linux-kernel - Re: [RESEND] [PATCH] VFS: make file->f

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Message-ID: <52983.1223556575@turing-police.cc.vt.edu>
Date:	Thu, 09 Oct 2008 08:49:35 -0400
From:	Valdis.Kletnieks@...edu
To:	Pavel Machek <pavel@...e.cz>
Cc:	Matthew Wilcox <matthew@....cx>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	torvalds@...ux-foundation.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Hisashi Hifumi <hifumi.hisashi@....ntt.co.jp>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	"Theodore Ts'o" <tytso@....edu>
Subject: Re: [RESEND] [PATCH] VFS: make file->f_pos access atomic on 32bit arch

On Thu, 09 Oct 2008 14:23:19 +0200, Pavel Machek said:

> We have append-only files, and normal users should not be able to work
> around that restriction.

Can you give an example of two *plausible* starting offsets, and 2 write
lengths, which when subjected to this race manage to override the append-only
attribute? I believe somebody already checked the code, and for append-only
we force the offset in the kernel for *each* write.


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