/* Copyright (c) 2017, Sabrina Dubroca <sd@queasysnail.net>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   1. Redistributions of source code must retain the above copyright
 *      notice, this list of conditions and the following disclaimer.
 *   2. Redistributions in binary form must reproduce the above copyright
 *      notice, this list of conditions and the following disclaimer in
 *      the documentation and/or other materials provided with the
 *      distribution.
 *   3. The names of the authors may not be used to endorse or promote
 *      products derived from this software without specific prior
 *      written permission.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 */

/* \summary: MACsec printer */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <netdissect-stdinc.h>

#include <string.h>

#include "netdissect.h"
#include "addrtoname.h"
#include "ethertype.h"
#include "extract.h"

#define MACSEC_DEFAULT_ICV_LEN 16

/* Header format (SecTAG), following an Ethernet header
 * IEEE 802.1AE-2006 9.3
 *
 * +---------------------------------+----------------+----------------+
 * |        (MACsec ethertype)       |     TCI_AN     |       SL       |
 * +---------------------------------+----------------+----------------+
 * |                           Packet Number                           |
 * +-------------------------------------------------------------------+
 * |                     Secure Channel Identifier                     |
 * |                            (optional)                             |
 * +-------------------------------------------------------------------+
 *
 * MACsec ethertype = 0x88e5
 * TCI: Tag Control Information, set of flags
 * AN: association number, 2 bits
 * SL (short length): 6-bit length of the protected payload, if < 48
 * Packet Number: 32-bits packet identifier
 * Secure Channel Identifier: 64-bit unique identifier, usually
 *     composed of a MAC address + 16-bit port number
 */
struct macsec_sectag {
	nd_uint8_t  tci_an;
	nd_uint8_t  short_length;
	nd_uint32_t packet_number;
	nd_uint8_t  secure_channel_id[8]; /* optional */
};

/* IEEE 802.1AE-2006 9.5 */
#define MACSEC_TCI_VERSION 0x80
#define MACSEC_TCI_ES      0x40 /* end station */
#define MACSEC_TCI_SC      0x20 /* SCI present */
#define MACSEC_TCI_SCB     0x10 /* epon */
#define MACSEC_TCI_E       0x08 /* encryption */
#define MACSEC_TCI_C       0x04 /* changed text */
#define MACSEC_AN_MASK     0x03 /* association number */
#define MACSEC_TCI_FLAGS   (MACSEC_TCI_ES | MACSEC_TCI_SC | MACSEC_TCI_SCB | MACSEC_TCI_E | MACSEC_TCI_C)
#define MACSEC_TCI_CONFID  (MACSEC_TCI_E | MACSEC_TCI_C)
#define MACSEC_SL_MASK     0x3F /* short length */

#define MACSEC_SECTAG_LEN_NOSCI 6  /* length of MACsec header without SCI */
#define MACSEC_SECTAG_LEN_SCI   14 /* length of MACsec header with SCI */

#define SCI_FMT "%016" PRIx64

static const struct tok macsec_flag_values[] = {
	{ MACSEC_TCI_E,   "E" },
	{ MACSEC_TCI_C,   "C" },
	{ MACSEC_TCI_ES,  "S" },
	{ MACSEC_TCI_SCB, "B" },
	{ MACSEC_TCI_SC,  "I" },
	{ 0, NULL }
};

/* returns < 0 iff the packet can be decoded completely */
int macsec_print(netdissect_options *ndo, const u_char **bp,
		 u_int *lengthp, u_int *caplenp, u_int *hdrlenp)
{
	const char *save_protocol;
	const u_char *p = *bp;
	u_int length = *lengthp;
	u_int caplen = *caplenp;
	u_int hdrlen = *hdrlenp;
	const struct macsec_sectag *sectag = (const struct macsec_sectag *)p;
	u_int sectag_len;

	save_protocol = ndo->ndo_protocol;
	ndo->ndo_protocol = "MACsec";

	/* we need the full MACsec header in the capture */
	if (caplen < MACSEC_SECTAG_LEN_NOSCI) {
		nd_print_trunc(ndo);
		ndo->ndo_protocol = save_protocol;
		return hdrlen + caplen;
	}
	if (length < MACSEC_SECTAG_LEN_NOSCI) {
		nd_print_trunc(ndo);
		ndo->ndo_protocol = save_protocol;
		return hdrlen + caplen;
	}

	if (GET_U_1(sectag->tci_an) & MACSEC_TCI_SC) {
		sectag_len = MACSEC_SECTAG_LEN_SCI;
		if (caplen < MACSEC_SECTAG_LEN_SCI) {
			nd_print_trunc(ndo);
			ndo->ndo_protocol = save_protocol;
			return hdrlen + caplen;
		}
		if (length < MACSEC_SECTAG_LEN_SCI) {
			nd_print_trunc(ndo);
			ndo->ndo_protocol = save_protocol;
			return hdrlen + caplen;
		}
	} else
		sectag_len = MACSEC_SECTAG_LEN_NOSCI;

	if ((GET_U_1(sectag->short_length) & ~MACSEC_SL_MASK) != 0 || 
	    GET_U_1(sectag->tci_an) & MACSEC_TCI_VERSION) {
		nd_print_invalid(ndo);
		ndo->ndo_protocol = save_protocol;
		return hdrlen + caplen;
	}

	if (ndo->ndo_eflag) {
		ND_PRINT("an %u, pn %u, flags %s",
			 GET_U_1(sectag->tci_an) & MACSEC_AN_MASK,
			 GET_BE_U_4(sectag->packet_number),
			 bittok2str_nosep(macsec_flag_values, "none",
					  GET_U_1(sectag->tci_an) & MACSEC_TCI_FLAGS));

		if ((GET_U_1(sectag->short_length) & MACSEC_SL_MASK) != 0)
			ND_PRINT(", sl %u", GET_U_1(sectag->short_length) & MACSEC_SL_MASK);

		if (GET_U_1(sectag->tci_an) & MACSEC_TCI_SC)
			ND_PRINT(", sci " SCI_FMT, GET_BE_U_8(sectag->secure_channel_id));
		
		ND_PRINT(", ");
	}

	/* Skip the MACsec header. */
	*bp += sectag_len;
	*hdrlenp += sectag_len;

	/* Remove it from the lengths, as it's been processed. */
	*lengthp -= sectag_len;
	*caplenp -= sectag_len;

	if ((GET_U_1(sectag->tci_an) & MACSEC_TCI_CONFID)) {
		/*
		 * The payload is encrypted.  Tell our
		 * caller it can't be dissected.
		 */
		ndo->ndo_protocol = save_protocol;
		return 0;
	} else {
		/*
		 * The payload isn't encrypted; remove the
		 * ICV length from the lengths, so our caller
		 * doesn't treat it as payload.
		 */
		if (*lengthp >= MACSEC_DEFAULT_ICV_LEN)
			*lengthp -= MACSEC_DEFAULT_ICV_LEN;
		if (*caplenp >= MACSEC_DEFAULT_ICV_LEN)
			*caplenp -= MACSEC_DEFAULT_ICV_LEN;
		ndo->ndo_protocol = save_protocol;
		return -1;
	}
}