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Re: [PATCH] xfs: change the immutable in xfs_open_by_handle

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: [PATCH] xfs: change the immutable in xfs_open_by_handle
From: Mark Tinguely <tinguely@xxxxxxx>
Date: Wed, 11 Sep 2013 09:22:46 -0500
Cc: xfs@xxxxxxxxxxx, Greg Banks <gbanks@xxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20130911135502.GA21898@xxxxxxxxxxxxx>
References: <20130910184724.726933044@xxxxxxx> <20130911135502.GA21898@xxxxxxxxxxxxx>
User-agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:9.0) Gecko/20120122 Thunderbird/9.0
On 09/11/13 08:55, Christoph Hellwig wrote:
On Tue, Sep 10, 2013 at 01:47:20PM -0500, Mark Tinguely wrote:
This patch allows clients like DMF to modify an immutable file
without changing the immutable capability on the file, which
would expose the file to change.

This patch is restricted to holders of the CAP_LINUX_IMMUTABLE,
so no addition security risk has been introduced.

The immutable flag means that the file can't be modified, and
CAP_LINUX_IMMUTABLE allows setting/removing that restriction, but not
ignoring it.

So: NAK, this is a change in semantics and long-standing behaviour.

As you said, the CAP_LINUX_IMMUTABLE allows the holder of the capability to turn on/off the restriction. The holder of CAP_LINUX_IMMUTABLE could turn off immutability, modify it and then turn it back on, but during that window, others could modify it too which may be more undesirable than changing the behavior.


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