ntpd: new applet by Adam Tkac. +5k.

Signed-off-by: Adam Tkac <vonsch@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 999 insertions, 0 deletions

diff --git a/networking/ntpd.c b/networking/ntpd.c
new file mode 100644
index 000000000..62a00a5bf
--- /dev/null
+++ b/networking/ntpd.c
@@ -0,0 +1,999 @@
+/*
+ * NTP client/server, based on OpenNTPD 3.9p1
+ *
+ * Author: Adam Tkac <vonsch@gmail.com>
+ *
+ * Licensed under GPLv2, see file LICENSE in this tarball for details.
+ */
+
+#include "libbb.h"
+#include <netinet/ip.h> /* For IPTOS_LOWDELAY definition */
+
+#ifndef IP_PKTINFO
+# error "Sorry, your kernel has to support IP_PKTINFO"
+#endif
+
+#define INTERVAL_QUERY_NORMAL           30      /* sync to peers every n secs */
+#define INTERVAL_QUERY_PATHETIC         60
+#define INTERVAL_QUERY_AGRESSIVE        5
+
+#define TRUSTLEVEL_BADPEER              6
+#define TRUSTLEVEL_PATHETIC             2
+#define TRUSTLEVEL_AGRESSIVE            8
+#define TRUSTLEVEL_MAX                  10
+
+#define QSCALE_OFF_MIN                  0.05
+#define QSCALE_OFF_MAX                  0.50
+
+#define QUERYTIME_MAX           15      /* single query might take n secs max */
+#define OFFSET_ARRAY_SIZE       8
+#define SETTIME_MIN_OFFSET      180     /* min offset for settime at start */
+#define SETTIME_TIMEOUT         15      /* max seconds to wait with -s */
+
+/* Style borrowed from NTP ref/tcpdump and updated for SNTPv4 (RFC2030). */
+
+/*
+ * RFC Section 3
+ *
+ *    0                   1                   2                   3
+ *    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ *   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *   |                         Integer Part                          |
+ *   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *   |                         Fraction Part                         |
+ *   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *
+ *    0                   1                   2                   3
+ *    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+ *   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *   |            Integer Part       |     Fraction Part             |
+ *   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+*/
+typedef struct {
+        uint32_t int_partl;
+        uint32_t fractionl;
+} l_fixedpt_t;
+
+typedef struct {
+        uint16_t int_parts;
+        uint16_t fractions;
+} s_fixedpt_t;
+
+#define NTP_DIGESTSIZE          16
+#define NTP_MSGSIZE_NOAUTH      48
+#define NTP_MSGSIZE             (NTP_MSGSIZE_NOAUTH + 4 + NTP_DIGESTSIZE)
+
+typedef struct {
+        uint8_t status; /* status of local clock and leap info */
+        uint8_t stratum;        /* Stratum level */
+        uint8_t ppoll;          /* poll value */
+        int8_t precision;
+        s_fixedpt_t rootdelay;
+        s_fixedpt_t dispersion;
+        uint32_t refid;
+        l_fixedpt_t reftime;
+        l_fixedpt_t orgtime;
+        l_fixedpt_t rectime;
+        l_fixedpt_t xmttime;
+        uint32_t keyid;
+        uint8_t digest[NTP_DIGESTSIZE];
+} ntp_msg_t;
+
+typedef struct {
+        int                     fd;
+        ntp_msg_t               msg;
+        double                  xmttime;
+} ntp_query_t;
+
+enum {
+        NTP_VERSION     = 4,
+        NTP_MAXSTRATUM  = 15,
+        /* Leap Second Codes (high order two bits) */
+        LI_NOWARNING    = (0 << 6),     /* no warning */
+        LI_PLUSSEC      = (1 << 6),     /* add a second (61 seconds) */
+        LI_MINUSSEC     = (2 << 6),     /* minus a second (59 seconds) */
+        LI_ALARM        = (3 << 6),     /* alarm condition */
+
+        /* Status Masks */
+        MODE_MASK       = (7 << 0),
+        VERSION_MASK    = (7 << 3),
+        LI_MASK         = (3 << 6),
+
+        /* Mode values */
+        MODE_RES0       = 0,    /* reserved */
+        MODE_SYM_ACT    = 1,    /* symmetric active */
+        MODE_SYM_PAS    = 2,    /* symmetric passive */
+        MODE_CLIENT     = 3,    /* client */
+        MODE_SERVER     = 4,    /* server */
+        MODE_BROADCAST  = 5,    /* broadcast */
