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

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Date: Mon, 20 May 2024 10:20:59 +0800
From: Gao Xiang <hsiangkao@...ux.alibaba.com>
To: libaokun@...weicloud.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>
Subject: Re: [PATCH v2 01/12] cachefiles: remove request from xarry during
 flush requests



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"

> 
> 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

> ---
>   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);
>