WSL2-Linux-Kernel/net/mptcp/sockopt.c

// SPDX-License-Identifier: GPL-2.0
/* Multipath TCP
 *
 * Copyright (c) 2021, Red Hat.
 */

#define pr_fmt(fmt) "MPTCP: " fmt

#include <linux/kernel.h>
#include <linux/module.h>
#include <net/sock.h>
#include <net/protocol.h>
#include <net/tcp.h>
#include <net/mptcp.h>
#include "protocol.h"

static struct sock *__mptcp_tcp_fallback(struct mptcp_sock *msk)
{
	sock_owned_by_me((const struct sock *)msk);

	if (likely(!__mptcp_check_fallback(msk)))
		return NULL;

	return msk->first;
}

static u32 sockopt_seq_reset(const struct sock *sk)
{
	sock_owned_by_me(sk);

	/* Highbits contain state.  Allows to distinguish sockopt_seq
	 * of listener and established:
	 * s0 = new_listener()
	 * sockopt(s0) - seq is 1
	 * s1 = accept(s0) - s1 inherits seq 1 if listener sk (s0)
	 * sockopt(s0) - seq increments to 2 on s0
	 * sockopt(s1) // seq increments to 2 on s1 (different option)
	 * new ssk completes join, inherits options from s0 // seq 2
	 * Needs sync from mptcp join logic, but ssk->seq == msk->seq
	 *
	 * Set High order bits to sk_state so ssk->seq == msk->seq test
	 * will fail.
	 */

	return (u32)sk->sk_state << 24u;
}

static void sockopt_seq_inc(struct mptcp_sock *msk)
{
	u32 seq = (msk->setsockopt_seq + 1) & 0x00ffffff;

	msk->setsockopt_seq = sockopt_seq_reset((struct sock *)msk) + seq;
}

static int mptcp_get_int_option(struct mptcp_sock *msk, sockptr_t optval,
				unsigned int optlen, int *val)
{
	if (optlen < sizeof(int))
		return -EINVAL;

	if (copy_from_sockptr(val, optval, sizeof(*val)))
		return -EFAULT;

	return 0;
}

static void mptcp_sol_socket_sync_intval(struct mptcp_sock *msk, int optname, int val)
{
	struct mptcp_subflow_context *subflow;
	struct sock *sk = (struct sock *)msk;

	lock_sock(sk);
	sockopt_seq_inc(msk);

	mptcp_for_each_subflow(msk, subflow) {
		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
		bool slow = lock_sock_fast(ssk);

		switch (optname) {
		case SO_DEBUG:
			sock_valbool_flag(ssk, SOCK_DBG, !!val);
			break;
		case SO_KEEPALIVE:
			if (ssk->sk_prot->keepalive)
				ssk->sk_prot->keepalive(ssk, !!val);
			sock_valbool_flag(ssk, SOCK_KEEPOPEN, !!val);
			break;
		case SO_PRIORITY:
			ssk->sk_priority = val;
			break;
		case SO_SNDBUF:
		case SO_SNDBUFFORCE:
			ssk->sk_userlocks |= SOCK_SNDBUF_LOCK;
			WRITE_ONCE(ssk->sk_sndbuf, sk->sk_sndbuf);
			break;
		case SO_RCVBUF:
		case SO_RCVBUFFORCE:
			ssk->sk_userlocks |= SOCK_RCVBUF_LOCK;
			WRITE_ONCE(ssk->sk_rcvbuf, sk->sk_rcvbuf);
			break;
		case SO_MARK:
			if (READ_ONCE(ssk->sk_mark) != sk->sk_mark) {
				ssk->sk_mark = sk->sk_mark;
				sk_dst_reset(ssk);
			}
			break;
		case SO_INCOMING_CPU:
			WRITE_ONCE(ssk->sk_incoming_cpu, val);
			break;
		}

