linux-kernel - Re: [PATCH v2012.1] fs: symlink restrictions on sticky directories

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Date:	Thu, 5 Jan 2012 11:34:43 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Nick Bowler <nbowler@...iptictech.com>
Cc:	linux-kernel@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Federica Teodori <federica.teodori@...glemail.com>,
	Lucian Adrian Grijincu <lucian.grijincu@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Eric Paris <eparis@...hat.com>,
	Randy Dunlap <rdunlap@...otime.net>,
	Dan Rosenberg <drosenberg@...curity.com>,
	linux-doc@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v2012.1] fs: symlink restrictions on sticky directories

On Thu, Jan 5, 2012 at 6:30 AM, Nick Bowler <nbowler@...iptictech.com> wrote:
> On 2012-01-04 12:18 -0800, Kees Cook wrote:
>> diff --git a/fs/Kconfig b/fs/Kconfig
>> index 5f4c45d..26ede24 100644
>> --- a/fs/Kconfig
>> +++ b/fs/Kconfig
>> @@ -278,3 +278,19 @@ source "fs/nls/Kconfig"
>>  source "fs/dlm/Kconfig"
>>
>>  endmenu
>> +
>> +config PROTECTED_STICKY_SYMLINKS
>> +     bool "Protect symlink following in sticky world-writable directories"
>> +     default y
> [...]
>
> Why do we need a config option for this?  What's wrong with just using
> the sysctl?

This way the sysctl can configured directly without needing to have a
distro add a new item to sysctl.conf.

> Why have you made this option "default y", when enabling it clearly
> makes user-visible changes to kernel behaviour?

Ingo specifically asked me to make it "default y".

-Kees

-- 
Kees Cook
ChromeOS Security
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