From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Stephen Smalley <sds@tycho.nsa.gov>
Cc: "Alexei Starovoitov" <alexei.starovoitov@gmail.com>,
"KP Singh" <kpsingh@chromium.org>,
"James Morris" <jmorris@namei.org>,
"Kees Cook" <keescook@chromium.org>,
"Casey Schaufler" <casey@schaufler-ca.com>,
"open list" <linux-kernel@vger.kernel.org>,
bpf <bpf@vger.kernel.org>,
linux-security-module@vger.kernel.org,
"Alexei Starovoitov" <ast@kernel.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
"Thomas Garnier" <thgarnie@chromium.org>,
"Michael Halcrow" <mhalcrow@google.com>,
"Paul Turner" <pjt@google.com>,
"Brendan Gregg" <brendan.d.gregg@gmail.com>,
"Jann Horn" <jannh@google.com>,
"Matthew Garrett" <mjg59@google.com>,
"Christian Brauner" <christian@brauner.io>,
"Mickaël Salaün" <mic@digikod.net>,
"Florent Revest" <revest@chromium.org>,
"Brendan Jackman" <jackmanb@chromium.org>,
"Martin KaFai Lau" <kafai@fb.com>,
"Song Liu" <songliubraving@fb.com>, "Yonghong Song" <yhs@fb.com>,
"Serge E. Hallyn" <serge@hallyn.com>,
"Mauro Carvalho Chehab" <mchehab+samsung@kernel.org>,
"David S. Miller" <davem@davemloft.net>,
"Nicolas Ferre" <nicolas.ferre@microchip.com>,
"Stanislav Fomichev" <sdf@google.com>,
"Quentin Monnet" <quentin.monnet@netronome.com>,
"Andrey Ignatov" <rdna@fb.com>, "Joe Stringer" <joe@wand.net.nz>,
"Paul Moore" <paul@paul-moore.com>
Subject: Re: [PATCH bpf-next v1 00/13] MAC and Audit policy using eBPF (KRSI)
Date: Wed, 15 Jan 2020 15:09:53 +0100 [thread overview]
Message-ID: <20200115140953.GB3627564@kroah.com> (raw)
In-Reply-To: <38a82df5-7610-efe1-d6cd-76f6f68c6110@tycho.nsa.gov>
On Wed, Jan 15, 2020 at 08:59:08AM -0500, Stephen Smalley wrote:
> On 1/14/20 9:48 PM, Alexei Starovoitov wrote:
> > On Tue, Jan 14, 2020 at 12:42:22PM -0500, Stephen Smalley wrote:
> > > On 1/14/20 11:54 AM, Stephen Smalley wrote:
> > > > On 1/10/20 12:53 PM, Alexei Starovoitov wrote:
> > > > > On Fri, Jan 10, 2020 at 04:27:58PM +0100, KP Singh wrote:
> > > > > > On 09-Jan 14:47, Stephen Smalley wrote:
> > > > > > > On 1/9/20 2:43 PM, KP Singh wrote:
> > > > > > > > On 10-Jan 06:07, James Morris wrote:
> > > > > > > > > On Thu, 9 Jan 2020, Stephen Smalley wrote:
> > > > > > > > >
> > > > > > > > > > On 1/9/20 1:11 PM, James Morris wrote:
> > > > > > > > > > > On Wed, 8 Jan 2020, Stephen Smalley wrote:
> > > > > > > > > > >
> > > > > > > > > > > > The cover letter subject line and the
> > > > > > > > > > > > Kconfig help text refer to it as a
> > > > > > > > > > > > BPF-based "MAC and Audit policy". It
> > > > > > > > > > > > has an enforce config option that
> > > > > > > > > > > > enables the bpf programs to deny access,
> > > > > > > > > > > > providing access control. IIRC,
> > > > > > > > > > > > in
> > > > > > > > > > > > the earlier discussion threads, the BPF
> > > > > > > > > > > > maintainers suggested that Smack
> > > > > > > > > > > > and
> > > > > > > > > > > > other LSMs could be entirely
> > > > > > > > > > > > re-implemented via it in the future, and
> > > > > > > > > > > > that
> > > > > > > > > > > > such an implementation would be more optimal.
> > > > > > > > > > >
> > > > > > > > > > > In this case, the eBPF code is similar to a
> > > > > > > > > > > kernel module, rather than a
> > > > > > > > > > > loadable policy file. It's a loadable
> > > > > > > > > > > mechanism, rather than a policy, in
> > > > > > > > > > > my view.
