ntpd: locally bind every peer socket. +22 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

3 files changed, 64 insertions, 28 deletions

diff --git a/include/libbb.h b/include/libbb.h
index 77c9e2888..1194f7eca 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -490,7 +490,8 @@ enum {
 /* Create stream socket, and allocate suitable lsa.
  * (lsa of correct size and lsa->sa.sa_family (AF_INET/AF_INET6))
  * af == AF_UNSPEC will result in trying to create IPv6 socket,
- * and if kernel doesn't support it, IPv4.
+ * and if kernel doesn't support it, fall back to IPv4.
+ * This is useful if you plan to bind to resulting local lsa.
  */
 #if ENABLE_FEATURE_IPV6
 int xsocket_type(len_and_sockaddr **lsap, int af, int sock_type) FAST_FUNC;
diff --git a/libbb/xconnect.c b/libbb/xconnect.c
index b6848ea6f..8a1e1c1b2 100644
--- a/libbb/xconnect.c
+++ b/libbb/xconnect.c
@@ -346,7 +346,7 @@ int FAST_FUNC xsocket_type(len_and_sockaddr **lsap, IF_FEATURE_IPV6(int family,)
                 len = sizeof(struct sockaddr_in6);
         }
 #endif
-        lsa = xzalloc(offsetof(len_and_sockaddr, u.sa) + len);
+        lsa = xzalloc(LSA_LEN_SIZE + len);
         lsa->len = len;
         lsa->u.sa.sa_family = family;
         *lsap = lsa;
diff --git a/networking/ntpd.c b/networking/ntpd.c
index 086b3ea74..12e498d48 100644
--- a/networking/ntpd.c
+++ b/networking/ntpd.c
@@ -12,22 +12,22 @@
 # 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 INTERVAL_QUERY_NORMAL           30      /* sync to peers every n secs */
+#define INTERVAL_QUERY_PATHETIC         60
+#define INTERVAL_QUERY_AGRESSIVE        5
 
-#define TRUSTLEVEL_BADPEER              6       /* bad if *less than* TRUSTLEVEL_BADPEER */
-#define TRUSTLEVEL_PATHETIC             2
-#define TRUSTLEVEL_AGRESSIVE            8
-#define TRUSTLEVEL_MAX                  10
+#define TRUSTLEVEL_BADPEER              6       /* bad if *less than* TRUSTLEVEL_BADPEER */
+#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 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 */
+#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). */
 
@@ -112,7 +112,7 @@ enum {
         MODE_RES2       = 7,    /* reserved for private use */
 };
 
-#define JAN_1970        2208988800UL    /* 1970 - 1900 in seconds */
+#define OFFSET_1900_1970 2208988800UL  /* 1970 - 1900 in seconds */
 
 enum client_state {
         STATE_NONE,
@@ -173,12 +173,12 @@ struct globals {
 #if ENABLE_FEATURE_NTPD_SERVER
         int             listen_fd;
 #endif
+        unsigned        peer_cnt;
         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)
 
@@ -214,11 +214,11 @@ add_peers(const char *s)
 }
 
 static double
-gettime_fp(void)
+gettime1900fp(void)
 {
         struct timeval tv;
         gettimeofday(&tv, NULL); /* never fails */
-        return (tv.tv_sec + 1.0e-6 * tv.tv_usec + JAN_1970);
+        return (tv.tv_sec + 1.0e-6 * tv.tv_usec + OFFSET_1900_1970);
 }
 
