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

[Gao Xiang]

On 2024/5/15 16:45, libao...@huaweicloud.com wrote:

From: Baokun Li <libaok...@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 <libaok...@huawei.com>
Reviewed-by: Jia Zhu <zhujia...@bytedance.com>

Reviewed-by: Gao Xiang <hsiang...@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);