linux-kernel - Re: Leaking Path in XFS's ioctl interface(missing LSM check)

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Message-ID: <20180926192426.472360ea@alans-desktop>
Date:   Wed, 26 Sep 2018 19:24:26 +0100
From:   Alan Cox <gnomes@...rguk.ukuu.org.uk>
To:     Dave Chinner <david@...morbit.com>
Cc:     TongZhang <ztong@...edu>, darrick.wong@...cle.com,
        linux-xfs@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        linux-security-module@...r.kernel.org,
        Wenbo Shen <shenwenbosmile@...il.com>
Subject: Re: Leaking Path in XFS's ioctl interface(missing LSM check)

On Wed, 26 Sep 2018 11:33:29 +1000
Dave Chinner <david@...morbit.com> wrote:

> On Tue, Sep 25, 2018 at 08:51:50PM -0400, TongZhang wrote:
> > Hi,
> > 
> > I'm bringing up this issue again to let of LSM developers know the situation, and would like to know your thoughts.
> > Several weeks ago I sent an email to the security list to discuss the issue where
> > XFS's ioctl interface can do things like vfs_readlink without asking LSM's
> > permission, which we think is kind of weird and this kind of operation should be
> > audited by LSM.  
> 
> These aren't user interfaces. They are filesystem maintenance and
> extension interfaces.  They are intended for low level filesystem
> utilities that require complete, unrestricted access to the
> underlying filesystem via holding CAP_SYSADMIN in the initns.

CAP_SYS_ADMIN is meaningless in an environment using a strong LSM set up.
So what if I have CAP_SYS_ADMIN ? In a secure environment low level
complete unrestricted access to the file system is most definitely
something that should be mediated.

CAP_SYS_ADMIN is also a bit weird because low level access usually
implies you can bypass access controls so you should also check
CAP_SYS_DAC ?

Alan