linux-kernel - Re: [PATCH v3 0/9] cachefiles: random bugfixes

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Date: Fri, 28 Jun 2024 15:39:24 +0800
From: Gao Xiang <hsiangkao@...ux.alibaba.com>
To: libaokun@...weicloud.com, netfs@...ts.linux.dev, dhowells@...hat.com,
 jlayton@...nel.org, Christian Brauner <brauner@...nel.org>
Cc: jefflexu@...ux.alibaba.com, zhujia.zj@...edance.com,
 linux-erofs@...ts.ozlabs.org, linux-fsdevel@...r.kernel.org,
 linux-kernel@...r.kernel.org, yangerkun@...wei.com, houtao1@...wei.com,
 yukuai3@...wei.com, wozizhi@...wei.com, Baokun Li <libaokun1@...wei.com>
Subject: Re: [PATCH v3 0/9] cachefiles: random bugfixes

Hi Baokun,

On 2024/6/28 14:29, libaokun@...weicloud.com wrote:
> From: Baokun Li <libaokun1@...wei.com>
> 
> Hi all!
> 
> This is the third version of this patch series, in which another patch set
> is subsumed into this one to avoid confusing the two patch sets.
> (https://patchwork.kernel.org/project/linux-fsdevel/list/?series=854914)
> 
> Thank you, Jia Zhu, Gao Xiang, Jeff Layton, for the feedback in the
> previous version.
> 
> We've been testing ondemand mode for cachefiles since January, and we're
> almost done. We hit a lot of issues during the testing period, and this
> patch series fixes some of the issues. The patches have passed internal
> testing without regression.
> 
> The following is a brief overview of the patches, see the patches for
> more details.
> 
> Patch 1-2: Add fscache_try_get_volume() helper function to avoid
> fscache_volume use-after-free on cache withdrawal.
> 
> Patch 3: Fix cachefiles_lookup_cookie() and cachefiles_withdraw_cache()
> concurrency causing cachefiles_volume use-after-free.
> 
> Patch 4: Propagate error codes returned by vfs_getxattr() to avoid
> endless loops.
> 
> Patch 5-7: A read request waiting for reopen could be closed maliciously
> before the reopen worker is executing or waiting to be scheduled. So
> ondemand_object_worker() may be called after the info and object and even
> the cache have been freed and trigger use-after-free. So use
> cancel_work_sync() in cachefiles_ondemand_clean_object() to cancel the
> reopen worker or wait for it to finish. Since it makes no sense to wait
> for the daemon to complete the reopen request, to avoid this pointless
> operation blocking cancel_work_sync(), Patch 1 avoids request generation
> by the DROPPING state when the request has not been sent, and Patch 2
> flushes the requests of the current object before cancel_work_sync().
> 
> Patch 8: Cyclic allocation of msg_id to avoid msg_id reuse misleading
> the daemon to cause hung.
> 
> Patch 9: Hold xas_lock during polling to avoid dereferencing reqs causing
> use-after-free. This issue was triggered frequently in our tests, and we
> found that anolis 5.10 had fixed it. So to avoid failing the test, this
> patch is pushed upstream as well.
> 
> Comments and questions are, as always, welcome.
> Please let me know what you think.

Patch 4-9 looks good to me, and they are independent to patch 1-3
so personally I guess they could go upstream in advance.

I hope the way to fix cachefiles in patch 1-4 could be also
confirmed by David and Jeff since they relates the generic
cachefiles logic anyway.

Thanks,
Gao Xiang

> 
> Thanks,
> Baokun