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

[Jingbo Xu]

On 5/15/24 4:45 PM, libaokun@xxxxxxxxxxxxxxx wrote:
> From: Baokun Li <libaokun1@xxxxxxxxxx>
> 
> 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@xxxxxxxxxx>
> Reviewed-by: Jia Zhu <zhujia.zj@xxxxxxxxxxxxx>

Reviewed-by: Jingbo Xu <jefflexu@xxxxxxxxxxxxxxxxx>

> ---
>  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);
>  

-- 
Thanks,
Jingbo