linux-kernel - Re: [PATCH] Yama: verify inode is symlink to avoid bind mounts

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Message-ID: <20100714065337.GY6104@outflux.net>
Date:	Tue, 13 Jul 2010 23:53:37 -0700
From:	Kees Cook <kees.cook@...onical.com>
To:	"Serge E. Hallyn" <serge@...lyn.com>
Cc:	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Yama: verify inode is symlink to avoid bind mounts

On Tue, Jul 13, 2010 at 09:30:48PM -0500, Serge E. Hallyn wrote:
> Quoting Kees Cook (kees.cook@...onical.com):
> > The inode_follow_link LSM hook is called in bind mount situations as
> > well as for symlink situations, so we must explicitly check for the
> > inode being a symlink to not reject bind mounts in 1777 directories,
> 
> Are you sure about that??
> 
> If that's true, you might also expand the comment in
> include/linux/security.h.
> 
> > which seems to be a common NFSv4 configuration.

Well, the issue is how the NFSv4 client deals with it. It seems to treat
the mounts from the NFSv4 root as a symlink when the server is using bind
mounts.  It's kind of weird:
https://launchpad.net/bugs/604407

-- 
Kees Cook
Ubuntu Security Team
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