linux-kernel - Re: [PATCH] mm: cleancache: fix corruption on missed inode invalidation

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Date:   Fri, 16 Nov 2018 10:55:45 +0300
From:   Vasily Averin <vvs@...tuozzo.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Pavel Tikhomirov <ptikhomirov@...tuozzo.com>
Cc:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Konstantin Khorenko <khorenko@...tuozzo.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Jan Kara <jack@...e.cz>, Matthew Wilcox <willy@...radead.org>,
        Andi Kleen <ak@...ux.intel.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: cleancache: fix corruption on missed inode
 invalidation

On 11/16/18 1:31 AM, Andrew Morton wrote:
> On Mon, 12 Nov 2018 12:57:34 +0300 Pavel Tikhomirov <ptikhomirov@...tuozzo.com> wrote:
> 
>> If all pages are deleted from the mapping by memory reclaim and also
>> moved to the cleancache:
>>
>> __delete_from_page_cache
>>   (no shadow case)
>>   unaccount_page_cache_page
>>     cleancache_put_page
>>   page_cache_delete
>>     mapping->nrpages -= nr
>>     (nrpages becomes 0)
>>
>> We don't clean the cleancache for an inode after final file truncation
>> (removal).
>>
>> truncate_inode_pages_final
>>   check (nrpages || nrexceptional) is false
>>     no truncate_inode_pages
>>       no cleancache_invalidate_inode(mapping)
>>
>> These way when reading the new file created with same inode we may get
>> these trash leftover pages from cleancache and see wrong data instead of
>> the contents of the new file.
>>
>> Fix it by always doing truncate_inode_pages which is already ready for
>> nrpages == 0 && nrexceptional == 0 case and just invalidates inode.
>>
> 
> Data corruption sounds serious.  Shouldn't we backport this into
> -stable kernels?

Yes, it was broken in 4.14 kernel and it should affect all who uses cleancache
Fixes: commit 91b0abe36a7b ("mm + fs: store shadow entries in page cache")