linux-kernel - Re: [PATCH v2 01/12] cachefiles: remove request from xarry during flush requests

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Date: Mon, 20 May 2024 12:11:35 +0800
From: Baokun Li <libaokun@...weicloud.com>
To: Gao Xiang <hsiangkao@...ux.alibaba.com>, netfs@...ts.linux.dev,
 dhowells@...hat.com, jlayton@...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>,
 libaokun@...weicloud.com
Subject: Re: [PATCH v2 01/12] cachefiles: remove request from xarry during
 flush requests

On 2024/5/20 10:20, Gao Xiang wrote:
>
>
> On 2024/5/15 16:45, libaokun@...weicloud.com wrote:
>> From: Baokun Li <libaokun1@...wei.com>
>
>
> The subject line can be
> "cachefiles: remove requests from xarray during flushing requests"
Thank you very much for the correction! I will update my patch.
>
>>
>> Even with CACHEFILES_DEAD set, we can still read the requests, so in the
>> following concurrency the request may be used after it has been freed:
>>
>>       mount  |   daemon_thread1    |    daemon_thread2
>> ------------------------------------------------------------
>>   cachefiles_ondemand_init_object
>>    cachefiles_ondemand_send_req
>>     REQ_A = kzalloc(sizeof(*req) + data_len)
>>     wait_for_completion(&REQ_A->done)
>>              cachefiles_daemon_read
>>               cachefiles_ondemand_daemon_read
>>                                    // close dev fd
>>                                    cachefiles_flush_reqs
>> complete(&REQ_A->done)
>>     kfree(REQ_A)
>>                xa_lock(&cache->reqs);
>>                cachefiles_ondemand_select_req
>>                  req->msg.opcode != CACHEFILES_OP_READ
>>                  // req use-after-free !!!
>>                xa_unlock(&cache->reqs);
>> xa_destroy(&cache->reqs)
>>
>> Hence remove requests from cache->reqs when flushing them to avoid
>> accessing freed requests.
>>
>> Fixes: c8383054506c ("cachefiles: notify the user daemon when looking 
>> up cookie")
>> Signed-off-by: Baokun Li <libaokun1@...wei.com>
>> Reviewed-by: Jia Zhu <zhujia.zj@...edance.com>
>
> Reviewed-by: Gao Xiang <hsiangkao@...ux.alibaba.com>
>
> Thanks,
> Gao Xiang
Thanks a lot for the review!

Cheers,
Baokun
>
>> ---
>>   fs/cachefiles/daemon.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/fs/cachefiles/daemon.c b/fs/cachefiles/daemon.c
>> index 6465e2574230..ccb7b707ea4b 100644
>> --- a/fs/cachefiles/daemon.c
>> +++ b/fs/cachefiles/daemon.c
>> @@ -159,6 +159,7 @@ static void cachefiles_flush_reqs(struct 
>> cachefiles_cache *cache)
>>       xa_for_each(xa, index, req) {
>>           req->error = -EIO;
>>           complete(&req->done);
>> +        __xa_erase(xa, index);
>>       }
>>       xa_unlock(xa);

-- 
With Best Regards,
Baokun Li