xref: /dflybsd-src/contrib/dhcpcd/src/auth.c (revision c80c9bba1b2fa2824af94c686145cb7eb7db2cd5)

/* SPDX-License-Identifier: BSD-2-Clause */
/*
 * dhcpcd - DHCP client daemon
 * Copyright (c) 2006-2023 Roy Marples <roy@marples.name>
 * All rights reserved

 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/file.h>
#include <sys/stat.h>

#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>

#include "config.h"
#include "auth.h"
#include "dhcp.h"
#include "dhcp6.h"
#include "dhcpcd.h"
#include "privsep-root.h"

#ifdef HAVE_HMAC_H
#include <hmac.h>
#endif

#ifdef __sun
#define htonll
#define ntohll
#endif

#ifndef htonll
#if (BYTE_ORDER == LITTLE_ENDIAN)
#define	htonll(x)	((uint64_t)htonl((uint32_t)((x) >> 32)) | \
			 (uint64_t)htonl((uint32_t)((x) & 0x00000000ffffffffULL)) << 32)
#else	/* (BYTE_ORDER == LITTLE_ENDIAN) */
#define	htonll(x)	(x)
#endif
#endif  /* htonll */

#ifndef ntohll
#if (BYTE_ORDER == LITTLE_ENDIAN)
#define	ntohll(x)	((uint64_t)ntohl((uint32_t)((x) >> 32)) | \
			 (uint64_t)ntohl((uint32_t)((x) & 0x00000000ffffffffULL)) << 32)
#else	/* (BYTE_ORDER == LITTLE_ENDIAN) */
#define	ntohll(x)	(x)
#endif
#endif  /* ntohll */

#define HMAC_LENGTH	16

void
dhcp_auth_reset(struct authstate *state)
{

	state->replay = 0;
	if (state->token) {
		free(state->token->key);
		free(state->token->realm);
		free(state->token);
		state->token = NULL;
	}
	if (state->reconf) {
		free(state->reconf->key);
		free(state->reconf->realm);
		free(state->reconf);
		state->reconf = NULL;
	}
}

/*
 * Authenticate a DHCP message.
 * m and mlen refer to the whole message.
 * t is the DHCP type, pass it 4 or 6.
 * data and dlen refer to the authentication option within the message.
 */
const struct token *
dhcp_auth_validate(struct authstate *state, const struct auth *auth,
    const void *vm, size_t mlen, int mp,  int mt,
    const void *vdata, size_t dlen)
{
	const uint8_t *m, *data;
	uint8_t protocol, algorithm, rdm, *mm, type;
	uint64_t replay;
	uint32_t secretid;
	const uint8_t *d, *realm;
	size_t realm_len;
	const struct token *t;
	time_t now;
	uint8_t hmac_code[HMAC_LENGTH];

	if (dlen < 3 + sizeof(replay)) {
		errno = EINVAL;
		return NULL;
	}

	m = vm;
	data = vdata;
	/* Ensure that d is inside m which *may* not be the case for DHCPv4.
	 * This can occur if the authentication option is split using
	 * DHCP long option from RFC 3399. Section 9 which does infact note that
	 * implementations should take this into account.
	 * Fixing this would be problematic, patches welcome. */
	if (data < m || data > m + mlen || data + dlen > m + mlen) {
		errno = ERANGE;
		return NULL;
	}

	d = data;
	protocol = *d++;
	algorithm = *d++;
	rdm = *d++;
	if (!(auth->options & DHCPCD_AUTH_SEND)) {
		/* If we didn't send any authorisation, it can only be a
		 * reconfigure key */
		if (protocol != AUTH_PROTO_RECONFKEY) {
			errno = EINVAL;
			return NULL;
		}
	} else if (protocol != auth->protocol ||
		    algorithm != auth->algorithm ||
		    rdm != auth->rdm)
	{
		/* As we don't require authentication, we should still
		 * accept a reconfigure key */
		if (protocol != AUTH_PROTO_RECONFKEY ||
		    auth->options & DHCPCD_AUTH_REQUIRE)
		{
			errno = EPERM;
			return NULL;
		}
	}
	dlen -= 3;

