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Message-ID: <20200910092656.GA800@gandi.net>
Date: Thu, 10 Sep 2020 11:26:56 +0200
From: Thibaut Sautereau <thibaut.sautereau@...p-os.org>
To: Matthew Wilcox <willy@...radead.org>, 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>,
Andy Lutomirski <luto@...nel.org>,
Christian Brauner <christian.brauner@...ntu.com>,
Christian Heimes <christian@...hon.org>,
Daniel Borkmann <daniel@...earbox.net>,
Deven Bowers <deven.desai@...ux.microsoft.com>,
Dmitry Vyukov <dvyukov@...gle.com>,
Eric Biggers <ebiggers@...nel.org>,
Eric Chiang <ericchiang@...gle.com>,
Florian Weimer <fweimer@...hat.com>,
James Morris <jmorris@...ei.org>, Jan Kara <jack@...e.cz>,
Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>,
Kees Cook <keescook@...omium.org>,
Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>,
Matthew Garrett <mjg59@...gle.com>,
Michael Kerrisk <mtk.manpages@...il.com>,
Miklos Szeredi <mszeredi@...hat.com>,
Mimi Zohar <zohar@...ux.ibm.com>,
Philippe Trébuchet <philippe.trebuchet@....gouv.fr>,
Scott Shell <scottsh@...rosoft.com>,
Sean Christopherson <sean.j.christopherson@...el.com>,
Shuah Khan <shuah@...nel.org>, Steve Dower <steve.dower@...hon.org>,
Steve Grubb <sgrubb@...hat.com>,
Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
Vincent Strubel <vincent.strubel@....gouv.fr>,
kernel-hardening@...ts.openwall.com, linux-api@...r.kernel.org,
linux-integrity@...r.kernel.org,
linux-security-module@...r.kernel.org,
linux-fsdevel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>
Subject: Re: [RFC PATCH v8 0/3] Add support for AT_INTERPRETED (was O_MAYEXEC)
On Wed, Sep 09, 2020 at 06:08:51PM +0100, Matthew Wilcox 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.
>
> Al is saying you should add a new syscall, not try to fold it into
> some existing syscall.
>
> I agree with him. Add a new syscall, just like you were told to do it
> last time.
Sure, we'll do it. In the meantime, could we at least get an explanation
about why using faccessat2() instead of a new syscall is wrong? I could
see the reasons for separating the exec checks from the file opening,
but this time I don't understand. Is it because it brings too much
complexity to do_faccessat()?
--
Thibaut Sautereau
CLIP OS developer
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