linux-kernel - Re: different capability from different namespace required for prctl_set_mm_exe

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Date:   Tue, 25 Sep 2018 21:34:27 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Tong Zhang <ztong@...edu>, tglx@...utronix.de,
        akpm@...ux-foundation.org, linux@...inikbrodowski.net,
        ebiederm@...ssion.com, keescook@...omium.org, Dave.Martin@....com,
        wolffhardt.schwabe@....de, yang.shi@...ux.alibaba.com,
        linux-kernel@...r.kernel.org, wenbo.s@...sung.com
Subject: Re: different capability from different namespace required for
 prctl_set_mm_exe_file

On Tue, Sep 25, 2018 at 07:37:45PM +0200, Greg KH wrote:
> On Tue, Sep 25, 2018 at 01:26:55PM -0400, Tong Zhang wrote:
> > Kernel Version: 4.18.5
> > 
> > Problem Description:
> > 
> > We discovered inconsistent check when using prctl_set_mm_exe_file(), which is used to setup exe file link.
> > 
> > It is required to have capable(CAP_SYS_RESOURCE) in prctl_set_mm().
> > while ns_capable(CAP_SYS_ADMIN) in prctl_set_mm_map().
> > 
> > There are two differences:
> > 1)requiring capability from: user namespace, init namespace.
> > 2)capability bit required is different
> 
> Can you submit a patch showing what you think is the correct fix here?

It is done this way on purpose. The prctl_set_mm_map is a complex call
which carries a bunch of parameters and allowed if you're inside user-ns admin,
in turn prctl_set_mm allows to modify settings one by one. So no, it is not
an error but rather call specifics.