xnu-1699.24.23.tar.gz

[apple/xnu.git] / bsd / net / if_llreach.c

/*
 * Copyright (c) 2011 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 *
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 *
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 *
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */

/*
 * Link-layer Reachability Record
 *
 * Each interface maintains a red-black tree which contains records related
 * to the on-link nodes which we are interested in communicating with.  Each
 * record gets allocated and inserted into the tree in the following manner:
 * upon processing an ARP announcement or reply from a known node (i.e. there
 * exists a ARP route entry for the node), and if a link-layer reachability
 * record for the node doesn't yet exist; and, upon processing a ND6 RS/RA/
 * NS/NA/redirect from a node, and if a link-layer reachability record for the
 * node doesn't yet exist.
 *
 * Each newly created record is then referred to by the resolver route entry;
 * if a record already exists, its reference count gets increased for the new
 * resolver entry which now refers to it.  A record gets removed from the tree
 * and freed once its reference counts drops to zero, i.e. when there is no
 * more resolver entry referring to it.
 *
 * A record contains the link-layer protocol (e.g. Ethertype IP/IPv6), the
 * HW address of the sender, the "last heard from" timestamp (lr_lastrcvd) and
 * the number of references made to it (lr_reqcnt).  Because the key for each
 * record in the red-black tree consists of the link-layer protocol, therefore
 * the namespace for the records is partitioned based on the type of link-layer
 * protocol, i.e. an Ethertype IP link-layer record is only referred to by one
 * or more ARP entries; an Ethernet IPv6 link-layer record is only referred to
 * by one or more ND6 entries.  Therefore, lr_reqcnt represents the number of
 * resolver entry references to the record for the same protocol family.
 *
 * Upon receiving packets from the network, the protocol's input callback
 * (e.g. ether_inet{6}_input) informs the corresponding resolver (ARP/ND6)
 * about the (link-layer) origin of the packet.  This results in searching
 * for a matching record in the red-black tree for the interface where the
 * packet arrived on.  If there's no match, no further processing takes place.
 * Otherwise, the lr_lastrcvd timestamp of the record is updated.
 *
 * When an IP/IPv6 packet is transmitted to the resolver (i.e. the destination
 * is on-link), ARP/ND6 records the "last spoken to" timestamp in the route
 * entry ({la,ln}_lastused).
 *
 * The reachability of the on-link node is determined by the following logic,
 * upon sending a packet thru the resolver:
 *
 *   a) If the record is only used by exactly one resolver entry (lr_reqcnt
 *      is 1), i.e. the target host does not have IP/IPv6 aliases that we know
 *      of, check if lr_lastrcvd is "recent."  If so, simply send the packet;
 *      otherwise, re-resolve the target node.
 *
 *   b) If the record is shared by multiple resolver entries (lr_reqcnt is
 *      greater than 1), i.e. the target host has more than one IP/IPv6 aliases
 *      on the same network interface, we can't rely on lr_lastrcvd alone, as
 *      one of the IP/IPv6 aliases could have been silently moved to another
 *      node for which we don't have a link-layer record.  If lr_lastrcvd is
 *      not "recent", we re-resolve the target node.  Otherwise, we perform
 *      an additional check against {la,ln}_lastused to see whether it is also
 *      "recent", relative to lr_lastrcvd.  If so, simply send the packet;
 *      otherwise, re-resolve the target node.
 *
 * The value for "recent" is configurable by adjusting the basetime value for
 * net.link.ether.inet.arp_llreach_base or net.inet6.icmp6.nd6_llreach_base.
 * The default basetime value is 30 seconds, and the actual expiration time
 * is calculated by multiplying the basetime value with some random factor,
 * which results in a number between 15 to 45 seconds.  Setting the basetime
 * value to 0 effectively disables this feature for the corresponding resolver.
 *
 * Assumptions:
 *
 * The above logic is based upon the following assumptions:
 *
 *   i) Network traffics are mostly bi-directional, i.e. the act of sending
 *      packets to an on-link node would most likely cause us to receive
 *      packets from that node.
 *
 *  ii) If the on-link node's IP/IPv6 address silently moves to another
 *      on-link node for which we are not aware of, non-unicast packets
 *      from the old node would trigger the record's lr_lastrcvd to be
 *      kept recent.
 *
 * We can mitigate the above by having the resolver check its {la,ln}_lastused
 * timestamp at all times, i.e. not only when lr_reqcnt is greater than 1; but
 * we currently optimize for the common cases.
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/tree.h>
#include <sys/sysctl.h>
#include <sys/mcache.h>
#include <sys/protosw.h>

