From: Miroslav Lichvar <mlichvar@redhat.com>
Date: Mon, 22 Nov 2021 10:39:29 +0000 (+0100)
Subject: ntp: add special value to experimental root delay/disp
X-Git-Tag: 4.2-pre1~19
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e7c2f71cea2f9eb8e6d107baa5908a546de25805;p=thirdparty%2Fchrony.git

ntp: add special value to experimental root delay/disp

The maximum value of the new 32-bit fields is slightly less than 16,
which can cause the NTP test #7 to pass for a server which has a zero
root delay but maximum root dispersion.

Interpret the maximum value as the maximum value of the original 32-bit
fields (~65536.0 seconds) for better compatibility with NTPv4.
---

diff --git a/test/unit/util.c b/test/unit/util.c
index 982a0ce8..4d7a4e8c 100644
--- a/test/unit/util.c
+++ b/test/unit/util.c
@@ -515,7 +515,9 @@ test_unit(void)
   TEST_CHECK(UTI_DoubleToNtp32f28(8.0) == htonl(0x80000000));
   TEST_CHECK(UTI_DoubleToNtp32f28(16.0) == htonl(0xffffffff));
   TEST_CHECK(UTI_DoubleToNtp32f28(16.1) == htonl(0xffffffff));
+  TEST_CHECK(UTI_DoubleToNtp32f28(16.1) == htonl(0xffffffff));
 
+  TEST_CHECK(UTI_Ntp32f28ToDouble(htonl(0xffffffff)) >= 65535.999);
   for (i = 0; i < 100000; i++) {
     UTI_GetRandomBytes(&ntp32_ts, sizeof (ntp32_ts));
     TEST_CHECK(UTI_DoubleToNtp32(UTI_Ntp32ToDouble(ntp32_ts)) == ntp32_ts);
diff --git a/util.c b/util.c
index 1f664801..69f523d7 100644
--- a/util.c
+++ b/util.c
@@ -640,7 +640,13 @@ UTI_DoubleToNtp32(double x)
 double
 UTI_Ntp32f28ToDouble(NTP_int32 x)
 {
-  return ntohl(x) / (double)(1U << 28);
+  uint32_t r = ntohl(x);
+
+  /* Maximum value is special */
+  if (r == 0xffffffff)
+    return MAX_NTP_INT32;
+
+  return r / (double)(1U << 28);
 }
 
 /* ================================================== */