linux-kernel - Re: [RFC PATCH v8 0/3] Add support for AT_INTERPRETED (was O

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Message-ID: <alpine.LRH.2.21.2009121014440.17638@namei.org>
Date:   Sat, 12 Sep 2020 10:16:49 +1000 (AEST)
From:   James Morris <jmorris@...ei.org>
To:     Al Viro <viro@...iv.linux.org.uk>
cc:     Mickaël Salaün <mic@...ikod.net>,
        linux-kernel@...r.kernel.org, Aleksa Sarai <cyphar@...har.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
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Subject: Re: [RFC PATCH v8 0/3] Add support for AT_INTERPRETED (was
 O_MAYEXEC)

On Wed, 9 Sep 2020, Al Viro wrote:

> On Wed, Sep 09, 2020 at 09:19:11AM +0200, Mickaël Salaün wrote:
> > 
> > On 08/09/2020 20:50, Al Viro wrote:
> > > On Tue, Sep 08, 2020 at 09:59:53AM +0200, Mickaël Salaün wrote:
> > >> Hi,
> > >>
> > >> This height patch series rework the previous O_MAYEXEC series by not
> > >> adding a new flag to openat2(2) but to faccessat2(2) instead.  As
> > >> suggested, this enables to perform the access check on a file descriptor
> > >> instead of on a file path (while opening it).  This may require two
> > >> checks (one on open and then with faccessat2) but it is a more generic
> > >> approach [8].
> > > 
> > > Again, why is that folded into lookup/open/whatnot, rather than being
> > > an operation applied to a file (e.g. O_PATH one)?
> > > 
> > 
> > I don't understand your question. AT_INTERPRETED can and should be used
> > with AT_EMPTY_PATH. The two checks I wrote about was for IMA.
> 
> Once more, with feeling: don't hide that behind existing syscalls.
> If you want to tell LSM have a look at given fs object in a special
> way, *add* *a* *new* *system* *call* *for* *doing* *just* *that*.

It's not just for LSM, though, and it has identical semantics from the 
caller's POV as faccessat().



-- 
James Morris
<jmorris@...ei.org>