https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=13955

            Bug ID: 13955
           Summary: UDP Checksum verification not working for 0x0000
                    checksum
           Product: Wireshark
           Version: 2.4.0
          Hardware: x86
                OS: Windows 7
            Status: UNCONFIRMED
          Severity: Normal
          Priority: Low
         Component: Dissection engine (libwireshark)
          Assignee: bugzilla-ad...@wireshark.org
          Reporter: a.robcampb...@gmail.com
  Target Milestone: ---

Created attachment 15750
  --> https://bugs.wireshark.org/bugzilla/attachment.cgi?id=15750&action=edit
pcap with UDP checksum set as 0x0000

Build Information:
Version 2.4.0 (8a3e6bb from master.el6-2.4)

Copyright 1998-2017 Gerald Combs <ger...@wireshark.org> and contributors.
License GPLv2+: GNU GPL version 2 or later
<http://www.gnu.org/licenses/old-licenses/gpl-2.0.html>
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Compiled (64-bit) with GTK+ 3.12.2, with Cairo 1.14.0, with Pango 1.36.8, with
libpcap, without POSIX capabilities, without libnl, with GLib 2.44.1, with zlib
1.2.3, without SMI, without c-ares, with Lua 5.1.4, with GnuTLS 3.5.11, with
Gcrypt 1.4.5, with MIT Kerberos, without GeoIP, without nghttp2, without LZ4,
without Snappy, with libxml2 2.7.6, with PortAudio V19-devel (built Aug  5 2017
01:57:53), without AirPcap, without SBC, without SpanDSP.

Running on Linux 2.6.32-358.el6.x86_64, with       Intel(R) Xeon(R) CPU E3-1230
V2 @ 3.30GHz (with SSE4.2), with 15920 MB of physical memory, with locale
en_US.UTF-8, with libpcap version 1.7.2, with GnuTLS 3.5.11, with Gcrypt 1.4.5,
with zlib 1.2.3.

Built using gcc 6.3.0.
--
In Wireshark 2.2 when UDP traffic came with a 0 checksum (disabled) the
dissector would show the checksum status as "Not Present".

It seems after updating to 2.4 it doesn't matter if I enable or disable UDP
checksum verification it always just shows "Unverified"  If the packet has a
non-zero checksum then it seems to work correctly.  But this change in behavior
for 0x0000 checksum seems incorrect.



Tshark example with UDP and IP checksum verification enabled/disabled to show
the difference in behavior:


With both IP and UDP checksum disabled:

/opt/wireshark/bin/tshark -i eth4 -o udp.check_checksum:FALSE -o
ip.check_checksum:FALSE -V

IP:
Header checksum: 0x6723 [validation disabled]
[Header checksum status: Unverified]

UDP:
Checksum: 0x0000 [unverified]
[Checksum Status: Unverified]


With both IP and UDP checksum enabled:
/opt/wireshark/bin/tshark -i eth4 -o udp.check_checksum:TRUE -o
ip.check_checksum:TRUE -V

IP:
Header checksum: 0x6722 [correct]
[Header checksum status: Good]

UDP:
Checksum: 0x0000 [unverified]
[Checksum Status: Unverified]

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