linux-kernel - [PATCH v3 7/9] cachefiles: wait for ondemand_object

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Message-Id: <20240628062930.2467993-8-libaokun@huaweicloud.com>
Date: Fri, 28 Jun 2024 14:29:28 +0800
From: libaokun@...weicloud.com
To: netfs@...ts.linux.dev,
	dhowells@...hat.com,
	jlayton@...nel.org
Cc: hsiangkao@...ux.alibaba.com,
	jefflexu@...ux.alibaba.com,
	zhujia.zj@...edance.com,
	linux-erofs@...ts.ozlabs.org,
	brauner@...nel.org,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	libaokun@...weicloud.com,
	yangerkun@...wei.com,
	houtao1@...wei.com,
	yukuai3@...wei.com,
	wozizhi@...wei.com,
	Baokun Li <libaokun1@...wei.com>
Subject: [PATCH v3 7/9] cachefiles: wait for ondemand_object_worker to finish when dropping object

From: Hou Tao <houtao1@...wei.com>

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@...wei.com>
Signed-off-by: Baokun Li <libaokun1@...wei.com>
Reviewed-by: Jia Zhu <zhujia.zj@...edance.com>
Acked-by: Jeff Layton <jlayton@...nel.org>
---
 fs/cachefiles/ondemand.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/cachefiles/ondemand.c b/fs/cachefiles/ondemand.c
index 36b97ded16b4..1d5b970206d0 100644
--- a/fs/cachefiles/ondemand.c
+++ b/fs/cachefiles/ondemand.c
@@ -694,6 +694,9 @@ void cachefiles_ondemand_clean_object(struct cachefiles_object *object)
 		}
 	}
 	xa_unlock(&cache->reqs);
+
+	/* Wait for ondemand_object_worker() to finish to avoid UAF. */
+	cancel_work_sync(&object->ondemand->ondemand_work);
 }
 
 int cachefiles_ondemand_init_obj_info(struct cachefiles_object *object,
-- 
2.39.2