dhcpcd/src/arp.c

/*
 * dhcpcd - ARP handler
 * Copyright (c) 2006-2018 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/socket.h>
#include <sys/types.h>

#include <arpa/inet.h>

#include <net/if.h>
#include <netinet/in.h>
#include <netinet/if_ether.h>

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

#define ELOOP_QUEUE 5
#include "config.h"
#include "arp.h"
#include "bpf.h"
#include "ipv4.h"
#include "common.h"
#include "dhcpcd.h"
#include "eloop.h"
#include "if.h"
#include "if-options.h"
#include "ipv4ll.h"
#include "logerr.h"

#if defined(ARP)
#define ARP_LEN								      \
	(sizeof(struct arphdr) + (2 * sizeof(uint32_t)) + (2 * HWADDR_LEN))

/* ARP debugging can be quite noisy. Enable this for more noise! */
//#define	ARP_DEBUG

/* Assert the correct structure size for on wire */
__CTASSERT(sizeof(struct arphdr) == 8);

ssize_t
arp_request(const struct interface *ifp, in_addr_t sip, in_addr_t tip)
{
	uint8_t arp_buffer[ARP_LEN];
	struct arphdr ar;
	size_t len;
	uint8_t *p;
	const struct iarp_state *state;

	ar.ar_hrd = htons(ifp->family);
	ar.ar_pro = htons(ETHERTYPE_IP);
	ar.ar_hln = ifp->hwlen;
	ar.ar_pln = sizeof(sip);
	ar.ar_op = htons(ARPOP_REQUEST);

	p = arp_buffer;
	len = 0;

#define CHECK(fun, b, l)						\
	do {								\
		if (len + (l) > sizeof(arp_buffer))			\
			goto eexit;					\
		fun(p, (b), (l));					\
		p += (l);						\
		len += (l);						\
	} while (/* CONSTCOND */ 0)
#define APPEND(b, l)	CHECK(memcpy, b, l)
#define ZERO(l)		CHECK(memset, 0, l)

	APPEND(&ar, sizeof(ar));
	APPEND(ifp->hwaddr, ifp->hwlen);
	APPEND(&sip, sizeof(sip));
	ZERO(ifp->hwlen);
	APPEND(&tip, sizeof(tip));

	state = ARP_CSTATE(ifp);
	return bpf_send(ifp, state->bpf_fd, ETHERTYPE_ARP, arp_buffer, len);

eexit:
	errno = ENOBUFS;
	return -1;
}

static void
arp_packet(struct interface *ifp, uint8_t *data, size_t len)
{
	const struct interface *ifn;
	struct arphdr ar;
	struct arp_msg arm;
	const struct iarp_state *state;
	struct arp_state *astate, *astaten;
	uint8_t *hw_s, *hw_t;

	/* We must have a full ARP header */
	if (len < sizeof(ar))
		return;
	memcpy(&ar, data, sizeof(ar));

	/* These checks are enforced in the BPF filter. */
#if 0
	/* Families must match */
	if (ar.ar_hrd != htons(ifp->family))
		return;
	/* Protocol must be IP. */
	if (ar.ar_pro != htons(ETHERTYPE_IP))
		continue;
	/* lladdr length matches */
	if (ar.ar_hln != ifp->hwlen)
		continue;
	/* Protocol length must match in_addr_t */
	if (ar.ar_pln != sizeof(arm.sip.s_addr))
		return;
	/* Only these types are recognised */
	if (ar.ar_op != htons(ARPOP_REPLY) &&
	    ar.ar_op != htons(ARPOP_REQUEST))
		continue;
#endif

	/* Get pointers to the hardware addresses */
	hw_s = data + sizeof(ar);
	hw_t = hw_s + ar.ar_hln + ar.ar_pln;
	/* Ensure we got all the data */
	if ((size_t)((hw_t + ar.ar_hln + ar.ar_pln) - data) > len)
		return;
	/* Ignore messages from ourself */
	TAILQ_FOREACH(ifn, ifp->ctx->ifaces, next) {
		if (ar.ar_hln == ifn->hwlen &&
		    memcmp(hw_s, ifn->hwaddr, ifn->hwlen) == 0)
			break;
	}
	if (ifn) {
#ifdef ARP_DEBUG
		logdebugx("%s: ignoring ARP from self", ifp->name);
#endif
		return;
	}
	/* Copy out the HW and IP addresses */
	memcpy(&arm.sha, hw_s, ar.ar_hln);
	memcpy(&arm.sip.s_addr, hw_s + ar.ar_hln, ar.ar_pln);
	memcpy(&arm.tha, hw_t, ar.ar_hln);
	memcpy(&arm.tip.s_addr, hw_t + ar.ar_hln, ar.ar_pln);

