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Message-ID: <CAEjxPJ7WjeQAz3XSCtgpYiRtH+Jx-UkSTaEcnVyz_jwXKE3dkw@mail.gmail.com>
Date: Thu, 14 May 2020 08:22:01 -0400
From: Stephen Smalley <stephen.smalley.work@...il.com>
To: Kees Cook <keescook@...omium.org>
Cc: Mickaël Salaün <mic@...ikod.net>,
linux-kernel <linux-kernel@...r.kernel.org>, Aleksa Sarai <cyphar@...har.com>,
Alexei Starovoitov <ast@...nel.org>, Al Viro <viro@...iv.linux.org.uk>,
Andy Lutomirski <luto@...nel.org>, Christian Heimes <christian@...hon.org>,
Daniel Borkmann <daniel@...earbox.net>, Deven Bowers <deven.desai@...ux.microsoft.com>,
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>,
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>,
Thibaut Sautereau <thibaut.sautereau@....gouv.fr>,
Vincent Strubel <vincent.strubel@....gouv.fr>, kernel-hardening@...ts.openwall.com,
linux-api@...r.kernel.org, linux-integrity@...r.kernel.org,
LSM List <linux-security-module@...r.kernel.org>,
Linux FS Devel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH v5 3/6] fs: Enable to enforce noexec mounts or file exec
through O_MAYEXEC
On Wed, May 13, 2020 at 11:05 PM Kees Cook <keescook@...omium.org> wrote:
>
> On Wed, May 13, 2020 at 04:27:39PM -0700, Kees Cook wrote:
> > Like, couldn't just the entire thing just be:
> >
> > diff --git a/fs/namei.c b/fs/namei.c
> > index a320371899cf..0ab18e19f5da 100644
> > --- a/fs/namei.c
> > +++ b/fs/namei.c
> > @@ -2849,6 +2849,13 @@ static int may_open(const struct path *path, int acc_mode, int flag)
> > break;
> > }
> >
> > + if (unlikely(mask & MAY_OPENEXEC)) {
> > + if (sysctl_omayexec_enforce & OMAYEXEC_ENFORCE_MOUNT &&
> > + path_noexec(path))
> > + return -EACCES;
> > + if (sysctl_omayexec_enforce & OMAYEXEC_ENFORCE_FILE)
> > + acc_mode |= MAY_EXEC;
> > + }
> > error = inode_permission(inode, MAY_OPEN | acc_mode);
> > if (error)
> > return error;
> >
>
> FYI, I've confirmed this now. Effectively with patch 2 dropped, patch 3
> reduced to this plus the Kconfig and sysctl changes, the self tests
> pass.
>
> I think this makes things much cleaner and correct.
I think that covers inode-based security modules but not path-based
ones (they don't implement the inode_permission hook). For those, I
would tentatively guess that we need to make sure FMODE_EXEC is set on
the open file and then they need to check for that in their file_open
hooks.
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