From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf1-f66.google.com ([209.85.167.66]:33674 "EHLO mail-lf1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728320AbeINAXg (ORCPT ); Thu, 13 Sep 2018 20:23:36 -0400 Received: by mail-lf1-f66.google.com with SMTP id m26-v6so5792648lfb.0 for ; Thu, 13 Sep 2018 12:12:44 -0700 (PDT) MIME-Version: 1.0 References: <99cb1ae7-8881-eb9a-a8cb-a787abe454e1@schaufler-ca.com> In-Reply-To: From: Paul Moore Date: Thu, 13 Sep 2018 15:12:32 -0400 Message-ID: Subject: Re: [PATCH 10/10] LSM: Blob sharing support for S.A.R.A and LandLock To: keescook@chromium.org Cc: casey@schaufler-ca.com, linux-security-module@vger.kernel.org, James Morris , linux-kernel@vger.kernel.org, selinux@tycho.nsa.gov, john.johansen@canonical.com, penguin-kernel@i-love.sakura.ne.jp, Stephen Smalley , linux-fsdevel@vger.kernel.org, adobriyan@gmail.com, casey.schaufler@intel.com Content-Type: text/plain; charset="UTF-8" Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Thu, Sep 13, 2018 at 11:19 AM Kees Cook wrote: > On Thu, Sep 13, 2018 at 6:16 AM, Paul Moore wrote: > > On Thu, Sep 13, 2018 at 12:19 AM Kees Cook wrote: > >> On Tue, Sep 11, 2018 at 9:42 AM, Casey Schaufler wrote: > >> > Two proposed security modules require the ability to > >> > share security blobs with existing "major" security modules. > >> > These modules, S.A.R.A and LandLock, provide significantly > >> > different services than SELinux, Smack or AppArmor. Using > >> > either in conjunction with the existing modules is quite > >> > reasonable. S.A.R.A requires access to the cred blob, while > >> > LandLock uses the cred, file and inode blobs. > >> > > >> > The use of the cred, file and inode blobs has been > >> > abstracted in preceding patches in the series. This > >> > patch teaches the affected security modules how to access > >> > the part of the blob set aside for their use in the case > >> > where blobs are shared. The configuration option > >> > CONFIG_SECURITY_STACKING identifies systems where the > >> > blobs may be shared. > >> > > >> > The mechanism for selecting which security modules are > >> > active has been changed to allow non-conflicting "major" > >> > security modules to be used together. At this time the > >> > TOMOYO module can safely be used with any of the others. > >> > The two new modules would be non-conflicting as well. > >> > > >> > Signed-off-by: Casey Schaufler > >> > --- > >> > Documentation/admin-guide/LSM/index.rst | 14 +++-- > >> > include/linux/lsm_hooks.h | 2 +- > >> > security/Kconfig | 81 +++++++++++++++++++++++++ > >> > security/apparmor/include/cred.h | 8 +++ > >> > security/apparmor/include/file.h | 9 ++- > >> > security/apparmor/include/lib.h | 4 ++ > >> > security/apparmor/lsm.c | 8 ++- > >> > security/security.c | 30 ++++++++- > >> > security/selinux/hooks.c | 3 +- > >> > security/selinux/include/objsec.h | 18 +++++- > >> > security/smack/smack.h | 19 +++++- > >> > security/smack/smack_lsm.c | 17 +++--- > >> > security/tomoyo/common.h | 12 +++- > >> > security/tomoyo/tomoyo.c | 3 +- > >> > 14 files changed, 200 insertions(+), 28 deletions(-) > > > > ... > > > >> > diff --git a/security/Kconfig b/security/Kconfig > >> > index 22f7664c4977..ed48025ae9e0 100644 > >> > --- a/security/Kconfig > >> > +++ b/security/Kconfig > >> > @@ -36,6 +36,28 @@ config SECURITY_WRITABLE_HOOKS > >> > bool > >> > default n > >> > > >> > +config SECURITY_STACKING > >> > + bool "Security module stacking" > >> > + depends on SECURITY > >> > + help > >> > + Allows multiple major security modules to be stacked. > >> > + Modules are invoked in the order registered with a > >> > + "bail on fail" policy, in which the infrastructure > >> > + will stop processing once a denial is detected. Not > >> > + all modules can be stacked. SELinux, Smack and AppArmor are > >> > + known to be incompatible. User space components may > >> > + have trouble identifying the security module providing > >> > + data in some cases. > >> > + > >> > + If you select this option you will have to select which > >> > + of the stackable modules you wish to be active. The > >> > + "Default security module" will be ignored. The boot line > >> > + "security=" option can be used to specify that one of > >> > + the modules identifed for stacking should be used instead > >> > + of the entire stack. > >> > + > >> > + If you are unsure how to answer this question, answer N. > >> > >> I don't see a good reason to make this a config. Why shouldn't this > >> always be enabled? > > > > I do. From a user perspective it is sometimes difficult to determine > > the reason behind a failed operation; its is a DAC based denial, the > > LSM, or some other failure? Stacking additional LSMs has the > > potential to make this worse. The boot time configuration adds to the > > complexity. > > Let me try to convince you otherwise. :) The reason I think there's no > need for this is because the only functional change here is how > _TOMOYO_ gets stacked. And in my proposal, we can convert TOMOYO to be > enabled/disabled like LoadPin. Given the configs I showed, stacking > TOMOYO with the other major LSMs becomes a config (and/or boottime) > option. > > The changes for TOMOYO are still needed even _with_ SECURITY_STACKING, > and I argue that the other major LSMs remain the same. It's only > infrastructure that has changed. So, I think having SECURITY_STACKING > actually makes things more complex internally (all the ifdefs, weird > enable logic) and for distros ("what's this stacking option", etc?) None of the above deals with the user experience or support burden a distro would have by forcing stacking on. If we make it an option the distros can choose for themselves; picking a kernel build config is not something new to distros, and I think Casey's text adequately explains CONFIG_SECURITY_STACKING in terms that would be sufficient. I currently have a neutral stance on stacking, making it mandatory pushes me more towards a "no". As far as the cpp ifdef's, and other conditionals are concerned, I remain unconvinced this is any worse than any other significant feature that is a build time option. -- paul moore www.paul-moore.com