BPF Archive on lore.kernel.org
 help / color / Atom feed
From: Kees Cook <keescook@chromium.org>
To: Casey Schaufler <casey@schaufler-ca.com>
Cc: Stephen Smalley <sds@tycho.nsa.gov>,
	KP Singh <kpsingh@chromium.org>, James Morris <jmorris@namei.org>,
	linux-kernel@vger.kernel.org, bpf@vger.kernel.org,
	linux-security-module@vger.kernel.org,
	Brendan Jackman <jackmanb@google.com>,
	Florent Revest <revest@google.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Paul Turner <pjt@google.com>, Jann Horn <jannh@google.com>,
	Florent Revest <revest@chromium.org>,
	Brendan Jackman <jackmanb@chromium.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Paul Moore <paul@paul-moore.com>
Subject: Re: [PATCH bpf-next v7 4/8] bpf: lsm: Implement attach, detach and execution
Date: Fri, 27 Mar 2020 11:59:48 -0700
Message-ID: <202003271143.71E0C591C1@keescook> (raw)
In-Reply-To: <a3f6d9f8-6425-af28-d472-fad642439b69@schaufler-ca.com>

On Fri, Mar 27, 2020 at 09:36:15AM -0700, Casey Schaufler wrote:
> On 3/27/2020 6:43 AM, Stephen Smalley wrote:
> > On 3/27/20 8:41 AM, KP Singh wrote:
> >> On 27-Mär 08:27, Stephen Smalley wrote:
> >>> On 3/26/20 8:24 PM, James Morris wrote:
> >>>> On Thu, 26 Mar 2020, KP Singh wrote:
> >>>>
> >>>>> +int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog,
> >>>>> +            const struct bpf_prog *prog)
> >>>>> +{
> >>>>> +    /* Only CAP_MAC_ADMIN users are allowed to make changes to LSM hooks
> >>>>> +     */
> >>>>> +    if (!capable(CAP_MAC_ADMIN))
> >>>>> +        return -EPERM;
> >>>>> +
> >>>>
> >>>> Stephen, can you confirm that your concerns around this are resolved
> >>>> (IIRC, by SELinux implementing a bpf_prog callback) ?
> >>>
> >>> I guess the only residual concern I have is that CAP_MAC_ADMIN means
> >>> something different to SELinux (ability to get/set file security contexts
> >>> unknown to the currently loaded policy), so leaving the CAP_MAC_ADMIN check
> >>> here (versus calling a new security hook here and checking CAP_MAC_ADMIN in
> >>> the implementation of that hook for the modules that want that) conflates
> >>> two very different things.  Prior to this patch, there are no users of
> >>> CAP_MAC_ADMIN outside of individual security modules; it is only checked in
> >>> module-specific logic within apparmor, safesetid, selinux, and smack, so the
> >>> meaning was module-specific.
> >>
> >> As we had discussed, We do have a security hook as well:
> >>
> >> https://lore.kernel.org/bpf/20200324180652.GA11855@chromium.org/
> >>
> >> The bpf_prog hook which can check for BPF_PROG_TYPE_LSM and implement
> >> module specific logic for LSM programs. I thougt that was okay?
> >>
> >> Kees was in favor of keeping the CAP_MAC_ADMIN check here:
> >>
> >> https://lore.kernel.org/bpf/202003241133.16C02BE5B@keescook
> >>
> >> If you feel strongly and Kees agrees, we can remove the CAP_MAC_ADMIN
> >> check here, but given that we already have a security hook that meets
> >> the requirements, we probably don't need another one.
> >
> > I would favor removing the CAP_MAC_ADMIN check here, and implementing it in a bpf_prog hook for Smack and AppArmor if they want that.  SELinux would implement its own check in its existing bpf_prog hook.
> >
> The whole notion of one security module calling into another for permission
> to do something still gives me the heebee jeebees, but if more nimble minds
> than mine think this is a good idea I won't nack it.

