linux-kernel - [PATCH AUTOSEL 5.4 29/34] nbd: call genl_unregister_family() first in nbd

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Message-Id: <20220607180011.481266-29-sashal@kernel.org>
Date:   Tue,  7 Jun 2022 14:00:04 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Yu Kuai <yukuai3@...wei.com>, Hou Tao <houtao1@...wei.com>,
        Josef Bacik <josef@...icpanda.com>,
        Jens Axboe <axboe@...nel.dk>, Sasha Levin <sashal@...nel.org>,
        linux-block@...r.kernel.org, nbd@...er.debian.org
Subject: [PATCH AUTOSEL 5.4 29/34] nbd: call genl_unregister_family() first in nbd_cleanup()

From: Yu Kuai <yukuai3@...wei.com>

[ Upstream commit 06c4da89c24e7023ea448cadf8e9daf06a0aae6e ]

Otherwise there may be race between module removal and the handling of
netlink command, which can lead to the oops as shown below:

  BUG: kernel NULL pointer dereference, address: 0000000000000098
  Oops: 0002 [#1] SMP PTI
  CPU: 1 PID: 31299 Comm: nbd-client Tainted: G            E     5.14.0-rc4
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)
  RIP: 0010:down_write+0x1a/0x50
  Call Trace:
   start_creating+0x89/0x130
   debugfs_create_dir+0x1b/0x130
   nbd_start_device+0x13d/0x390 [nbd]
   nbd_genl_connect+0x42f/0x748 [nbd]
   genl_family_rcv_msg_doit.isra.0+0xec/0x150
   genl_rcv_msg+0xe5/0x1e0
   netlink_rcv_skb+0x55/0x100
   genl_rcv+0x29/0x40
   netlink_unicast+0x1a8/0x250
   netlink_sendmsg+0x21b/0x430
   ____sys_sendmsg+0x2a4/0x2d0
   ___sys_sendmsg+0x81/0xc0
   __sys_sendmsg+0x62/0xb0
   __x64_sys_sendmsg+0x1f/0x30
   do_syscall_64+0x3b/0xc0
   entry_SYSCALL_64_after_hwframe+0x44/0xae
  Modules linked in: nbd(E-)

Signed-off-by: Hou Tao <houtao1@...wei.com>
Signed-off-by: Yu Kuai <yukuai3@...wei.com>
Reviewed-by: Josef Bacik <josef@...icpanda.com>
Link: https://lore.kernel.org/r/20220521073749.3146892-2-yukuai3@huawei.com
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/block/nbd.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 25e81b1a59a5..927f287681b2 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -2441,6 +2441,12 @@ static void __exit nbd_cleanup(void)
 	struct nbd_device *nbd;
 	LIST_HEAD(del_list);
 
+	/*
+	 * Unregister netlink interface prior to waiting
+	 * for the completion of netlink commands.
+	 */
+	genl_unregister_family(&nbd_genl_family);
+
 	nbd_dbg_close();
 
 	mutex_lock(&nbd_index_mutex);
@@ -2456,7 +2462,6 @@ static void __exit nbd_cleanup(void)
 	}
 
 	idr_destroy(&nbd_index_idr);
-	genl_unregister_family(&nbd_genl_family);
 	unregister_blkdev(NBD_MAJOR, "nbd");
 }
 
-- 
2.35.1