linux-kernel - Re: [PATCH net 2/3] mptcp: sockopt: fix getting IPV6

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Message-ID: <20250319153827.GC768132@kernel.org>
Date: Wed, 19 Mar 2025 15:38:27 +0000
From: Simon Horman <horms@...nel.org>
To: "Matthieu Baerts (NGI0)" <matttbe@...nel.org>
Cc: mptcp@...ts.linux.dev, Mat Martineau <martineau@...nel.org>,
	Geliang Tang <geliang@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Florian Westphal <fw@...len.de>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH net 2/3] mptcp: sockopt: fix getting IPV6_V6ONLY

On Fri, Mar 14, 2025 at 09:11:32PM +0100, Matthieu Baerts (NGI0) wrote:
> When adding a socket option support in MPTCP, both the get and set parts
> are supposed to be implemented.
> 
> IPV6_V6ONLY support for the setsockopt part has been added a while ago,
> but it looks like the get part got forgotten. It should have been
> present as a way to verify a setting has been set as expected, and not
> to act differently from TCP or any other socket types.
> 
> Not supporting this getsockopt(IPV6_V6ONLY) blocks some apps which want
> to check the default value, before doing extra actions. On Linux, the
> default value is 0, but this can be changed with the net.ipv6.bindv6only
> sysctl knob. On Windows, it is set to 1 by default. So supporting the
> get part, like for all other socket options, is important.
> 
> Everything was in place to expose it, just the last step was missing.
> Only new code is added to cover this specific getsockopt(), that seems
> safe.
> 
> Fixes: c9b95a135987 ("mptcp: support IPV6_V6ONLY setsockopt")
> Cc: stable@...r.kernel.org
> Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/550
> Reviewed-by: Mat Martineau <martineau@...nel.org>
> Signed-off-by: Matthieu Baerts (NGI0) <matttbe@...nel.org>

Hi Matthieu, all,

TBH, I would lean towards this being net-next material rather than a fix
for net. But that notwithstanding this looks good to me.

Reviewed-by: Simon Horman <horms@...nel.org>