From: "Konstantin Meskhidze (A)" <konstantin.meskhidze@huawei.com>
To: "Mickaël Salaün" <mic@digikod.net>,
"Günther Noack" <gnoack3000@gmail.com>
Cc: <willemdebruijn.kernel@gmail.com>,
<linux-security-module@vger.kernel.org>, <netdev@vger.kernel.org>,
<netfilter-devel@vger.kernel.org>, <yusongping@huawei.com>,
<artem.kuzin@huawei.com>
Subject: Re: [PATCH v9 12/12] landlock: Document Landlock's network support
Date: Mon, 6 Mar 2023 16:43:25 +0300 [thread overview]
Message-ID: <85b31cb8-1aeb-d6f0-6c7d-91cea6b563d4@huawei.com> (raw)
In-Reply-To: <278ab07f-7583-a4e0-3d37-1bacd091531d@digikod.net>
2/21/2023 7:16 PM, Mickaël Salaün пишет:
>
> On 30/01/2023 11:03, Konstantin Meskhidze (A) wrote:
>>
>>
>> 1/27/2023 9:22 PM, Mickaël Salaün пишет:
>>>
>>> On 23/01/2023 10:38, Konstantin Meskhidze (A) wrote:
>>>>
>>>>
>>>> 1/22/2023 2:07 AM, Günther Noack пишет:
>>>
>>> [...]
>>>
>>>>>> @@ -143,10 +157,24 @@ for the ruleset creation, by filtering access rights according to the Landlock
>>>>>> ABI version. In this example, this is not required because all of the requested
>>>>>> ``allowed_access`` rights are already available in ABI 1.
>>>>>>
>>>>>> -We now have a ruleset with one rule allowing read access to ``/usr`` while
>>>>>> -denying all other handled accesses for the filesystem. The next step is to
>>>>>> -restrict the current thread from gaining more privileges (e.g. thanks to a SUID
>>>>>> -binary).
>>>>>> +For network access-control, we can add a set of rules that allow to use a port
>>>>>> +number for a specific action. All ports values must be defined in network byte
>>>>>> +order.
>>>>>
>>>>> What is the point of asking user space to convert this to network byte
>>>>> order? It seems to me that the kernel would be able to convert it to
>>>>> network byte order very easily internally and in a single place -- why
>>>>> ask all of the users to deal with that complexity? Am I overlooking
>>>>> something?
>>>>
>>>> I had a discussion about this issue with Mickaёl.
>>>> Please check these threads:
>>>> 1.
>>>> https://lore.kernel.org/netdev/49391484-7401-e7c7-d909-3bd6bd024731@digikod.net/
>>>> 2.
>>>> https://lore.kernel.org/netdev/1ed20e34-c252-b849-ab92-78c82901c979@huawei.com/
>>>
>>> I'm definitely not sure if this is the right solution, or if there is
>>> one. The rationale is to make it close to the current (POSIX) API. We
>>> didn't get many opinion about that but I'd really like to have a
>>> discussion about port endianness for this Landlock API.
>>
>> As for me, the kernel should take care about port converting. This
>> work should be done under the hood.
>>
>> Any thoughts?
>>
>>>
>>> I looked at some code (e.g. see [1]) and it seems that using htons()
>>> might make application patching more complex after all. What do you
>>> think? Is there some network (syscall) API that don't use this convention?
>>>
>>> [1] https://github.com/landlock-lsm/tuto-lighttpd
>>>
>>>>>
>>>>>> +
>>>>>> +.. code-block:: c
>>>>>> +
>>>>>> + struct landlock_net_service_attr net_service = {
>>>>>> + .allowed_access = LANDLOCK_ACCESS_NET_BIND_TCP,
>>>>>> + .port = htons(8080),
>>>>>> + };
>>>>>
>>>>> This is a more high-level comment:
>>>>>
>>>>> The notion of a 16-bit "port" seems to be specific to TCP and UDP --
>>>>> how do you envision this struct to evolve if other protocols need to
>>>>> be supported in the future?
>>>>
>>>> When TCP restrictions land into Linux, we need to think about UDP
>>>> support. Then other protocols will be on the road. Anyway you are right
>>>> this struct will be evolving in long term, but I don't have a particular
>>>> envision now. Thanks for the question - we need to think about it.
>>>>>
>>>>> Should this struct and the associated constants have "TCP" in its
>>>>> name, and other protocols use a separate struct in the future?