#include <net/if_dl.h>
#include <net/if.h>
#include <net/if_var.h>
#include <net/if_llreach.h>
#include <net/dlil.h>

#include <kern/assert.h>
#include <kern/locks.h>
#include <kern/zalloc.h>

#if INET6
#include <netinet6/in6_var.h>
#include <netinet6/nd6.h>
#endif /* INET6 */

static unsigned int iflr_size;          /* size of if_llreach */
static struct zone *iflr_zone;          /* zone for if_llreach */

#define IFLR_ZONE_MAX           128             /* maximum elements in zone */
#define IFLR_ZONE_NAME          "if_llreach"    /* zone name */

static struct if_llreach *iflr_alloc(int);
static void iflr_free(struct if_llreach *);
static __inline int iflr_cmp(const struct if_llreach *,
    const struct if_llreach *);
static __inline int iflr_reachable(struct if_llreach *, int, u_int64_t);
static int sysctl_llreach_ifinfo SYSCTL_HANDLER_ARGS;

/* The following is protected by if_llreach_lock */
RB_GENERATE_PREV(ll_reach_tree, if_llreach, lr_link, iflr_cmp);

SYSCTL_DECL(_net_link_generic_system);

SYSCTL_NODE(_net_link_generic_system, OID_AUTO, llreach_info,
    CTLFLAG_RD | CTLFLAG_LOCKED, sysctl_llreach_ifinfo,
    "Per-interface tree of source link-layer reachability records");

/*
 * Link-layer reachability is based off node constants in RFC4861.
 */
#if INET6
#define LL_COMPUTE_RTIME(x)     ND_COMPUTE_RTIME(x)
#else
#define LL_MIN_RANDOM_FACTOR    512     /* 1024 * 0.5 */
#define LL_MAX_RANDOM_FACTOR    1536    /* 1024 * 1.5 */
#define LL_COMPUTE_RTIME(x)                                             \
        (((LL_MIN_RANDOM_FACTOR * (x >> 10)) + (random() &              \
        ((LL_MAX_RANDOM_FACTOR - LL_MIN_RANDOM_FACTOR) * (x >> 10)))) / 1000)
#endif /* !INET6 */

void
ifnet_llreach_init(void)
{
        iflr_size = sizeof (struct if_llreach);
        iflr_zone = zinit(iflr_size,
            IFLR_ZONE_MAX * iflr_size, 0, IFLR_ZONE_NAME);
        if (iflr_zone == NULL) {
                panic("%s: failed allocating %s", __func__, IFLR_ZONE_NAME);
                /* NOTREACHED */
        }
        zone_change(iflr_zone, Z_EXPAND, TRUE);
        zone_change(iflr_zone, Z_CALLERACCT, FALSE);
}

void
ifnet_llreach_ifattach(struct ifnet *ifp, boolean_t reuse)
{
        lck_rw_lock_exclusive(&ifp->if_llreach_lock);
        /* Initialize link-layer source tree (if not already) */
        if (!reuse)
                RB_INIT(&ifp->if_ll_srcs);
        lck_rw_done(&ifp->if_llreach_lock);
}

void
ifnet_llreach_ifdetach(struct ifnet *ifp)
{
#pragma unused(ifp)
        /*
         * Nothing to do for now; the link-layer source tree might
         * contain entries at this point, that are still referred
         * to by route entries pointing to this ifp.
         */
}

