yubikey.c

/*
 * OpenConnect (SSL + DTLS) VPN client
 *
 * Copyright © 2008-2015 Intel Corporation.
 *
 * Author: David Woodhouse <dwmw2@infradead.org>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public License
 * version 2.1, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 */

#include <config.h>

#include <ctype.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>

#include "openconnect-internal.h"

#define NAME_TAG	0x71
#define NAME_LIST_TAG	0x72
#define KEY_TAG		0x73
#define CHALLENGE_TAG	0x74
#define RESPONSE_TAG	0x75
#define T_RESPONSE_TAG	0x76
#define NO_RESPONSE_TAG	0x77
#define PROPERTY_TAG	0x78
#define VERSION_TAG	0x79
#define IMF_TAG		0x7a

#define PUT_INS		0x01
#define DELETE_INS	0x02
#define SET_CODE_INS	0x03
#define RESET_INS	0x04
#define LIST_INS	0xa1
#define CALCULATE_INS	0xa2
#define VALIDATE_INS	0xa3
#define CALCULATE_ALL_INS 0xa4
#define SEND_REMAINING_INS 0xa5

static const unsigned char appselect[] = { 0x00, 0xa4, 0x04, 0x00, 0x07,
					   0xa0, 0x00, 0x00, 0x05, 0x27, 0x21, 0x01 };
static const unsigned char list_keys[] = { 0x00, LIST_INS, 0x00, 0x00 };
static const unsigned char send_remaining[] = { 0x00, SEND_REMAINING_INS, 0x00, 0x00 };

#ifdef _WIN32
#define scard_error(st) openconnect__win32_strerror(st)
#define free_scard_error(str) free(str)
#else
#define scard_error(st) ((char *)pcsc_stringify_error(st))
#define free_scard_error(str) do { ; } while (0)

#endif

#ifdef __APPLE__
#include <PCSC/wintypes.h>
#include <PCSC/winscard.h>
#else
#include <winscard.h>
#endif


struct oc_pcsc_ctx {
	SCARDHANDLE pcsc_ctx, pcsc_card;
	char *yubikey_objname;
	int yubikey_pw_set;
	int yubikey_mode;
};

static int yubikey_cmd(struct openconnect_info *vpninfo, SCARDHANDLE card, int errlvl,
		       const char *desc,
		       const unsigned char *out, size_t outlen, struct oc_text_buf *buf)
{
	DWORD status;

	buf_truncate(buf);

	do {
		DWORD respsize = 258;

		if (buf_ensure_space(buf, 258))
			return -ENOMEM;

		status = SCardTransmit (card, SCARD_PCI_T1, out, outlen,
					NULL, (unsigned char *)&buf->data[buf->pos], &respsize);
		if (status != SCARD_S_SUCCESS) {
			char *pcsc_err = scard_error(status);
			vpn_progress(vpninfo, errlvl,
				     _("Failed to send \"%s\" to ykneo-oath applet: %s\n"),
				     desc, pcsc_err);
			free_scard_error(pcsc_err);
			return -EIO;
		}
		if (respsize < 2) {
			vpn_progress(vpninfo, errlvl,
				     _("Invalid short response to \"%s\" from ykneo-oath applet\n"),
				     desc);
			return -EIO;
		}

		buf->pos += respsize - 2;

		/* Continuation */
		out = send_remaining;
		outlen = sizeof(send_remaining);
	} while (buf->data[buf->pos] == 0x61);

	status = load_be16(buf->data + buf->pos);
	if (status == 0x9000)
		return 0;

	vpn_progress(vpninfo, errlvl,
		     _("Failure response to \"%s\": %04x\n"),
		     desc, (unsigned)status);
	switch (status) {
	case 0x6a80:
		return -EINVAL;
	default:
		return -EIO;
	}
}

static int buf_tlv(struct oc_text_buf *buf, int *loc, unsigned char *type)
{
	int len;
	int left = buf->pos - *loc;

	if (left < 2)
		return -EINVAL;