		subflow->setsockopt_seq = msk->setsockopt_seq;
		unlock_sock_fast(ssk, slow);
	}

	release_sock(sk);
}

static int mptcp_sol_socket_intval(struct mptcp_sock *msk, int optname, int val)
{
	sockptr_t optval = KERNEL_SOCKPTR(&val);
	struct sock *sk = (struct sock *)msk;
	int ret;

	ret = sock_setsockopt(sk->sk_socket, SOL_SOCKET, optname,
			      optval, sizeof(val));
	if (ret)
		return ret;

	mptcp_sol_socket_sync_intval(msk, optname, val);
	return 0;
}

static void mptcp_so_incoming_cpu(struct mptcp_sock *msk, int val)
{
	struct sock *sk = (struct sock *)msk;

	WRITE_ONCE(sk->sk_incoming_cpu, val);

	mptcp_sol_socket_sync_intval(msk, SO_INCOMING_CPU, val);
}

static int mptcp_setsockopt_sol_socket_tstamp(struct mptcp_sock *msk, int optname, int val)
{
	sockptr_t optval = KERNEL_SOCKPTR(&val);
	struct mptcp_subflow_context *subflow;
	struct sock *sk = (struct sock *)msk;
	int ret;

	ret = sock_setsockopt(sk->sk_socket, SOL_SOCKET, optname,
			      optval, sizeof(val));
	if (ret)
		return ret;

	lock_sock(sk);
	mptcp_for_each_subflow(msk, subflow) {
		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
		bool slow = lock_sock_fast(ssk);

		sock_set_timestamp(sk, optname, !!val);
		unlock_sock_fast(ssk, slow);
	}

	release_sock(sk);
	return 0;
}

static int mptcp_setsockopt_sol_socket_int(struct mptcp_sock *msk, int optname,
					   sockptr_t optval,
					   unsigned int optlen)
{
	int val, ret;

	ret = mptcp_get_int_option(msk, optval, optlen, &val);
	if (ret)
		return ret;

	switch (optname) {
	case SO_KEEPALIVE:
		mptcp_sol_socket_sync_intval(msk, optname, val);
		return 0;
	case SO_DEBUG:
	case SO_MARK:
	case SO_PRIORITY:
	case SO_SNDBUF:
	case SO_SNDBUFFORCE:
	case SO_RCVBUF:
	case SO_RCVBUFFORCE:
		return mptcp_sol_socket_intval(msk, optname, val);
	case SO_INCOMING_CPU:
		mptcp_so_incoming_cpu(msk, val);
		return 0;
	case SO_TIMESTAMP_OLD:
	case SO_TIMESTAMP_NEW:
	case SO_TIMESTAMPNS_OLD:
	case SO_TIMESTAMPNS_NEW:
		return mptcp_setsockopt_sol_socket_tstamp(msk, optname, val);
	}

	return -ENOPROTOOPT;
}

static int mptcp_setsockopt_sol_socket_timestamping(struct mptcp_sock *msk,
						    int optname,
						    sockptr_t optval,
						    unsigned int optlen)
{
	struct mptcp_subflow_context *subflow;
	struct sock *sk = (struct sock *)msk;
	struct so_timestamping timestamping;
	int ret;

	if (optlen == sizeof(timestamping)) {
		if (copy_from_sockptr(&timestamping, optval,
				      sizeof(timestamping)))
			return -EFAULT;
	} else if (optlen == sizeof(int)) {
		memset(&timestamping, 0, sizeof(timestamping));

		if (copy_from_sockptr(&timestamping.flags, optval, sizeof(int)))
			return -EFAULT;
	} else {
		return -EINVAL;
	}

	ret = sock_setsockopt(sk->sk_socket, SOL_SOCKET, optname,
			      KERNEL_SOCKPTR(&timestamping),
			      sizeof(timestamping));
	if (ret)
		return ret;

	lock_sock(sk);

	mptcp_for_each_subflow(msk, subflow) {
		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
		bool slow = lock_sock_fast(ssk);