+        MODE_RES1       = 6,    /* reserved for NTP control message */
+        MODE_RES2       = 7     /* reserved for private use */
+};
+
+#define JAN_1970        2208988800UL    /* 1970 - 1900 in seconds */
+
+enum client_state {
+        STATE_NONE,
+        STATE_QUERY_SENT,
+        STATE_REPLY_RECEIVED
+};
+
+typedef struct {
+        double          rootdelay;
+        double          rootdispersion;
+        double          reftime;
+        uint32_t        refid;
+        uint32_t        refid4;
+        uint8_t         synced;
+        uint8_t         leap;
+        int8_t          precision;
+        uint8_t         poll;
+        uint8_t         stratum;
+} ntp_status_t;
+
+typedef struct {
+        ntp_status_t            status;
+        double                  offset;
+        double                  delay;
+        double                  error;
+        time_t                  rcvd;
+        uint8_t                 good;
+} ntp_offset_t;
+
+typedef struct {
+        len_and_sockaddr        *lsa;
+        ntp_query_t              query;
+        ntp_offset_t             reply[OFFSET_ARRAY_SIZE];
+        ntp_offset_t             update;
+        enum client_state        state;
+        time_t                   next;
+        time_t                   deadline;
+        uint8_t                  shift;
+        uint8_t                  trustlevel;
+} ntp_peer_t;
+
+
+struct globals {
+        unsigned        verbose;
+#if ENABLE_FEATURE_NTPD_SERVER
+        int             listen_fd;
+#endif
+        llist_t         *ntp_peers;
+        ntp_status_t    status;
+        uint32_t        scale;
+        uint8_t         settime;
+        uint8_t         firstadj;
+        smallint        peer_cnt;
+
+};
+#define G (*ptr_to_globals)
+
+
+static const int const_IPTOS_LOWDELAY = IPTOS_LOWDELAY;
+
+
+static void
+set_next(ntp_peer_t *p, time_t t)
+{
+        p->next = time(NULL) + t;
+        p->deadline = 0;
+}
+
+static void
+add_peers(const char *s)
+{
+        ntp_peer_t *p;
+
+        p = xzalloc(sizeof(*p));
+//TODO: big ntpd uses all IPs, not just 1st, do we need to mimic that?
+        p->lsa = xhost2sockaddr(s, 123);
+        p->query.fd = -1;
+        p->query.msg.status = MODE_CLIENT | (NTP_VERSION << 3);
+        if (STATE_NONE != 0)
+                p->state = STATE_NONE;
+        p->trustlevel = TRUSTLEVEL_PATHETIC;
+        p->query.fd = -1;
+        set_next(p, 0);
+
+        llist_add_to(&G.ntp_peers, p);
+        G.peer_cnt++;
+}
+
+static double
+gettime(void)
+{
+        struct timeval  tv;
+
+        gettimeofday(&tv, NULL); /* never fails */
+        return (tv.tv_sec + JAN_1970 + 1.0e-6 * tv.tv_usec);
+}
+
+
+static void
+d_to_tv(double d, struct timeval *tv)
+{
+        tv->tv_sec = (long)d;
+        tv->tv_usec = (d - tv->tv_sec) * 1000000;
+}
+
+static double
+lfp_to_d(l_fixedpt_t lfp)
+{
+        double  ret;
+
+        lfp.int_partl = ntohl(lfp.int_partl);
+        lfp.fractionl = ntohl(lfp.fractionl);
+        ret = (double)(lfp.int_partl) + ((double)lfp.fractionl / UINT_MAX);
+        return ret;
+}
+
+#if ENABLE_FEATURE_NTPD_SERVER
+static l_fixedpt_t
+d_to_lfp(double d)
+{
+        l_fixedpt_t     lfp;
+
+        lfp.int_partl = htonl((uint32_t)d);
+        lfp.fractionl = htonl((uint32_t)((d - (u_int32_t)d) * UINT_MAX));
+        return lfp;
+}
+#endif
+
+static double
+sfp_to_d(s_fixedpt_t sfp)
+{
+        double  ret;
+
+        sfp.int_parts = ntohs(sfp.int_parts);
+        sfp.fractions = ntohs(sfp.fractions);
+        ret = (double)(sfp.int_parts) + ((double)sfp.fractions / USHRT_MAX);
+        return ret;
+}
+
+#if ENABLE_FEATURE_NTPD_SERVER
+static s_fixedpt_t
+d_to_sfp(double d)
+{
+        s_fixedpt_t     sfp;
+
+        sfp.int_parts = htons((uint16_t)d);
+        sfp.fractions = htons((uint16_t)((d - (u_int16_t)d) * USHRT_MAX));
+        return sfp;
+}
+#endif
+
+static void
+set_deadline(ntp_peer_t *p, time_t t)
+{
+        p->deadline = time(NULL) + t;
+        p->next = 0;
+}
+
+static time_t
+error_interval(void)
+{
+        time_t interval, r;
+