	*type = (unsigned char)buf->data[(*loc)++];
	len = (unsigned char)buf->data[(*loc)++];
	left -= 2;

	if (len > 0x82)
		return -EINVAL;
	else if (len == 0x81) {
		if (left < 1)
			return -EINVAL;
		len = (unsigned char)buf->data[(*loc)++];
		left--;
	} else if (len == 0x82) {
		if (left < 2)
			return -EINVAL;
		len = (unsigned char)buf->data[(*loc)++];
		len <<= 8;
		len |= (unsigned char)buf->data[(*loc)++];
		left -= 2;
	}

	if (left < len)
		return -EINVAL;

	return len;
}

static int select_yubioath_applet(struct openconnect_info *vpninfo,
				  SCARDHANDLE pcsc_card, struct oc_text_buf *buf)
{
	int ret, tlvlen, tlvpos, id_len, chall_len;
	unsigned char type;
	unsigned char applet_id[16], challenge[16];
	unsigned char *applet_ver;
	char *pin = NULL;
	int pin_len = 0;

	ret = yubikey_cmd(vpninfo, pcsc_card, PRG_DEBUG, _("select applet command"),
			  appselect, sizeof(appselect), buf);
	if (ret)
		return ret;

	tlvpos = 0;
	tlvlen = buf_tlv(buf, &tlvpos, &type);

	if (tlvlen < 0 || type != VERSION_TAG || tlvlen != 3) {
	bad_applet:
		vpn_progress(vpninfo, PRG_ERR,
			     _("Unrecognised response from ykneo-oath applet\n"));
		return -EIO;
	}
	applet_ver = (void *)&buf->data[tlvpos];

	tlvpos += tlvlen;
	tlvlen = buf_tlv(buf, &tlvpos, &type);

	if (tlvlen < 0 || type != NAME_TAG || tlvlen > sizeof(applet_id))
		goto bad_applet;
	memcpy(applet_id, &buf->data[tlvpos], tlvlen);
	id_len = tlvlen;
	tlvpos += tlvlen;

	/* Only print this during the first discovery loop */
	if (!vpninfo->pcsc)
		vpn_progress(vpninfo, PRG_INFO,  _("Found ykneo-oath applet v%d.%d.%d.\n"),
			     applet_ver[0], applet_ver[1], applet_ver[2]);

	if (tlvpos != buf->pos) {
		unsigned char chalresp[7 + SHA1_SIZE + 10];

		tlvlen = buf_tlv(buf, &tlvpos, &type);
		if (tlvlen < 0 || type != CHALLENGE_TAG || tlvlen > sizeof(challenge))
			goto bad_applet;

		memcpy(challenge, &buf->data[tlvpos], tlvlen);
		chall_len = tlvlen;

		/* On later invocations, we know there must have been a
		 * successfui authentication in the past. So try the same
		 * hash first, and only retry in the loop on failure. */
		if (!vpninfo->pcsc) {
			struct oc_auth_form f;
			struct oc_form_opt o;

		retry_pass:
			memset(&f, 0, sizeof(f));
			f.auth_id = (char *)"yubikey_oath_pin";
			f.opts = &o;
			f.message = (char *)_("PIN required for Yubikey OATH applet");

			o.next = NULL;
			o.type = OC_FORM_OPT_PASSWORD;
			o.name = (char *)"yubikey_pin";
			o.label = (char *)_("Yubikey PIN:");
			o._value = NULL;

			ret = process_auth_form(vpninfo, &f);
			if (ret)
				goto out;
			if (!o._value) {
				ret = -EPERM;
				goto out;
			}

			if (pin) {
				memset(pin, 0, pin_len);
				free(pin);
			}
			pin = o._value;
			pin_len = strlen(pin);
			/* This *should* be UTF-8 but see the workaround below. */
			ret = openconnect_hash_yubikey_password(vpninfo, o._value, pin_len,
								applet_id, id_len);
			if (ret)
				goto out;
		}
	retry_hash:
		if (openconnect_yubikey_chalresp(vpninfo, &challenge, chall_len,
						  chalresp + 7)) {
			vpn_progress(vpninfo, PRG_ERR,
				     _("Failed to calculate Yubikey unlock response\n"));
			ret = -EIO;
			goto out;
		}