		sock_set_timestamping(sk, optname, timestamping);
		unlock_sock_fast(ssk, slow);
	}

	release_sock(sk);

	return 0;
}

static int mptcp_setsockopt_sol_socket_linger(struct mptcp_sock *msk, sockptr_t optval,
					      unsigned int optlen)
{
	struct mptcp_subflow_context *subflow;
	struct sock *sk = (struct sock *)msk;
	struct linger ling;
	sockptr_t kopt;
	int ret;

	if (optlen < sizeof(ling))
		return -EINVAL;

	if (copy_from_sockptr(&ling, optval, sizeof(ling)))
		return -EFAULT;

	kopt = KERNEL_SOCKPTR(&ling);
	ret = sock_setsockopt(sk->sk_socket, SOL_SOCKET, SO_LINGER, kopt, sizeof(ling));
	if (ret)
		return ret;

	lock_sock(sk);
	sockopt_seq_inc(msk);
	mptcp_for_each_subflow(msk, subflow) {
		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
		bool slow = lock_sock_fast(ssk);

		if (!ling.l_onoff) {
			sock_reset_flag(ssk, SOCK_LINGER);
		} else {
			ssk->sk_lingertime = sk->sk_lingertime;
			sock_set_flag(ssk, SOCK_LINGER);
		}

		subflow->setsockopt_seq = msk->setsockopt_seq;
		unlock_sock_fast(ssk, slow);
	}

	release_sock(sk);
	return 0;
}

static int mptcp_setsockopt_sol_socket(struct mptcp_sock *msk, int optname,
				       sockptr_t optval, unsigned int optlen)
{
	struct sock *sk = (struct sock *)msk;
	struct socket *ssock;
	int ret;

	switch (optname) {
	case SO_REUSEPORT:
	case SO_REUSEADDR:
	case SO_BINDTODEVICE:
	case SO_BINDTOIFINDEX:
		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;
			else if (optname == SO_BINDTODEVICE)
				sk->sk_bound_dev_if = ssock->sk->sk_bound_dev_if;
			else if (optname == SO_BINDTOIFINDEX)
				sk->sk_bound_dev_if = ssock->sk->sk_bound_dev_if;
		}
		release_sock(sk);
		return ret;
	case SO_KEEPALIVE:
	case SO_PRIORITY:
	case SO_SNDBUF:
	case SO_SNDBUFFORCE:
	case SO_RCVBUF:
	case SO_RCVBUFFORCE:
	case SO_MARK:
	case SO_INCOMING_CPU:
	case SO_DEBUG:
	case SO_TIMESTAMP_OLD:
	case SO_TIMESTAMP_NEW:
	case SO_TIMESTAMPNS_OLD:
	case SO_TIMESTAMPNS_NEW:
		return mptcp_setsockopt_sol_socket_int(msk, optname, optval,
						       optlen);
	case SO_TIMESTAMPING_OLD:
	case SO_TIMESTAMPING_NEW:
		return mptcp_setsockopt_sol_socket_timestamping(msk, optname,
								optval, optlen);
	case SO_LINGER:
		return mptcp_setsockopt_sol_socket_linger(msk, optval, optlen);
	case SO_RCVLOWAT:
	case SO_RCVTIMEO_OLD:
	case SO_RCVTIMEO_NEW:
	case SO_BUSY_POLL:
	case SO_PREFER_BUSY_POLL:
	case SO_BUSY_POLL_BUDGET:
		/* No need to copy: only relevant for msk */
		return sock_setsockopt(sk->sk_socket, SOL_SOCKET, optname, optval, optlen);
	case SO_NO_CHECK:
	case SO_DONTROUTE:
	case SO_BROADCAST:
	case SO_BSDCOMPAT:
	case SO_PASSCRED:
	case SO_PASSSEC:
	case SO_RXQ_OVFL:
	case SO_WIFI_STATUS:
	case SO_NOFCS:
	case SO_SELECT_ERR_QUEUE:
		return 0;
	}

