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From: Casey Schaufler <casey-iSGtlc1asvQWG2LlvL+J4A@public.gmane.org>
To: "Mickaël Salaün" <mic-WFhQfpSGs3bR7s880joybQ@public.gmane.org>,
	"Kees Cook" <keescook-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
Cc: LKML <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
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	Arnaldo Carvalho de Melo
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	Daniel Borkmann <daniel-FeC+5ew28dpmcu3hnIyYJQ@public.gmane.org>,
	David Drysdale <drysdale-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>,
	"David S . Miller"
	<davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org>,
	"Eric W . Biederman"
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	Will Drewry <wad-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>,
	kernel-hardening@lists.o
Subject: Re: [kernel-hardening] Re: [PATCH net-next v6 04/11] landlock: Add LSM hooks related to filesystem
Date: Wed, 19 Apr 2017 16:58:17 -0700	[thread overview]
Message-ID: <ccad825b-7a58-e499-e51b-bd7c98581afe@schaufler-ca.com> (raw)
In-Reply-To: <35272f2b-ec5f-d032-ae2e-9fc0b4c0e2e3-WFhQfpSGs3bR7s880joybQ@public.gmane.org>

On 4/19/2017 3:03 PM, Mickaël Salaün wrote:
> On 19/04/2017 01:40, Kees Cook wrote:
>> On Tue, Apr 18, 2017 at 4:16 PM, Casey Schaufler <casey-iSGtlc1asvQWG2LlvL+J4A@public.gmane.org> wrote:
>>> On 4/18/2017 3:44 PM, Mickaël Salaün wrote:
>>>> On 19/04/2017 00:17, Kees Cook wrote:
>>>>> On Tue, Mar 28, 2017 at 4:46 PM, Mickaël Salaün <mic-WFhQfpSGs3bR7s880joybQ@public.gmane.org> wrote:
>>>>>> +void __init landlock_add_hooks(void)
>>>>>> +{
>>>>>> +       pr_info("landlock: Version %u", LANDLOCK_VERSION);
>>>>>> +       landlock_add_hooks_fs();
>>>>>> +       security_add_hooks(NULL, 0, "landlock");
>>>>>> +       bpf_register_prog_type(&bpf_landlock_type);
>>>>> I'm confused by the separation of hook registration here. The call to
>>>>> security_add_hooks is with count=0 is especially weird. Why isn't this
>>>>> just a single call with security_add_hooks(landlock_hooks,
>>>>> ARRAY_SIZE(landlock_hooks), "landlock")?
>>>> Yes, this is ugly with the new security_add_hooks() with three arguments
>>>> but I wanted to split the hooks definition in multiple files.
>>> Why? I'll buy a good argument, but there are dangers in
>>> allowing multiple calls to security_add_hooks().
> I prefer to have one file per hook "family" (e.g. filesystem, network,
> ptrace…). This reduce the mess with all the included files (needed for
> LSM hook argument types) and make the files easier to read, understand
> and maintain.

Yeah, there's that tradeoff and it really is a matter
of taste I suppose.

>>>> The current security_add_hooks() use lsm_append(lsm, &lsm_names) which
>>>> is not exported. Unfortunately, calling multiple security_add_hooks()
>>>> with the same LSM name would register multiple names for the same LSM…
>>>> Is it OK if I modify this function to not add duplicated entries?
>>> It may seem absurd, but it's conceivable that a module might
>>> have two hooks it wants called. My example is a module that
>>> counts the number of times SELinux denies a process access to
>>> things (which needs to be called before and after SELinux in
>>> order to detect denials) and takes "appropriate action" if
>>> too many denials occur. It would be weird, wonky and hackish,
>>> but that never stopped anybody before.
> Right, but now, with the new lsm_append(), module names are concatenated
> ("%s,%s") in the lsm_names variable. It would be nice to not pollute
> this string with multiple time the same module name.

All it would take is a check that the module name
isn't already on the list. It's a trivial change.

>> If ends up being sane and clear, I'm fine with allowing multiple calls.
>>
>> -Kees
>>

  parent reply	other threads:[~2017-04-19 23:58 UTC|newest]