		chalresp[0] = 0;
		chalresp[1] = VALIDATE_INS;
		chalresp[2] = 0;
		chalresp[3] = 0;
		chalresp[4] = sizeof(chalresp) - 5;
		chalresp[5] = RESPONSE_TAG;
		chalresp[6] = SHA1_SIZE;
		/* Response is already filled in */
		chalresp[7 + SHA1_SIZE] = CHALLENGE_TAG;
		chalresp[8 + SHA1_SIZE] = 8;
		memset(chalresp + 9 + SHA1_SIZE, 0xff, 8);

		ret = yubikey_cmd(vpninfo, pcsc_card, PRG_ERR, _("unlock command"),
				  chalresp, sizeof(chalresp), buf);
		if (ret == -EINVAL) {
			memset(vpninfo->yubikey_pwhash, 0, sizeof(vpninfo->yubikey_pwhash));
			if (pin) {
				/* Try working around pre-KitKat PBKDF2 bug discussed at
				 * http://forum.yubico.com/viewtopic.php?f=26&t=1601#p6807 and
				 * http://android-developers.blogspot.se/2013/12/changes-to-secretkeyfactory-api-in.html */
				const char *in;
				char *out;

				/* Convert the UTF-8 PIN to byte-truncated form in-place */
				in = out = pin;
				while (*in) {
					int c = get_utf8char(&in);
					if (c < 0) {
						/* Screw it. Break out of the loop in such a fashion
						 * that we don't try the 'converted' result. */
						in = out;
						break;
					}
					*(out++) = c;
				}
				/* If out == in then the string only contained ASCII so
				 * there was no conversion to be done (or was invalid
				 * UTF-8 and hit the error case above). So don't try. */
				if (out != in &&
				    !openconnect_hash_yubikey_password(vpninfo, pin, out - pin,
								       applet_id, id_len)) {
					/* We'll have printed with PRG_ERR when the proper
					 * encoding failed. So use PRG_ERR here too. */
					vpn_progress(vpninfo, PRG_ERR,
						     _("Trying truncated-char PBKBF2 variant of Yubikey PIN\n"));
					goto retry_hash;
				}
			}
			goto retry_pass;
		}
	}
 out:
	free_pass(&pin);
	return ret;
}

#ifdef _WIN32
#define reader_len wcslen
#else
#define SCardListReadersW SCardListReaders
#define SCardConnectW SCardConnect
#define reader_len strlen
#endif

int set_yubikey_mode(struct openconnect_info *vpninfo, const char *token_str)
{
	SCARDHANDLE pcsc_ctx, pcsc_card;
	LONG status;
#ifdef _WIN32
	wchar_t *readers = NULL, *reader;
#else
	char *readers = NULL, *reader;
#endif
	DWORD readers_size, proto;
	int ret, tlvlen, tlvpos;
	struct oc_text_buf *buf = NULL;

	status = SCardEstablishContext(SCARD_SCOPE_USER, NULL, NULL, &pcsc_ctx);
	if (status != SCARD_S_SUCCESS) {
		char *pcsc_err = scard_error(status);
		vpn_progress(vpninfo, PRG_ERR, _("Failed to establish PC/SC context: %s\n"),
			     pcsc_err);
		free_scard_error(pcsc_err);
		return -EIO;
	}
	vpn_progress(vpninfo, PRG_TRACE, _("Established PC/SC context\n"));

	ret = -ENOENT;
	status = SCardListReadersW(pcsc_ctx, NULL, NULL, &readers_size);
	if (status != SCARD_S_SUCCESS) {
		char *pcsc_err = scard_error(status);
		vpn_progress(vpninfo, PRG_ERR, _("Failed to query reader list: %s\n"),
			     pcsc_err);
		free_scard_error(pcsc_err);
		goto out_ctx;
	}
	readers = calloc(readers_size, sizeof(readers[0]));
	if (!readers)
		goto out_ctx;

