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

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Message-ID: <5105E4A3.9040102@redhat.com>
Date:	Mon, 28 Jan 2013 10:38:27 +0800
From:	Lingzhu Xiang <lxiang@...hat.com>
To:	Matt Fleming <matt.fleming@...el.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 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
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