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

[Gao Xiang]

On 2024/5/15 16:45, libaokun@xxxxxxxxxxxxxxx wrote:
> From: Baokun Li <libaokun1@xxxxxxxxxx>


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@xxxxxxxxxx>
> Reviewed-by: Jia Zhu <zhujia.zj@xxxxxxxxxxxxx>

Reviewed-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>

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);
>