From: Nick Bowler <nbowler@elliptictech.com>
To: Kees Cook <keescook@chromium.org>
Cc: linux-kernel@vger.kernel.org,
Alexander Viro <viro@zeniv.linux.org.uk>,
Ingo Molnar <mingo@elte.hu>,
Andrew Morton <akpm@linux-foundation.org>,
Rik van Riel <riel@redhat.com>,
Federica Teodori <federica.teodori@googlemail.com>,
Lucian Adrian Grijincu <lucian.grijincu@gmail.com>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Eric Paris <eparis@redhat.com>,
Randy Dunlap <rdunlap@xenotime.net>,
Dan Rosenberg <drosenberg@vsecurity.com>,
linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org,
kernel-hardening@lists.openwall.com
Subject: Re: [PATCH v2012.1] fs: symlink restrictions on sticky directories
Date: Thu, 5 Jan 2012 09:30:08 -0500 [thread overview]
Message-ID: <20120105143008.GA31728@elliptictech.com> (raw)
In-Reply-To: <20120104201800.GA2587@www.outflux.net>
On 2012-01-04 12:18 -0800, Kees Cook wrote:
> A long-standing class of security issues is the symlink-based
> time-of-check-time-of-use race, most commonly seen in world-writable
> directories like /tmp. The common method of exploitation of this flaw
> is to cross privilege boundaries when following a given symlink (i.e. a
> root process follows a symlink belonging to another user). For a likely
> incomplete list of hundreds of examples across the years, please see:
> http://cve.mitre.org/cgi-bin/cvekey.cgi?keyword=/tmp
>
> The solution is to permit symlinks to only be followed when outside
> a sticky world-writable directory, or when the uid of the symlink and
> follower match, or when the directory owner matches the symlink's owner.
[...]
> 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?
Why have you made this option "default y", when enabling it clearly
makes user-visible changes to kernel behaviour?
Cheers,
--
Nick Bowler, Elliptic Technologies (http://www.elliptictech.com/)
next prev parent reply other threads:[~2012-01-05 14:40 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-04 20:18 [PATCH v2012.1] fs: symlink restrictions on sticky directories Kees Cook
2012-01-05 9:17 ` Ingo Molnar
2012-01-05 19:36 ` Kees Cook
2012-01-06 7:36 ` Ingo Molnar
2012-01-06 9:21 ` Andrew Morton
2012-01-06 9:43 ` Ingo Molnar
2012-01-06 9:58 ` Andrew Morton
2012-01-06 10:05 ` Ingo Molnar
2012-01-06 10:33 ` Andrew Morton
2012-01-06 11:16 ` Ingo Molnar
2012-01-06 18:34 ` Kees Cook
2012-01-06 18:44 ` Kees Cook
2012-01-05 14:30 ` Nick Bowler [this message]
2012-01-05 19:34 ` Kees Cook
2012-01-05 20:08 ` Nick Bowler
2012-01-05 20:55 ` Kees Cook
2012-01-05 22:18 ` Nick Bowler
2012-01-06 0:08 ` Kees Cook
2012-01-06 2:05 ` Rik van Riel
2012-01-06 7:34 ` Ingo Molnar
2012-01-06 7:10 ` Ingo Molnar
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