nbd: fix uaf in nbd_open

stable inclusion
from stable-v6.6.2
commit 56bd7901b5e9dbc9112036ea615ebcba1565fafe
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8IW7G

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=56bd7901b5e9dbc9112036ea615ebcba1565fafe



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[ Upstream commit 327462725b0f759f093788dfbcb2f1fd132f956b ]

Commit 4af5f2e0 ("nbd: use blk_mq_alloc_disk and
blk_cleanup_disk") cleans up disk by blk_cleanup_disk() and it won't set
disk->private_data as NULL as before. UAF may be triggered in nbd_open()
if someone tries to open nbd device right after nbd_put() since nbd has
been free in nbd_dev_remove().

Fix this by implementing ->free_disk and free private data in it.

Fixes: 4af5f2e0 ("nbd: use blk_mq_alloc_disk and blk_cleanup_disk")
Signed-off-by: Li Lingfeng <lilingfeng3@huawei.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Link: https://lore.kernel.org/r/20231107103435.2074904-1-lilingfeng@huaweicloud.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>