libceph: remove debugfs files before client teardown

commit e4c8047 upstream.

ceph_destroy_client() tears down the monitor client before removing
the per-client debugfs files. A concurrent read of the monmap debugfs
file can enter monmap_show() after ceph_monc_stop() has freed
monc->monmap, triggering a use-after-free.

Remove the debugfs files before stopping the OSD and monitor clients.
debugfs_remove() drains active handlers and prevents new accesses, so
the debugfs callbacks can no longer race the rest of client teardown.

Cc: stable@vger.kernel.org
Fixes: 76aa844 ("ceph: debugfs")
Reported-by: Yuan Tan <yuantan098@gmail.com>
Reported-by: Zhengchuan Liang <zcliangcn@gmail.com>
Reported-by: Xin Liu <bird@lzu.edu.cn>
Assisted-by: Codex:GPT-5.4
Signed-off-by: Douya Le <ldy3087146292@gmail.com>
Signed-off-by: Ren Wei <n05ec@lzu.edu.cn>
Reviewed-by: Viacheslav Dubeyko <slava@dubeyko.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: lexiaox

net/ceph/ceph_common.c

@@ -763,13 +763,13 @@ void ceph_destroy_client(struct ceph_client *client)
 
 	atomic_set(&client->msgr.stopping, 1);
 
+	ceph_debugfs_client_cleanup(client);
+
 	/* unmount */
 	ceph_osdc_stop(&client->osdc);
 	ceph_monc_stop(&client->monc);
 	ceph_messenger_fini(&client->msgr);
 
-	ceph_debugfs_client_cleanup(client);
-
 	ceph_destroy_options(client->options);
 
 	kfree(client);