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From: Kees Cook <keescook@chromium.org>
To: "Mickaël Salaün" <mic@digikod.net>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Andy Lutomirski <luto@amacapital.net>,
	Arnd Bergmann <arnd@arndb.de>,
	Casey Schaufler <casey@schaufler-ca.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Daniel Mack <daniel@zonque.org>,
	David Drysdale <drysdale@google.com>,
	"David S . Miller" <davem@davemloft.net>,
	Elena Reshetova <elena.reshetova@intel.com>,
	"Eric W . Biederman" <ebiederm@xmission.com>,
	James Morris <james.l.morris@oracle.com>,
	Paul Moore <pmoore@redhat.com>, Sargun Dhillon <sargun@sargun.me>,
	"Serge E . Hallyn" <serge@hallyn.com>, Tejun Heo <tj@kernel.org>,
	Will Drewry <wad@chromium.org>,
	"kernel-hardening@lists.openwall.com" 
	<kernel-hardening@lists.openwall.com>,
	Linux API <linux-api@vger.kernel.org>,
	linux-security-module <linux-security-module@vger.kernel.org>,
	Network Development <netdev@vger.kernel.org>,
	Cgroups <cgroups@vger.kernel.org>
Subject: Re: [RFC v3 16/22] bpf/cgroup,landlock: Handle Landlock hooks per cgroup
Date: Mon, 3 Oct 2016 16:43:26 -0700
Message-ID: <CAGXu5jJ-Heb0nnLygYo0xHaJKSrQM5RSVRNYN2NnYddwGHtWkA@mail.gmail.com> (raw)
In-Reply-To: <20160914072415.26021-17-mic@digikod.net>

On Wed, Sep 14, 2016 at 12:24 AM, Mickaël Salaün <mic@digikod.net> wrote:
> This allows to add new eBPF programs to Landlock hooks dedicated to a
> cgroup thanks to the BPF_PROG_ATTACH command. Like for socket eBPF
> programs, the Landlock hooks attached to a cgroup are propagated to the
> nested cgroups. However, when a new Landlock program is attached to one
> of this nested cgroup, this cgroup hierarchy fork the Landlock hooks.
> This design is simple and match the current CONFIG_BPF_CGROUP
> inheritance. The difference lie in the fact that Landlock programs can
> only be stacked but not removed. This match the append-only seccomp
> behavior. Userland is free to handle Landlock hooks attached to a cgroup
> in more complicated ways (e.g. continuous inheritance), but care should
> be taken to properly handle error cases (e.g. memory allocation errors).
>
> Changes since v2:
> * new design based on BPF_PROG_ATTACH (suggested by Alexei Starovoitov)
>
> Signed-off-by: Mickaël Salaün <mic@digikod.net>
> Cc: Alexei Starovoitov <ast@kernel.org>
> Cc: Andy Lutomirski <luto@amacapital.net>
> Cc: Daniel Borkmann <daniel@iogearbox.net>
> Cc: Daniel Mack <daniel@zonque.org>
> Cc: David S. Miller <davem@davemloft.net>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Tejun Heo <tj@kernel.org>
> Link: https://lkml.kernel.org/r/20160826021432.GA8291@ast-mbp.thefacebook.com
> Link: https://lkml.kernel.org/r/20160827204307.GA43714@ast-mbp.thefacebook.com
> ---
>  include/linux/bpf-cgroup.h  |  7 +++++++
>  include/linux/cgroup-defs.h |  2 ++
>  include/linux/landlock.h    |  9 +++++++++
>  include/uapi/linux/bpf.h    |  1 +
>  kernel/bpf/cgroup.c         | 33 ++++++++++++++++++++++++++++++---
>  kernel/bpf/syscall.c        | 11 +++++++++++
>  security/landlock/lsm.c     | 40 +++++++++++++++++++++++++++++++++++++++-
>  security/landlock/manager.c | 32 ++++++++++++++++++++++++++++++++
>  8 files changed, 131 insertions(+), 4 deletions(-)
>
> [...]
> diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
> index 7b75fa692617..1c18fe46958a 100644
> --- a/kernel/bpf/cgroup.c
> +++ b/kernel/bpf/cgroup.c
> @@ -15,6 +15,7 @@
>  #include <linux/bpf.h>
>  #include <linux/bpf-cgroup.h>
>  #include <net/sock.h>
> +#include <linux/landlock.h>
>
>  DEFINE_STATIC_KEY_FALSE(cgroup_bpf_enabled_key);
>  EXPORT_SYMBOL(cgroup_bpf_enabled_key);
> @@ -31,7 +32,15 @@ void cgroup_bpf_put(struct cgroup *cgrp)
>                 union bpf_object pinned = cgrp->bpf.pinned[type];
>
>                 if (pinned.prog) {
> -                       bpf_prog_put(pinned.prog);
> +                       switch (type) {
> +                       case BPF_CGROUP_LANDLOCK:
> +#ifdef CONFIG_SECURITY_LANDLOCK
> +                               put_landlock_hooks(pinned.hooks);
> +                               break;
> +#endif /* CONFIG_SECURITY_LANDLOCK */
> +                       default:
> +                               bpf_prog_put(pinned.prog);
> +                       }
>                         static_branch_dec(&cgroup_bpf_enabled_key);
>                 }
>         }

I get creeped out by type-controlled unions of pointers. :P I don't
have a suggestion to improve this, but I don't like seeing a pointer
type managed separately from the pointer itself as it tends to bypass
a lot of both static and dynamic checking. A union is better than a
cast of void *, but it still worries me. :)