/*
 * Link-layer source tree comparison function.
 *
 * An ordered predicate is necessary; bcmp() is not documented to return
 * an indication of order, memcmp() is, and is an ISO C99 requirement.
 */
static __inline int
iflr_cmp(const struct if_llreach *a, const struct if_llreach *b)
{
        return (memcmp(&a->lr_key, &b->lr_key, sizeof (a->lr_key)));
}

static __inline int
iflr_reachable(struct if_llreach *lr, int cmp_delta, u_int64_t tval)
{
        u_int64_t now;
        u_int64_t expire;

        now = net_uptime();             /* current approx. uptime */
        /*
         * No need for lr_lock; atomically read the last rcvd uptime.
         */
        expire = lr->lr_lastrcvd + lr->lr_reachable;
        /*
         * If we haven't heard back from the local host for over
         * lr_reachable seconds, consider that the host is no
         * longer reachable.
         */
        if (!cmp_delta)
                return (expire >= now);
        /*
         * If the caller supplied a reference time, consider the
         * host is reachable if the record hasn't expired (see above)
         * and if the reference time is within the past lr_reachable
         * seconds.
         */
        return ((expire >= now) && (now - tval) < lr->lr_reachable);
}

int
ifnet_llreach_reachable(struct if_llreach *lr)
{
        /*
         * Check whether the cache is too old to be trusted.
         */
        return (iflr_reachable(lr, 0, 0));
}

int
ifnet_llreach_reachable_delta(struct if_llreach *lr, u_int64_t tval)
{
        /*
         * Check whether the cache is too old to be trusted.
         */
        return (iflr_reachable(lr, 1, tval));
}

void
ifnet_llreach_set_reachable(struct ifnet *ifp, u_int16_t llproto, void *addr,
    unsigned int alen)
{
        struct if_llreach find, *lr;

        VERIFY(alen == IF_LLREACH_MAXLEN);      /* for now */

        find.lr_key.proto = llproto;
        bcopy(addr, &find.lr_key.addr, IF_LLREACH_MAXLEN);

        lck_rw_lock_shared(&ifp->if_llreach_lock);
        lr = RB_FIND(ll_reach_tree, &ifp->if_ll_srcs, &find);
        if (lr == NULL) {
                lck_rw_done(&ifp->if_llreach_lock);
                return;
        }
        /*
         * No need for lr_lock; atomically update the last rcvd uptime.
         */
        lr->lr_lastrcvd = net_uptime();
        lck_rw_done(&ifp->if_llreach_lock);
}

struct if_llreach *
ifnet_llreach_alloc(struct ifnet *ifp, u_int16_t llproto, void *addr,
    unsigned int alen, u_int64_t llreach_base)
{
        struct if_llreach find, *lr;
        struct timeval now;

        if (llreach_base == 0)
                return (NULL);

        VERIFY(alen == IF_LLREACH_MAXLEN);      /* for now */

        find.lr_key.proto = llproto;
        bcopy(addr, &find.lr_key.addr, IF_LLREACH_MAXLEN);

        lck_rw_lock_shared(&ifp->if_llreach_lock);
        lr = RB_FIND(ll_reach_tree, &ifp->if_ll_srcs, &find);
        if (lr != NULL) {
found:
                IFLR_LOCK(lr);
                VERIFY(lr->lr_reqcnt >= 1);
                lr->lr_reqcnt++;
                VERIFY(lr->lr_reqcnt != 0);
                IFLR_ADDREF_LOCKED(lr);         /* for caller */
                lr->lr_lastrcvd = net_uptime(); /* current approx. uptime */
                IFLR_UNLOCK(lr);
                lck_rw_done(&ifp->if_llreach_lock);
                return (lr);
        }

        if (!lck_rw_lock_shared_to_exclusive(&ifp->if_llreach_lock))
                lck_rw_lock_exclusive(&ifp->if_llreach_lock);

        lck_rw_assert(&ifp->if_llreach_lock, LCK_RW_ASSERT_EXCLUSIVE);

