Message-ID: <41405B51.20705@yahoo.com.au>
Date: Thu, 09 Sep 2004 23:32:01 +1000
From: Nick Piggin <nickpiggin@yahoo.com.au>
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To: Pavel Machek <pavel@ucw.cz>
CC: Andrew Morton <akpm@osdl.org>, Andrey Savochkin <saw@saw.sw.com.sg>,
       linux-kernel@vger.kernel.org
Subject: Re: Q about pagecache data never written to disk
References: <20040905120147.A9202@castle.nmd.msu.ru> <20040905035233.6a6b5823.akpm@osdl.org> <20040905154336.B9202@castle.nmd.msu.ru> <20040905140040.58a5fcdc.akpm@osdl.org> <20040909123957.GB1065@elf.ucw.cz> <41405773.3090403@yahoo.com.au> <20040909133703.GA32038@atrey.karlin.mff.cuni.cz>
In-Reply-To: <20040909133703.GA32038@atrey.karlin.mff.cuni.cz>
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Pavel Machek wrote:

>>>kernel realizes that there's not enough disk space, and discard
>>>changes, therefore /tmp/sign.me reverts to previous, evil, content.
>>>
>>
>>root would have to make that change while user has the file open,
>>and should welcome the subsequent unleashing of evil content as a
>>valuable lesson.
> 
> 
> Really? I thought that writeback is not synchronous at close()
> time.... Hmm.... It probably could be in case of mmap....
> 

writeback isn't, but the pages will get marked dirty at unmap.
But I think I am wrong actually - I don't actually see why the
user would have to have the file open.

> It is still pretty unexpected. Like "root sees you have that file
> open, so he stops you via ptrace".... but ok....

Or maybe

cp /tmp/sign.me ~/
chown ... ~/sign.me
chmod ... ~/sign.me
mv ~/sign.me /tmp/signed
-
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