> > > > > > > > > >
> > > > > > > > > > I thought you frowned on dynamically loadable
> > > > > > > > > > LSMs for both security and
> > > > > > > > > > correctness reasons?
> > > > > > > >
> > > > > > > > Based on the feedback from the lists we've updated the design for v2.
> > > > > > > >
> > > > > > > > In v2, LSM hook callbacks are allocated dynamically using BPF
> > > > > > > > trampolines, appended to a separate security_hook_heads and run
> > > > > > > > only after the statically allocated hooks.
> > > > > > > >
> > > > > > > > The security_hook_heads for all the other LSMs (SELinux, AppArmor etc)
> > > > > > > > still remains __lsm_ro_after_init and cannot be modified. We are still
> > > > > > > > working on v2 (not ready for review yet) but the general idea can be
> > > > > > > > seen here:
> > > > > > > >
> > > > > > > > https://github.com/sinkap/linux-krsi/blob/patch/v1/trampoline_prototype/security/bpf/lsm.c
> > > > > > > >
> > > > > > > >
> > > > > > > > >
> > > > > > > > > Evaluating the security impact of this is the next
> > > > > > > > > step. My understanding
> > > > > > > > > is that eBPF via BTF is constrained to read only access to hook
> > > > > > > > > parameters, and that its behavior would be entirely restrictive.
> > > > > > > > >
> > > > > > > > > I'd like to understand the security impact more
> > > > > > > > > fully, though. Can the
> > > > > > > > > eBPF code make arbitrary writes to the kernel, or
> > > > > > > > > read anything other than
> > > > > > > > > the correctly bounded LSM hook parameters?
> > > > > > > > >
> > > > > > > >
> > > > > > > > As mentioned, the BPF verifier does not allow writes to BTF types.
> > > > > > > >
> > > > > > > > > > And a traditional security module would necessarily fall
> > > > > > > > > > under GPL; is the eBPF code required to be
> > > > > > > > > > likewise? If not, KRSI is a
> > > > > > > > > > gateway for proprietary LSMs...
> > > > > > > > >
> > > > > > > > > Right, we do not want this to be a GPL bypass.
> > > > > > > >
> > > > > > > > This is not intended to be a GPL bypass and the BPF verifier checks
> > > > > > > > for license compatibility of the loaded program with GPL.
> > > > > > >
> > > > > > > IIUC, it checks that the program is GPL compatible if it
> > > > > > > uses a function
> > > > > > > marked GPL-only. But what specifically is marked GPL-only
> > > > > > > that is required
> > > > > > > for eBPF programs using KRSI?
> > > > > >
> > > > > > Good point! If no-one objects, I can add it to the BPF_PROG_TYPE_LSM
> > > > > > specific verification for the v2 of the patch-set which would require
> > > > > > all BPF-LSM programs to be GPL.
> > > > >
> > > > > I don't think it's a good idea to enforce license on the program.
> > > > > The kernel doesn't do it for modules.
> > > > > For years all of BPF tracing progs were GPL because they have to use
> > > > > GPL-ed helpers to do anything meaningful.
> > > > > So for KRSI just make sure that all helpers are GPL-ed as well.
> > > >
> > > > IIUC, the example eBPF code included in this patch series showed a
> > > > program that used a GPL-only helper for the purpose of reporting event
> > > > output to userspace. But it could have just as easily omitted the use of
> > > > that helper and still implemented its own arbitrary access control model
> > > > on the LSM hooks to which it attached. It seems like the question is
> > > > whether the kernel developers are ok with exposing the entire LSM hook
> > > > interface and all the associated data structures to non-GPLd code,
> > > > irrespective of what helpers it may or may not use.
> > >
> > > Also, to be clear, while kernel modules aren't necessarily GPL, prior to
> > > this patch series, all Linux security modules were necessarily GPLd in order
> > > to use the LSM interface.
> >
> > Because they use securityfs_create_file() GPL-ed api, right?
> > but not because module license is enforced.
>
> No, securityfs was a later addition and is not required by all LSMs either.
