linux-kernel - Re: [PATCH v2] fs: select: fix information leak to userspace

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Date:	Tue, 23 Nov 2010 23:23:55 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	walter harms <wharms@....de>
Cc:	Américo Wang <xiyou.wangcong@...il.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	kernel-janitors@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jakub Jelinek <jakub@...hat.com>
Subject: Re: [PATCH v2] fs: select: fix information leak to userspace

On Tue, Nov 23, 2010 at 03:45:18PM +0100, walter harms wrote:
>Am 23.11.2010 15:01, schrieb Américo Wang:
>> On Mon, Nov 15, 2010 at 08:12:21PM +0100, Eric Dumazet wrote:
>>>
>>> In my understanding, gcc should initialize all holes (and other not
>>> mentioned fields) with 0, even for automatic storage [C99 only mandates
>>> this on static storage]
>>>
>>> I tested on x86_64 and this is the case, but could not find a definitive
>>> answer in gcc documentation.
>>>
>> 
>> Yeah, this is not clearly defined by C99 I think, but we can still
>> find some clues in 6.2.6.1, Paragraph 6,
>> 
>> "
>> When a value is stored in an object of structure or union type,
>> including in a member object, the bytes of the object representation
>> that correspond to any padding bytes take unspecified values.
>> "
>> 
>> So we can't rely on the compiler to initialize the padding bytes
>> too.
>> 
>hi all,
>as we see this is not a question of c99.
>Maybe we can convince the gcc people to make 0 padding default. That will not solve the
>problems for other compilers but when they claim "works like gcc" we can press then to
>support this also. I can imagine that this will close some other subtle leaks also.
>
>People that still want a "undefined" (for what ever reason) can use an option to enable it
>again (e.g.  --no-zero-padding).


Well, IMHO, the default behavior should be "undefined", thus
"-fzero-padding" is needed. But, you know, I am not a compiler
people at all. :)

>
>do anyone have a contact so we can forward that request ?
>

gcc@....gnu.org ?

-- 
Live like a child, think like the god.
 
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