	/* Run the conflicts */
	state = ARP_CSTATE(ifp);
	TAILQ_FOREACH_SAFE(astate, &state->arp_states, next, astaten) {
		if (arm.sip.s_addr != astate->addr.s_addr &&
		    arm.tip.s_addr != astate->addr.s_addr)
			continue;
		if (astate->conflicted_cb)
			astate->conflicted_cb(astate, &arm);
	}
}

void
arp_close(struct interface *ifp)
{
	struct iarp_state *state;

	if ((state = ARP_STATE(ifp)) != NULL && state->bpf_fd != -1) {
		eloop_event_delete(ifp->ctx->eloop, state->bpf_fd);
		bpf_close(ifp, state->bpf_fd);
		state->bpf_fd = -1;
		state->bpf_flags |= BPF_EOF;
	}
}

static void
arp_tryfree(struct interface *ifp)
{
	struct iarp_state *state = ARP_STATE(ifp);

	/* If there are no more ARP states, close the socket. */
	if (TAILQ_FIRST(&state->arp_states) == NULL) {
		arp_close(ifp);
		if (state->bpf_flags & BPF_READING)
			state->bpf_flags |= BPF_EOF;
		else {
			free(state);
			ifp->if_data[IF_DATA_ARP] = NULL;
		}
	} else {
		if (bpf_arp(ifp, state->bpf_fd) == -1)
			logerr(__func__);
	}
}

static void
arp_read(void *arg)
{
	struct interface *ifp = arg;
	struct iarp_state *state;
	uint8_t buf[ARP_LEN];
	ssize_t bytes;

	/* Some RAW mechanisms are generic file descriptors, not sockets.
	 * This means we have no kernel call to just get one packet,
	 * so we have to process the entire buffer. */
	state = ARP_STATE(ifp);
	state->bpf_flags &= ~BPF_EOF;
	state->bpf_flags |= BPF_READING;
	while (!(state->bpf_flags & BPF_EOF)) {
		bytes = bpf_read(ifp, state->bpf_fd, buf, sizeof(buf),
				 &state->bpf_flags);
		if (bytes == -1) {
			logerr("%s: %s", __func__, ifp->name);
			arp_close(ifp);
			break;
		}
		arp_packet(ifp, buf, (size_t)bytes);
		/* Check we still have a state after processing. */
		if ((state = ARP_STATE(ifp)) == NULL)
			break;
	}
	if (state != NULL) {
		state->bpf_flags &= ~BPF_READING;
		/* Try and free the state if nothing left to do. */
		arp_tryfree(ifp);
	}
}

int
arp_open(struct interface *ifp)
{
	struct iarp_state *state;

	state = ARP_STATE(ifp);
	if (state->bpf_fd == -1) {
		state->bpf_fd = bpf_open(ifp, bpf_arp);
		if (state->bpf_fd == -1) {
			logerr("%s: %s", __func__, ifp->name);
			return -1;
		}
		eloop_event_add(ifp->ctx->eloop, state->bpf_fd, arp_read, ifp);
	}
	return state->bpf_fd;
}

static void
arp_probed(void *arg)
{
	struct arp_state *astate = arg;

	astate->probed_cb(astate);
}

static void
arp_probe1(void *arg)
{
	struct arp_state *astate = arg;
	struct interface *ifp = astate->iface;
	struct timespec tv;

	if (++astate->probes < PROBE_NUM) {
		tv.tv_sec = PROBE_MIN;
		tv.tv_nsec = (suseconds_t)arc4random_uniform(
		    (PROBE_MAX - PROBE_MIN) * NSEC_PER_SEC);
		timespecnorm(&tv);
		eloop_timeout_add_tv(ifp->ctx->eloop, &tv, arp_probe1, astate);
	} else {
		tv.tv_sec = ANNOUNCE_WAIT;
		tv.tv_nsec = 0;
		eloop_timeout_add_tv(ifp->ctx->eloop, &tv, arp_probed, astate);
	}
	logdebugx("%s: ARP probing %s (%d of %d), next in %0.1f seconds",
	    ifp->name, inet_ntoa(astate->addr),
	    astate->probes ? astate->probes : PROBE_NUM, PROBE_NUM,
	    timespec_to_double(&tv));
	if (arp_request(ifp, 0, astate->addr.s_addr) == -1)
		logerr(__func__);
}