 static void
@@ -311,12 +311,43 @@ sendmsg_wrap(int fd,
 static int
 send_query_to_peer(ntp_peer_t *p)
 {
+        // Why do we need to bind()?
+        // See what happens when we don't bind:
+        //
+        // socket(PF_INET, SOCK_DGRAM, IPPROTO_IP) = 3
+        // setsockopt(3, SOL_IP, IP_TOS, [16], 4) = 0
+        // gettimeofday({1259071266, 327885}, NULL) = 0
+        // sendto(3, "xxx", 48, MSG_DONTWAIT, {sa_family=AF_INET, sin_port=htons(123), sin_addr=inet_addr("10.34.32.125")}, 16) = 48
+        // ^^^ we sent it from some source port picked by kernel.
+        // time(NULL)              = 1259071266
+        // write(2, "ntpd: entering poll 15 secs\n", 28) = 28
+        // poll([{fd=3, events=POLLIN}], 1, 15000) = 1 ([{fd=3, revents=POLLIN}])
+        // recv(3, "yyy", 68, MSG_DONTWAIT) = 48
+        // ^^^ this recv will receive packets to any local port!
+        //
+        // Uncomment this and use strace to see it in action:
+#define PROBE_LOCAL_ADDR // { len_and_sockaddr lsa; lsa.len = LSA_SIZEOF_SA; getsockname(p->query.fd, &lsa.u.sa, &lsa.len); }
+
         if (p->query.fd == -1) {
-                p->query.fd = xsocket(p->lsa->u.sa.sa_family, SOCK_DGRAM, 0);
+                int fd, family;
+                len_and_sockaddr *local_lsa;
+
+                family = p->lsa->u.sa.sa_family;
+                //was: p->query.fd = xsocket(family, SOCK_DGRAM, 0);
+                p->query.fd = fd = xsocket_type(&local_lsa, family, SOCK_DGRAM);
+                /* local_lsa has "null" address and port 0 now.
+                 * bind() ensures we have a *particular port* selected by kernel
+                 * and remembered in p->query.fd, thus later recv(p->query.fd)
+                 * receives only packets sent to this port.
+                 */
+                PROBE_LOCAL_ADDR
+                xbind(fd, &local_lsa->u.sa, local_lsa->len);
+                PROBE_LOCAL_ADDR
 #if ENABLE_FEATURE_IPV6
-                if (p->lsa->u.sa.sa_family == AF_INET)
+                if (family == AF_INET)
 #endif
-                        setsockopt(p->query.fd, IPPROTO_IP, IP_TOS, &const_IPTOS_LOWDELAY, sizeof(const_IPTOS_LOWDELAY));
+                        setsockopt(fd, IPPROTO_IP, IP_TOS, &const_IPTOS_LOWDELAY, sizeof(const_IPTOS_LOWDELAY));
+                free(local_lsa);
         }
 
         /*
@@ -335,7 +366,7 @@ send_query_to_peer(ntp_peer_t *p)
 
         p->query.msg.xmttime.int_partl = random();
         p->query.msg.xmttime.fractionl = random();
-        p->query.xmttime = gettime_fp();
+        p->query.xmttime = gettime1900fp();
 
         if (sendmsg_wrap(p->query.fd, /*from:*/ NULL, /*to:*/ &p->lsa->u.sa, /*addrlen:*/ p->lsa->len,
                         &p->query.msg, NTP_MSGSIZE_NOAUTH) == -1) {
@@ -437,7 +468,7 @@ adjtime_wrap(void)
         }
 
         G.firstadj = 0;
-        G.status.reftime = gettime_fp();
+        G.status.reftime = gettime1900fp();
         G.status.stratum++;     /* one more than selected peer */
         G.scale = updated_scale(offset_median);
 
@@ -568,6 +599,10 @@ recv_and_process_peer_pkt(ntp_peer_t *p)
 
         addr = xmalloc_sockaddr2dotted_noport(&p->lsa->u.sa);
 
+        /* We can recvfrom here and check from.IP, but some multihomed
+         * ntp servers reply from their *other IP*.
+         * TODO: maybe we should check at least what we can: from.port == 123?
+         */
         size = recv(p->query.fd, &msg, sizeof(msg), MSG_DONTWAIT);
         if (size == -1) {
                 bb_perror_msg("recv(%s) error", addr);
@@ -583,7 +618,7 @@ recv_and_process_peer_pkt(ntp_peer_t *p)
                 xfunc_die();
         }
 
-        T4 = gettime_fp();
+        T4 = gettime1900fp();
 
         if (size != NTP_MSGSIZE_NOAUTH && size != NTP_MSGSIZE) {
                 bb_error_msg("malformed packet received from %s", addr);
@@ -635,7 +670,7 @@ recv_and_process_peer_pkt(ntp_peer_t *p)
                 goto bail;
         }
         offset->error = (T2 - T1) - (T3 - T4);
-// Can we use (T4 - JAN_1970) instead of time(NULL)?
+// Can we use (T4 - OFFSET_1900_1970) instead of time(NULL)?
         offset->rcvd = time(NULL);
         offset->good = 1;
 
@@ -724,10 +759,10 @@ recv_and_process_client_pkt(void /*int fd*/)
         msg.stratum = G.status.stratum;
         msg.ppoll = query_ppoll;
         msg.precision = G.status.precision;
-        rectime = gettime_fp();
+        rectime = gettime1900fp();
         msg.xmttime = msg.rectime = d_to_lfp(rectime);
         msg.reftime = d_to_lfp(G.status.reftime);
-        //msg.xmttime = d_to_lfp(gettime_fp()); // = msg.rectime
+        //msg.xmttime = d_to_lfp(gettime1900fp()); // = msg.rectime
         msg.orgtime = query_xmttime;
         msg.rootdelay = d_to_sfp(G.status.rootdelay);
         version = (query_status & VERSION_MASK); /* ... >> VERSION_SHIFT - done below instead */