ntp_restrict.c   [plain text]

/*
 * ntp_restrict.c - determine host restrictions
 */
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdio.h>
#include <sys/types.h>

#include "ntpd.h"
#include "ntp_if.h"
#include "ntp_lists.h"
#include "ntp_stdlib.h"
#include "ntp_assert.h"

/*
 * This code keeps a simple address-and-mask list of hosts we want
 * to place restrictions on (or remove them from). The restrictions
 * are implemented as a set of flags which tell you what the host
 * can't do. There is a subroutine entry to return the flags. The
 * list is kept sorted to reduce the average number of comparisons
 * and make sure you get the set of restrictions most specific to
 * the address.
 *
 * The algorithm is that, when looking up a host, it is first assumed
 * that the default set of restrictions will apply. It then searches
 * down through the list. Whenever it finds a match it adopts the
 * match's flags instead. When you hit the point where the sorted
 * address is greater than the target, you return with the last set of
 * flags you found. Because of the ordering of the list, the most
 * specific match will provide the final set of flags.
 *
 * This was originally intended to restrict you from sync'ing to your
 * own broadcasts when you are doing that, by restricting yourself from
 * your own interfaces. It was also thought it would sometimes be useful
 * to keep a misbehaving host or two from abusing your primary clock. It
 * has been expanded, however, to suit the needs of those with more
 * restrictive access policies.
 */
/*
 * We will use two lists, one for IPv4 addresses and one for IPv6
 * addresses. This is not protocol-independant but for now I can't
 * find a way to respect this. We'll check this later... JFB 07/2001
 */
#define MASK_IPV6_ADDR(dst, src, msk)					\
	do {								\
		int idx;						\
		for (idx = 0; idx < (int)COUNTOF((dst)->s6_addr); idx++) { \
			(dst)->s6_addr[idx] = (src)->s6_addr[idx]	\
					      & (msk)->s6_addr[idx];	\
		}							\
	} while (0)

/*
 * We allocate INC_RESLIST{4|6} entries to the free list whenever empty.
 * Auto-tune these to be just less than 1KB (leaving at least 16 bytes
 * for allocator overhead).
 */
#define	INC_RESLIST4	((1024 - 16) / V4_SIZEOF_RESTRICT_U)
#define	INC_RESLIST6	((1024 - 16) / V6_SIZEOF_RESTRICT_U)

/*
 * The restriction list
 */
restrict_u *restrictlist4;
restrict_u *restrictlist6;
static int restrictcount;	/* count in the restrict lists */

/*
 * The free list and associated counters.  Also some uninteresting
 * stat counters.
 */
static restrict_u *resfree4;	/* available entries (free list) */
static restrict_u *resfree6;

static u_long res_calls;
static u_long res_found;
static u_long res_not_found;

/*
 * Count number of restriction entries referring to RES_LIMITED, to
 * control implicit activation/deactivation of the MRU monlist.
 */
static	u_long res_limited_refcnt;

/*
 * Our default entries.
 */
static	restrict_u	restrict_def4;
static	restrict_u	restrict_def6;

/*
 * "restrict source ..." enabled knob and restriction bits.
 */
static	int		restrict_source_enabled;
static	u_short		restrict_source_flags;
static	u_short		restrict_source_mflags;

/*
 * private functions
 */
static restrict_u *	alloc_res4(void);
static restrict_u *	alloc_res6(void);
static void		free_res(restrict_u *, int);
static void		inc_res_limited(void);
static void		dec_res_limited(void);
static restrict_u *	match_restrict4_addr(u_int32, u_short);
static restrict_u *	match_restrict6_addr(const struct in6_addr *,
					     u_short);
static restrict_u *	match_restrict_entry(const restrict_u *, int);
static int		res_sorts_before4(restrict_u *, restrict_u *);
static int		res_sorts_before6(restrict_u *, restrict_u *);