void
arp_probe(struct arp_state *astate)
{

	if (arp_open(astate->iface) == -1) {
		logerr(__func__);
		return;
	} else {
		const struct iarp_state *state = ARP_CSTATE(astate->iface);

		if (bpf_arp(astate->iface, state->bpf_fd) == -1)
			logerr(__func__);
	}
	astate->probes = 0;
	logdebugx("%s: probing for %s",
	    astate->iface->name, inet_ntoa(astate->addr));
	arp_probe1(astate);
}
#endif	/* ARP */

static void
arp_announced(void *arg)
{
	struct arp_state *astate = arg;

	if (astate->announced_cb) {
		astate->announced_cb(astate);
		return;
	}

	/* Keep the ARP state open to handle ongoing ACD. */
}

static void
arp_announce1(void *arg)
{
	struct arp_state *astate = arg;
	struct interface *ifp = astate->iface;

	if (++astate->claims < ANNOUNCE_NUM)
		logdebugx("%s: ARP announcing %s (%d of %d), "
		    "next in %d.0 seconds",
		    ifp->name, inet_ntoa(astate->addr),
		    astate->claims, ANNOUNCE_NUM, ANNOUNCE_WAIT);
	else
		logdebugx("%s: ARP announcing %s (%d of %d)",
		    ifp->name, inet_ntoa(astate->addr),
		    astate->claims, ANNOUNCE_NUM);
	if (arp_request(ifp, astate->addr.s_addr, astate->addr.s_addr) == -1)
		logerr(__func__);
	eloop_timeout_add_sec(ifp->ctx->eloop, ANNOUNCE_WAIT,
	    astate->claims < ANNOUNCE_NUM ? arp_announce1 : arp_announced,
	    astate);
}

/*
 * XXX FIXME
 * Kernels supporting RFC5227 will announce the address when it's
 * added.
 * dhcpcd should not announce when this happens, nor need to open
 * a BPF socket for it.
 * Also, an address might be added to a non preferred inteface when
 * the same address exists on a preferred one so we need to instruct
 * the kernel not to announce the address somehow.
 */

void
arp_announce(struct arp_state *astate)
{
	struct iarp_state *state;
	struct interface *ifp;
	struct arp_state *a2;
	int r;

	if (arp_open(astate->iface) == -1) {
		logerr(__func__);
		return;
	}

	/* Cancel any other ARP announcements for this address. */
	TAILQ_FOREACH(ifp, astate->iface->ctx->ifaces, next) {
		state = ARP_STATE(ifp);
		if (state == NULL)
			continue;
		TAILQ_FOREACH(a2, &state->arp_states, next) {
			if (astate == a2 ||
			    a2->addr.s_addr != astate->addr.s_addr)
				continue;
			r = eloop_timeout_delete(a2->iface->ctx->eloop,
			    a2->claims < ANNOUNCE_NUM
			    ? arp_announce1 : arp_announced,
			    a2);
			if (r == -1)
				logerr(__func__);
			else if (r != 0)
				logdebugx("%s: ARP announcement "
				    "of %s cancelled",
				    a2->iface->name,
				    inet_ntoa(a2->addr));
		}
	}

	astate->claims = 0;
	arp_announce1(astate);
}

void
arp_announceaddr(struct dhcpcd_ctx *ctx, struct in_addr *ia)
{
	struct interface *ifp;
	struct ipv4_addr *iaf;
	struct arp_state *astate;

