Fix printing of NTP poll interval.

The poll value in an NTP packet is a signed integer. For negative values
print the interval as a fraction of second. Also, ignore values outside
of interval (-32, 32).

diff --git a/print-ntp.c b/print-ntp.c
index 0689264ff74bbe8fb31ce051a3bab99612394a11..1593ca6bdb061d536f554d3d0d748e0d1507d91c 100644 (file)
--- a/print-ntp.c
+++ b/print-ntp.c
@@ -116,7 +116,7 @@ struct s_fixedpt {
 struct ntpdata {
        u_char status;          /* status of local clock and leap info */
        u_char stratum;         /* Stratum level */
-       u_char ppoll;           /* poll value */
+       int ppoll:8;            /* poll value */
        int precision:8;
        struct s_fixedpt root_delay;
        struct s_fixedpt root_dispersion;
@@ -170,6 +170,7 @@ struct ntpdata {
 static void p_sfix(netdissect_options *ndo, const struct s_fixedpt *);
 static void p_ntp_time(netdissect_options *, const struct l_fixedpt *);
 static void p_ntp_delta(netdissect_options *, const struct l_fixedpt *, const struct l_fixedpt *);
+static void p_poll(netdissect_options *, register const int);
 
 static const struct tok ntp_mode_values[] = {
     { MODE_UNSPEC,    "unspecified" },
@@ -236,8 +237,10 @@ ntp_print(netdissect_options *ndo,
                bp->stratum,
                tok2str(ntp_stratum_values, (bp->stratum >=2 && bp->stratum<=15) ? "secondary reference" : "reserved", bp->stratum)));
 
-       ND_TCHECK(bp->ppoll);
-       ND_PRINT((ndo, ", poll %u (%us)", bp->ppoll, 1 << bp->ppoll));
+       /* Can't ND_TCHECK bp->ppoll bitfield so bp->stratum + 2 instead */
+       ND_TCHECK2(bp->stratum, 2);
+       ND_PRINT((ndo, ", poll %d", bp->ppoll));
+       p_poll(ndo, bp->ppoll);
 
        /* Can't ND_TCHECK bp->precision bitfield so bp->distance + 0 instead */
        ND_TCHECK2(bp->root_delay, 0);
@@ -425,3 +428,17 @@ p_ntp_delta(netdissect_options *ndo,
        ND_PRINT((ndo, "%s%d.%09d", signbit ? "-" : "+", i, f));
 }
 
+/* Prints polling interval in log2 as seconds or fraction of second */
+static void
+p_poll(netdissect_options *ndo,
+       register const int poll)
+{
+       if (poll <= -32 || poll >= 32)
+               return;
+
+       if (poll >= 0)
+               ND_PRINT((ndo, " (%us)", 1U << poll));
+       else
+               ND_PRINT((ndo, " (1/%us)", 1U << -poll));
+}
+