Well, it's a hook into BPF prog creation, not the BPF LSM specifically,
so that's why I think it's general enough control without it being
directly weird. :)

As far as dropping CAP_MAC_ADMIN, yeah, that should be fine. Creating LSM
BPF programs already requires CAP_SYS_ADMIN, so for SELinux-less systems,
that's likely fine. If we need to change the BPF program creation access
control in the future we can revisit it then.

-- 
Kees Cook

  reply index

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-26 14:28 [PATCH bpf-next v7 0/8] MAC and Audit policy using eBPF (KRSI) KP Singh
2020-03-26 14:28 ` [PATCH bpf-next v7 1/8] bpf: Introduce BPF_PROG_TYPE_LSM KP Singh
2020-03-27  0:27   ` James Morris
2020-03-26 14:28 ` [PATCH bpf-next v7 2/8] security: Refactor declaration of LSM hooks KP Singh
2020-03-27  0:28   ` James Morris
2020-03-26 14:28 ` [PATCH bpf-next v7 3/8] bpf: lsm: provide attachment points for BPF LSM programs KP Singh
2020-03-27  0:29   ` James Morris
2020-03-26 14:28 ` [PATCH bpf-next v7 4/8] bpf: lsm: Implement attach, detach and execution KP Singh
2020-03-26 19:12   ` Andrii Nakryiko
2020-03-26 19:39     ` KP Singh
2020-03-27  0:24   ` James Morris
2020-03-27 12:27     ` Stephen Smalley
2020-03-27 12:41       ` KP Singh
2020-03-27 13:43         ` Stephen Smalley
2020-03-27 14:29           ` KP Singh
2020-03-27 16:36           ` Casey Schaufler
2020-03-27 18:59             ` Kees Cook [this message]
2020-03-27 19:17               ` KP Singh
2020-03-27  3:12   ` Alexei Starovoitov
2020-03-27 15:06     ` KP Singh
2020-03-26 14:28 ` [PATCH bpf-next v7 5/8] bpf: lsm: Initialize the BPF LSM hooks KP Singh
2020-03-27  0:29   ` James Morris
2020-03-26 14:28 ` [PATCH bpf-next v7 6/8] tools/libbpf: Add support for BPF_PROG_TYPE_LSM KP Singh
2020-03-27  0:30   ` James Morris
2020-03-26 14:28 ` [PATCH bpf-next v7 7/8] bpf: lsm: Add selftests " KP Singh
2020-03-26 19:24   ` Andrii Nakryiko
2020-03-26 19:44     ` KP Singh
2020-03-27  0:31   ` James Morris
2020-03-26 14:28 ` [PATCH bpf-next v7 8/8] bpf: lsm: Add Documentation KP Singh
2020-03-26 19:31   ` Andrii Nakryiko
2020-03-26 20:56     ` KP Singh
2020-03-26 22:01       ` Andrii Nakryiko
2020-03-27  0:33   ` James Morris

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=202003271143.71E0C591C1@keescook \
    --to=keescook@chromium.org \
    --cc=ast@kernel.org \
    --cc=bpf@vger.kernel.org \
    --cc=casey@schaufler-ca.com \
    --cc=daniel@iogearbox.net \
    --cc=gregkh@linuxfoundation.org \
    --cc=jackmanb@chromium.org \
    --cc=jackmanb@google.com \
    --cc=jannh@google.com \
    --cc=jmorris@namei.org \
    --cc=kpsingh@chromium.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-security-module@vger.kernel.org \
    --cc=paul@paul-moore.com \
    --cc=pjt@google.com \
    --cc=revest@chromium.org \
    --cc=revest@google.com \
    --cc=sds@tycho.nsa.gov \
    /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

BPF Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/bpf/0 bpf/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 bpf bpf/ https://lore.kernel.org/bpf \
		bpf@vger.kernel.org
	public-inbox-index bpf

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.bpf


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git