	status = SCardListReadersW(pcsc_ctx, NULL, readers, &readers_size);
	if (status != SCARD_S_SUCCESS) {
		char *pcsc_err = scard_error(status);
		vpn_progress(vpninfo, PRG_ERR, _("Failed to query reader list: %s\n"),
			     pcsc_err);
		free_scard_error(pcsc_err);
		goto out_ctx;
	}

	buf = buf_alloc();

	reader = readers;
	while (reader[0]) {
		unsigned char type;
#ifdef _WIN32
		char *reader_utf8;
		int reader_len;
		reader_len = WideCharToMultiByte(CP_UTF8, 0, reader, -1, NULL, 0, NULL, NULL);
		reader_utf8 = malloc(reader_len);
		if (!reader_utf8)
			goto next_reader;
		WideCharToMultiByte(CP_UTF8, 0, reader, -1, reader_utf8, reader_len, NULL, NULL);
#else
#define reader_utf8 reader
#endif
		status = SCardConnectW(pcsc_ctx, reader, SCARD_SHARE_SHARED,
				       SCARD_PROTOCOL_T1,
				       &pcsc_card, &proto);
		if (status != SCARD_S_SUCCESS) {
			char *pcsc_err = scard_error(status);
			vpn_progress(vpninfo, PRG_ERR, _("Failed to connect to PC/SC reader '%s': %s\n"),
				     reader_utf8, pcsc_err);
			free_scard_error(pcsc_err);
			goto free_reader_utf8;
		}
		vpn_progress(vpninfo, PRG_TRACE, _("Connected PC/SC reader '%s'\n"), reader_utf8);

		status = SCardBeginTransaction(pcsc_card);
		if (status != SCARD_S_SUCCESS) {
			char *pcsc_err = scard_error(status);
			vpn_progress(vpninfo, PRG_ERR, _("Failed to obtain exclusive access to reader '%s': %s\n"),
				     reader_utf8, pcsc_err);
			free_scard_error(pcsc_err);
			goto disconnect;
		}

		ret = select_yubioath_applet(vpninfo, pcsc_card, buf);
		if (ret)
			goto end_trans;

		ret = yubikey_cmd(vpninfo, pcsc_card, PRG_ERR, _("list keys command"), list_keys, sizeof(list_keys), buf);
		if (ret)
			goto end_trans;

		tlvpos = 0;
		while (tlvpos < buf->pos) {
			unsigned char mode, hash;

			tlvlen = buf_tlv(buf, &tlvpos, &type);
			if (type != NAME_LIST_TAG || tlvlen < 1) {
			bad_applet:
				vpn_progress(vpninfo, PRG_ERR,
					     _("Unrecognised response from ykneo-oath applet\n"));
				goto end_trans;
			}
			mode = buf->data[tlvpos] & 0xf0;
			hash = buf->data[tlvpos] & 0x0f;
			if (mode != 0x10 && mode != 0x20)
				goto bad_applet;
			if (hash != 0x01 && hash != 0x02)
				goto bad_applet;

			if (!token_str ||
			    ((tlvlen - 1 == strlen(token_str)) && !memcmp(token_str, &buf->data[tlvpos+1], tlvlen-1))) {
				char *objname = strndup(&buf->data[tlvpos+1], tlvlen-1);
				if (!objname) {
					ret = -ENOMEM;
					SCardEndTransaction(pcsc_card, SCARD_LEAVE_CARD);
					SCardDisconnect(pcsc_card, SCARD_LEAVE_CARD);
					goto out_ctx;
				}
				/* Translators: This is filled in with mode and hash type, and the key identifier.
				   e.g. "Found HOTP/SHA1 key: 'Work VPN key'\n" */
				vpn_progress(vpninfo, PRG_INFO, _("Found %s/%s key '%s' on '%s'\n"),
					     (mode == 0x20) ? "TOTP" : "HOTP",
					     (hash == 0x2) ? "SHA256" : "SHA1",
					     objname, reader_utf8);

