linux-kernel - Re: [PATCH] ipv6: add `do_forwarding` sysctl to enable per-interface forwarding

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: <hx3lbafvwebj7u7eqh4zz72gu6r7y6dn2il7vepylecvvrkeeh@hybyi2oizwuj>
Date: Fri, 27 Jun 2025 16:47:26 +0200
From: Gabriel Goller <g.goller@...xmox.com>
To: Nicolas Dichtel <nicolas.dichtel@...nd.com>
Cc: "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	Jonathan Corbet <corbet@....net>, David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org, 
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ipv6: add `do_forwarding` sysctl to enable per-interface
 forwarding

On 26.06.2025 16:51, Nicolas Dichtel wrote:
>Le 25/06/2025 à 16:26, Gabriel Goller a écrit :
>> It is currently impossible to enable ipv6 forwarding on a per-interface
>> basis like in ipv4. To enable forwarding on an ipv6 interface we need to
>> enable it on all interfaces and disable it on the other interfaces using
>> a netfilter rule. This is especially cumbersome if you have lots of
>> interface and only want to enable forwarding on a few. According to the
>> sysctl docs [0] the `net.ipv6.conf.all.forwarding` enables forwarding
>> for all interfaces, while the interface-specific
>> `net.ipv6.conf.<interface>.forwarding` configures the interface
>> Host/Router configuration.
>>
>> Introduce a new sysctl flag `do_forwarding`, which can be set on every
>> interface. The ip6_forwarding function will then check if the global
>> forwarding flag OR the do_forwarding flag is active and forward the
>> packet. To preserver backwards-compatibility also reset the flag on all
>> interfaces when setting the global forwarding flag to 0.
>>
>> [0]: https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt
>>
>> Signed-off-by: Gabriel Goller <g.goller@...xmox.com>
>Please, export this sysctl via a NETCONFA_DO_FORWARDING attribute also.

Yep, will do.

>> ---
>>
>> * I don't have any hard feelings about the naming, Nicolas Dichtel
>>   proposed `fwd_per_iface` but I think `do_forwarding` is a better fit.
>What about force_forwarding?

I Agree!

>> * I'm also not sure about the reset when setting the global forwarding
>>   flag; don't know if I did that right. Feedback is welcome!
>It seems correct to me.
>
>> * Thanks for the help!
>Maybe you could align ipv6.all.do_forwarding on ipv4.all.forwarding, ie setting
>all existing ipv6.*.do_forwarding.
>https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/net/ipv4/devinet.c#n2423

Also done!

>Regards,
>Nicolas

Sent a new patch just now, thanks for reviewing!