        /* in case things have changed while becoming writer */
        lr = RB_FIND(ll_reach_tree, &ifp->if_ll_srcs, &find);
        if (lr != NULL)
                goto found;

        lr = iflr_alloc(M_WAITOK);
        if (lr == NULL) {
                lck_rw_done(&ifp->if_llreach_lock);
                return (NULL);
        }
        IFLR_LOCK(lr);
        lr->lr_reqcnt++;
        VERIFY(lr->lr_reqcnt == 1);
        IFLR_ADDREF_LOCKED(lr);                 /* for RB tree */
        IFLR_ADDREF_LOCKED(lr);                 /* for caller */
        lr->lr_lastrcvd = net_uptime();         /* current approx. uptime */
        lr->lr_baseup = lr->lr_lastrcvd;        /* base uptime */
        microtime(&now);
        lr->lr_basecal = now.tv_sec;            /* base calendar time */
        lr->lr_basereachable = llreach_base;
        lr->lr_reachable = LL_COMPUTE_RTIME(lr->lr_basereachable * 1000);
        lr->lr_debug |= IFD_ATTACHED;
        lr->lr_ifp = ifp;
        lr->lr_key.proto = llproto;
        bcopy(addr, &lr->lr_key.addr, IF_LLREACH_MAXLEN);
        RB_INSERT(ll_reach_tree, &ifp->if_ll_srcs, lr);
        IFLR_UNLOCK(lr);
        lck_rw_done(&ifp->if_llreach_lock);

        return (lr);
}

void
ifnet_llreach_free(struct if_llreach *lr)
{
        struct ifnet *ifp;

        /* no need to lock here; lr_ifp never changes */
        ifp = lr->lr_ifp;

        lck_rw_lock_exclusive(&ifp->if_llreach_lock);
        IFLR_LOCK(lr);
        if (lr->lr_reqcnt == 0) {
                panic("%s: lr=%p negative reqcnt", __func__, lr);
                /* NOTREACHED */
        }
        --lr->lr_reqcnt;
        if (lr->lr_reqcnt > 0) {
                IFLR_UNLOCK(lr);
                lck_rw_done(&ifp->if_llreach_lock);
                IFLR_REMREF(lr);                /* for caller */
                return;
        }
        if (!(lr->lr_debug & IFD_ATTACHED)) {
                panic("%s: Attempt to detach an unattached llreach lr=%p",
                    __func__, lr);
                /* NOTREACHED */
        }
        lr->lr_debug &= ~IFD_ATTACHED;
        RB_REMOVE(ll_reach_tree, &ifp->if_ll_srcs, lr);
        IFLR_UNLOCK(lr);
        lck_rw_done(&ifp->if_llreach_lock);

        IFLR_REMREF(lr);                        /* for RB tree */
        IFLR_REMREF(lr);                        /* for caller */
}

u_int64_t
ifnet_llreach_up2cal(struct if_llreach *lr, u_int64_t uptime)
{
        u_int64_t calendar = 0;

        if (uptime != 0) {
                struct timeval cnow;
                u_int64_t unow;

                getmicrotime(&cnow);    /* current calendar time */
                unow = net_uptime();    /* current approx. uptime */
                /*
                 * Take into account possible calendar time changes;
                 * adjust base calendar value if necessary, i.e.
                 * the calendar skew should equate to the uptime skew.
                 */
                lr->lr_basecal += (cnow.tv_sec - lr->lr_basecal) -
                    (unow - lr->lr_baseup);

                calendar = lr->lr_basecal + lr->lr_reachable +
                    (uptime - lr->lr_baseup);
        }

        return (calendar);
}

static struct if_llreach *
iflr_alloc(int how)
{
        struct if_llreach *lr;

        lr = (how == M_WAITOK) ? zalloc(iflr_zone) : zalloc_noblock(iflr_zone);
        if (lr != NULL) {
                bzero(lr, iflr_size);
                lck_mtx_init(&lr->lr_lock, ifnet_lock_group, ifnet_lock_attr);
                lr->lr_debug |= IFD_ALLOC;
        }
        return (lr);
}

static void
iflr_free(struct if_llreach *lr)
{
        IFLR_LOCK(lr);
        if (lr->lr_debug & IFD_ATTACHED) {
                panic("%s: attached lr=%p is being freed", __func__, lr);
                /* NOTREACHED */
        } else if (!(lr->lr_debug & IFD_ALLOC)) {
                panic("%s: lr %p cannot be freed", __func__, lr);
                /* NOTREACHED */
        } else if (lr->lr_refcnt != 0) {
                panic("%s: non-zero refcount lr=%p", __func__, lr);
                /* NOTREACHED */
        } else if (lr->lr_reqcnt != 0) {
                panic("%s: non-zero reqcnt lr=%p", __func__, lr);
                /* NOTREACHED */
        }
        lr->lr_debug &= ~IFD_ALLOC;
        IFLR_UNLOCK(lr);

