zloop: fix KASAN use-after-free of tag set

In the Linux kernel, the following vulnerability has been resolved:

zloop: fix KASAN use-after-free of tag set

When a zoned loop device, or zloop device, is removed, KASAN enabled

kernel reports "BUG KASAN use-after-free" in blk_mq_free_tag_set(). The

BUG happens because zloop_ctl_remove() calls put_disk(), which invokes

zloop_free_disk(). The zloop_free_disk() frees the memory allocated for

the zlo pointer. However, after the memory is freed, zloop_ctl_remove()

calls blk_mq_free_tag_set(&zlo->tag_set), which accesses the freed zlo.

Hence the KASAN use-after-free.

zloop_ctl_remove()

put_disk(zlo->disk)

put_device()

kobject_put()

...

zloop_free_disk()

kvfree(zlo)

blk_mq_free_tag_set(&zlo->tag_set)

To avoid the BUG, move the call to blk_mq_free_tag_set(&zlo->tag_set)

from zloop_ctl_remove() into zloop_free_disk(). This ensures that

the tag_set is freed before the call to kvfree(zlo).