/*
 * init_restrict - initialize the restriction data structures
 */
void
init_restrict(void)
{
	/*
	 * The restriction lists begin with a default entry with address
	 * and mask 0, which will match any entry.  The lists are kept
	 * sorted by descending address followed by descending mask:
	 *
	 *   address	  mask
	 * 192.168.0.0	255.255.255.0	kod limited noquery nopeer
	 * 192.168.0.0	255.255.0.0	kod limited
	 * 0.0.0.0	0.0.0.0		kod limited noquery
	 *
	 * The first entry which matches an address is used.  With the
	 * example restrictions above, 192.168.0.0/24 matches the first
	 * entry, the rest of 192.168.0.0/16 matches the second, and
	 * everything else matches the third (default).
	 *
	 * Note this achieves the same result a little more efficiently
	 * than the documented behavior, which is to keep the lists
	 * sorted by ascending address followed by ascending mask, with
	 * the _last_ matching entry used.
	 *
	 * An additional wrinkle is we may have multiple entries with
	 * the same address and mask but differing match flags (mflags).
	 * At present there is only one, RESM_NTPONLY.  Entries with
	 * RESM_NTPONLY are sorted earlier so they take precedence over
	 * any otherwise similar entry without.  Again, this is the same
	 * behavior as but reversed implementation compared to the docs.
	 * 
	 */
	LINK_SLIST(restrictlist4, &restrict_def4, link);
	LINK_SLIST(restrictlist6, &restrict_def6, link);
	restrictcount = 2;
}


static restrict_u *
alloc_res4(void)
{
	const size_t	cb = V4_SIZEOF_RESTRICT_U;
	const size_t	count = INC_RESLIST4;
	restrict_u *	rl;
	restrict_u *	res;
	size_t		i;

	UNLINK_HEAD_SLIST(res, resfree4, link);
	if (res != NULL)
		return res;

	rl = eallocarray(count, cb);
	/* link all but the first onto free list */
	res = (void *)((char *)rl + (count - 1) * cb);
	for (i = count - 1; i > 0; i--) {
		LINK_SLIST(resfree4, res, link);
		res = (void *)((char *)res - cb);
	}
	INSIST(rl == res);
	/* allocate the first */
	return res;
}


static restrict_u *
alloc_res6(void)
{
	const size_t	cb = V6_SIZEOF_RESTRICT_U;
	const size_t	count = INC_RESLIST6;
	restrict_u *	rl;
	restrict_u *	res;
	size_t		i;

	UNLINK_HEAD_SLIST(res, resfree6, link);
	if (res != NULL)
		return res;

	rl = eallocarray(count, cb);
	/* link all but the first onto free list */
	res = (void *)((char *)rl + (count - 1) * cb);
	for (i = count - 1; i > 0; i--) {
		LINK_SLIST(resfree6, res, link);
		res = (void *)((char *)res - cb);
	}
	INSIST(rl == res);
	/* allocate the first */
	return res;
}


static void
free_res(
	restrict_u *	res,
	int		v6
	)
{
	restrict_u **	plisthead;
	restrict_u *	unlinked;

	restrictcount--;
	if (RES_LIMITED & res->flags)
		dec_res_limited();

	if (v6)
		plisthead = &restrictlist6;
	else
		plisthead = &restrictlist4;
	UNLINK_SLIST(unlinked, *plisthead, res, link, restrict_u);
	INSIST(unlinked == res);

	if (v6) {
		zero_mem(res, V6_SIZEOF_RESTRICT_U);
		plisthead = &resfree6;
	} else {
		zero_mem(res, V4_SIZEOF_RESTRICT_U);
		plisthead = &resfree4;
	}
	LINK_SLIST(*plisthead, res, link);
}


static void
inc_res_limited(void)
{
	if (!res_limited_refcnt)
		mon_start(MON_RES);
	res_limited_refcnt++;
}


static void
dec_res_limited(void)
{
	res_limited_refcnt--;
	if (!res_limited_refcnt)
		mon_stop(MON_RES);
}


static restrict_u *
match_restrict4_addr(
	u_int32	addr,
	u_short	port
	)
{
	const int	v6 = 0;
	restrict_u *	res;
	restrict_u *	next;