+        interval = INTERVAL_QUERY_PATHETIC * QSCALE_OFF_MAX / QSCALE_OFF_MIN;
+        r = random() % (interval / 10);
+        return (interval + r);
+}
+
+static int
+sendmsg_wrap(int fd,
+                const struct sockaddr *from, const struct sockaddr *to, socklen_t addrlen,
+                ntp_msg_t *msg, ssize_t len)
+{
+        ssize_t ret;
+
+        errno = 0;
+        if (!from) {
+                ret = sendto(fd, msg, len, 0, to, addrlen);
+        } else {
+                ret = send_to_from(fd, msg, len, 0, to, from, addrlen);
+        }
+        if (ret != len) {
+                bb_perror_msg("send failed");
+                return -1;
+        }
+        return 0;
+}
+
+static int
+client_query(ntp_peer_t *p)
+{
+        if (p->query.fd == -1) {
+                p->query.fd = xsocket(p->lsa->u.sa.sa_family, SOCK_DGRAM, 0);
+#if ENABLE_FEATURE_IPV6
+                if (p->lsa->u.sa.sa_family == AF_INET)
+#endif
+                        setsockopt(p->query.fd, IPPROTO_IP, IP_TOS, &const_IPTOS_LOWDELAY, sizeof(const_IPTOS_LOWDELAY));
+        }
+
+        /*
+         * Send out a random 64-bit number as our transmit time.  The NTP
+         * server will copy said number into the originate field on the
+         * response that it sends us.  This is totally legal per the SNTP spec.
+         *
+         * The impact of this is two fold: we no longer send out the current
+         * system time for the world to see (which may aid an attacker), and
+         * it gives us a (not very secure) way of knowing that we're not
+         * getting spoofed by an attacker that can't capture our traffic
+         * but can spoof packets from the NTP server we're communicating with.
+         *
+         * Save the real transmit timestamp locally.
+         */
+
+        p->query.msg.xmttime.int_partl = random();
+        p->query.msg.xmttime.fractionl = random();
+        p->query.xmttime = gettime();
+
+        if (sendmsg_wrap(p->query.fd, /*from:*/ NULL, /*to:*/ &p->lsa->u.sa, /*addrlen:*/ p->lsa->len,
+                        &p->query.msg, NTP_MSGSIZE_NOAUTH) == -1) {
+                set_next(p, INTERVAL_QUERY_PATHETIC);
+                return -1;
+        }
+
+        p->state = STATE_QUERY_SENT;
+        set_deadline(p, QUERYTIME_MAX);
+
+        return 0;
+}
+
+static int
+offset_compare(const void *aa, const void *bb)
+{
+        const ntp_peer_t * const *a;
+        const ntp_peer_t * const *b;
+
+        a = aa;
+        b = bb;
+
+        if ((*a)->update.offset < (*b)->update.offset)
+                return -1;
+        return ((*a)->update.offset > (*b)->update.offset);
+}
+
+static uint32_t
+updated_scale(double offset)
+{
+        if (offset < 0)
+                offset = -offset;
+
+        if (offset > QSCALE_OFF_MAX)
+                return 1;
+        if (offset < QSCALE_OFF_MIN)
+                return QSCALE_OFF_MAX / QSCALE_OFF_MIN;
+        return QSCALE_OFF_MAX / offset;
+}
+
+static void
+adjtime_wrap(void)
+{
+        ntp_peer_t       *p;
+        unsigned          offset_cnt;
+        int               i = 0;
+        ntp_peer_t      **peers;
+        double            offset_median;
+        llist_t          *item;
+        len_and_sockaddr *lsa;
+        struct timeval    tv, olddelta;
+
+        offset_cnt = 0;
+        for (item = G.ntp_peers; item != NULL; item = item->link) {
+                p = (ntp_peer_t *) item->data;
+                if (p->trustlevel < TRUSTLEVEL_BADPEER)
+                        continue;
+                if (!p->update.good)
+                        return;
+                offset_cnt++;
+        }
+
+        peers = xzalloc(sizeof(ntp_peer_t *) * offset_cnt);
+        for (item = G.ntp_peers; item != NULL; item = item->link) {
+                p = (ntp_peer_t *) item->data;
+                if (p->trustlevel < TRUSTLEVEL_BADPEER)
+                        continue;
+                peers[i++] = p;
+        }
+
+        qsort(peers, offset_cnt, sizeof(ntp_peer_t *), offset_compare);
+
+        if (offset_cnt != 0) {
+                if ((offset_cnt & 1) == 0) {
+//TODO: try offset_cnt /= 2...
