linux-kernel - Re: [RFC v3 16/22] bpf/cgroup,landlock: Handle Landlock hooks per cgroup

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <57F5696E.6020502@digikod.net>
Date:   Wed, 5 Oct 2016 22:58:22 +0200
From:   Mickaël Salaün <mic@...ikod.net>
To:     Kees Cook <keescook@...omium.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Arnd Bergmann <arnd@...db.de>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Daniel Mack <daniel@...que.org>,
        David Drysdale <drysdale@...gle.com>,
        "David S . Miller" <davem@...emloft.net>,
        Elena Reshetova <elena.reshetova@...el.com>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        James Morris <james.l.morris@...cle.com>,
        Paul Moore <pmoore@...hat.com>,
        Sargun Dhillon <sargun@...gun.me>,
        "Serge E . Hallyn" <serge@...lyn.com>, Tejun Heo <tj@...nel.org>,
        Will Drewry <wad@...omium.org>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        Linux API <linux-api@...r.kernel.org>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Cgroups <cgroups@...r.kernel.org>
Subject: Re: [RFC v3 16/22] bpf/cgroup,landlock: Handle Landlock hooks per
 cgroup



On 04/10/2016 01:43, Kees Cook wrote:
> On Wed, Sep 14, 2016 at 12:24 AM, Mickaël Salaün <mic@...ikod.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@...ikod.net>
>> Cc: Alexei Starovoitov <ast@...nel.org>
>> Cc: Andy Lutomirski <luto@...capital.net>
>> Cc: Daniel Borkmann <daniel@...earbox.net>
>> Cc: Daniel Mack <daniel@...que.org>
>> Cc: David S. Miller <davem@...emloft.net>
>> Cc: Kees Cook <keescook@...omium.org>
>> Cc: Tejun Heo <tj@...nel.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. :)

This is not fully satisfactory for me neither but the other approach is
to use two distinct struct fields instead of a union.
Do you prefer if there is a "type" field in the "pinned" struct to
select the union?

 Mickaël



Download attachment "signature.asc" of type "application/pgp-signature" (456 bytes)