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From: Lingzhu Xiang <lxiang-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
To: Matt Fleming <matt.fleming-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Cc: Al Viro <viro-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>,
	linux-efi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	Jeremy Kerr <jeremy.kerr-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org>
Subject: Re: [RFC] efivars write(2) races
Date: Mon, 28 Jan 2013 10:38:27 +0800	[thread overview]
Message-ID: <5105E4A3.9040102@redhat.com> (raw)
In-Reply-To: <1359119883.2496.156.camel-ZqTwcBeJ+wsBof6jY8KHXm7IUlhRatedral2JQCrhuEAvxtiuMwx3w@public.gmane.org>

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

WARNING: multiple messages have this Message-ID (diff)
From: Lingzhu Xiang <lxiang@redhat.com>
To: Matt Fleming <matt.fleming@intel.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>,
	linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org,
	Jeremy Kerr <jeremy.kerr@canonical.com>
Subject: Re: [RFC] efivars write(2) races
Date: Mon, 28 Jan 2013 10:38:27 +0800	[thread overview]
Message-ID: <5105E4A3.9040102@redhat.com> (raw)
In-Reply-To: <1359119883.2496.156.camel@mfleming-mobl1.ger.corp.intel.com>

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

  parent reply	other threads:[~2013-01-28  2:38 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-01-25  0:25 [RFC] efivars write(2) races Al Viro
2013-01-25  0:25 ` Al Viro
     [not found] ` <20130125002552.GC4503-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>
2013-01-25  3:50   ` Lingzhu Xiang
2013-01-25  3:50     ` Lingzhu Xiang
     [not found]     ` <51020120.5000500-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2013-01-25 13:18       ` Matt Fleming
2013-01-25 13:18         ` Matt Fleming
     [not found]         ` <1359119883.2496.156.camel-ZqTwcBeJ+wsBof6jY8KHXm7IUlhRatedral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2013-01-28  2:38           ` Lingzhu Xiang [this message]
2013-01-28  2:38             ` Lingzhu Xiang
     [not found]             ` <5105E4A3.9040102-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2013-01-28 12:38               ` Matt Fleming
2013-01-28 12:38                 ` Matt Fleming
     [not found]                 ` <1359376730.8282.20.camel-ZqTwcBeJ+wsBof6jY8KHXm7IUlhRatedral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2013-01-29  2:30                   ` Lingzhu Xiang
2013-01-29  2:30                     ` Lingzhu Xiang
2013-01-25 12:50 ` Matt Fleming

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