+                        offset_median =
+                            (peers[offset_cnt / 2 - 1]->update.offset +
+                            peers[offset_cnt / 2]->update.offset) / 2;
+                        G.status.rootdelay =
+                            (peers[offset_cnt / 2 - 1]->update.delay +
+                            peers[offset_cnt / 2]->update.delay) / 2;
+                        G.status.stratum = MAX(
+                            peers[offset_cnt / 2 - 1]->update.status.stratum,
+                            peers[offset_cnt / 2]->update.status.stratum);
+                } else {
+                        offset_median = peers[offset_cnt / 2]->update.offset;
+                        G.status.rootdelay = peers[offset_cnt / 2]->update.delay;
+                        G.status.stratum = peers[offset_cnt / 2]->update.status.stratum;
+                }
+                G.status.leap = peers[offset_cnt / 2]->update.status.leap;
+
+                bb_info_msg("adjusting local clock by %fs", offset_median);
+
+                d_to_tv(offset_median, &tv);
+                if (adjtime(&tv, &olddelta) == -1)
+                        bb_error_msg("adjtime failed");
+                else if (!G.firstadj
+                 && olddelta.tv_sec == 0
+                 && olddelta.tv_usec == 0
+                 && !G.status.synced
+                ) {
+                        bb_info_msg("clock synced");
+                        G.status.synced = 1;
+                } else if (G.status.synced) {
+                        bb_info_msg("clock unsynced");
+                        G.status.synced = 0;
+                }
+
+                G.firstadj = 0;
+                G.status.reftime = gettime();
+                G.status.stratum++;     /* one more than selected peer */
+                G.scale = updated_scale(offset_median);
+
+                G.status.refid4 = peers[offset_cnt / 2]->update.status.refid4;
+
+                lsa = peers[offset_cnt / 2]->lsa;
+                G.status.refid =
+#if ENABLE_FEATURE_IPV6
+                        lsa->u.sa.sa_family != AF_INET ?
+                                G.status.refid4 :
+#endif
+                                lsa->u.sin.sin_addr.s_addr;
+        }
+
+        free(peers);
+
+        for (item = G.ntp_peers; item != NULL; item = item->link) {
+                p = (ntp_peer_t *) item->data;
+                p->update.good = 0;
+        }
+}
+
+static void
+settime(double offset)
+{
+        ntp_peer_t *p;
+        llist_t         *item;
+        struct timeval  tv, curtime;
+        char            buf[80];
+        time_t          tval;
+
+#if 0
+        if (!G.settime)
+                return;
+#endif
+
+        /* if the offset is small, don't call settimeofday */
+        if (offset < SETTIME_MIN_OFFSET && offset > -SETTIME_MIN_OFFSET)
+                return;
+
+        gettimeofday(&curtime, NULL); /* never fails */
+
+        d_to_tv(offset, &tv);
+        curtime.tv_usec += tv.tv_usec + 1000000;
+        curtime.tv_sec += tv.tv_sec - 1 + (curtime.tv_usec / 1000000);
+        curtime.tv_usec %= 1000000;
+
+        if (settimeofday(&curtime, NULL) == -1) {
+                bb_error_msg("settimeofday");
+                return;
+        }
+
+        G.settime = 0;
+
+        tval = curtime.tv_sec;
+        strftime(buf, sizeof(buf), "%a %b %e %H:%M:%S %Z %Y", localtime(&tval));
+
+        /* Do we want to print message below to system log when daemonized? */
+        bb_info_msg("set local clock to %s (offset %fs)", buf, offset);
+
+        for (item = G.ntp_peers; item != NULL; item = item->link) {
+                p = (ntp_peer_t *) item->data;
+                if (p->next)
+                        p->next -= offset;
+                if (p->deadline)
+                        p->deadline -= offset;
+        }
+}
+
+static void
+client_update(ntp_peer_t *p)
+{
+        int i, best = 0, good = 0;
+
+        /*
+         * clock filter
+         * find the offset which arrived with the lowest delay
+         * use that as the peer update
+         * invalidate it and all older ones
+         */
+
+        for (i = 0; good == 0 && i < OFFSET_ARRAY_SIZE; i++) {
+                if (p->reply[i].good) {
+                        good++;
+                        best = i;
+                }
+        }
+
+        for (; i < OFFSET_ARRAY_SIZE; i++) {
+                if (p->reply[i].good) {