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-03-28 23:46 [PATCH net-next v6 00/11] Landlock LSM: Toward unprivileged sandboxing Mickaël Salaün
     [not found] ` <20170328234650.19695-1-mic-WFhQfpSGs3bR7s880joybQ@public.gmane.org>
2017-03-28 23:46   ` [PATCH net-next v6 01/11] bpf: Add eBPF program subtype and is_valid_subtype() verifier Mickaël Salaün
     [not found]     ` <20170328234650.19695-2-mic-WFhQfpSGs3bR7s880joybQ@public.gmane.org>
2017-03-29 13:48       ` kbuild test robot
2017-04-18 21:48     ` Kees Cook
2017-03-28 23:46 ` [PATCH net-next v6 02/11] bpf,landlock: Define an eBPF program type for Landlock Mickaël Salaün
2017-04-16 21:57   ` Mickaël Salaün
     [not found]   ` <20170328234650.19695-3-mic-WFhQfpSGs3bR7s880joybQ@public.gmane.org>
2017-04-18 21:58     ` Kees Cook
2017-03-28 23:46 ` [PATCH net-next v6 03/11] bpf: Define handle_fs and add a new helper bpf_handle_fs_get_mode() Mickaël Salaün
2017-03-28 23:46 ` [PATCH net-next v6 04/11] landlock: Add LSM hooks related to filesystem Mickaël Salaün
2017-03-29 15:18   ` kbuild test robot
     [not found]   ` <20170328234650.19695-5-mic-WFhQfpSGs3bR7s880joybQ@public.gmane.org>
2017-04-18 22:17     ` Kees Cook
2017-04-18 22:44       ` Mickaël Salaün
     [not found]         ` <9a69055a-b4cf-00b0-da5e-2e45ff88059c-WFhQfpSGs3bR7s880joybQ@public.gmane.org>
2017-04-18 23:16           ` Casey Schaufler
2017-04-18 23:40             ` Kees Cook
2017-04-19 22:03               ` Mickaël Salaün
     [not found]                 ` <35272f2b-ec5f-d032-ae2e-9fc0b4c0e2e3-WFhQfpSGs3bR7s880joybQ@public.gmane.org>
2017-04-19 23:58                   ` Casey Schaufler [this message]
2017-04-20  1:48                 ` Kees Cook
2017-04-18 23:39         ` Kees Cook
2017-03-28 23:46 ` [PATCH net-next v6 05/11] seccomp: Split put_seccomp_filter() with put_seccomp() Mickaël Salaün
2017-04-18 22:23   ` Kees Cook
2017-04-18 22:47     ` Mickaël Salaün
2017-04-19 22:18       ` Mickaël Salaün
     [not found]         ` <96024881-1bcc-33af-6285-d9a904de963e-WFhQfpSGs3bR7s880joybQ@public.gmane.org>
2017-04-20  1:54           ` Kees Cook
2017-03-28 23:46 ` [PATCH net-next v6 06/11] seccomp,landlock: Handle Landlock events per process hierarchy Mickaël Salaün
2017-03-29 10:35   ` Djalal Harouni
2017-03-31 21:15     ` Mickaël Salaün
2017-04-18 22:54       ` [kernel-hardening] " Kees Cook
     [not found]   ` <20170328234650.19695-7-mic-WFhQfpSGs3bR7s880joybQ@public.gmane.org>
2017-04-18 22:53     ` Kees Cook
2017-04-18 23:24       ` Mickaël Salaün
     [not found]         ` <a3c71579-4238-0967-b61d-522859f740aa-WFhQfpSGs3bR7s880joybQ@public.gmane.org>
2017-04-18 23:48           ` Kees Cook
2017-03-28 23:46 ` [PATCH net-next v6 07/11] landlock: Add ptrace restrictions Mickaël Salaün
     [not found]   ` <20170328234650.19695-8-mic-WFhQfpSGs3bR7s880joybQ@public.gmane.org>
2017-04-10  6:48     ` [kernel-hardening] " Djalal Harouni
2017-04-11  7:19       ` Mickaël Salaün
2017-03-28 23:46 ` [PATCH net-next v6 08/11] bpf: Add a Landlock sandbox example Mickaël Salaün
2017-04-18 23:06   ` Kees Cook
2017-04-18 23:35     ` Mickaël Salaün
2017-03-28 23:46 ` [PATCH net-next v6 09/11] seccomp: Enhance test_harness with an assert step mechanism Mickaël Salaün
     [not found]   ` <20170328234650.19695-10-mic-WFhQfpSGs3bR7s880joybQ@public.gmane.org>
2017-04-19  0:02     ` Kees Cook
2017-04-19 21:51       ` Mickaël Salaün
     [not found]         ` <94ac6ddc-eaac-8548-f83f-826ddf05ac69-WFhQfpSGs3bR7s880joybQ@public.gmane.org>
2017-04-19 22:02           ` Kees Cook
2017-04-19 22:05             ` Mickaël Salaün
2017-04-20  1:50               ` Kees Cook
2017-03-28 23:46 ` [PATCH net-next v6 10/11] bpf,landlock: Add tests for Landlock Mickaël Salaün
2017-04-18 23:16   ` Kees Cook
2017-04-18 23:53     ` Mickaël Salaün
2017-04-18 23:59       ` Kees Cook
2017-03-28 23:46 ` [PATCH net-next v6 11/11] landlock: Add user and kernel documentation " Mickaël Salaün
2017-03-29 15:58   ` kbuild test robot
2017-04-18 23:26 ` [PATCH net-next v6 00/11] Landlock LSM: Toward unprivileged sandboxing Kees Cook
2017-04-19  0:12   ` Mickaël Salaün

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