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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20101124123213.GB2922@hack>
Date:	Wed, 24 Nov 2010 20:32:13 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Pádraig Brady <P@...igBrady.com>
Cc:	Américo Wang <xiyou.wangcong@...il.com>,
	Andreas Dilger <adilger.kernel@...ger.ca>, wharms@....de,
	Eric Dumazet <eric.dumazet@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	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 Wed, Nov 24, 2010 at 11:46:33AM +0000, Pádraig Brady wrote:
>On 24/11/10 11:05, Américo Wang wrote:
>> On Wed, Nov 24, 2010 at 10:44:50AM +0000, Pádraig 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. 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.
>>>>
>>>> It makes the most sense to tackle this at the GCC level, since the added overhead of doing memset(0) on the whole struct may be non-trivial for commonly-used and/or large structures.  Since GCC is already explicitly 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.
>
>Looks like gcc is following the standard exactly.
>
>C90 - 6.5.7
>C99 - 6.7.8
>
>  If there are fewer initializers in a brace-enclosed list than
>  there are elements or members of an aggregate ... the remainder
>  of the aggregate shall be initialized implicitly the same as
>  objects that have static storage duration.
>

Depends on if "the remainder of the aggregate" includes padding bytes
or not.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/