Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Subject: Re: [PATCH v3 1/3] mm/swapfile: unuse_pte can map random data if swap
 read fails
To:     =?UTF-8?B?SE9SSUdVQ0hJIE5BT1lBKOWggOWPoyDnm7TkuZ8p?= 
        <naoya.horiguchi@nec.com>
CC:     David Hildenbrand <david@redhat.com>,
        "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
        "willy@infradead.org" <willy@infradead.org>,
        "vbabka@suse.cz" <vbabka@suse.cz>,
        "dhowells@redhat.com" <dhowells@redhat.com>,
        "neilb@suse.de" <neilb@suse.de>,
        "apopple@nvidia.com" <apopple@nvidia.com>,
        "surenb@google.com" <surenb@google.com>,
        "minchan@kernel.org" <minchan@kernel.org>,
        "peterx@redhat.com" <peterx@redhat.com>,
        "sfr@canb.auug.org.au" <sfr@canb.auug.org.au>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <20220424091105.48374-1-linmiaohe@huawei.com>
 <20220424091105.48374-2-linmiaohe@huawei.com>
 <20220425010804.GA3746096@hori.linux.bs1.fc.nec.co.jp>
 <febd6309-b2a5-ef79-daa2-8000af09e291@redhat.com>
 <3ab987be-614a-4757-4124-26bb09d3f160@huawei.com>
 <20220426003118.GA3829204@hori.linux.bs1.fc.nec.co.jp>
From:   Miaohe Lin <linmiaohe@huawei.com>
Message-ID: <45a5052b-5c6e-1d5e-6c90-eb3ff2ed1130@huawei.com>
Date:   Tue, 26 Apr 2022 15:06:38 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101
 Thunderbird/78.6.0
MIME-Version: 1.0
In-Reply-To: <20220426003118.GA3829204@hori.linux.bs1.fc.nec.co.jp>
Content-Type: text/plain; charset="utf-8"
Content-Language: en-US
Content-Transfer-Encoding: 8bit
Precedence: bulk

On 2022/4/26 8:31, HORIGUCHI NAOYA(堀口 直也) wrote:
> On Mon, Apr 25, 2022 at 04:47:41PM +0800, Miaohe Lin wrote:
>> On 2022/4/25 15:45, David Hildenbrand wrote:
>>> On 25.04.22 03:08, HORIGUCHI NAOYA(堀口 直也) wrote:
>>>> On Sun, Apr 24, 2022 at 05:11:03PM +0800, Miaohe Lin wrote:
>>>>> There is a bug in unuse_pte(): when swap page happens to be unreadable,
>>>>> page filled with random data is mapped into user address space.  In case
>>>>> of error, a special swap entry indicating swap read fails is set to the
>>>>> page table.  So the swapcache page can be freed and the user won't end up
>>>>> with a permanently mounted swap because a sector is bad.  And if the page
>>>>> is accessed later, the user process will be killed so that corrupted data
>>>>> is never consumed.  On the other hand, if the page is never accessed, the
>>>>> user won't even notice it.
>>>>>
>>>>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
>>>>> Acked-by: David Hildenbrand <david@redhat.com>
>>>>
>>>> Hi Miaohe,
>>>>
>>>> This bug sounds relatively serious to me, and it seems old, so is it worth
>>>> sending to -stable?
>>>
>>> I'm not sure if this is worth -stable, but no strong opinion.
>>
>> I have no strong opinion too. I'm just afraid someone might run into it. But swapoff is
>> expected to be a rare operation anyway...
>>
>>>
>>> The do_swap_page() part was added in 2005:
>>>
>>> commit b81074800b98ac50b64d4c8d34e8abf0fda5e3d1
>>> Author: Kirill Korotaev <dev@sw.ru>
>>> Date:   Mon May 16 21:53:50 2005 -0700
>>>
>>>     [PATCH] do_swap_page() can map random data if swap read fails
>>>     
>>>     There is a bug in do_swap_page(): when swap page happens to be unreadable,
>>>     page filled with random data is mapped into user address space.  The fix is
>>>     to check for PageUptodate and send SIGBUS in case of error.
>>>     
>>>     Signed-Off-By: Kirill Korotaev <dev@sw.ru>
>>>     Signed-Off-By: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
>>>     Acked-by: Hugh Dickins <hugh@veritas.com>
>>>     Signed-off-by: Andrew Morton <akpm@osdl.org>
>>>     Signed-off-by: Linus Torvalds <torvalds@osdl.org>
>>>
>>> So the do_swap_page() part has been fixed for quite a while already.
>>
>> Does this mean only do_swap_page maps random data if swap read fails is observed from that time on?
>> So this might not be worth -stable as it's never seen more than a decade?
> 
> OK, both choices seems possible, so not sending to -stable is fine to me.
> It's finally up to you.

I tend not to send it to -stable due to the above concern now.

Thanks!

> 
> Thanks,
> Naoya Horiguchi
>