> Originally LSMs had to register their hooks via register_security(), which
> was intentionally EXPORT_SYMBOL_GPL() to avoid exposing the LSM interface to
> non-GPLd modules because there were significant concerns with doing so when
> LSM was first merged. Then in 20510f2f4e2dabb0ff6c13901807627ec9452f98
> ("security: Convert LSM into a static interface"), the ability for loadable
> modules to use register_security() at all was removed, limiting its use to
> built-in modules. In commit b1d9e6b0646d0e5ee5d9050bd236b6c65d66faef ("LSM:
> Switch to lists of hooks"), register_security() was replaced by
> security_add_hooks(), but this was likewise not exported for use by modules
> and could only be used by built-in code. The bpf LSM is providing a shim
> that allows eBPF code to attach to these hooks that would otherwise not be
> exposed to non-GPLd code, so if the bpf LSM does not require the eBPF
> programs to also be GPLd, then that is a change from current practice.
>
> > > So allowing non-GPL eBPF-based LSMs would be a
> > > change.
> >
> > I don't see it this way. seccomp progs technically unlicensed. Yet they can
> > disallow any syscall. Primitive KRSI progs like
> > int bpf-prog(void*) { return REJECT; }
> > would be able to do selectively disable a syscall with an overhead acceptable
> > in production systems (unlike seccomp). I want this use case to be available to
> > people. It's a bait, because to do real progs people would need to GPL them.
> > Key helpers bpf_perf_event_output, bpf_ktime_get_ns, bpf_trace_printk are all
> > GPL-ed. It may look that most networking helpers are not-GPL, but real life is
> > different. To debug programs bpf_trace_printk() is necessary. To have
> > communication with user space bpf_perf_event_output() is necssary. To measure
> > anything or implement timestamps bpf_ktime_get_ns() is necessary. So today all
> > meaninful bpf programs are GPL. Those that are not GPL probably exist, but
> > they're toy programs. Hence I have zero concerns about GPL bypass coming from
> > tracing, networking, and, in the future, KRSI progs too.
>
> You have more confidence than I do about that. I would anticipate
> developers of out-of-tree LSMs latching onto this bpf LSM and using it to
> avoid GPL. I don't see that any of those helpers are truly needed to
> implement an access control model.
Yeah, I'm with Stephen here, this should be explicitly marked for
GPL-only bpf code to prevent anyone from trying to route around the LSM
apis we have today. We have enough problem with companies trying to do
that as-is, let's not give them any other ways to abuse our license.
thanks,
greg k-h
next prev parent reply other threads:[~2020-01-15 14:09 UTC|newest]
Thread overview: 74+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-20 15:41 [PATCH bpf-next v1 00/13] MAC and Audit policy using eBPF (KRSI) KP Singh
2019-12-20 15:41 ` [PATCH bpf-next v1 01/13] bpf: Refactor BPF_EVENT context macros to its own header KP Singh
2019-12-20 20:10 ` Andrii Nakryiko
2019-12-20 20:26 ` KP Singh
2019-12-20 15:41 ` [PATCH bpf-next v1 02/13] bpf: lsm: Add a skeleton and config options KP Singh
2020-01-07 21:13 ` James Morris
2019-12-20 15:41 ` [PATCH bpf-next v1 03/13] bpf: lsm: Introduce types for eBPF based LSM KP Singh
2019-12-20 15:41 ` [PATCH bpf-next v1 04/13] bpf: lsm: Allow btf_id based attachment for LSM hooks KP Singh
2019-12-23 23:54 ` Andrii Nakryiko
2019-12-30 19:22 ` KP Singh
2019-12-20 15:42 ` [PATCH bpf-next v1 05/13] tools/libbpf: Add support in libbpf for BPF_PROG_TYPE_LSM KP Singh
2019-12-24 0:07 ` Andrii Nakryiko
2019-12-24 0:09 ` Andrii Nakryiko
2020-01-03 23:59 ` KP Singh
