netdev - Re: [PATCH net-next v2 09/14] net: ipv6: Add ip6_mr

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Message-ID: <875xgz4fag.fsf@nvidia.com>
Date: Fri, 13 Jun 2025 20:59:27 +0200
From: Petr Machata <petrm@...dia.com>
To: Jakub Kicinski <kuba@...nel.org>
CC: Petr Machata <petrm@...dia.com>, "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, "David
 Ahern" <dsahern@...il.com>, <netdev@...r.kernel.org>, Simon Horman
	<horms@...nel.org>, Nikolay Aleksandrov <razor@...ckwall.org>, Ido Schimmel
	<idosch@...dia.com>, <mlxsw@...dia.com>
Subject: Re: [PATCH net-next v2 09/14] net: ipv6: Add ip6_mr_output()


Jakub Kicinski <kuba@...nel.org> writes:

> On Thu, 12 Jun 2025 22:10:43 +0200 Petr Machata wrote:
>> +static inline int
>> +ip6_mr_output(struct net *net, struct sock *sk, struct sk_buff *skb)
>> +{
>> +	return 0;
>> +}
>
> Shouldn't this free the skb?
>
> That would explain why you're not seeing the problem our netdevsim
> runner doesn't have IPV6_MROUTE set, and you probably do?

Yep, that's what reproduces it. The NIPA how-to-reproduce instructions
show they use tools/testing/selftests/net/forwarding/config, but those
enable IPV6_MROUTE, hence why it didn't reproduce for me.

This ip6_mr_output() fallback is completely broken, it should be calling
ip6_output() obviously instead of silently leaking the packet :-|