From mboxrd@z Thu Jan  1 00:00:00 1970
From: =?utf-8?Q?Am=C3=A9rico?= Wang <xiyou.wangcong@gmail.com>
Subject: Re: [PATCH v2] fs: select: fix information leak to userspace
Date: Wed, 24 Nov 2010 19:05:35 +0800
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Cc: Andreas Dilger <adilger.kernel@dilger.ca>, wharms@bfs.de,
	=?utf-8?Q?Am=C3=A9rico?= Wang <xiyou.wangcong@gmail.com>,
	Eric Dumazet <eric.dumazet@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Vasiliy Kulikov <segoon@openwall.com>,
	kernel-janitors@vger.kernel.org,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	Jakub Jelinek <jakub@redhat.com>
To: =?utf-8?Q?P=C3=A1draig?= Brady <P@draigBrady.com>
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On Wed, Nov 24, 2010 at 10:44:50AM +0000, P=C3=A1draig Brady wrote:
>On 23/11/10 18:02, Andreas Dilger wrote:
>> On 2010-11-23, at 07:45, walter harms wrote:
>>> Maybe we can convince the gcc people to make 0 padding default. Tha=
t 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 t=
hat this will close some other subtle leaks also.
>>=20
>> It makes the most sense to tackle this at the GCC level, since the a=
dded overhead of doing memset(0) on the whole struct may be non-trivial=
 for commonly-used and/or large structures.  Since GCC is already expli=
citly zeroing the _used_ fields in the struct, it can much more easily =
determine whether there is padding in the structure, and zero those few=
 bytes as needed.
>
>Zero padding structs is part of C90. Details here:
>http://www.pixelbeat.org/programming/gcc/auto_init.html

Nope.

>
>gcc doesn't zero pad when _all_ elements are specified.
>

That is what gcc does, not what C standard specifies.