	/* SO_OOBINLINE is not supported, let's avoid the related mess
	 * SO_ATTACH_FILTER, SO_ATTACH_BPF, SO_ATTACH_REUSEPORT_CBPF,
	 * SO_DETACH_REUSEPORT_BPF, SO_DETACH_FILTER, SO_LOCK_FILTER,
	 * we must be careful with subflows
	 *
	 * SO_ATTACH_REUSEPORT_EBPF is not supported, at it checks
	 * explicitly the sk_protocol field
	 *
	 * SO_PEEK_OFF is unsupported, as it is for plain TCP
	 * SO_MAX_PACING_RATE is unsupported, we must be careful with subflows
	 * SO_CNX_ADVICE is currently unsupported, could possibly be relevant,
	 * but likely needs careful design
	 *
	 * SO_ZEROCOPY is currently unsupported, TODO in sndmsg
	 * SO_TXTIME is currently unsupported
	 */

	return -EOPNOTSUPP;
}

static int mptcp_setsockopt_v6(struct mptcp_sock *msk, int optname,
			       sockptr_t 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 bool mptcp_supported_sockopt(int level, int optname)
{
	if (level == SOL_IP) {
		switch (optname) {
		/* should work fine */
		case IP_FREEBIND:
		case IP_TRANSPARENT:

		/* the following are control cmsg related */
		case IP_PKTINFO:
		case IP_RECVTTL:
		case IP_RECVTOS:
		case IP_RECVOPTS:
		case IP_RETOPTS:
		case IP_PASSSEC:
		case IP_RECVORIGDSTADDR:
		case IP_CHECKSUM:
		case IP_RECVFRAGSIZE:

		/* common stuff that need some love */
		case IP_TOS:
		case IP_TTL:
		case IP_BIND_ADDRESS_NO_PORT:
		case IP_MTU_DISCOVER:
		case IP_RECVERR:

		/* possibly less common may deserve some love */
		case IP_MINTTL:

		/* the following is apparently a no-op for plain TCP */
		case IP_RECVERR_RFC4884:
			return true;
		}

		/* IP_OPTIONS is not supported, needs subflow care */
		/* IP_HDRINCL, IP_NODEFRAG are not supported, RAW specific */
		/* IP_MULTICAST_TTL, IP_MULTICAST_LOOP, IP_UNICAST_IF,
		 * IP_ADD_MEMBERSHIP, IP_ADD_SOURCE_MEMBERSHIP, IP_DROP_MEMBERSHIP,
		 * IP_DROP_SOURCE_MEMBERSHIP, IP_BLOCK_SOURCE, IP_UNBLOCK_SOURCE,
		 * MCAST_JOIN_GROUP, MCAST_LEAVE_GROUP MCAST_JOIN_SOURCE_GROUP,
		 * MCAST_LEAVE_SOURCE_GROUP, MCAST_BLOCK_SOURCE, MCAST_UNBLOCK_SOURCE,
		 * MCAST_MSFILTER, IP_MULTICAST_ALL are not supported, better not deal
		 * with mcast stuff
		 */
		/* IP_IPSEC_POLICY, IP_XFRM_POLICY are nut supported, unrelated here */
		return false;
	}
	if (level == SOL_IPV6) {
		switch (optname) {
		case IPV6_V6ONLY:

		/* the following are control cmsg related */
		case IPV6_RECVPKTINFO:
		case IPV6_2292PKTINFO:
		case IPV6_RECVHOPLIMIT:
		case IPV6_2292HOPLIMIT:
		case IPV6_RECVRTHDR:
		case IPV6_2292RTHDR:
		case IPV6_RECVHOPOPTS:
		case IPV6_2292HOPOPTS:
		case IPV6_RECVDSTOPTS:
		case IPV6_2292DSTOPTS:
		case IPV6_RECVTCLASS:
		case IPV6_FLOWINFO:
		case IPV6_RECVPATHMTU:
		case IPV6_RECVORIGDSTADDR:
		case IPV6_RECVFRAGSIZE:

		/* the following ones need some love but are quite common */
		case IPV6_TCLASS:
		case IPV6_TRANSPARENT:
		case IPV6_FREEBIND:
		case IPV6_PKTINFO:
		case IPV6_2292PKTOPTIONS:
		case IPV6_UNICAST_HOPS:
		case IPV6_MTU_DISCOVER:
		case IPV6_MTU:
		case IPV6_RECVERR:
		case IPV6_FLOWINFO_SEND:
		case IPV6_FLOWLABEL_MGR:
		case IPV6_MINHOPCOUNT:
		case IPV6_DONTFRAG:
		case IPV6_AUTOFLOWLABEL:

		/* the following one is a no-op for plain TCP */
		case IPV6_RECVERR_RFC4884:
			return true;
		}

		/* IPV6_HOPOPTS, IPV6_RTHDRDSTOPTS, IPV6_RTHDR, IPV6_DSTOPTS are
		 * not supported
		 */
		/* IPV6_MULTICAST_HOPS, IPV6_MULTICAST_LOOP, IPV6_UNICAST_IF,
		 * IPV6_MULTICAST_IF, IPV6_ADDRFORM,
		 * IPV6_ADD_MEMBERSHIP, IPV6_DROP_MEMBERSHIP, IPV6_JOIN_ANYCAST,
		 * IPV6_LEAVE_ANYCAST, IPV6_MULTICAST_ALL, MCAST_JOIN_GROUP, MCAST_LEAVE_GROUP,
		 * MCAST_JOIN_SOURCE_GROUP, MCAST_LEAVE_SOURCE_GROUP,
		 * MCAST_BLOCK_SOURCE, MCAST_UNBLOCK_SOURCE, MCAST_MSFILTER
		 * are not supported better not deal with mcast
		 */
		/* IPV6_ROUTER_ALERT, IPV6_ROUTER_ALERT_ISOLATE are not supported, since are evil */

		/* IPV6_IPSEC_POLICY, IPV6_XFRM_POLICY are not supported */
		/* IPV6_ADDR_PREFERENCES is not supported, we must be careful with subflows */
		return false;
	}
	if (level == SOL_TCP) {
		switch (optname) {
		/* the following are no-op or should work just fine */
		case TCP_THIN_DUPACK:
		case TCP_DEFER_ACCEPT:

		/* the following need some love */
		case TCP_MAXSEG:
		case TCP_NODELAY:
		case TCP_THIN_LINEAR_TIMEOUTS:
		case TCP_CONGESTION:
		case TCP_ULP:
		case TCP_CORK:
		case TCP_KEEPIDLE:
		case TCP_KEEPINTVL:
		case TCP_KEEPCNT:
		case TCP_SYNCNT:
		case TCP_SAVE_SYN:
		case TCP_LINGER2:
		case TCP_WINDOW_CLAMP:
		case TCP_QUICKACK:
		case TCP_USER_TIMEOUT:
		case TCP_TIMESTAMP:
		case TCP_NOTSENT_LOWAT:
		case TCP_TX_DELAY:
			return true;
		}

		/* TCP_MD5SIG, TCP_MD5SIG_EXT are not supported, MD5 is not compatible with MPTCP */

		/* TCP_REPAIR, TCP_REPAIR_QUEUE, TCP_QUEUE_SEQ, TCP_REPAIR_OPTIONS,
		 * TCP_REPAIR_WINDOW are not supported, better avoid this mess
		 */
		/* TCP_FASTOPEN_KEY, TCP_FASTOPEN TCP_FASTOPEN_CONNECT, TCP_FASTOPEN_NO_COOKIE,
		 * are not supported fastopen is currently unsupported
		 */
		/* TCP_INQ is currently unsupported, needs some recvmsg work */
	}
	return false;
}