	for (res = restrictlist4; res != NULL; res = next) {
		next = res->link;
		if (res->expire &&
		    res->expire <= current_time)
			free_res(res, v6);
		if (res->u.v4.addr == (addr & res->u.v4.mask)
		    && (!(RESM_NTPONLY & res->mflags)
			|| NTP_PORT == port))
			break;
	}
	return res;
}


static restrict_u *
match_restrict6_addr(
	const struct in6_addr *	addr,
	u_short			port
	)
{
	const int	v6 = 1;
	restrict_u *	res;
	restrict_u *	next;
	struct in6_addr	masked;

	for (res = restrictlist6; res != NULL; res = next) {
		next = res->link;
		INSIST(next != res);
		if (res->expire &&
		    res->expire <= current_time)
			free_res(res, v6);
		MASK_IPV6_ADDR(&masked, addr, &res->u.v6.mask);
		if (ADDR6_EQ(&masked, &res->u.v6.addr)
		    && (!(RESM_NTPONLY & res->mflags)
			|| NTP_PORT == (int)port))
			break;
	}
	return res;
}


/*
 * match_restrict_entry - find an exact match on a restrict list.
 *
 * Exact match is addr, mask, and mflags all equal.
 * In order to use more common code for IPv4 and IPv6, this routine
 * requires the caller to populate a restrict_u with mflags and either
 * the v4 or v6 address and mask as appropriate.  Other fields in the
 * input restrict_u are ignored.
 */
static restrict_u *
match_restrict_entry(
	const restrict_u *	pmatch,
	int			v6
	)
{
	restrict_u *res;
	restrict_u *rlist;
	size_t cb;

	if (v6) {
		rlist = restrictlist6;
		cb = sizeof(pmatch->u.v6);
	} else {
		rlist = restrictlist4;
		cb = sizeof(pmatch->u.v4);
	}

	for (res = rlist; res != NULL; res = res->link)
		if (res->mflags == pmatch->mflags &&
		    !memcmp(&res->u, &pmatch->u, cb))
			break;
	return res;
}


/*
 * res_sorts_before4 - compare two restrict4 entries
 *
 * Returns nonzero if r1 sorts before r2.  We sort by descending
 * address, then descending mask, then descending mflags, so sorting
 * before means having a higher value.
 */
static int
res_sorts_before4(
	restrict_u *r1,
	restrict_u *r2
	)
{
	int r1_before_r2;

	if (r1->u.v4.addr > r2->u.v4.addr)
		r1_before_r2 = 1;
	else if (r1->u.v4.addr < r2->u.v4.addr)
		r1_before_r2 = 0;
	else if (r1->u.v4.mask > r2->u.v4.mask)
		r1_before_r2 = 1;
	else if (r1->u.v4.mask < r2->u.v4.mask)
		r1_before_r2 = 0;
	else if (r1->mflags > r2->mflags)
		r1_before_r2 = 1;
	else
		r1_before_r2 = 0;

	return r1_before_r2;
}


/*
 * res_sorts_before6 - compare two restrict6 entries
 *
 * Returns nonzero if r1 sorts before r2.  We sort by descending
 * address, then descending mask, then descending mflags, so sorting
 * before means having a higher value.
 */
static int
res_sorts_before6(
	restrict_u *r1,
	restrict_u *r2
	)
{
	int r1_before_r2;
	int cmp;

	cmp = ADDR6_CMP(&r1->u.v6.addr, &r2->u.v6.addr);
	if (cmp > 0)		/* r1->addr > r2->addr */
		r1_before_r2 = 1;
	else if (cmp < 0)	/* r2->addr > r1->addr */
		r1_before_r2 = 0;
	else {
		cmp = ADDR6_CMP(&r1->u.v6.mask, &r2->u.v6.mask);
		if (cmp > 0)		/* r1->mask > r2->mask*/
			r1_before_r2 = 1;
		else if (cmp < 0)	/* r2->mask > r1->mask */
			r1_before_r2 = 0;
		else if (r1->mflags > r2->mflags)
			r1_before_r2 = 1;
		else
			r1_before_r2 = 0;
	}

