 25 Apr 2024 13:41:20 +0800
From: Jia Zhu <zhujia.zj@...edance.com>
To: libaokun@...weicloud.com, netfs@...ts.linux.dev
Cc: dhowells@...hat.com, jlayton@...nel.org, jefflexu@...ux.alibaba.com,
linux-cachefs@...hat.com, linux-erofs@...ts.ozlabs.org,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
Hou Tao <houtao1@...wei.com>, Baokun Li <libaokun1@...wei.com>,
zhujia.zj@...edance.com
Subject: Re: [PATCH 3/5] cachefiles: flush ondemand_object_worker during clean
object
Thanks for catching this. How about adding a Fixes tag.
Reviewed-by: Jia Zhu <zhujia.zj@...edance.com>
在 2024/4/24 11:34, libaokun@...weicloud.com 写道:
> From: Hou Tao <houtao1@...wei.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@...wei.com>
> Signed-off-by: Baokun Li <libaokun1@...wei.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,
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