drivers/block/null_blk/main: Fix a double free in null_init.

stable inclusion
from linux-4.19.191
commit 7585643856ae82e1ed105b261d4e57b384648a69

--------------------------------

[ Upstream commit 72ce11dd ]

In null_init, null_add_dev(dev) is called.
In null_add_dev, it calls null_free_zoned_dev(dev) to free dev->zones
via kvfree(dev->zones) in out_cleanup_zone branch and returns err.
Then null_init accept the err code and then calls null_free_dev(dev).

But in null_free_dev(dev), dev->zones is freed again by
null_free_zoned_dev().

My patch set dev->zones to NULL in null_free_zoned_dev() after
kvfree(dev->zones) is called, to avoid the double free.

Fixes: 2984c868 ("nullb: factor disk parameters")
Signed-off-by: NLv Yunlong <lyl2019@mail.ustc.edu.cn>
Link: https://lore.kernel.org/r/20210426143229.7374-1-lyl2019@mail.ustc.edu.cnSigned-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

drivers/block/null_blk_zoned.c

@@ -52,6 +52,7 @@ int null_zone_init(struct nullb_device *dev)
 void null_zone_exit(struct nullb_device *dev)
 {
 	kvfree(dev->zones);
+	dev->zones = NULL;
 }
 
 static void null_zone_fill_bio(struct nullb_device *dev, struct bio *bio,