2019-12-20 15:42 ` [PATCH bpf-next v1 06/13] bpf: lsm: Init Hooks and create files in securityfs KP Singh
2019-12-24 6:28 ` Andrii Nakryiko
2019-12-30 15:37 ` KP Singh
2019-12-30 18:52 ` Andrii Nakryiko
2019-12-30 19:20 ` Kees Cook
2020-01-03 23:53 ` KP Singh
2020-01-07 21:22 ` James Morris
2019-12-20 15:42 ` [PATCH bpf-next v1 07/13] bpf: lsm: Implement attach, detach and execution KP Singh
2019-12-24 5:48 ` Andrii Nakryiko
2020-01-07 21:27 ` James Morris
2019-12-20 15:42 ` [PATCH bpf-next v1 08/13] bpf: lsm: Show attached program names in hook read handler KP Singh
2020-01-07 21:28 ` James Morris
2019-12-20 15:42 ` [PATCH bpf-next v1 09/13] bpf: lsm: Add a helper function bpf_lsm_event_output KP Singh
2019-12-24 6:36 ` Andrii Nakryiko
2019-12-30 15:11 ` KP Singh
2019-12-30 18:56 ` Andrii Nakryiko
2019-12-20 15:42 ` [PATCH bpf-next v1 10/13] bpf: lsm: Handle attachment of the same program KP Singh
2019-12-24 6:38 ` Andrii Nakryiko
2020-01-08 18:21 ` James Morris
2019-12-20 15:42 ` [PATCH bpf-next v1 11/13] tools/libbpf: Add bpf_program__attach_lsm KP Singh
2019-12-24 6:44 ` Andrii Nakryiko
2020-01-08 18:24 ` James Morris
2019-12-20 15:42 ` [PATCH bpf-next v1 12/13] bpf: lsm: Add selftests for BPF_PROG_TYPE_LSM KP Singh
2019-12-24 6:49 ` Andrii Nakryiko
2020-01-04 0:09 ` KP Singh
2020-01-09 17:59 ` Andrii Nakryiko
2020-01-08 18:25 ` James Morris
2019-12-20 15:42 ` [PATCH bpf-next v1 13/13] bpf: lsm: Add Documentation KP Singh
2019-12-20 17:17 ` [PATCH bpf-next v1 00/13] MAC and Audit policy using eBPF (KRSI) Casey Schaufler
2019-12-20 17:38 ` KP Singh
2019-12-30 19:15 ` Kees Cook
2020-01-08 15:25 ` Stephen Smalley
2020-01-08 18:58 ` James Morris
2020-01-08 19:33 ` Stephen Smalley
2020-01-09 18:11 ` James Morris
2020-01-09 18:23 ` Greg Kroah-Hartman
2020-01-09 18:58 ` Stephen Smalley
2020-01-09 19:07 ` James Morris
2020-01-09 19:43 ` KP Singh
2020-01-09 19:47 ` Stephen Smalley
2020-01-10 15:27 ` KP Singh
2020-01-10 17:48 ` James Morris
2020-01-10 17:53 ` Alexei Starovoitov
2020-01-14 16:54 ` Stephen Smalley
2020-01-14 17:42 ` Stephen Smalley
2020-01-15 2:48 ` Alexei Starovoitov
2020-01-15 13:59 ` Stephen Smalley
2020-01-15 14:09 ` Greg Kroah-Hartman [this message]
2020-01-15 22:23 ` Alexei Starovoitov
2020-01-09 19:11 ` KP Singh
2020-01-08 18:27 ` James Morris
2019-12-20 22:46 ` Mickaël Salaün
2019-12-30 19:30 ` Kees Cook
2019-12-31 12:11 ` Mickaël Salaün
2019-12-22 1:27 ` Alexei Starovoitov
2019-12-30 14:58 ` KP Singh
2019-12-30 19:14 ` Andrii Nakryiko
2019-12-24 6:51 ` Andrii Nakryiko
2019-12-30 15:04 ` KP Singh
2019-12-30 18:58 ` Andrii Nakryiko
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200115140953.GB3627564@kroah.com \
--to=gregkh@linuxfoundation.org \
--cc=alexei.starovoitov@gmail.com \
--cc=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=brendan.d.gregg@gmail.com \
--cc=casey@schaufler-ca.com \
--cc=christian@brauner.io \
--cc=daniel@iogearbox.net \
--cc=davem@davemloft.net \
--cc=jackmanb@chromium.org \
--cc=jannh@google.com \
--cc=jmorris@namei.org \
--cc=joe@wand.net.nz \
--cc=kafai@fb.com \
--cc=keescook@chromium.org \
--cc=kpsingh@chromium.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-security-module@vger.kernel.org \
--cc=mchehab+samsung@kernel.org \
--cc=mhalcrow@google.com \
--cc=mic@digikod.net \
--cc=mjg59@google.com \
--cc=nicolas.ferre@microchip.com \
--cc=paul@paul-moore.com \
--cc=pjt@google.com \
--cc=quentin.monnet@netronome.com \
--cc=rdna@fb.com \
--cc=revest@chromium.org \
--cc=sdf@google.com \
--cc=sds@tycho.nsa.gov \
--cc=serge@hallyn.com \
--cc=songliubraving@fb.com \
--cc=thgarnie@chromium.org \
--cc=yhs@fb.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).