+                        good++;
+                        if (p->reply[i].delay < p->reply[best].delay)
+                                best = i;
+                }
+        }
+
+        if (good < 8)
+                return;
+
+        memcpy(&p->update, &p->reply[best], sizeof(p->update));
+        adjtime_wrap();
+
+        for (i = 0; i < OFFSET_ARRAY_SIZE; i++)
+                if (p->reply[i].rcvd <= p->reply[best].rcvd)
+                        p->reply[i].good = 0;
+}
+
+static time_t
+scale_interval(time_t requested)
+{
+        time_t interval, r;
+
+        interval = requested * G.scale;
+        r = random() % MAX(5, interval / 10);
+        return (interval + r);
+}
+
+static void
+client_dispatch(ntp_peer_t *p)
+{
+        char                     *addr;
+        ssize_t                  size;
+        ntp_msg_t                msg;
+        double                   T1, T2, T3, T4;
+        time_t                   interval;
+        ntp_offset_t            *offset;
+
+        addr = xmalloc_sockaddr2dotted_noport(&p->lsa->u.sa);
+
+        size = recvfrom(p->query.fd, &msg, sizeof(msg), 0, NULL, NULL);
+        if (size == -1) {
+                bb_perror_msg("recvfrom(%s) error", addr);
+                if (errno == EHOSTUNREACH || errno == EHOSTDOWN
+                 || errno == ENETUNREACH || errno == ENETDOWN
+                 || errno == ECONNREFUSED || errno == EADDRNOTAVAIL
+                ) {
+//TODO: always do this?
+                        set_next(p, error_interval());
+                        goto bail;
+                }
+                xfunc_die();
+        }
+
+        T4 = gettime();
+
+        if (size != NTP_MSGSIZE_NOAUTH && size != NTP_MSGSIZE) {
+                bb_error_msg("malformed packet received from %s", addr);
+                goto bail;
+        }
+
+        if (msg.orgtime.int_partl != p->query.msg.xmttime.int_partl
+         || msg.orgtime.fractionl != p->query.msg.xmttime.fractionl
+        ) {
+                goto bail;
+        }
+
+        if ((msg.status & LI_ALARM) == LI_ALARM
+         || msg.stratum == 0
+         || msg.stratum > NTP_MAXSTRATUM
+        ) {
+                interval = error_interval();
+                bb_info_msg("reply from %s: not synced, next query %ds", addr, (int) interval);
+                goto bail;
+        }
+
+        /*
+         * From RFC 2030 (with a correction to the delay math):
+         *
+         *     Timestamp Name          ID   When Generated
+         *     ------------------------------------------------------------
+         *     Originate Timestamp     T1   time request sent by client
+         *     Receive Timestamp       T2   time request received by server
+         *     Transmit Timestamp      T3   time reply sent by server
+         *     Destination Timestamp   T4   time reply received by client
+         *
+         *  The roundtrip delay d and local clock offset t are defined as
+         *
+         *    d = (T4 - T1) - (T3 - T2)     t = ((T2 - T1) + (T3 - T4)) / 2.
+         */
+
+        T1 = p->query.xmttime;
+        T2 = lfp_to_d(msg.rectime);
+        T3 = lfp_to_d(msg.xmttime);
+
+        offset = &p->reply[p->shift];
+
+        offset->offset = ((T2 - T1) + (T3 - T4)) / 2;
+        offset->delay = (T4 - T1) - (T3 - T2);
+        if (offset->delay < 0) {
+                interval = error_interval();
+                set_next(p, interval);
+                bb_info_msg("reply from %s: negative delay %f", addr, p->reply[p->shift].delay);
+                goto bail;
+        }
+        offset->error = (T2 - T1) - (T3 - T4);
+        offset->rcvd = time(NULL);
+        offset->good = 1;
+
+        offset->status.leap = (msg.status & LI_MASK);
+        offset->status.precision = msg.precision;
+        offset->status.rootdelay = sfp_to_d(msg.rootdelay);
+        offset->status.rootdispersion = sfp_to_d(msg.dispersion);
+        offset->status.refid = ntohl(msg.refid);
+        offset->status.refid4 = msg.xmttime.fractionl;
+        offset->status.reftime = lfp_to_d(msg.reftime);
+        offset->status.poll = msg.ppoll;
+        offset->status.stratum = msg.stratum;
+
+        if (p->trustlevel < TRUSTLEVEL_PATHETIC)
+                interval = scale_interval(INTERVAL_QUERY_PATHETIC);
+        else if (p->trustlevel < TRUSTLEVEL_AGRESSIVE)
+                interval = scale_interval(INTERVAL_QUERY_AGRESSIVE);
