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

[Baokun Li]

On 2024/5/6 11:48, Jingbo Xu wrote:
>
> On 4/24/24 11:39 AM, libaokun at huaweicloud.com wrote:
>> From: Baokun Li <libaokun1 at huawei.com>
>>
>> This prevents concurrency from causing access to a freed req.
> Could you give more details on how the concurrent access will happen?
> How could another process access the &cache->reqs xarray after it has
> been flushed?

Similar logic to restore leading to UAF:

      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
               REQ_A = cachefiles_ondemand_select_req
               cachefiles_ondemand_get_fd
               copy_to_user(_buffer, msg, n)
             process_open_req(REQ_A)
                                   // close dev fd
                                   cachefiles_flush_reqs
                                    complete(&REQ_A->done)
    kfree(REQ_A)
              cachefiles_ondemand_get_fd(REQ_A)
               fd = get_unused_fd_flags
               file = anon_inode_getfile
               fd_install(fd, file)
               load = (void *)REQ_A->msg.data;
               load->fd = fd;
               // load UAF !!!

>> ---
>>   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);
>>