static int mptcp_setsockopt_sol_tcp_congestion(struct mptcp_sock *msk, sockptr_t optval,
					       unsigned int optlen)
{
	struct mptcp_subflow_context *subflow;
	struct sock *sk = (struct sock *)msk;
	char name[TCP_CA_NAME_MAX];
	bool cap_net_admin;
	int ret;

	if (optlen < 1)
		return -EINVAL;

	ret = strncpy_from_sockptr(name, optval,
				   min_t(long, TCP_CA_NAME_MAX - 1, optlen));
	if (ret < 0)
		return -EFAULT;

	name[ret] = 0;

	cap_net_admin = ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN);

	ret = 0;
	lock_sock(sk);
	sockopt_seq_inc(msk);
	mptcp_for_each_subflow(msk, subflow) {
		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
		int err;

		lock_sock(ssk);
		err = tcp_set_congestion_control(ssk, name, true, cap_net_admin);
		if (err < 0 && ret == 0)
			ret = err;
		subflow->setsockopt_seq = msk->setsockopt_seq;
		release_sock(ssk);
	}

	if (ret == 0)
		strcpy(msk->ca_name, name);

	release_sock(sk);
	return ret;
}

static int mptcp_setsockopt_sol_tcp(struct mptcp_sock *msk, int optname,
				    sockptr_t optval, unsigned int optlen)
{
	switch (optname) {
	case TCP_ULP:
		return -EOPNOTSUPP;
	case TCP_CONGESTION:
		return mptcp_setsockopt_sol_tcp_congestion(msk, optval, optlen);
	}

	return -EOPNOTSUPP;
}

int mptcp_setsockopt(struct sock *sk, int level, int optname,
		     sockptr_t optval, unsigned int optlen)
{
	struct mptcp_sock *msk = mptcp_sk(sk);
	struct sock *ssk;

	pr_debug("msk=%p", msk);

	if (level == SOL_SOCKET)
		return mptcp_setsockopt_sol_socket(msk, optname, optval, optlen);

	if (!mptcp_supported_sockopt(level, optname))
		return -ENOPROTOOPT;

	/* @@ 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
	 * is in TCP fallback, when TCP socket options are passed through
	 * to the one remaining subflow.
	 */
	lock_sock(sk);
	ssk = __mptcp_tcp_fallback(msk);
	release_sock(sk);
	if (ssk)
		return tcp_setsockopt(ssk, level, optname, optval, optlen);

	if (level == SOL_IPV6)
		return mptcp_setsockopt_v6(msk, optname, optval, optlen);

	if (level == SOL_TCP)
		return mptcp_setsockopt_sol_tcp(msk, optname, optval, optlen);

	return -EOPNOTSUPP;
}

static int mptcp_getsockopt_first_sf_only(struct mptcp_sock *msk, int level, int optname,
					  char __user *optval, int __user *optlen)
{
	struct sock *sk = (struct sock *)msk;
	struct socket *ssock;
	int ret = -EINVAL;
	struct sock *ssk;

	lock_sock(sk);
	ssk = msk->first;
	if (ssk) {
		ret = tcp_getsockopt(ssk, level, optname, optval, optlen);
		goto out;
	}

	ssock = __mptcp_nmpc_socket(msk);
	if (!ssock)
		goto out;

	ret = tcp_getsockopt(ssock->sk, level, optname, optval, optlen);

out:
	release_sock(sk);
	return ret;
}

static int mptcp_getsockopt_sol_tcp(struct mptcp_sock *msk, int optname,
				    char __user *optval, int __user *optlen)
{
	switch (optname) {
	case TCP_ULP:
	case TCP_CONGESTION:
	case TCP_INFO:
	case TCP_CC_INFO:
		return mptcp_getsockopt_first_sf_only(msk, SOL_TCP, optname,
						      optval, optlen);
	}
	return -EOPNOTSUPP;
}

int mptcp_getsockopt(struct sock *sk, int level, int optname,
		     char __user *optval, int __user *option)
{
	struct mptcp_sock *msk = mptcp_sk(sk);
	struct sock *ssk;

	pr_debug("msk=%p", msk);