				vpninfo->pcsc = calloc(1, sizeof(*vpninfo->pcsc));
				if (!vpninfo->pcsc) {
					free(objname);
					goto out_ctx;
				}
				vpninfo->pcsc->yubikey_objname = objname;
				vpninfo->pcsc->yubikey_mode = mode;
				vpninfo->pcsc->pcsc_ctx = pcsc_ctx;
				vpninfo->pcsc->pcsc_card = pcsc_card;
				vpninfo->token_mode = OC_TOKEN_MODE_YUBIOATH;
				SCardEndTransaction(pcsc_card, SCARD_LEAVE_CARD);

				goto success;
			}
			tlvpos += tlvlen;
		}
		if (token_str) {
			vpn_progress(vpninfo, PRG_ERR,
				     _("Token '%s' not found on Yubikey '%s'. Searching for another Yubikey...\n"),
				       token_str, reader_utf8);
		}

	end_trans:
		SCardEndTransaction(pcsc_card, SCARD_LEAVE_CARD);
	disconnect:
		SCardDisconnect(pcsc_card, SCARD_LEAVE_CARD);
	free_reader_utf8:
#ifdef _WIN32
		free(reader_utf8);
	next_reader:
#endif
		while (*reader)
			reader++;
		reader++;
	}
	ret = -ENOENT;
 out_ctx:
	SCardReleaseContext(pcsc_ctx);
 success:
	free(readers);
	buf_free(buf);

	return ret;
}

/* Return value:
 *  < 0, if unable to generate a tokencode
 *  = 0, on success
 */
int can_gen_yubikey_code(struct openconnect_info *vpninfo,
			 struct oc_auth_form *form,
			 struct oc_form_opt *opt)
{
	if (vpninfo->token_bypassed)
		return -EINVAL;
	if (vpninfo->token_tries == 0) {
		vpn_progress(vpninfo, PRG_DEBUG,
			     _("OK to generate INITIAL tokencode\n"));
		vpninfo->token_time = 0;
	} else if (vpninfo->token_tries == 1) {
		vpn_progress(vpninfo, PRG_DEBUG,
			     _("OK to generate NEXT tokencode\n"));
		vpninfo->token_time += 30;
	} else {
		/* limit the number of retries, to avoid account lockouts */
		vpn_progress(vpninfo, PRG_INFO,
			     _("Server is rejecting the Yubikey token; switching to manual entry\n"));
		return -ENOENT;
	}
	return 0;
}

static int tlvlen_len(int tlvlen)
{
	if (tlvlen < 0x80)
		return 1;
	else if (tlvlen < 0x100)
		return 2;
	else
		return 3;
}

static int append_tlvlen(unsigned char *p, int tlvlen)
{
	if (tlvlen < 0x80) {
		if (p)
			p[0] = tlvlen;
		return 1;
	} else if (tlvlen < 0x100) {
		if (p) {
			p[0] = 0x81;
			p[1] = tlvlen;
		}
		return 2;
	} else {
		if (p) {
			p[0] = 0x82;
			store_be16(p + 1, tlvlen);
		}
		return 3;
	}
}

int do_gen_yubikey_code(struct openconnect_info *vpninfo,
			struct oc_auth_form *form,
			struct oc_form_opt *opt)
{
	struct oc_text_buf *respbuf = NULL;
	DWORD status;
	int name_len = strlen(vpninfo->pcsc->yubikey_objname);
	int name_tlvlen;
	int calc_tlvlen;
	unsigned char *reqbuf = NULL;
	int tokval;
	int i = 0;
	int ret;

	if (!vpninfo->token_time)
		vpninfo->token_time = time(NULL);

	vpn_progress(vpninfo, PRG_INFO, _("Generating Yubikey token code\n"));

