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: c9b95a1 ("mptcp: support IPV6_V6ONLY setsockopt")
Closes: #550
Signed-off-by: Matthieu Baerts (NGI0) <[email protected]>
Message-Id: <[email protected]>

Author: matttbe

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)