>>>
>>> Other protocols such as AF_VSOCK uses a 32-bit port. We could use a
>>> 32-bits port field or ever a 64-bit one. The later could make more sense
>>> because each field would eventually be aligned on 64-bit. Picking a
>>> 16-bit value was to help developers (and compilers/linters) with the
>>> "correct" type (for TCP).
>
> Thinking more about this, let's use a __u64 port (and remove the
> explicit packing). The landlock_append_net_rule() function should use a
> __u16 port argument, but the add_rule_net_service() function should
> check that there is no overflow with the port attribute (not higher than
> U16_MAX) before passing it to landlock_append_net_rule(). We should
> prioritize flexibility for the kernel UAPI over stricter types. User
> space libraries can improve this kind of types with a more complex API.
>
> Big endian can make sense for a pure network API because the port value
> (and the IP address) is passed to other machines through the network,
> as-is. However, with Landlock, the port value is only used by the
> kernel. Moreover, in practice, port values are mostly converted when
> filling the sockaddr*_in structs. It would then make it more risky to
> ask developers another explicit htons() conversion for Landlock
> syscalls. Let's stick to the host endianess and let the kernel do the
> conversion.
>
> Please include these rationales in code comments. We also need to update
> the tests for endianess, but still check big and little endian
> consistency as it is currently done in these tests. A new test should be
> added to check port boundaries with:
> - port = 0
> - port = U16_MAX
port = U16_MAX value passes.
> - port = U16_MAX + 1 (which should get an EINVAL)
port = U16_MAX + 1 after casting is 0, EINVAL is returned.
> - port = U16_MAX + 2 (to check u16 casting != 0)
port = U16_MAX + 2 after casting is 1, is it passes?
> - port = U32_MAX + 1
> - port = U32_MAX + 2
Don't you think that all port values >= U16_MAX + 1, EINVAL should
be returned?
>
>
>>>
>>> If we think about protocols other than TCP and UDP (e.g. AF_VSOCK), it
>>> could make sense to have a dedicated attr struct specifying other
>>> properties (e.g. CID). Anyway, the API is flexible but it would be nice
>>> to not mess with it too much. What do you think?
>>>
>>>
>>>>>
>>>>>> +
>>>>>> + err = landlock_add_rule(ruleset_fd, LANDLOCK_RULE_NET_SERVICE,
>>>>>> + &net_service, 0);
>>>>>> +
>>>>>> +The next step is to restrict the current thread from gaining more privileges
>>>>>> +(e.g. thanks to a SUID binary). We now have a ruleset with the first rule allowing
>>>>> ^^^^^^
>>>>> "through" a SUID binary? "thanks to" sounds like it's desired
>>>>> to do that, while we're actually trying to prevent it here?
>>>>
>>>> This is Mickaёl's part. Let's ask his opinion here.
>>>>
>>>> Mickaёl, any thoughts?
>>>
>>> Yep, "through" looks better.
>>> .
> .
next prev parent reply other threads:[~2023-03-06 13:43 UTC|newest]
Thread overview: 74+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-16 8:58 [PATCH v9 00/12] Network support for Landlock Konstantin Meskhidze
2023-01-16 8:58 ` [PATCH v9 01/12] landlock: Make ruleset's access masks more generic Konstantin Meskhidze
2023-01-16 8:58 ` [PATCH v9 02/12] landlock: Allow filesystem layout changes for domains without such rule type Konstantin Meskhidze
2023-02-10 17:34 ` Mickaël Salaün
2023-02-14 8:51 ` Konstantin Meskhidze (A)
2023-02-14 12:07 ` Mickaël Salaün
