path: root/net/mptcp/options.c

// SPDX-License-Identifier: GPL-2.0
/* Multipath TCP
 *
 * Copyright (c) 2017 - 2019, Intel Corporation.
 */

#define pr_fmt(fmt) "MPTCP: " fmt

#include <linux/kernel.h>
#include <crypto/sha2.h>
#include <net/tcp.h>
#include <net/mptcp.h>
#include "protocol.h"
#include "mib.h"

#include <trace/events/mptcp.h>

static bool mptcp_cap_flag_sha256(u8 flags)
{
	return (flags & MPTCP_CAP_FLAG_MASK) == MPTCP_CAP_HMAC_SHA256;
}

static void mptcp_parse_option(const struct sk_buff *skb,
			       const unsigned char *ptr, int opsize,
			       struct mptcp_options_received *mp_opt)
{
	u8 subtype = *ptr >> 4;
	int expected_opsize;
	u16 subopt;
	u8 version;
	u8 flags;
	u8 i;

	switch (subtype) {
	case MPTCPOPT_MP_CAPABLE:
		/* strict size checking */
		if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
			if (skb->len > tcp_hdr(skb)->doff << 2)
				expected_opsize = TCPOLEN_MPTCP_MPC_ACK_DATA;
			else
				expected_opsize = TCPOLEN_MPTCP_MPC_ACK;
			subopt = OPTION_MPTCP_MPC_ACK;
		} else {
			if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK) {
				expected_opsize = TCPOLEN_MPTCP_MPC_SYNACK;
				subopt = OPTION_MPTCP_MPC_SYNACK;
			} else {
				expected_opsize = TCPOLEN_MPTCP_MPC_SYN;
				subopt = OPTION_MPTCP_MPC_SYN;
			}
		}

		/* Cfr RFC 8684 Section 3.3.0:
		 * If a checksum is present but its use had
		 * not been negotiated in the MP_CAPABLE handshake, the receiver MUST
		 * close the subflow with a RST, as it is not behaving as negotiated.
		 * If a checksum is not present when its use has been negotiated, the
		 * receiver MUST close the subflow with a RST, as it is considered
		 * broken
		 * We parse even option with mismatching csum presence, so that
		 * later in subflow_data_ready we can trigger the reset.
		 */
		if (opsize != expected_opsize &&
		    (expected_opsize != TCPOLEN_MPTCP_MPC_ACK_DATA ||
		     opsize != TCPOLEN_MPTCP_MPC_ACK_DATA_CSUM))
			break;

		/* try to be gentle vs future versions on the initial syn */
		version = *ptr++ & MPTCP_VERSION_MASK;
		if (opsize != TCPOLEN_MPTCP_MPC_SYN) {
			if (version != MPTCP_SUPPORTED_VERSION)
				break;
		} else if (version < MPTCP_SUPPORTED_VERSION) {
			break;
		}

		flags = *ptr++;
		if (!mptcp_cap_flag_sha256(flags) ||
		    (flags & MPTCP_CAP_EXTENSIBILITY))
			break;

		/* RFC 6824, Section 3.1:
		 * "For the Checksum Required bit (labeled "A"), if either
		 * host requires the use of checksums, checksums MUST be used.
		 * In other words, the only way for checksums not to be used
		 * is if both hosts in their SYNs set A=0."
		 */
		if (flags & MPTCP_CAP_CHECKSUM_REQD)
			mp_opt->suboptions |= OPTION_MPTCP_CSUMREQD;

		mp_opt->deny_join_id0 = !!(flags & MPTCP_CAP_DENY_JOIN_ID0);

		mp_opt->suboptions |= subopt;
		if (opsize >= TCPOLEN_MPTCP_MPC_SYNACK) {
			mp_opt->sndr_key = get_unaligned_be64(ptr);
			ptr += 8;
		}
		if (opsize >= TCPOLEN_MPTCP_MPC_ACK) {
			mp_opt->rcvr_key = get_unaligned_be64(ptr);
			ptr += 8;
		}
		if (opsize &g