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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id k3sm15204752pgh.34.2020.03.24.10.57.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 24 Mar 2020 10:57:46 -0700 (PDT) Date: Tue, 24 Mar 2020 10:57:45 -0700 From: Kees Cook To: KP Singh Cc: Stephen Smalley , Casey Schaufler , linux-kernel@vger.kernel.org, bpf@vger.kernel.org, LSM List , Brendan Jackman , Florent Revest , Alexei Starovoitov , Daniel Borkmann , James Morris , Paul Turner , Jann Horn , Florent Revest , Brendan Jackman , Greg Kroah-Hartman Subject: Re: [PATCH bpf-next v5 5/7] bpf: lsm: Initialize the BPF LSM hooks Message-ID: <202003241056.C28E520@keescook> References: <20200323164415.12943-1-kpsingh@chromium.org> <20200323164415.12943-6-kpsingh@chromium.org> <6d45de0d-c59d-4ca7-fcc5-3965a48b5997@schaufler-ca.com> <20200324015217.GA28487@chromium.org> <20200324144214.GA1040@chromium.org> <20200324145155.GB2685@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20200324145155.GB2685@chromium.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 24, 2020 at 03:51:55PM +0100, KP Singh wrote: > On 24-Mär 10:51, Stephen Smalley wrote: > > On Tue, Mar 24, 2020 at 10:42 AM KP Singh wrote: > > > > > > On 24-Mär 10:37, Stephen Smalley wrote: > > > > On Mon, Mar 23, 2020 at 9:52 PM KP Singh wrote: > > > > > > > > > > On 23-Mär 18:13, Casey Schaufler wrote: > > > > > > Have you given up on the "BPF must be last" requirement? > > > > > > > > > > Yes, we dropped it for as the BPF programs require CAP_SYS_ADMIN > > > > > anwyays so the position ~shouldn't~ matter. (based on some of the > > > > > discussions we had on the BPF_MODIFY_RETURN patches). > > > > > > > > > > However, This can be added later (in a separate patch) if really > > > > > deemed necessary. > > > > > > > > It matters for SELinux, as I previously explained. A process that has > > > > CAP_SYS_ADMIN is not assumed to be able to circumvent MAC policy. > > > > And executing prior to SELinux allows the bpf program to access and > > > > potentially leak to userspace information that wouldn't be visible to > > > > the > > > > process itself. However, I thought you were handling the order issue > > > > by putting it last in the list of lsms? > > > > > > We can still do that if it does not work for SELinux. > > > > > > Would it be okay to add bpf as LSM_ORDER_LAST? > > > > > > LSMs like Landlock can then add LSM_ORDER_UNPRIVILEGED to even end up > > > after bpf? > > > > I guess the question is whether we need an explicit LSM_ORDER_LAST or > > can just handle it via the default > > values for the lsm= parameter, where you are already placing bpf last > > IIUC? If someone can mess with the kernel boot > > parameters, they already have options to mess with SELinux, so it is no worse... > > Yeah, we do add BPF as the last LSM in the default list. So, I will > avoid adding LSM_ORDER_LAST for now. FWIW, this is my preference as well. If there ends up being a stronger need, then we can implement LSM_ORDER_LAST at that time. -- Kees Cook