+        else
+                interval = scale_interval(INTERVAL_QUERY_NORMAL);
+
+        set_next(p, interval);
+        p->state = STATE_REPLY_RECEIVED;
+
+        /* every received reply which we do not discard increases trust */
+        if (p->trustlevel < TRUSTLEVEL_MAX) {
+                if (p->trustlevel < TRUSTLEVEL_BADPEER
+                 && p->trustlevel + 1 >= TRUSTLEVEL_BADPEER
+                ) {
+                        bb_info_msg("peer %s now valid", addr);
+                }
+                p->trustlevel++;
+        }
+
+        bb_info_msg("reply from %s: offset %f delay %f, next query %ds", addr,
+                        offset->offset, offset->delay, (int) interval);
+
+        client_update(p);
+        if (!G.settime)
+                settime(offset->offset);
+
+        if (++p->shift >= OFFSET_ARRAY_SIZE)
+                p->shift = 0;
+
+ bail:
+        free(addr);
+}
+
+#if ENABLE_FEATURE_NTPD_SERVER
+static void
+server_dispatch(int fd)
+{
+        ssize_t                 size;
+        uint8_t                 version;
+        double                  rectime;
+        len_and_sockaddr        *to;
+        struct sockaddr         *from;
+        ntp_msg_t               query, reply;
+
+        to = get_sock_lsa(G.listen_fd);
+        from = xzalloc(to->len);
+
+        size = recv_from_to(fd, &query, sizeof(query), 0, from, &to->u.sa, to->len);
+        if (size == -1)
+                bb_error_msg_and_die("recv_from_to");
+        if (size != NTP_MSGSIZE_NOAUTH && size != NTP_MSGSIZE) {
+                char *addr = xmalloc_sockaddr2dotted_noport(from);
+                bb_error_msg("malformed packet received from %s", addr);
+                free(addr);
+                goto bail;
+        }
+
+        rectime = gettime();
+        version = (query.status & VERSION_MASK) >> 3;
+
+        memset(&reply, 0, sizeof(reply));
+        reply.status = G.status.synced ? G.status.leap : LI_ALARM;
+        reply.status |= (query.status & VERSION_MASK);
+        reply.status |= ((query.status & MODE_MASK) == MODE_CLIENT) ?
+                         MODE_SERVER : MODE_SYM_PAS;
+        reply.stratum = G.status.stratum;
+        reply.ppoll = query.ppoll;
+        reply.precision = G.status.precision;
+        reply.rectime = d_to_lfp(rectime);
+        reply.reftime = d_to_lfp(G.status.reftime);
+        reply.xmttime = d_to_lfp(gettime());
+        reply.orgtime = query.xmttime;
+        reply.rootdelay = d_to_sfp(G.status.rootdelay);
+        reply.refid = (version > 3) ? G.status.refid4 : G.status.refid;
+
+        /* We reply from the address packet was sent to,
+         * this makes to/from look swapped here: */
+        sendmsg_wrap(fd, /*from:*/ &to->u.sa, /*to:*/ from, /*addrlen:*/ to->len,
+                        &reply, size);
+
+ bail:
+        free(to);
+        free(from);
+}
+#endif
+
+/* Upstream ntpd's options:
+ *
+ * -4   Force DNS resolution of host names to the IPv4 namespace.
+ * -6   Force DNS resolution of host names to the IPv6 namespace.
+ * -a   Require cryptographic authentication for broadcast client,
+ *      multicast client and symmetric passive associations.
+ *      This is the default.
+ * -A   Do not require cryptographic authentication for broadcast client,
+ *      multicast client and symmetric passive associations.
+ *      This is almost never a good idea.
+ * -b   Enable the client to synchronize to broadcast servers.
+ * -c conffile
+ *      Specify the name and path of the configuration file,
+ *      default /etc/ntp.conf
+ * -d   Specify debugging mode. This option may occur more than once,
+ *      with each occurrence indicating greater detail of display.
+ * -D level
+ *      Specify debugging level directly.
+ * -f driftfile
+ *      Specify the name and path of the frequency file.
+ *      This is the same operation as the "driftfile FILE"
+ *      configuration command.
+ * -g   Normally, ntpd exits with a message to the system log
+ *      if the offset exceeds the panic threshold, which is 1000 s
+ *      by default. This option allows the time to be set to any value
+ *      without restriction; however, this can happen only once.
+ *      If the threshold is exceeded after that, ntpd will exit
+ *      with a message to the system log. This option can be used
+ *      with the -q and -x options. See the tinker command for other options.
