netdev - Re: [RFC PATCH v4 03/15] landlock: landlock_find/insert

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Message-ID: <0e5afeaf-0569-d0b5-b701-0f611d103732@digikod.net>
Date:   Tue, 12 Apr 2022 13:07:39 +0200
From:   Mickaël Salaün <mic@...ikod.net>
To:     Konstantin Meskhidze <konstantin.meskhidze@...wei.com>,
        willemdebruijn.kernel@...il.com
Cc:     linux-security-module@...r.kernel.org, netdev@...r.kernel.org,
        netfilter-devel@...r.kernel.org, yusongping@...wei.com,
        artem.kuzin@...wei.com, anton.sirazetdinov@...wei.com
Subject: Re: [RFC PATCH v4 03/15] landlock: landlock_find/insert_rule
 refactoring (TCP port 0)


On 23/03/2022 09:41, Konstantin Meskhidze wrote:
> 
> 
> 3/22/2022 4:24 PM, Mickaël Salaün пишет:
>>

[...]
>> The remaining question is: should we need to accept 0 as a valid TCP 
>> port? Can it be used? How does the kernel handle it?
> 
>   I agree that must be a check for port 0 in add_rule_net_service(), 
> cause unlike most port numbers, port 0 is a reserved port in TCP/IP 
> networking, meaning that it should not be used in TCP or UDP messages.
> Also network traffic sent across the internet to hosts listening on port 
> 0 might be generated from network attackers or accidentally by 
> applications programmed incorrectly.
> Source: https://www.lifewire.com/port-0-in-tcp-and-udp-818145

OK, so denying this port by default without a way to allow it should not 
be an issue. I guess an -EINVAL error would make sense when trying to 
allow this port. This should be documented in a comment (with a link to 
the RFC/section) and a dedicated test should check that behavior.

What is the behavior of firewalls (e.g. Netfiler) when trying to filter 
port 0?

This doesn't seem to be settle though: 
https://www.austingroupbugs.net/view.php?id=1068

Interesting article: 
https://z3r0trust.medium.com/socket-programming-the-bizarre-tcp-ip-port-0-saga-fcfbc0e0a276