	memcpy(&replay, d, sizeof(replay));
	replay = ntohll(replay);
	/*
	 * Test for a replay attack.
	 *
	 * NOTE: Some servers always send a replay data value of zero.
	 * This is strictly compliant with RFC 3315 and 3318 which say:
	 * "If the RDM field contains 0x00, the replay detection field MUST be
	 *    set to the value of a monotonically increasing counter."
	 * An example of a monotonically increasing sequence is:
	 * 1, 2, 2, 2, 2, 2, 2
	 * Errata 3474 updates RFC 3318 to say:
	 * "If the RDM field contains 0x00, the replay detection field MUST be
	 *    set to the value of a strictly increasing counter."
	 *
	 * Taking the above into account, dhcpcd will only test for
	 * strictly speaking replay attacks if it receives any non zero
	 * replay data to validate against.
	 */
	if (state->token && state->replay != 0) {
		if (state->replay == (replay ^ 0x8000000000000000ULL)) {
			/* We don't know if the singular point is increasing
			 * or decreasing. */
			errno = EPERM;
			return NULL;
		}
		if ((uint64_t)(replay - state->replay) <= 0) {
			/* Replay attack detected */
			errno = EPERM;
			return NULL;
		}
	}
	d+= sizeof(replay);
	dlen -= sizeof(replay);

	realm = NULL;
	realm_len = 0;

	/* Extract realm and secret.
	 * Rest of data is MAC. */
	switch (protocol) {
	case AUTH_PROTO_TOKEN:
		secretid = auth->token_rcv_secretid;
		break;
	case AUTH_PROTO_DELAYED:
		if (dlen < sizeof(secretid) + sizeof(hmac_code)) {
			errno = EINVAL;
			return NULL;
		}
		memcpy(&secretid, d, sizeof(secretid));
		secretid = ntohl(secretid);
		d += sizeof(secretid);
		dlen -= sizeof(secretid);
		break;
	case AUTH_PROTO_DELAYEDREALM:
		if (dlen < sizeof(secretid) + sizeof(hmac_code)) {
			errno = EINVAL;
			return NULL;
		}
		realm_len = dlen - (sizeof(secretid) + sizeof(hmac_code));
		if (realm_len) {
			realm = d;
			d += realm_len;
			dlen -= realm_len;
		}
		memcpy(&secretid, d, sizeof(secretid));
		secretid = ntohl(secretid);
		d += sizeof(secretid);
		dlen -= sizeof(secretid);
		break;
	case AUTH_PROTO_RECONFKEY:
		if (dlen != 1 + 16) {
			errno = EINVAL;
			return NULL;
		}
		type = *d++;
		dlen--;
		switch (type) {
		case 1:
			if ((mp == 4 && mt == DHCP_ACK) ||
			    (mp == 6 && mt == DHCP6_REPLY))
			{
				if (state->reconf == NULL) {
					state->reconf =
					    malloc(sizeof(*state->reconf));
					if (state->reconf == NULL)
						return NULL;
					state->reconf->key = malloc(16);
					if (state->reconf->key == NULL) {
						free(state->reconf);
						state->reconf = NULL;
						return NULL;
					}
					state->reconf->secretid = 0;
					state->reconf->expire = 0;
					state->reconf->realm = NULL;
					state->reconf->realm_len = 0;
					state->reconf->key_len = 16;
				}
				memcpy(state->reconf->key, d, 16);
			} else {
				errno = EINVAL;
				return NULL;
			}
			if (state->reconf == NULL)
				errno = ENOENT;
			/* Free the old token so we log acceptance */
			if (state->token) {
				free(state->token);
				state->token = NULL;
			}
			/* Nothing to validate, just accepting the key */
			return state->reconf;
		case 2:
			if (!((mp == 4 && mt == DHCP_FORCERENEW) ||
			    (mp == 6 && mt == DHCP6_RECONFIGURE)))
			{
				errno = EINVAL;
				return NULL;
			}
			if (state->reconf == NULL) {
				errno = ENOENT;
				return NULL;
			}
			t = state->reconf;
			goto gottoken;
		default:
			errno = EINVAL;
			return NULL;
		}
	default:
		errno = ENOTSUP;
		return NULL;
	}