+ * -i jaildir
+ *      Chroot the server to the directory jaildir. This option also implies
+ *      that the server attempts to drop root privileges at startup
+ *      (otherwise, chroot gives very little additional security).
+ *      You may need to also specify a -u option.
+ * -k keyfile
+ *      Specify the name and path of the symmetric key file,
+ *      default /etc/ntp/keys. This is the same operation
+ *      as the "keys FILE" configuration command.
+ * -l logfile
+ *      Specify the name and path of the log file. The default
+ *      is the system log file. This is the same operation as
+ *      the "logfile FILE" configuration command.
+ * -L   Do not listen to virtual IPs. The default is to listen.
+ * -n   Don't fork.
+ * -N   To the extent permitted by the operating system,
+ *      run the ntpd at the highest priority.
+ * -p pidfile
+ *      Specify the name and path of the file used to record the ntpd
+ *      process ID. This is the same operation as the "pidfile FILE"
+ *      configuration command.
+ * -P priority
+ *      To the extent permitted by the operating system,
+ *      run the ntpd at the specified priority.
+ * -q   Exit the ntpd just after the first time the clock is set.
+ *      This behavior mimics that of the ntpdate program, which is
+ *      to be retired. The -g and -x options can be used with this option.
+ *      Note: The kernel time discipline is disabled with this option.
+ * -r broadcastdelay
+ *      Specify the default propagation delay from the broadcast/multicast
+ *      server to this client. This is necessary only if the delay
+ *      cannot be computed automatically by the protocol.
+ * -s statsdir
+ *      Specify the directory path for files created by the statistics
+ *      facility. This is the same operation as the "statsdir DIR"
+ *      configuration command.
+ * -t key
+ *      Add a key number to the trusted key list. This option can occur
+ *      more than once.
+ * -u user[:group]
+ *      Specify a user, and optionally a group, to switch to.
+ * -v variable
+ * -V variable
+ *      Add a system variable listed by default.
+ * -x   Normally, the time is slewed if the offset is less than the step
+ *      threshold, which is 128 ms by default, and stepped if above
+ *      the threshold. This option sets the threshold to 600 s, which is
+ *      well within the accuracy window to set the clock manually.
+ *      Note: since the slew rate of typical Unix kernels is limited
+ *      to 0.5 ms/s, each second of adjustment requires an amortization
+ *      interval of 2000 s. Thus, an adjustment as much as 600 s
+ *      will take almost 14 days to complete. This option can be used
+ *      with the -g and -q options. See the tinker command for other options.
+ *      Note: The kernel time discipline is disabled with this option.
+ */
+
+enum {
+        OPT_n = (1 << 0),
+        OPT_g = (1 << 1),
+        OPT_p = (1 << 2),
+        OPT_l = (1 << 3),
+};
+
+/* By doing init in a separate function we decrease stack usage
+ * in main loop.
+ */
+static NOINLINE void ntp_init(char **argv)
+{
+        unsigned opts;
+        llist_t *peers;
+
+        tzset();
+
+        if (getuid())
+                bb_error_msg_and_die("need root privileges");
+
+        peers = NULL;
+        opt_complementary = "dd:p::"; /* d: counter, p: list */
+        opts = getopt32(argv,
+                        "ng" /* compat */
+                        "p:"IF_FEATURE_NTPD_SERVER("l") /* NOT compat */
+                        "d" /* compat */
+                        "46aAbLNx", /* compat, ignored */
+                        &peers, &G.verbose);
+#if ENABLE_FEATURE_NTPD_SERVER
+        G.listen_fd = -1;
+        if (opts & OPT_l) {
+                G.listen_fd = create_and_bind_dgram_or_die(NULL, 123);
+                socket_want_pktinfo(G.listen_fd);
+                setsockopt(G.listen_fd, IPPROTO_IP, IP_TOS, &const_IPTOS_LOWDELAY, sizeof(const_IPTOS_LOWDELAY));
+        }
+#endif
+        if (opts & OPT_g)
+                G.settime = 1;
+        while (peers)
+                add_peers(llist_pop(&peers));
+        if (!(opts & OPT_n)) {
+                logmode = LOGMODE_NONE;
+                bb_daemonize(DAEMON_DEVNULL_STDIO);
+        }
+
+        /* Set some globals */
+        {
+                int prec = 0;
+                int b;
+#if 0
+                struct timespec tp;
+                /* We can use sys_clock_getres but assuming 10ms tick should be fine */
+                clock_getres(CLOCK_REALTIME, &tp);
+                tp.tv_sec = 0;
+                tp.tv_nsec = 10000000;
+                b = 1000000000 / tp.tv_nsec;    /* convert to Hz */
