linux-kernel - Re: [PATCH 3/5] cachefiles: flush ondemand_object

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Date: Thu, 25 Apr 2024 14:53:02 +0800
From: Baokun Li <libaokun@...weicloud.com>
To: Jia Zhu <zhujia.zj@...edance.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>, libaokun@...weicloud.com
Subject: Re: [PATCH 3/5] cachefiles: flush ondemand_object_worker during clean
 object

Hi Jia,

On 2024/4/25 13:41, Jia Zhu wrote:
> Thanks for catching this. How about adding a Fixes tag.
>
> Reviewed-by: Jia Zhu <zhujia.zj@...edance.com>
>
>
Ok, I will add the Fixes tag in the next iteration.
Thank you very much for your review!

Cheers!
Baokun
> 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,