	/* Find a token for the realm and secret */
	TAILQ_FOREACH(t, &auth->tokens, next) {
		if (t->secretid == secretid &&
		    t->realm_len == realm_len &&
		    (t->realm_len == 0 ||
		    memcmp(t->realm, realm, t->realm_len) == 0))
			break;
	}
	if (t == NULL) {
		errno = ESRCH;
		return NULL;
	}
	if (t->expire) {
		if (time(&now) == -1)
			return NULL;
		if (t->expire < now) {
			errno = EFAULT;
			return NULL;
		}
	}

gottoken:
	/* First message from the server */
	if (state->token &&
	    (state->token->secretid != t->secretid ||
	    state->token->realm_len != t->realm_len ||
	    memcmp(state->token->realm, t->realm, t->realm_len)))
	{
		errno = EPERM;
		return NULL;
	}

	/* Special case as no hashing needs to be done. */
	if (protocol == AUTH_PROTO_TOKEN) {
		if (dlen != t->key_len || memcmp(d, t->key, dlen)) {
			errno = EPERM;
			return NULL;
		}
		goto finish;
	}

	/* Make a duplicate of the message, but zero out the MAC part */
	mm = malloc(mlen);
	if (mm == NULL)
		return NULL;
	memcpy(mm, m, mlen);
	memset(mm + (d - m), 0, dlen);

	/* RFC3318, section 5.2 - zero giaddr and hops */
	if (mp == 4) {
		/* Assert the bootp structure is correct size. */
		__CTASSERT(sizeof(struct bootp) == 300);

		*(mm + offsetof(struct bootp, hops)) = '\0';
		memset(mm + offsetof(struct bootp, giaddr), 0, 4);
	}

	memset(hmac_code, 0, sizeof(hmac_code));
	switch (algorithm) {
	case AUTH_ALG_HMAC_MD5:
		hmac("md5", t->key, t->key_len, mm, mlen,
		     hmac_code, sizeof(hmac_code));
		break;
	default:
		errno = ENOSYS;
		free(mm);
		return NULL;
	}

	free(mm);
	if (!consttime_memequal(d, &hmac_code, dlen)) {
		errno = EPERM;
		return NULL;
	}

finish:
	/* If we got here then authentication passed */
	state->replay = replay;
	if (state->token == NULL) {
		/* We cannot just save a pointer because a reconfigure will
		 * recreate the token list. So we duplicate it. */
		state->token = malloc(sizeof(*state->token));
		if (state->token) {
			state->token->secretid = t->secretid;
			state->token->key = malloc(t->key_len);
			if (state->token->key) {
				state->token->key_len = t->key_len;
				memcpy(state->token->key, t->key, t->key_len);
			} else {
				free(state->token);
				state->token = NULL;
				return NULL;
			}
			if (t->realm_len) {
				state->token->realm = malloc(t->realm_len);
				if (state->token->realm) {
					state->token->realm_len = t->realm_len;
					memcpy(state->token->realm, t->realm,
					    t->realm_len);
				} else {
					free(state->token->key);
					free(state->token);
					state->token = NULL;
					return NULL;
				}
			} else {
				state->token->realm = NULL;
				state->token->realm_len = 0;
			}
		}
		/* If we cannot save the token, we must invalidate */
		if (state->token == NULL)
			return NULL;
	}

	return t;
}

int
auth_get_rdm_monotonic(uint64_t *rdm)
{
	FILE *fp;
	int err;
#ifdef LOCK_EX
	int flocked;
#endif

	fp = fopen(RDM_MONOFILE, "r+");
	if (fp == NULL) {
		if (errno != ENOENT)
			return -1;
		fp = fopen(RDM_MONOFILE, "w");
		if (fp == NULL)
			return -1;
		if (chmod(RDM_MONOFILE, 0400) == -1) {
			fclose(fp);
			unlink(RDM_MONOFILE);
			return -1;
		}
#ifdef LOCK_EX
		flocked = flock(fileno(fp), LOCK_EX);
#endif
		*rdm = 0;
	} else {
#ifdef LOCK_EX
		flocked = flock(fileno(fp), LOCK_EX);
#endif
		if (fscanf(fp, "0x%016" PRIu64, rdm) != 1) {
			fclose(fp);
			return -1;
		}
	}

	(*rdm)++;
	if (fseek(fp, 0, SEEK_SET) == -1 ||
	    ftruncate(fileno(fp), 0) == -1 ||
	    fprintf(fp, "0x%016" PRIu64 "\n", *rdm) != 19 ||
	    fflush(fp) == EOF)
		err = -1;
	else
		err = 0;
#ifdef LOCK_EX
	if (flocked == 0)
		flock(fileno(fp), LOCK_UN);
#endif
	fclose(fp);
	return err;
}

