Fix crash in hybrid E2E mode.

Richard Hill reported an occasional NULL pointer deference in
port_delay_request() when in hybrid mode.

	if (p->hybrid_e2e) {
		struct ptp_message *dst = TAILQ_FIRST(&p->best->messages);
		msg->address = dst->address;
		...
	}

The code assumes that the p->best->messages list can't be empty
because:

    The function, port_delay_request(), is called only when
    FD_DELAY_TIMER expires.  That timer is only set by the function,
    port_set_delay_tmo(), which is called:

    1. from process_delay_resp(), but only when state is UNCALIBRATED
       or SLAVE.

    2. from port_e2e_transition(), but only when state is UNCALIBRATED
       or SLAVE.

    Looking at handle_state_decision_event(), a port can only enter
    UNCALIBRATED or SLAVE when it has a valid foreign master record,
    ie p->best->messages is not null.

    A port also only clears p->best->messages when it leaves
    UNCALIBRATED or SLAVE, at which point the FD_DELAY_TIMER is also
    cleared.

*However* the p->best->messages list *can* be empty if the
FD_ANNOUNCE_TIMER and the FD_DELAY_TIMER expire at the same time.  In
this case, the poll() call indicates events on both file descriptors.
The announce timeout is handled like this:

	case FD_ANNOUNCE_TIMER:
        case FD_SYNC_RX_TIMER:
                if (p->best)
                        fc_clear(p->best);

So then the port_delay_request() call de-references the null
TAILQ_FIRST message pointer.

This patch fixes the issue by re-ordering the timer file descriptors
within the polling list.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Reported-by: Richard Hill <plonta@gmx.de>

fd.h

@@ -22,12 +22,18 @@
 
 #define N_TIMER_FDS 6
 
+/*
+ * The order matters here.  The DELAY timer must appear before the
+ * ANNOUNCE and SYNC_RX timers in order to correctly handle the case
+ * when the DELAY timer and one of the other two expire during the
+ * same call to poll().
+ */
 enum {
 	FD_EVENT,
 	FD_GENERAL,
+	FD_DELAY_TIMER,
 	FD_ANNOUNCE_TIMER,
 	FD_SYNC_RX_TIMER,
-	FD_DELAY_TIMER,
 	FD_QUALIFICATION_TIMER,
 	FD_MANNO_TIMER,
 	FD_SYNC_TX_TIMER,
@@ -35,6 +41,8 @@ enum {
 	N_POLLFD,
 };
 
+#define FD_FIRST_TIMER FD_DELAY_TIMER
+
 struct fdarray {
 	int fd[N_POLLFD];
 };

port.c

@@ -1545,7 +1545,7 @@ void port_disable(struct port *p)
 	transport_close(p->trp, &p->fda);
 
 	for (i = 0; i < N_TIMER_FDS; i++) {
-		close(p->fda.fd[FD_ANNOUNCE_TIMER + i]);
+		close(p->fda.fd[FD_FIRST_TIMER + i]);
 	}
 
 	/* Keep rtnl socket to get link status info. */
@@ -1590,7 +1590,7 @@ int port_initialize(struct port *p)
 		goto no_tropen;
 
 	for (i = 0; i < N_TIMER_FDS; i++) {
-		p->fda.fd[FD_ANNOUNCE_TIMER + i] = fd[i];
+		p->fda.fd[FD_FIRST_TIMER + i] = fd[i];
 	}
 
 	if (port_set_announce_tmo(p))
@@ -1628,7 +1628,7 @@ static int port_renew_transport(struct port *p)
 		return 0;
 	}
 	transport_close(p->trp, &p->fda);
-	port_clear_fda(p, FD_ANNOUNCE_TIMER);
+	port_clear_fda(p, FD_FIRST_TIMER);
 	res = transport_open(p->trp, p->iface, &p->fda, p->timestamping);
 	/* Need to call clock_fda_changed even if transport_open failed in
 	 * order to update clock to the now closed descriptors. */