2023-02-14 12:57 ` Konstantin Meskhidze (A)
2023-01-16 8:58 ` [PATCH v9 03/12] landlock: Refactor landlock_find_rule/insert_rule Konstantin Meskhidze
2023-02-10 17:36 ` Mickaël Salaün
2023-02-14 10:15 ` Konstantin Meskhidze (A)
2023-02-14 12:09 ` Mickaël Salaün
2023-02-14 13:28 ` Konstantin Meskhidze (A)
2023-01-16 8:58 ` [PATCH v9 04/12] landlock: Refactor merge/inherit_ruleset functions Konstantin Meskhidze
2023-01-16 8:58 ` [PATCH v9 05/12] landlock: Move and rename umask_layers() and init_layer_masks() Konstantin Meskhidze
2023-02-10 17:37 ` Mickaël Salaün
2023-02-14 10:15 ` Konstantin Meskhidze (A)
2023-01-16 8:58 ` [PATCH v9 06/12] landlock: Refactor _unmask_layers() and _init_layer_masks() Konstantin Meskhidze
2023-02-10 17:38 ` Mickaël Salaün
2023-02-14 10:16 ` Konstantin Meskhidze (A)
2023-02-21 18:07 ` Mickaël Salaün
2023-03-06 7:52 ` Konstantin Meskhidze (A)
2023-01-16 8:58 ` [PATCH v9 07/12] landlock: Refactor landlock_add_rule() syscall Konstantin Meskhidze
2023-02-10 17:38 ` Mickaël Salaün
2023-02-14 10:18 ` Konstantin Meskhidze (A)
2023-01-16 8:58 ` [PATCH v9 08/12] landlock: Add network rules and TCP hooks support Konstantin Meskhidze
2023-02-10 17:39 ` Mickaël Salaün
2023-02-14 10:19 ` Konstantin Meskhidze (A)
2023-03-13 9:33 ` Konstantin Meskhidze (A)
2023-03-14 12:13 ` Mickaël Salaün
2023-03-14 14:38 ` Konstantin Meskhidze (A)
2023-02-21 18:04 ` Mickaël Salaün
2023-03-06 10:18 ` Konstantin Meskhidze (A)
2023-01-16 8:58 ` [PATCH v9 09/12] selftests/landlock: Share enforce_ruleset() Konstantin Meskhidze
2023-01-16 8:58 ` [PATCH v9 10/12] selftests/landlock: Add 10 new test suites dedicated to network Konstantin Meskhidze
2023-02-10 17:40 ` Mickaël Salaün
2023-02-14 10:36 ` Konstantin Meskhidze (A)
2023-02-14 12:13 ` Mickaël Salaün
2023-02-14 13:28 ` Konstantin Meskhidze (A)
2023-02-21 18:05 ` Mickaël Salaün
2023-03-06 12:03 ` Konstantin Meskhidze (A)
2023-03-06 16:00 ` Mickaël Salaün
2023-03-06 18:13 ` Konstantin Meskhidze (A)
2023-01-16 8:58 ` [PATCH v9 11/12] samples/landlock: Add network demo Konstantin Meskhidze
2023-01-16 8:58 ` [PATCH v9 12/12] landlock: Document Landlock's network support Konstantin Meskhidze
2023-01-21 23:07 ` Günther Noack
2023-01-23 9:38 ` Konstantin Meskhidze (A)
2023-01-27 18:22 ` Mickaël Salaün
2023-01-30 10:03 ` Konstantin Meskhidze (A)
2023-02-21 16:16 ` Mickaël Salaün
2023-03-06 13:43 ` Konstantin Meskhidze (A) [this message]
2023-03-06 16:09 ` Mickaël Salaün
2023-03-06 17:55 ` Konstantin Meskhidze (A)
2023-01-30 12:26 ` Konstantin Meskhidze (A)
2023-02-23 22:17 ` [PATCH v9 00/12] Network support for Landlock Günther Noack
2023-03-06 7:45 ` Konstantin Meskhidze (A)
2023-03-13 17:16 ` Konstantin Meskhidze (A)
2023-03-14 13:28 ` Mickaël Salaün
2023-06-26 15:29 ` [PATCH v9 00/12] Network support for Landlock - allowed list of protocols Mickaël Salaün
2023-06-28 2:33 ` Jeff Xu
2023-06-28 19:03 ` Mickaël Salaün
2023-06-28 21:56 ` Jeff Xu
2023-06-28 8:44 ` Günther Noack
2023-06-28 17:03 ` Jeff Xu
2023-06-28 19:29 ` Mickaël Salaün
2023-06-29 3:18 ` Jeff Xu
2023-06-29 11:07 ` Mickaël Salaün
2023-06-30 4:18 ` Jeff Xu
2023-06-30 18:23 ` Mickaël Salaün
2023-07-05 15:00 ` Jeff Xu
2023-07-12 11:30 ` Mickaël Salaün
2023-07-13 13:20 ` Konstantin Meskhidze (A)
2023-07-13 14:52 ` Mickaël Salaün
2023-07-13 11:44 ` Konstantin Meskhidze (A)
2023-06-28 19:07 ` Mickaël Salaün
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