	TAILQ_FOREACH(ifp, ctx->ifaces, next) {
		iaf = ipv4_iffindaddr(ifp, ia, NULL);
#ifdef IN_IFF_NOTUSEABLE
		if (iaf && !(iaf->addr_flags & IN_IFF_NOTUSEABLE))
#else
		if (iaf)
#endif
			break;
	}
	if (ifp == NULL)
		return;

	astate = arp_find(ifp, ia);
	if (astate != NULL)
		arp_announce(astate);
}

void
arp_ifannounceaddr(struct interface *ifp, struct in_addr *ia)
{
	struct arp_state *astate;

	astate = arp_new(ifp, ia);
	if (astate != NULL)
		arp_announce(astate);
}

void
arp_report_conflicted(const struct arp_state *astate,
    const struct arp_msg *amsg)
{

	if (amsg != NULL) {
		char buf[HWADDR_LEN * 3];

		logerrx("%s: hardware address %s claims %s",
		    astate->iface->name,
		    hwaddr_ntoa(amsg->sha, astate->iface->hwlen,
		    buf, sizeof(buf)),
		    inet_ntoa(astate->failed));
	} else
		logerrx("%s: DAD detected %s",
		    astate->iface->name, inet_ntoa(astate->failed));
}

struct arp_state *
arp_find(struct interface *ifp, const struct in_addr *addr)
{
	struct iarp_state *state;
	struct arp_state *astate;

	if ((state = ARP_STATE(ifp)) == NULL)
		goto out;
	TAILQ_FOREACH(astate, &state->arp_states, next) {
		if (astate->addr.s_addr == addr->s_addr && astate->iface == ifp)
			return astate;
	}
out:
	errno = ESRCH;
	return NULL;
}

struct arp_state *
arp_new(struct interface *ifp, const struct in_addr *addr)
{
	struct iarp_state *state;
	struct arp_state *astate;

	if ((state = ARP_STATE(ifp)) == NULL) {
	        ifp->if_data[IF_DATA_ARP] = malloc(sizeof(*state));
		state = ARP_STATE(ifp);
		if (state == NULL) {
			logerr(__func__);
			return NULL;
		}
		state->bpf_fd = -1;
		state->bpf_flags = 0;
		TAILQ_INIT(&state->arp_states);
	} else {
		if (addr && (astate = arp_find(ifp, addr)))
			return astate;
	}

	if ((astate = calloc(1, sizeof(*astate))) == NULL) {
		logerr(__func__);
		return NULL;
	}
	astate->iface = ifp;
	if (addr)
		astate->addr = *addr;
	state = ARP_STATE(ifp);
	TAILQ_INSERT_TAIL(&state->arp_states, astate, next);

	if (bpf_arp(ifp, state->bpf_fd) == -1)
		logerr(__func__); /* try and continue */

	return astate;
}

void
arp_cancel(struct arp_state *astate)
{

	eloop_timeout_delete(astate->iface->ctx->eloop, NULL, astate);
}

void
arp_free(struct arp_state *astate)
{
	struct interface *ifp;
	struct iarp_state *state;

	if (astate == NULL)
		return;

	ifp = astate->iface;
	eloop_timeout_delete(ifp->ctx->eloop, NULL, astate);
	state =	ARP_STATE(ifp);
	TAILQ_REMOVE(&state->arp_states, astate, next);
	if (astate->free_cb)
		astate->free_cb(astate);
	free(astate);
	arp_tryfree(ifp);
}

static void
arp_free_but1(struct interface *ifp, struct arp_state *astate)
{
	struct iarp_state *state;

	if ((state = ARP_STATE(ifp)) != NULL) {
		struct arp_state *p, *n;

		TAILQ_FOREACH_SAFE(p, &state->arp_states, next, n) {
			if (p != astate)
				arp_free(p);
		}
	}
}

void
arp_free_but(struct arp_state *astate)
{

	arp_free_but1(astate->iface, astate);
}

void
arp_drop(struct interface *ifp)
{

	arp_free_but1(ifp, NULL);
	arp_close(ifp);
}

void
arp_handleifa(int cmd, struct ipv4_addr *addr)
{
	struct iarp_state *state;
	struct arp_state *astate, *asn;

	state = ARP_STATE(addr->iface);
	if (state == NULL)
		return;

	TAILQ_FOREACH_SAFE(astate, &state->arp_states, next, asn) {
		if (astate->addr.s_addr != addr->addr.s_addr)
			continue;
		if (cmd == RTM_DELADDR)
			arp_free(astate);
#ifdef IN_IFF_DUPLICATED
		if (cmd != RTM_NEWADDR)
			continue;
		if (addr->addr_flags & IN_IFF_DUPLICATED) {
			if (astate->conflicted_cb)
				astate->conflicted_cb(astate, NULL);
		} else if (!(addr->addr_flags & IN_IFF_NOTUSEABLE)) {
			if (astate->probed_cb)
				astate->probed_cb(astate);
		}
#endif
	}
}