linux-kernel - Re: [RFC] efivars write(2) races

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Message-ID: <1359376730.8282.20.camel@mfleming-mobl1.ger.corp.intel.com>
Date:	Mon, 28 Jan 2013 12:38:50 +0000
From:	Matt Fleming <matt.fleming@...el.com>
To:	Lingzhu Xiang <lxiang@...hat.com>
Cc:	Al Viro <viro@...IV.linux.org.uk>, linux-efi@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Jeremy Kerr <jeremy.kerr@...onical.com>
Subject: Re: [RFC] efivars write(2) races

On Mon, 2013-01-28 at 10:38 +0800, Lingzhu Xiang wrote:
> On 01/25/2013 09:18 PM, Matt Fleming wrote:
> >> 4. EFI_VARIABLE_APPEND_WRITE with EFI_OUT_OF_RESOURCES truncates size but you
> >>     can still read its content.
> >
> > I'm not sure what you mean by this. Could you please explain?
> 
> Oops, this one is incorrect. I was testing EFI_VARIABLE_APPEND_WRITE
> using this:
> 
> printf "\x47\x00\x00\x00\x00" >test-1-$guid
> 
> So it truncates the file before writing, but efivarfs figures out the right
> size afterwards. The size remains zero if the write fails.
> 
> I should be using this for appending:
> 
> printf "\x47\x00\x00\x00\x00" >>test-1-$guid

Does this mean that these two test cases work as expected?

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