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From: Jann Horn <jannh@google.com>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	KP Singh <kpsingh@chromium.org>
Cc: "kernel list" <linux-kernel@vger.kernel.org>,
	bpf@vger.kernel.org,
	linux-security-module <linux-security-module@vger.kernel.org>,
	"Brendan Jackman" <jackmanb@google.com>,
	"Florent Revest" <revest@google.com>,
	"Thomas Garnier" <thgarnie@google.com>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"James Morris" <jmorris@namei.org>,
	"Kees Cook" <keescook@chromium.org>,
	"Thomas Garnier" <thgarnie@chromium.org>,
	"Michael Halcrow" <mhalcrow@google.com>,
	"Paul Turner" <pjt@google.com>,
	"Brendan Gregg" <brendan.d.gregg@gmail.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>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	"Mauro Carvalho Chehab" <mchehab+samsung@kernel.org>,
	"David S. Miller" <davem@davemloft.net>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Kernel Team" <kernel-team@fb.com>
Subject: BPF LSM and fexit [was: [PATCH bpf-next v3 04/10] bpf: lsm: Add mutable hooks list for the BPF LSM]
Date: Tue, 11 Feb 2020 19:44:05 +0100
Message-ID: <CAG48ez25mW+_oCxgCtbiGMX07g_ph79UOJa07h=o_6B6+Q-u5g@mail.gmail.com> (raw)
In-Reply-To: <20200211175825.szxaqaepqfbd2wmg@ast-mbp>

On Tue, Feb 11, 2020 at 6:58 PM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
> On Tue, Feb 11, 2020 at 01:43:34PM +0100, KP Singh wrote:
[...]
> > * When using the semantic provided by fexit, the BPF LSM program will
> >   always be executed and will be able to override / clobber the
> >   decision of LSMs which appear before it in the ordered list. This
> >   semantic is very different from what we currently have (i.e. the BPF
> >   LSM hook is only called if all the other LSMs allow the action) and
> >   seems to be bypassing the LSM framework.
>
> It that's a concern it's trivial to add 'if (RC == 0)' check to fexit
> trampoline generator specific to lsm progs.
[...]
> Using fexit mechanism and bpf_sk_storage generalization is
> all that is needed. None of it should touch security/*.

If I understand your suggestion correctly, that seems like a terrible
idea to me from the perspective of inspectability and debuggability.
If at runtime, a function can branch off elsewhere to modify its
decision, I want to see that in the source code. If someone e.g.
changes the parameters or the locking rules around a security hook,
how are they supposed to understand the implications if that happens
through some magic fexit trampoline that is injected at runtime?

  reply index

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-23 15:24 [PATCH bpf-next v3 00/10] MAC and Audit policy using eBPF (KRSI) KP Singh
2020-01-23 15:24 ` [PATCH bpf-next v3 01/10] bpf: btf: Add btf_type_by_name_kind KP Singh
2020-01-23 20:06   ` Andrii Nakryiko
2020-01-24 14:12     ` KP Singh
2020-01-23 15:24 ` [PATCH bpf-next v3 02/10] bpf: lsm: Add a skeleton and config options KP Singh
2020-02-10 23:52   ` Alexei Starovoitov
2020-02-11 12:45     ` KP Singh
2020-01-23 15:24 ` [PATCH bpf-next v3 03/10] bpf: lsm: Introduce types for eBPF based LSM KP Singh
2020-02-10 23:58   ` Alexei Starovoitov
2020-02-11 12:44     ` KP Singh
2020-01-23 15:24 ` [PATCH bpf-next v3 04/10] bpf: lsm: Add mutable hooks list for the BPF LSM KP Singh
2020-01-23 17:03   ` Casey Schaufler
2020-01-23 17:59     ` KP Singh
2020-01-23 19:09       ` Casey Schaufler
2020-01-23 22:24         ` KP Singh
2020-01-23 23:50           ` Casey Schaufler
2020-01-24  1:25             ` KP Singh
2020-01-24 21:55               ` James Morris
2020-02-11  3:12   ` Alexei Starovoitov
2020-02-11 12:43     ` KP Singh
2020-02-11 17:58       ` Alexei Starovoitov
2020-02-11 18:44         ` Jann Horn [this message]
2020-02-11 19:09           ` BPF LSM and fexit [was: [PATCH bpf-next v3 04/10] bpf: lsm: Add mutable hooks list for the BPF LSM] Alexei Starovoitov
2020-02-11 19:36             ` Jann Horn
2020-02-11 20:10               ` Alexei Starovoitov
2020-02-11 20:33                 ` Jann Horn
2020-02-11 21:32                   ` Jann Horn
2020-02-11 21:38                   ` Alexei Starovoitov
2020-02-11 23:26                     ` Alexei Starovoitov
2020-02-12  0:09                       ` Daniel Borkmann
2020-02-12  2:45                         ` Alexei Starovoitov
2020-02-12 13:27                           ` Daniel Borkmann
2020-02-12 16:04                             ` KP Singh
2020-02-12 15:52                           ` Casey Schaufler
2020-02-12 16:26                             ` KP Singh
2020-02-12 18:59                               ` Casey Schaufler
2020-01-23 15:24 ` [PATCH bpf-next v3 05/10] bpf: lsm: BTF API for LSM hooks KP Singh
2020-01-23 15:24 ` [PATCH bpf-next v3 06/10] bpf: lsm: Implement attach, detach and execution KP Singh
2020-01-23 15:24 ` [PATCH bpf-next v3 07/10] bpf: lsm: Make the allocated callback RO+X KP Singh
2020-01-23 15:24 ` [PATCH bpf-next v3 08/10] tools/libbpf: Add support for BPF_PROG_TYPE_LSM KP Singh
2020-01-23 18:00   ` Andrii Nakryiko
2020-01-24 14:16     ` KP Singh
2020-01-23 15:24 ` [PATCH bpf-next v3 09/10] bpf: lsm: Add selftests " KP Singh
2020-01-23 15:24 ` [PATCH bpf-next v3 10/10] bpf: lsm: Add Documentation KP Singh

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