+#else
+                b = 100; /* b = 1000000000/10000000 = 100 */
+#endif
+                while (b > 1)
+                        prec--, b >>= 1;
+                G.status.precision = prec;
+        }
+        G.scale = 1;
+        G.firstadj = 1;
+
+        bb_signals((1 << SIGTERM) | (1 << SIGINT), record_signo);
+        bb_signals((1 << SIGPIPE) | (1 << SIGHUP), SIG_IGN);
+}
+
+int ntpd_main(int argc UNUSED_PARAM, char **argv) MAIN_EXTERNALLY_VISIBLE;
+int ntpd_main(int argc UNUSED_PARAM, char **argv)
+{
+        struct globals g;
+        unsigned new_cnt;
+        struct pollfd *pfd;
+        ntp_peer_t **idx2peer;
+
+        memset(&g, 0, sizeof(g));
+        SET_PTR_TO_GLOBALS(&g);
+
+        ntp_init(argv);
+
+        new_cnt = g.peer_cnt;
+        idx2peer = xzalloc(sizeof(void *) * new_cnt);
+#if ENABLE_FEATURE_NTPD_SERVER
+        if (g.listen_fd != -1)
+                new_cnt++;
+#endif
+        pfd = xzalloc(sizeof(pfd[0]) * new_cnt);
+
+        while (!bb_got_signal) {
+                llist_t *item;
+                unsigned i, j, idx_peers;
+                unsigned sent_cnt, trial_cnt;
+                int nfds, timeout;
+                time_t nextaction;
+
+                nextaction = time(NULL) + 3600;
+
+                i = 0;
+#if ENABLE_FEATURE_NTPD_SERVER
+                if (g.listen_fd != -1) {
+                        pfd[0].fd = g.listen_fd;
+                        pfd[0].events = POLLIN;
+                        i++;
+                }
+#endif
+                idx_peers = i;
+                sent_cnt = trial_cnt = 0;
+                for (item = g.ntp_peers; item != NULL; item = item->link) {
+                        ntp_peer_t *p = (ntp_peer_t *) item->data;
+
+                        if (p->next > 0 && p->next <= time(NULL)) {
+                                trial_cnt++;
+                                if (client_query(p) == 0)
+                                        sent_cnt++;
+                        }
+                        if (p->next > 0 && p->next < nextaction)
+                                nextaction = p->next;
+                        if (p->deadline > 0 && p->deadline < nextaction)
+                                nextaction = p->deadline;
+
+                        if (p->deadline > 0 && p->deadline <= time(NULL)) {
+                                char *addr = xmalloc_sockaddr2dotted_noport(&p->lsa->u.sa);
+
+                                timeout = error_interval();
+                                bb_info_msg("no reply from %s received in time, "
+                                                "next query %ds", addr, timeout);
+                                if (p->trustlevel >= TRUSTLEVEL_BADPEER) {
+                                        p->trustlevel /= 2;
+                                        if (p->trustlevel < TRUSTLEVEL_BADPEER)
+                                                bb_info_msg("peer %s now invalid", addr);
+                                }
+                                free(addr);
+
+                                set_next(p, timeout);
+                        }
+
+                        if (p->state == STATE_QUERY_SENT) {
+                                pfd[i].fd = p->query.fd;
+                                pfd[i].events = POLLIN;
+                                idx2peer[i - idx_peers] = p;
+                                i++;
+                        }
+                }
+
+                if (g.settime
+                 && ((trial_cnt > 0 && sent_cnt == 0) || g.peer_cnt == 0)
+                ) {
+                        settime(0);     /* no good peers, don't wait */
+                }
+
+                timeout = nextaction - time(NULL);
+                if (timeout < 0)
+                        timeout = 0;
+
+                if (g.verbose)
+                        bb_error_msg("entering poll %u secs", timeout);
+                nfds = poll(pfd, i, timeout * 1000);
+
+                j = 0;
+#if ENABLE_FEATURE_NTPD_SERVER
+                for (; nfds > 0 && j < idx_peers; j++) {
+                        if (pfd[j].revents & (POLLIN|POLLERR)) {
+                                nfds--;
+                                server_dispatch(pfd[j].fd);
+                        }
+                }
+#endif
+                for (; nfds > 0 && j < i; j++) {
+                        if (pfd[j].revents & (POLLIN|POLLERR)) {
+                                nfds--;
+                                client_dispatch(idx2peer[j - idx_peers]);
+                        }
+                }
+        } /* while (!bb_got_signal) */
+
+        kill_myself_with_sig(bb_got_signal);
+}