#define	NTP_EPOCH	2208988800U	/* 1970 - 1900 in seconds */
#define	NTP_SCALE_FRAC	4294967295.0	/* max value of the fractional part */
static uint64_t
get_next_rdm_monotonic_clock(struct auth *auth)
{
	struct timespec ts;
	uint64_t secs, rdm;
	double frac;

	if (clock_gettime(CLOCK_REALTIME, &ts) != 0)
		return ++auth->last_replay; /* report error? */

	secs = (uint64_t)ts.tv_sec + NTP_EPOCH;
	frac = ((double)ts.tv_nsec / 1e9 * NTP_SCALE_FRAC);
	rdm = (secs << 32) | (uint64_t)frac;
	return rdm;
}

static uint64_t
get_next_rdm_monotonic(struct dhcpcd_ctx *ctx, struct auth *auth)
{
#ifndef PRIVSEP
	UNUSED(ctx);
#endif

	if (auth->options & DHCPCD_AUTH_RDM_COUNTER) {
		uint64_t rdm;
		int err;

#ifdef PRIVSEP
		if (IN_PRIVSEP(ctx)) {

			err = ps_root_getauthrdm(ctx, &rdm);
		} else
#endif
			err = auth_get_rdm_monotonic(&rdm);
		if (err == -1)
			return ++auth->last_replay;

		auth->last_replay = rdm;
		return rdm;
	}
	return get_next_rdm_monotonic_clock(auth);
}

/*
 * Encode a DHCP message.
 * Either we know which token to use from the server response
 * or we are using a basic configuration token.
 * token is the token to encrypt with.
 * m and mlen refer to the whole message.
 * mp is the DHCP type, pass it 4 or 6.
 * mt is the DHCP message type.
 * data and dlen refer to the authentication option within the message.
 */
ssize_t
dhcp_auth_encode(struct dhcpcd_ctx *ctx, struct auth *auth,
    const struct token *t,
    void *vm, size_t mlen, int mp, int mt,
    void *vdata, size_t dlen)
{
	uint64_t rdm;
	uint8_t hmac_code[HMAC_LENGTH];
	time_t now;
	uint8_t hops, *p, *m, *data;
	uint32_t giaddr, secretid;
	bool auth_info;

	/* Ignore the token argument given to us - always send using the
	 * configured token. */
	if (auth->protocol == AUTH_PROTO_TOKEN) {
		TAILQ_FOREACH(t, &auth->tokens, next) {
			if (t->secretid == auth->token_snd_secretid)
				break;
		}
		if (t == NULL) {
			errno = EINVAL;
			return -1;
		}
		if (t->expire) {
			if (time(&now) == -1)
				return -1;
			if (t->expire < now) {
				errno = EPERM;
				return -1;
			}
		}
	}

	switch(auth->protocol) {
	case AUTH_PROTO_TOKEN:
	case AUTH_PROTO_DELAYED:
	case AUTH_PROTO_DELAYEDREALM:
		/* We don't ever send a reconf key */
		break;
	default:
		errno = ENOTSUP;
		return -1;
	}

	switch(auth->algorithm) {
	case AUTH_ALG_NONE:
	case AUTH_ALG_HMAC_MD5:
		break;
	default:
		errno = ENOTSUP;
		return -1;
	}

	switch(auth->rdm) {
	case AUTH_RDM_MONOTONIC:
		break;
	default:
		errno = ENOTSUP;
		return -1;
	}

	/* DISCOVER or INFORM messages don't write auth info */
	if ((mp == 4 && (mt == DHCP_DISCOVER || mt == DHCP_INFORM)) ||
	    (mp == 6 && (mt == DHCP6_SOLICIT || mt == DHCP6_INFORMATION_REQ)))
		auth_info = false;
	else
		auth_info = true;

	/* Work out the auth area size.
	 * We only need to do this for DISCOVER messages */
	if (vdata == NULL) {
		dlen = 1 + 1 + 1 + 8;
		switch(auth->protocol) {
		case AUTH_PROTO_TOKEN:
			dlen += t->key_len;
			break;
		case AUTH_PROTO_DELAYEDREALM:
			if (auth_info && t)
				dlen += t->realm_len;
			/* FALLTHROUGH */
		case AUTH_PROTO_DELAYED:
			if (auth_info && t)
				dlen += sizeof(t->secretid) + sizeof(hmac_code);
			break;
		}
		return (ssize_t)dlen;
	}

	if (dlen < 1 + 1 + 1 + 8) {
		errno = ENOBUFS;
		return -1;
	}

	/* Ensure that d is inside m which *may* not be the case for DHPCPv4 */
	m = vm;
	data = vdata;
	if (data < m || data > m + mlen || data + dlen > m + mlen) {
		errno = ERANGE;
		return -1;
	}

