From: Yu Kuai yukuai3@huawei.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@huawei.com Signed-off-by: Yu Kuai yukuai3@huawei.com Reviewed-by: Josef Bacik josef@toxicpanda.com Link: https://lore.kernel.org/r/20220521073749.3146892-2-yukuai3@huawei.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.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 8704212482e5..4be8ae20d1da 100644 --- a/drivers/block/nbd.c +++ b/drivers/block/nbd.c @@ -2478,6 +2478,12 @@ 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); @@ -2496,7 +2502,6 @@ static void __exit nbd_cleanup(void) destroy_workqueue(nbd_del_wq);
idr_destroy(&nbd_index_idr); - genl_unregister_family(&nbd_genl_family); unregister_blkdev(NBD_MAJOR, "nbd"); }