[RFC PATCH v2 0/9] Support TCP listen access-control

[Mikhail Ivanov]

8/20/2024 4:23 PM, Günther Noack wrote:
> On Tue, Aug 20, 2024 at 03:11:07PM +0200, Günther Noack wrote:
>> Hello!
>>
>> Thanks for sending v2 of this patchset!
>>
>> On Wed, Aug 14, 2024 at 11:01:42AM +0800, Mikhail Ivanov wrote:
>>> Hello! This is v2 RFC patch dedicated to restriction of listening sockets.
>>>
>>> It is based on the landlock's mic-next branch on top of 6.11-rc1 kernel
>>> version.
>>>
>>> Description
>>> ===========
>>> LANDLOCK_ACCESS_NET_BIND_TCP is useful to limit the scope of "bindable"
>>> ports to forbid a malicious sandboxed process to impersonate a legitimate
>>> server process. However, bind(2) might be used by (TCP) clients to set the
>>> source port to a (legitimate) value. Controlling the ports that can be
>>> used for listening would allow (TCP) clients to explicitly bind to ports
>>> that are forbidden for listening.
>>>
>>> Such control is implemented with a new LANDLOCK_ACCESS_NET_LISTEN_TCP
>>> access right that restricts listening on undesired ports with listen(2).
>>>
>>> It's worth noticing that this access right doesn't affect changing
>>> backlog value using listen(2) on already listening socket. For this case
>>> test ipv4_tcp.double_listen is provided.
>>
>> This is a good catch, btw, that seems like the right thing to do. 👍
>>
>>
>> I am overall happy with this patch set, but left a few remarks in the tests so
>> far.  There are a few style nits here and there.
>>
>> A thing that makes me uneasy is that the tests have a lot of logic in
>> test_restricted_net_fixture(), where instead of the test logic being
>> straightforward, there are conditionals to tell apart different scenarios and
>> expect different results.  I wish that the style of these tests was more linear.
>> This patch set is making it a little bit worse, because the logic in
>> test_restricted_net_fixture() increases.
>>
>> I have also made some restructuring suggestions for the kernel code, in the hope
>> that they simplify things.  If they don't because I overlooked something, we can
>> skip that though.
> 
> I missed to mention it -- the documentation in
> Documentation/userspace-api/landlock.rst needs updating as well.

I'll do it. Thank you for reviewing this patch set!

> 
> —Günther