        lck_mtx_destroy(&lr->lr_lock, ifnet_lock_group);
        zfree(iflr_zone, lr);
}

void
iflr_addref(struct if_llreach *lr, int locked)
{
        if (!locked)
                IFLR_LOCK(lr);
        else
                IFLR_LOCK_ASSERT_HELD(lr);

        if (++lr->lr_refcnt == 0) {
                panic("%s: lr=%p wraparound refcnt", __func__, lr);
                /* NOTREACHED */
        }
        if (!locked)
                IFLR_UNLOCK(lr);
}

void
iflr_remref(struct if_llreach *lr)
{
        IFLR_LOCK(lr);
        if (lr->lr_refcnt == 0) {
                panic("%s: lr=%p negative refcnt", __func__, lr);
                /* NOTREACHED */
        }
        --lr->lr_refcnt;
        if (lr->lr_refcnt > 0) {
                IFLR_UNLOCK(lr);
                return;
        }
        IFLR_UNLOCK(lr);

        iflr_free(lr);  /* deallocate it */
}

void
ifnet_lr2ri(struct if_llreach *lr, struct rt_reach_info *ri)
{
        struct if_llreach_info lri;

        IFLR_LOCK_ASSERT_HELD(lr);

        bzero(ri, sizeof (*ri));
        ifnet_lr2lri(lr, &lri);
        ri->ri_refcnt = lri.lri_refcnt;
        ri->ri_probes = lri.lri_probes;
        ri->ri_rcv_expire = lri.lri_expire;
}

void
ifnet_lr2lri(struct if_llreach *lr, struct if_llreach_info *lri)
{
        IFLR_LOCK_ASSERT_HELD(lr);

        bzero(lri, sizeof (*lri));
        /*
         * Note here we return request count, not actual memory refcnt.
         */
        lri->lri_refcnt = lr->lr_reqcnt;
        lri->lri_ifindex = lr->lr_ifp->if_index;
        lri->lri_probes = lr->lr_probes;
        lri->lri_expire = ifnet_llreach_up2cal(lr, lr->lr_lastrcvd);
        lri->lri_proto = lr->lr_key.proto;
        bcopy(&lr->lr_key.addr, &lri->lri_addr, IF_LLREACH_MAXLEN);
}

static int
sysctl_llreach_ifinfo SYSCTL_HANDLER_ARGS
{
#pragma unused(oidp)
        int             *name, retval = 0;
        unsigned int    namelen;
        uint32_t        ifindex;
        struct if_llreach *lr;
        struct if_llreach_info lri;
        struct ifnet    *ifp;

        name = (int *)arg1;
        namelen = (unsigned int)arg2;

        if (req->newptr != USER_ADDR_NULL)
                return (EPERM);

        if (namelen != 1)
                return (EINVAL);

        ifindex = name[0];
        ifnet_head_lock_shared();
        if (ifindex <= 0 || ifindex > (u_int)if_index) {
                printf("%s: ifindex %u out of range\n", __func__, ifindex);
                ifnet_head_done();
                return (ENOENT);
        }

        ifp = ifindex2ifnet[ifindex];
        ifnet_head_done();
        if (ifp == NULL) {
                printf("%s: no ifp for ifindex %u\n", __func__, ifindex);
                return (ENOENT);
        }

        lck_rw_lock_shared(&ifp->if_llreach_lock);
        RB_FOREACH(lr, ll_reach_tree, &ifp->if_ll_srcs) {
                /* Export to if_llreach_info structure */
                IFLR_LOCK(lr);
                ifnet_lr2lri(lr, &lri);
                IFLR_UNLOCK(lr);

                if ((retval = SYSCTL_OUT(req, &lri, sizeof (lri))) != 0)
                        break;
        }
        lck_rw_done(&ifp->if_llreach_lock);

        return (retval);
}