ubi: Fix UAF wear-leveling entry in eraseblk_count_seq_show()

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

ubi: Fix UAF wear-leveling entry in eraseblk_count_seq_show()

Wear-leveling entry could be freed in error path, which may be accessed

again in eraseblk_count_seq_show(), for example:

__erase_worker eraseblk_count_seq_show

wl = ubi->lookuptbl[*block_number]

if (wl)

wl_entry_destroy

ubi->lookuptbl[e->pnum] = NULL

kmem_cache_free(ubi_wl_entry_slab, e)

erase_count = wl->ec // UAF!

Wear-leveling entry updating/accessing in ubi->lookuptbl should be

protected by ubi->wl_lock, fix it by adding ubi->wl_lock to serialize

wl entry accessing between wl_entry_destroy() and

eraseblk_count_seq_show().

Fetch a reproducer in [Link].