[ntp:bugs] [Bug 1245] New: Broken xmt time sent in fast_xmit() of 4.2.5p187

[Martin Burnicki via the NTP Bugzilla]

http://bugs.ntp.org/1245

           Summary: Broken xmt time sent in fast_xmit() of 4.2.5p187
           Product: ntp
           Version: 4.2.5
          Platform: Other
        OS/Version: N/A
            Status: NEW
          Severity: normal
          Priority: P3
         Component: ntpd
        AssignedTo: stenn at ntp.org
        ReportedBy: burnicki at ntp.org
                CC: bugs at ntp.org


While running some tests to verify the fix for bug #1242 I stumbled across a 
problem which has been introduced in p187.

The symptom was that ntpd p187 sends reply packets where the xmt timestamp is 
broken. This did not happen in p186.

A quick look at the changes for p187 shows that in ntp_proto.c, in the 
fast_xmit() function in line 3252 (at the end of the "else" part after "if 
(flags & RES_KOD)" a line has been added to set the xmt timestamp in the reply 
package from the xmt_tx variable:

HTONL_FP(&xmt_tx, &xpkt.xmt)

However, the xmt_tx variable is a local variable which has not been set in the 
execution part before. get_systime(&xmt_tx) needs to be called before, similar 
to other execution paths in fast_xmit().

The xmt timestamp in some of the reply packets looks OK at the first glance, so 
the bug is not so obvious. I think this is when some previous value on the 
stack has not been overwritten since an earlier all. 

Martin

-- 
Martin Burnicki <burnicki at ntp.org>



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