Re: [PATCH v3 7/9] cachefiles: wait for ondemand_object_worker to finish when dropping object

From: Gao Xiang
Date: Fri Jun 28 2024 - 03:22:33 EST




On 2024/6/28 14:29, libaokun@xxxxxxxxxxxxxxx wrote:
From: Hou Tao <houtao1@xxxxxxxxxx>

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.

Fixes: 0a7e54c1959c ("cachefiles: resend an open request if the read request's object is closed")
Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx>
Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
Reviewed-by: Jia Zhu <zhujia.zj@xxxxxxxxxxxxx>
Acked-by: Jeff Layton <jlayton@xxxxxxxxxx>

Reviewed-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>

Thanks,
Gao Xiang