cachefiles: wait for ondemand_object_worker to finish when dropping object

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: cachefiles: wait for ondemand_object_worker to finish when dropping object When queuing ondemand_object_worker() to re-open the object, cachefiles_object is not pinned. The cachefiles_object may be freed when the pending read request is completed intentionally and the related erofs is umounted. If ondemand_object_worker() runs after the object is freed, it will incur use-after-free problem as shown below. process A processs B process C process D cachefiles_ondemand_send_req() // send a read req X // wait for its completion // close ondemand fd cachefiles_ondemand_fd_release() // set object as CLOSE cachefiles_ondemand_daemon_read() // set object as REOPENING queue_work(fscache_wq, &info->ondemand_work) // close /dev/cachefiles cachefiles_daemon_release cachefiles_flush_reqs complete(&req->done) // read req X is completed // umount the erofs fs cachefiles_put_object() // object will be freed cachefiles_ondemand_deinit_obj_info() kmem_cache_free(object) // both info and object are freed ondemand_object_worker() When dropping an object, it is no longer necessary to reopen the object, so use cancel_work_sync() to cancel or wait for ondemand_object_worker() to finish.

References

• https://git.kernel.org/stable/c/ec9289369259d982e735a71437e32e6b4035290c
• https://git.kernel.org/stable/c/d3179bae72b1b5e555ba839d6d9f40a350a4d78a
• https://git.kernel.org/stable/c/b26525b2183632f16a3a4108fe6a4bfa8afac6ed
• https://git.kernel.org/stable/c/12e009d60852f7bce0afc373ca0b320f14150418