-Kees

-- 
Kees Cook
Nexus Security

  reply index

Thread overview: 76+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-14  7:23 [RFC v3 00/22] Landlock LSM: Unprivileged sandboxing Mickaël Salaün
2016-09-14  7:23 ` [RFC v3 01/22] landlock: Add Kconfig Mickaël Salaün
2016-09-14  7:23 ` [RFC v3 02/22] bpf: Move u64_to_ptr() to BPF headers and inline it Mickaël Salaün
2016-09-14  7:23 ` [RFC v3 03/22] bpf,landlock: Add a new arraymap type to deal with (Landlock) handles Mickaël Salaün
2016-09-14 18:51   ` Alexei Starovoitov
2016-09-14 23:22     ` Mickaël Salaün
2016-09-14 23:28       ` Alexei Starovoitov
2016-09-15 21:51         ` Mickaël Salaün
2016-10-03 23:53   ` Kees Cook
2016-10-05 22:02     ` Mickaël Salaün
2016-09-14  7:23 ` [RFC v3 04/22] bpf: Set register type according to is_valid_access() Mickaël Salaün
2016-10-19 14:54   ` Thomas Graf
2016-10-19 15:10     ` Daniel Borkmann
2016-09-14  7:23 ` [RFC v3 05/22] bpf,landlock: Add eBPF program subtype and is_valid_subtype() verifier Mickaël Salaün
2016-10-19 15:01   ` Thomas Graf
2016-09-14  7:23 ` [RFC v3 06/22] landlock: Add LSM hooks Mickaël Salaün
2016-10-19 15:19   ` Thomas Graf
2016-10-19 22:42     ` Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 07/22] landlock: Handle file comparisons Mickaël Salaün
2016-09-14 19:07   ` Jann Horn
2016-09-14 22:39     ` Mickaël Salaün
2016-09-14 21:06   ` Alexei Starovoitov
2016-09-14 23:02     ` Mickaël Salaün
2016-09-14 23:24       ` Alexei Starovoitov
2016-09-15 21:25         ` Mickaël Salaün
2016-09-20  0:12           ` lsm naming dilemma. " Alexei Starovoitov
2016-09-20  1:10             ` Sargun Dhillon
2016-09-20 16:58               ` Mickaël Salaün
2016-10-03 23:30   ` Kees Cook
2016-09-14  7:24 ` [RFC v3 08/22] seccomp: Fix documentation for struct seccomp_filter Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 09/22] seccomp: Move struct seccomp_filter in seccomp.h Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 10/22] seccomp: Split put_seccomp_filter() with put_seccomp() Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 11/22] seccomp,landlock: Handle Landlock hooks per process hierarchy Mickaël Salaün
2016-09-14 18:43   ` Andy Lutomirski
2016-09-14 22:34     ` Mickaël Salaün
2016-10-03 23:52       ` Kees Cook
2016-10-05 21:05         ` Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 12/22] bpf: Cosmetic change for bpf_prog_attach() Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 13/22] bpf/cgroup: Replace struct bpf_prog with union bpf_object Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 14/22] bpf/cgroup: Make cgroup_bpf_update() return an error code Mickaël Salaün
2016-09-14 21:16   ` Alexei Starovoitov
2016-09-14  7:24 ` [RFC v3 15/22] bpf/cgroup: Move capability check Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 16/22] bpf/cgroup,landlock: Handle Landlock hooks per cgroup Mickaël Salaün
2016-10-03 23:43   ` Kees Cook [this message]
2016-10-05 20:58     ` Mickaël Salaün
2016-10-05 21:25       ` Kees Cook
2016-09-14  7:24 ` [RFC v3 17/22] cgroup: Add access check for cgroup_get_from_fd() Mickaël Salaün
2016-09-14 22:06   ` Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 18/22] cgroup,landlock: Add CGRP_NO_NEW_PRIVS to handle unprivileged hooks Mickaël Salaün
2016-09-14 18:27   ` Andy Lutomirski
2016-09-14 22:11     ` Mickaël Salaün
2016-09-15  1:25       ` Andy Lutomirski
2016-09-15  2:19         ` Alexei Starovoitov
2016-09-15  2:27           ` Andy Lutomirski
2016-09-15  4:00             ` Alexei Starovoitov
2016-09-15  4:08               ` Andy Lutomirski
2016-09-15  4:31                 ` Alexei Starovoitov
2016-09-15  4:38                   ` Andy Lutomirski
2016-09-15  4:48                     ` Alexei Starovoitov
2016-09-15 19:41                       ` Mickaël Salaün
2016-09-20  4:37                         ` Sargun Dhillon
2016-09-20 17:02                           ` Mickaël Salaün
2016-09-15 19:35         ` Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 19/22] landlock: Add interrupted origin Mickaël Salaün
2016-09-14 18:29   ` Andy Lutomirski
2016-09-14 22:14     ` Mickaël Salaün
2016-09-15  1:19       ` Andy Lutomirski
2016-10-03 23:46         ` Kees Cook
2016-10-05 21:01           ` Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 20/22] landlock: Add update and debug access flags Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 21/22] bpf,landlock: Add optional skb pointer in the Landlock context Mickaël Salaün
2016-09-14 21:20   ` Alexei Starovoitov
2016-09-14 22:46     ` Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 22/22] samples/landlock: Add sandbox example Mickaël Salaün
2016-09-14 21:24   ` Alexei Starovoitov
2016-09-14 14:36 ` [RFC v3 00/22] Landlock LSM: Unprivileged sandboxing David Laight

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