zsmalloc: fix races between asynchronous zspage free and page migration

stable inclusion
from stable-4.19.246
commit 645996efc2ae391246d595832aaa6f9d3cc338c7
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5FNPY
CVE: NA

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

commit 2505a981114dcb715f8977b8433f7540854851d8 upstream.

The asynchronous zspage free worker tries to lock a zspage's entire page
list without defending against page migration.  Since pages which haven't
yet been locked can concurrently migrate off the zspage page list while
lock_zspage() churns away, lock_zspage() can suffer from a few different
lethal races.

It can lock a page which no longer belongs to the zspage and unsafely
dereference page_private(), it can unsafely dereference a torn pointer to
the next page (since there's a data race), and it can observe a spurious
NULL pointer to the next page and thus not lock all of the zspage's pages
(since a single page migration will reconstruct the entire page list, and
create_page_chain() unconditionally zeroes out each list pointer in the
process).

Fix the races by using migrate_read_lock() in lock_zspage() to synchronize
with page migration.

Link: https://lkml.kernel.org/r/20220509024703.243847-1-sultan@kerneltoast.com


Fixes: 77ff4657 ("zsmalloc: zs_page_migrate: skip unnecessary loops but not return -EBUSY if zspage is not inuse")
Signed-off-by: Sultan Alsawaf <sultan@kerneltoast.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>
Signed-off-by: Laibin Qiu <qiulaibin@huawei.com>