	/* Write out our option */
	*data++ = auth->protocol;
	*data++ = auth->algorithm;
	/*
	 * RFC 3315 21.4.4.1 says that SOLICIT in DELAYED authentication
	 * should not set RDM or it's data.
	 * An expired draft draft-ietf-dhc-dhcpv6-clarify-auth-01 suggets
	 * this should not be set for INFORMATION REQ messages as well,
	 * which is probably a good idea because both states start from zero.
	 */
	if (auth_info ||
	    !(auth->protocol & (AUTH_PROTO_DELAYED | AUTH_PROTO_DELAYEDREALM)))
	{
		*data++ = auth->rdm;
		switch (auth->rdm) {
		case AUTH_RDM_MONOTONIC:
			rdm = get_next_rdm_monotonic(ctx, auth);
			break;
		default:
			/* This block appeases gcc, clang doesn't need it */
			rdm = get_next_rdm_monotonic(ctx, auth);
			break;
		}
		rdm = htonll(rdm);
		memcpy(data, &rdm, 8);
	} else {
		*data++ = 0;		/* rdm */
		memset(data, 0, 8);	/* replay detection data */
	}
	data += 8;
	dlen -= 1 + 1 + 1 + 8;

	/* Special case as no hashing needs to be done. */
	if (auth->protocol == AUTH_PROTO_TOKEN) {
		/* Should be impossible, but still */
		if (t == NULL) {
			errno = EINVAL;
			return -1;
		}
		if (dlen < t->key_len) {
			errno =	ENOBUFS;
			return -1;
		}
		memcpy(data, t->key, t->key_len);
		return (ssize_t)(dlen - t->key_len);
	}

	/* DISCOVER or INFORM messages don't write auth info */
	if (!auth_info)
		return (ssize_t)dlen;

	/* Loading a saved lease without an authentication option */
	if (t == NULL)
		return 0;

	/* Write out the Realm */
	if (auth->protocol == AUTH_PROTO_DELAYEDREALM) {
		if (dlen < t->realm_len) {
			errno = ENOBUFS;
			return -1;
		}
		memcpy(data, t->realm, t->realm_len);
		data += t->realm_len;
		dlen -= t->realm_len;
	}

	/* Write out the SecretID */
	if (auth->protocol == AUTH_PROTO_DELAYED ||
	    auth->protocol == AUTH_PROTO_DELAYEDREALM)
	{
		if (dlen < sizeof(t->secretid)) {
			errno = ENOBUFS;
			return -1;
		}
		secretid = htonl(t->secretid);
		memcpy(data, &secretid, sizeof(secretid));
		data += sizeof(secretid);
		dlen -= sizeof(secretid);
	}

	/* Zero what's left, the MAC */
	memset(data, 0, dlen);

	/* RFC3318, section 5.2 - zero giaddr and hops */
	if (mp == 4) {
		p = m + offsetof(struct bootp, hops);
		hops = *p;
		*p = '\0';
		p = m + offsetof(struct bootp, giaddr);
		memcpy(&giaddr, p, sizeof(giaddr));
		memset(p, 0, sizeof(giaddr));
	} else {
		/* appease GCC again */
		hops = 0;
		giaddr = 0;
	}

	/* Create our hash and write it out */
	switch(auth->algorithm) {
	case AUTH_ALG_HMAC_MD5:
		hmac("md5", t->key, t->key_len, m, mlen,
		     hmac_code, sizeof(hmac_code));
		memcpy(data, hmac_code, sizeof(hmac_code));
		break;
	}

	/* RFC3318, section 5.2 - restore giaddr and hops */
	if (mp == 4) {
		p = m + offsetof(struct bootp, hops);
		*p = hops;
		p = m + offsetof(struct bootp, giaddr);
		memcpy(p, &giaddr, sizeof(giaddr));
	}

	/* Done! */
	return (int)(dlen - sizeof(hmac_code)); /* should be zero */
}