	status = SCardBeginTransaction(vpninfo->pcsc->pcsc_card);
	if (status != SCARD_S_SUCCESS) {
		char *pcsc_err = scard_error(status);
		vpn_progress(vpninfo, PRG_ERR, _("Failed to obtain exclusive access to Yubikey: %s\n"),
			     pcsc_err);
		free_scard_error(pcsc_err);
		return -EIO;
	}

	respbuf = buf_alloc();
	ret = select_yubioath_applet(vpninfo, vpninfo->pcsc->pcsc_card, respbuf);
	if (ret)
		goto out;

	name_tlvlen = tlvlen_len(strlen(vpninfo->pcsc->yubikey_objname));
	calc_tlvlen = 1 /* NAME_TAG */ + name_tlvlen + name_len +
		1 /* CHALLENGE_TAG */ + 1 /* Challenge TLV len */;
	if (vpninfo->pcsc->yubikey_mode == 0x20)
		calc_tlvlen += 8; /* TOTP needs the time as challenge */

	reqbuf = malloc(4 + tlvlen_len(calc_tlvlen) + calc_tlvlen);
	if (!reqbuf)
		goto out;

	reqbuf[i++] = 0;
	reqbuf[i++] = CALCULATE_INS;
	reqbuf[i++] = 0;
	reqbuf[i++] = 1;
	i += append_tlvlen(reqbuf + i, calc_tlvlen);
	reqbuf[i++] = NAME_TAG;
	i += append_tlvlen(reqbuf + i, name_len);
	memcpy(reqbuf + i, vpninfo->pcsc->yubikey_objname, name_len);
	i += name_len;
	reqbuf[i++] = CHALLENGE_TAG;
	if (vpninfo->pcsc->yubikey_mode == 0x20) {
		long token_steps = vpninfo->token_time / 30;
		reqbuf[i++] = 8;
		reqbuf[i++] = 0;
		reqbuf[i++] = 0;
		reqbuf[i++] = 0;
		reqbuf[i++] = 0;
		store_be32(reqbuf + i, token_steps);
		i += 4;
	} else {
		reqbuf[i++] = 0; /* HOTP mode, zero-length challenge */
	}

	ret = yubikey_cmd(vpninfo, vpninfo->pcsc->pcsc_card, PRG_ERR, _("calculate command"),
			  reqbuf, i, respbuf);
	if (ret)
		goto out;

	if (respbuf->pos != 7 || (unsigned char)respbuf->data[0] != T_RESPONSE_TAG ||
	    respbuf->data[1] != 5 || respbuf->data[2] > 8 || respbuf->data[2] < 6) {
		vpn_progress(vpninfo, PRG_ERR,
			     _("Unrecognised response from Yubikey when generating tokencode\n"));
		ret = -EIO;
		goto out;
	}

	tokval = load_be32(respbuf->data + 3);
	opt->_value = malloc(respbuf->data[2] + 1);
	if (!opt->_value) {
		ret = -ENOMEM;
		goto out;
	}

	i = respbuf->data[2];
	opt->_value[i] = 0;
	while (i--) {
		opt->_value[i] = '0' + tokval % 10;
		tokval /= 10;
	}
	vpninfo->token_tries++;

 out:
	SCardEndTransaction(vpninfo->pcsc->pcsc_card, SCARD_LEAVE_CARD);
	buf_free(respbuf);
	free(reqbuf);

	return ret;
}


void release_pcsc_ctx(struct openconnect_info *vpninfo)
{
	if (!vpninfo->pcsc)
		return;

	if (vpninfo->token_mode == OC_TOKEN_MODE_YUBIOATH) {
		SCardDisconnect(vpninfo->pcsc->pcsc_card, SCARD_LEAVE_CARD);
		SCardReleaseContext(vpninfo->pcsc->pcsc_ctx);
	}
	memset(vpninfo->yubikey_pwhash, 0, sizeof(vpninfo->yubikey_pwhash));
	free(vpninfo->pcsc->yubikey_objname);
	free(vpninfo->pcsc);
	vpninfo->pcsc = NULL;
}