	return r1_before_r2;
}


/*
 * restrictions - return restrictions for this host
 */
u_short
restrictions(
	sockaddr_u *srcadr
	)
{
	restrict_u *match;
	struct in6_addr *pin6;
	u_short flags;

	res_calls++;
	flags = 0;
	/* IPv4 source address */
	if (IS_IPV4(srcadr)) {
		/*
		 * Ignore any packets with a multicast source address
		 * (this should be done early in the receive process,
		 * not later!)
		 */
		if (IN_CLASSD(SRCADR(srcadr)))
			return (int)RES_IGNORE;

		match = match_restrict4_addr(SRCADR(srcadr),
					     SRCPORT(srcadr));

		INSIST(match != NULL);

		match->count++;
		/*
		 * res_not_found counts only use of the final default
		 * entry, not any "restrict default ntpport ...", which
		 * would be just before the final default.
		 */
		if (&restrict_def4 == match)
			res_not_found++;
		else
			res_found++;
		flags = match->flags;
	}

	/* IPv6 source address */
	if (IS_IPV6(srcadr)) {
		pin6 = PSOCK_ADDR6(srcadr);

		/*
		 * Ignore any packets with a multicast source address
		 * (this should be done early in the receive process,
		 * not later!)
		 */
		if (IN6_IS_ADDR_MULTICAST(pin6))
			return (int)RES_IGNORE;

		match = match_restrict6_addr(pin6, SRCPORT(srcadr));
		INSIST(match != NULL);
		match->count++;
		if (&restrict_def6 == match)
			res_not_found++;
		else
			res_found++;
		flags = match->flags;
	}
	return (flags);
}


/*
 * hack_restrict - add/subtract/manipulate entries on the restrict list
 */
void
hack_restrict(
	int		op,
	sockaddr_u *	resaddr,
	sockaddr_u *	resmask,
	u_short		mflags,
	u_short		flags,
	u_long		expire
	)
{
	int		v6;
	restrict_u	match;
	restrict_u *	res;
	restrict_u **	plisthead;

	DPRINTF(1, ("restrict: op %d addr %s mask %s mflags %08x flags %08x\n",
		    op, stoa(resaddr), stoa(resmask), mflags, flags));

	if (NULL == resaddr) {
		REQUIRE(NULL == resmask);
		REQUIRE(RESTRICT_FLAGS == op);
		restrict_source_flags = flags;
		restrict_source_mflags = mflags;
		restrict_source_enabled = 1;
		return;
	}

	ZERO(match);

#if 0
	/* silence VC9 potentially uninit warnings */
	// HMS: let's use a compiler-specific "enable" for this.
	res = NULL;
	v6 = 0;
#endif

	if (IS_IPV4(resaddr)) {
		v6 = 0;
		/*
		 * Get address and mask in host byte order for easy
		 * comparison as u_int32
		 */
		match.u.v4.addr = SRCADR(resaddr);
		match.u.v4.mask = SRCADR(resmask);
		match.u.v4.addr &= match.u.v4.mask;

	} else if (IS_IPV6(resaddr)) {
		v6 = 1;
		/*
		 * Get address and mask in network byte order for easy
		 * comparison as byte sequences (e.g. memcmp())
		 */
		match.u.v6.mask = SOCK_ADDR6(resmask);
		MASK_IPV6_ADDR(&match.u.v6.addr, PSOCK_ADDR6(resaddr),
			       &match.u.v6.mask);