	/* @@ 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
	 * is in TCP fallback, when socket options are passed through
	 * to the one remaining subflow.
	 */
	lock_sock(sk);
	ssk = __mptcp_tcp_fallback(msk);
	release_sock(sk);
	if (ssk)
		return tcp_getsockopt(ssk, level, optname, optval, option);

	if (level == SOL_TCP)
		return mptcp_getsockopt_sol_tcp(msk, optname, optval, option);
	return -EOPNOTSUPP;
}

static void sync_socket_options(struct mptcp_sock *msk, struct sock *ssk)
{
	static const unsigned int tx_rx_locks = SOCK_RCVBUF_LOCK | SOCK_SNDBUF_LOCK;
	struct sock *sk = (struct sock *)msk;

	if (ssk->sk_prot->keepalive) {
		if (sock_flag(sk, SOCK_KEEPOPEN))
			ssk->sk_prot->keepalive(ssk, 1);
		else
			ssk->sk_prot->keepalive(ssk, 0);
	}

	ssk->sk_priority = sk->sk_priority;
	ssk->sk_bound_dev_if = sk->sk_bound_dev_if;
	ssk->sk_incoming_cpu = sk->sk_incoming_cpu;

	if (sk->sk_userlocks & tx_rx_locks) {
		ssk->sk_userlocks |= sk->sk_userlocks & tx_rx_locks;
		if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
			WRITE_ONCE(ssk->sk_sndbuf, sk->sk_sndbuf);
		if (sk->sk_userlocks & SOCK_RCVBUF_LOCK)
			WRITE_ONCE(ssk->sk_rcvbuf, sk->sk_rcvbuf);
	}

	if (sock_flag(sk, SOCK_LINGER)) {
		ssk->sk_lingertime = sk->sk_lingertime;
		sock_set_flag(ssk, SOCK_LINGER);
	} else {
		sock_reset_flag(ssk, SOCK_LINGER);
	}

	if (sk->sk_mark != ssk->sk_mark) {
		ssk->sk_mark = sk->sk_mark;
		sk_dst_reset(ssk);
	}

	sock_valbool_flag(ssk, SOCK_DBG, sock_flag(sk, SOCK_DBG));

	if (inet_csk(sk)->icsk_ca_ops != inet_csk(ssk)->icsk_ca_ops)
		tcp_set_congestion_control(ssk, msk->ca_name, false, true);
}

static void __mptcp_sockopt_sync(struct mptcp_sock *msk, struct sock *ssk)
{
	bool slow = lock_sock_fast(ssk);

	sync_socket_options(msk, ssk);

	unlock_sock_fast(ssk, slow);
}

void mptcp_sockopt_sync(struct mptcp_sock *msk, struct sock *ssk)
{
	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);

	msk_owned_by_me(msk);

	if (READ_ONCE(subflow->setsockopt_seq) != msk->setsockopt_seq) {
		__mptcp_sockopt_sync(msk, ssk);

		subflow->setsockopt_seq = msk->setsockopt_seq;
	}
}

void mptcp_sockopt_sync_all(struct mptcp_sock *msk)
{
	struct mptcp_subflow_context *subflow;
	struct sock *sk = (struct sock *)msk;
	u32 seq;

	seq = sockopt_seq_reset(sk);

	mptcp_for_each_subflow(msk, subflow) {
		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
		u32 sseq = READ_ONCE(subflow->setsockopt_seq);

		if (sseq != msk->setsockopt_seq) {
			__mptcp_sockopt_sync(msk, ssk);
			WRITE_ONCE(subflow->setsockopt_seq, seq);
		} else if (sseq != seq) {
			WRITE_ONCE(subflow->setsockopt_seq, seq);
		}

		cond_resched();
	}

	msk->setsockopt_seq = seq;
}