The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y git checkout FETCH_HEAD git cherry-pick -x 8c39633759885b6ff85f6d96cf445560e74df5e8 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2025041742-gurgle-parking-5fbb@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 8c39633759885b6ff85f6d96cf445560e74df5e8 Mon Sep 17 00:00:00 2001 From: "Matthieu Baerts (NGI0)" matttbe@kernel.org Date: Fri, 14 Mar 2025 21:11:32 +0100 Subject: [PATCH] mptcp: sockopt: fix getting IPV6_V6ONLY

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@vger.kernel.org Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/550 Reviewed-by: Mat Martineau martineau@kernel.org Signed-off-by: Matthieu Baerts (NGI0) matttbe@kernel.org Reviewed-by: Simon Horman horms@kernel.org Link: https://patch.msgid.link/20250314-net-mptcp-fix-data-stream-corr-sockopt-v1-... Signed-off-by: Paolo Abeni pabeni@redhat.com

diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c index 505445a9598f..4b99eb796855 100644 --- a/net/mptcp/sockopt.c +++ b/net/mptcp/sockopt.c @@ -1430,6 +1430,20 @@ static int mptcp_getsockopt_v4(struct mptcp_sock *msk, int optname, return -EOPNOTSUPP; }

+static int mptcp_getsockopt_v6(struct mptcp_sock *msk, int optname, + char __user *optval, int __user *optlen) +{ + struct sock *sk = (void *)msk; + + switch (optname) { + case IPV6_V6ONLY: + return mptcp_put_int_option(msk, optval, optlen, + sk->sk_ipv6only); + } + + return -EOPNOTSUPP; +} + static int mptcp_getsockopt_sol_mptcp(struct mptcp_sock *msk, int optname, char __user *optval, int __user *optlen) { @@ -1469,6 +1483,8 @@ int mptcp_getsockopt(struct sock *sk, int level, int optname,

if (level == SOL_IP) return mptcp_getsockopt_v4(msk, optname, optval, option); + if (level == SOL_IPV6) + return mptcp_getsockopt_v6(msk, optname, optval, option); if (level == SOL_TCP) return mptcp_getsockopt_sol_tcp(msk, optname, optval, option); if (level == SOL_MPTCP)