	} else	{ /* not IPv4 nor IPv6 */
		REQUIRE(0);
	}

	match.flags = flags;
	match.mflags = mflags;
	match.expire = expire;
	res = match_restrict_entry(&match, v6);

	switch (op) {

	case RESTRICT_FLAGS:
		/*
		 * Here we add bits to the flags. If this is a
		 * new restriction add it.
		 */
		if (NULL == res) {
			if (v6) {
				res = alloc_res6();
				memcpy(res, &match,
				       V6_SIZEOF_RESTRICT_U);
				plisthead = &restrictlist6;
			} else {
				res = alloc_res4();
				memcpy(res, &match,
				       V4_SIZEOF_RESTRICT_U);
				plisthead = &restrictlist4;
			}
			LINK_SORT_SLIST(
				*plisthead, res,
				(v6)
				  ? res_sorts_before6(res, L_S_S_CUR())
				  : res_sorts_before4(res, L_S_S_CUR()),
				link, restrict_u);
			restrictcount++;
			if (RES_LIMITED & flags)
				inc_res_limited();
		} else {
			if ((RES_LIMITED & flags) &&
			    !(RES_LIMITED & res->flags))
				inc_res_limited();
			res->flags |= flags;
		}
		break;

	case RESTRICT_UNFLAG:
		/*
		 * Remove some bits from the flags. If we didn't
		 * find this one, just return.
		 */
		if (res != NULL) {
			if ((RES_LIMITED & res->flags)
			    && (RES_LIMITED & flags))
				dec_res_limited();
			res->flags &= ~flags;
		}
		break;

	case RESTRICT_REMOVE:
	case RESTRICT_REMOVEIF:
		/*
		 * Remove an entry from the table entirely if we
		 * found one. Don't remove the default entry and
		 * don't remove an interface entry.
		 */
		if (res != NULL
		    && (RESTRICT_REMOVEIF == op
			|| !(RESM_INTERFACE & res->mflags))
		    && res != &restrict_def4
		    && res != &restrict_def6)
			free_res(res, v6);
		break;

	default:	/* unknown op */
		INSIST(0);
		break;
	}

}


/*
 * restrict_source - maintains dynamic "restrict source ..." entries as
 *		     peers come and go.
 */
void
restrict_source(
	sockaddr_u *	addr,
	int		farewell,	/* 0 to add, 1 to remove */
	u_long		expire		/* 0 is infinite, valid until */
	)
{
	sockaddr_u	onesmask;
	restrict_u *	res;
	int		found_specific;

	if (!restrict_source_enabled || SOCK_UNSPEC(addr) ||
	    IS_MCAST(addr) || ISREFCLOCKADR(addr))
		return;

	REQUIRE(AF_INET == AF(addr) || AF_INET6 == AF(addr));

	SET_HOSTMASK(&onesmask, AF(addr));
	if (farewell) {
		hack_restrict(RESTRICT_REMOVE, addr, &onesmask,
			      0, 0, 0);
		DPRINTF(1, ("restrict_source: %s removed", stoa(addr)));
		return;
	}

	/*
	 * If there is a specific entry for this address, hands
	 * off, as it is condidered more specific than "restrict
	 * server ...".
	 * However, if the specific entry found is a fleeting one
	 * added by pool_xmit() before soliciting, replace it
	 * immediately regardless of the expire value to make way
	 * for the more persistent entry.
	 */
	if (IS_IPV4(addr)) {
		res = match_restrict4_addr(SRCADR(addr), SRCPORT(addr));
		INSIST(res != NULL);
		found_specific = (SRCADR(&onesmask) == res->u.v4.mask);
	} else {
		res = match_restrict6_addr(&SOCK_ADDR6(addr),
					   SRCPORT(addr));
		INSIST(res != NULL);
		found_specific = ADDR6_EQ(&res->u.v6.mask,
					  &SOCK_ADDR6(&onesmask));
	}
	if (!expire && found_specific && res->expire) {
		found_specific = 0;
		free_res(res, IS_IPV6(addr));
	}
	if (found_specific)
		return;

	hack_restrict(RESTRICT_FLAGS, addr, &onesmask,
		      restrict_source_mflags, restrict_source_flags,
		      expire);
	DPRINTF(1, ("restrict_source: %s host restriction added\n", 
		    stoa(addr)));
}