Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <20190326182742.16950-1-matthewgarrett@google.com> <20190326182742.16950-26-matthewgarrett@google.com>
In-Reply-To: <20190326182742.16950-26-matthewgarrett@google.com>
From:   Andy Lutomirski <luto@kernel.org>
Date:   Tue, 26 Mar 2019 12:20:24 -0700
Message-ID: <CALCETrXDF2c2-gnOyNTnEn-uPAZp0AaSB_PB8e2y8jf7zo=Cyg@mail.gmail.com>
Subject: Re: [PATCH V31 25/25] debugfs: Disable open() when kernel is locked down
To:     Matthew Garrett <matthewgarrett@google.com>
Cc:     James Morris <jmorris@namei.org>,
        LSM List <linux-security-module@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        David Howells <dhowells@redhat.com>,
        Linux API <linux-api@vger.kernel.org>,
        Andrew Lutomirski <luto@kernel.org>,
        Matthew Garrett <mjg59@google.com>,
        Greg KH <gregkh@linuxfoundation.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, Mar 26, 2019 at 11:28 AM Matthew Garrett
<matthewgarrett@google.com> wrote:
>
> From: Matthew Garrett <mjg59@google.com>
>
> debugfs has not been meaningfully audited in terms of ensuring that
> userland cannot trample over the kernel. At Greg's request, disable
> access to it entirely when the kernel is locked down. This is done at
> open() time rather than init time as the kernel lockdown status may be
> made stricter at runtime.

Ugh.  Some of those files are very useful.  Could this perhaps still
allow O_RDONLY if we're in INTEGRITY mode?