rsync - May 2014 - [Bug 10643] New: cmp_time() returns incorrect result due to integer overflow

https://bugzilla.samba.org/show_bug.cgi?id=10643

           Summary: cmp_time() returns incorrect result due to integer
                    overflow
           Product: rsync
           Version: 3.1.1
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P5
         Component: core
        AssignedTo: wayned at samba.org
        ReportedBy: William.Hooper at ntc.com
         QAContact: rsync-qa at samba.org


Created attachment 9998
  --> https://bugzilla.samba.org/attachment.cgi?id=9998
Patch to change cmp_time() to use difftime(3)

In rsync-3.1.1pre1, if time_t is a signed integer, the cmp_time() function in
util.c returns an incorrect result if one of its arguments is far in the past
and the other is close to the present or in the future. This causes rsync to
treat the times as equal when they actually differ by many years.

For example, if time_t is a 32-bit signed integer, when cmp_time() is called
with the following times (in either order):

   1401411396   (May 30 00:56:36 2014)
  -2146953600   (Dec 20 00:00:00 1901)

it returns 0, indicating that the times should be treated as the same, not the
expected -1 or +1, indicating that the times are different.

This behavior is apparently caused by integer overflows in the subtraction
operations in the conditional expressions on lines 1322 and 1326 of util.c. The
difference between two signed integer values can be greater than can be
represented in a signed integer of the same size.

Attached is a patch to change cmp_time() to use the difftime() library
function, available in C89 and later, to compute the difference between the
time_t values.

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https://bugzilla.samba.org/show_bug.cgi?id=10643

Wayne Davison <wayned at samba.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED

--- Comment #1 from Wayne Davison <wayned at samba.org> 2014-06-16
01:02:30 UTC ---
To avoid having to figure out if a system has difftime(), I just fixed the
logic in cmp_time() to work even if things overflow.  Thanks for noticing the
wacko result and diagnosing the cause.

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