Merge branch 'mptcp-add-REUSEADDR-REUSEPORT-V6ONLY-setsockopt-support'

Florian Westphal says:

====================
mptcp: add REUSEADDR/REUSEPORT/V6ONLY setsockopt support

restarting an mptcp-patched sshd yields following error:

  sshd: error: Bind to port 22 on 0.0.0.0 failed: Address already in use.
  sshd: error: setsockopt IPV6_V6ONLY: Operation not supported
  sshd: error: Bind to port 22 on :: failed: Address already in use.
  sshd: fatal: Cannot bind any address.

This series adds support for the needed setsockopts:

First patch skips the generic SOL_SOCKET handler for MPTCP:
in mptcp case, the setsockopt needs to alter the tcp socket, not the mptcp
parent socket.

Second patch adds minimal SOL_SOCKET support: REUSEPORT and REUSEADDR.
Rest is still handled by the generic SOL_SOCKET code.

Last patch adds IPV6ONLY support.  This makes ipv6 work for openssh:
It creates two listening sockets, before this patch, binding the ipv6
socket will fail because the port is already bound by the ipv4 one.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

net/mptcp/protocol.c

@@ -1601,6 +1601,64 @@ static void mptcp_destroy(struct sock *sk)
 	sk_sockets_allocated_dec(sk);
 }
 
+static int mptcp_setsockopt_sol_socket(struct mptcp_sock *msk, int optname,
+				       char __user *optval, unsigned int optlen)
+{
+	struct sock *sk = (struct sock *)msk;
+	struct socket *ssock;
+	int ret;
+
+	switch (optname) {
+	case SO_REUSEPORT:
+	case SO_REUSEADDR:
+		lock_sock(sk);
+		ssock = __mptcp_nmpc_socket(msk);
+		if (!ssock) {
+			release_sock(sk);
+			return -EINVAL;
+		}
+
+		ret = sock_setsockopt(ssock, SOL_SOCKET, optname, optval, optlen);
+		if (ret == 0) {
+			if (optname == SO_REUSEPORT)
+				sk->sk_reuseport = ssock->sk->sk_reuseport;
+			else if (optname == SO_REUSEADDR)
+				sk->sk_reuse = ssock->sk->sk_reuse;
+		}
+		release_sock(sk);
+		return ret;
+	}
+
+	return sock_setsockopt(sk->sk_socket, SOL_SOCKET, optname, optval, optlen);
+}
+
+static int mptcp_setsockopt_v6(struct mptcp_sock *msk, int optname,
+			       char __user *optval, unsigned int optlen)
+{
+	struct sock *sk = (struct sock *)msk;
+	int ret = -EOPNOTSUPP;
+	struct socket *ssock;
+
+	switch (optname) {
+	case IPV6_V6ONLY:
+		lock_sock(sk);
+		ssock = __mptcp_nmpc_socket(msk);
+		if (!ssock) {
+			release_sock(sk);
+			return -EINVAL;
+		}
+
+		ret = tcp_setsockopt(ssock->sk, SOL_IPV6, optname, optval, optlen);
+		if (ret == 0)
+			sk->sk_ipv6only = ssock->sk->sk_ipv6only;
+
+		release_sock(sk);
+		break;
+	}
+
+	return ret;
+}
+
 static int mptcp_setsockopt(struct sock *sk, int level, int optname,
 			    char __user *optval, unsigned int optlen)
 {
@@ -1609,6 +1667,9 @@ static int mptcp_setsockopt(struct sock *sk, int level, int optname,
 
 	pr_debug("msk=%p", msk);
 
+	if (level == SOL_SOCKET)
+		return mptcp_setsockopt_sol_socket(msk, optname, optval, optlen);
+
 	/* @@ the meaning of setsockopt() when the socket is connected and
 	 * there are multiple subflows is not yet defined. It is up to the
 	 * MPTCP-level socket to configure the subflows until the subflow
@@ -1621,6 +1682,9 @@ static int mptcp_setsockopt(struct sock *sk, int level, int optname,
 	if (ssk)
 		return tcp_setsockopt(ssk, level, optname, optval, optlen);
 
+	if (level == SOL_IPV6)
+		return mptcp_setsockopt_v6(msk, optname, optval, optlen);
+
 	return -EOPNOTSUPP;
 }
 

net/socket.c

@@ -2080,6 +2080,17 @@ SYSCALL_DEFINE4(recv, int, fd, void __user *, ubuf, size_t, size,
 	return __sys_recvfrom(fd, ubuf, size, flags, NULL, NULL);
 }
 
+static bool sock_use_custom_sol_socket(const struct socket *sock)
+{
+	const struct sock *sk = sock->sk;
+
+	/* Use sock->ops->setsockopt() for MPTCP */
+	return IS_ENABLED(CONFIG_MPTCP) &&
+	       sk->sk_protocol == IPPROTO_MPTCP &&
+	       sk->sk_type == SOCK_STREAM &&
+	       (sk->sk_family == AF_INET || sk->sk_family == AF_INET6);
+}
+
 /*
  *	Set a socket option. Because we don't know the option lengths we have
  *	to pass the user mode parameter for the protocols to sort out.
@@ -2118,7 +2129,7 @@ static int __sys_setsockopt(int fd, int level, int optname,
 			optval = (char __user __force *)kernel_optval;
 		}
 
-		if (level == SOL_SOCKET)
+		if (level == SOL_SOCKET && !sock_use_custom_sol_socket(sock))
 			err =
 			    sock_setsockopt(sock, level, optname, optval,
 					    optlen);