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Date: Fri, 15 May 2020 01:01:32 -0700
From: Kees Cook <keescook@...omium.org>
To: Mickaël Salaün <mic@...ikod.net>
Cc: Al Viro <viro@...iv.linux.org.uk>, Aleksa Sarai <cyphar@...har.com>,
Andy Lutomirski <luto@...nel.org>, Mimi Zohar <zohar@...ux.ibm.com>,
Stephen Smalley <stephen.smalley.work@...il.com>,
Christian Heimes <christian@...hon.org>,
Deven Bowers <deven.desai@...ux.microsoft.com>,
Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
John Johansen <john.johansen@...onical.com>,
Kentaro Takeda <takedakn@...data.co.jp>,
"Lev R. Oshvang ." <levonshe@...il.com>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
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>,
Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>,
Matthew Garrett <mjg59@...gle.com>,
Matthew Wilcox <willy@...radead.org>,
Michael Kerrisk <mtk.manpages@...il.com>,
Mickaël Salaün <mickael.salaun@....gouv.fr>,
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>,
Thibaut Sautereau <thibaut.sautereau@....gouv.fr>,
Vincent Strubel <vincent.strubel@....gouv.fr>,
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linux-integrity@...r.kernel.org,
LSM List <linux-security-module@...r.kernel.org>,
Linux FS Devel <linux-fsdevel@...r.kernel.org>
Subject: How about just O_EXEC? (was Re: [PATCH v5 3/6] fs: Enable to enforce
noexec mounts or file exec through O_MAYEXEC)
On Thu, May 14, 2020 at 09:16:13PM +0200, Mickaël Salaün wrote:
> On 14/05/2020 18:10, Stephen Smalley wrote:
> > On Thu, May 14, 2020 at 11:45 AM Kees Cook <keescook@...omium.org> wrote:
> >> So, it looks like adding FMODE_EXEC into f_flags in do_open() is needed in
> >> addition to injecting MAY_EXEC into acc_mode in do_open()? Hmmm
> >
> > Just do both in build_open_flags() and be done with it? Looks like he
> > was already setting FMODE_EXEC in patch 1 so we just need to teach
> > AppArmor/TOMOYO to check for it and perform file execute checking in
> > that case if !current->in_execve?
>
> I can postpone the file permission check for another series to make this
> one simpler (i.e. mount noexec only). Because it depends on the sysctl
> setting, it is OK to add this check later, if needed. In the meantime,
> AppArmor and Tomoyo could be getting ready for this.
So, after playing around with this series, investigating Stephen's
comments, digging through the existing FMODE_EXEC uses, and spending a
bit more time thinking about Lev and Aleksa's dislike of the sysctls, I've
got a much more radically simplified solution that I think could work.
Maybe I've missed some earlier discussion that ruled this out, but I
couldn't find it: let's just add O_EXEC and be done with it. It actually
makes the execve() path more like openat2() and is much cleaner after
a little refactoring. Here are the results, though I haven't emailed it
yet since I still want to do some more testing:
https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/log/?h=kspp/o_exec/v1
I look forward to flames! ;)
--
Kees Cook
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