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

Gao Xiang
2024-05-20T02:21:11Z

On 2024/5/15 16:45, libaokun@huaweicloud.com wrote:
> From: Baokun Li <libaokun1@huawei.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@huawei.com>
> Reviewed-by: Jia Zhu <zhujia.zj@bytedance.com>

Reviewed-by: Gao Xiang <hsiangkao@linux.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);
>