[bIackr0se]

Description

IE_GSNAddress and IE_CharginGatewayAddress condition their address fields on length == 4 and length == 16 (gtp.py#L658-L665, gtp.py#L891-L899). With the default length=None, IE_GSNAddress(ipv4_address="10.0.0.1") builds Length 0 and no address, and so do the GSN Address IEs in the default GTPUpdatePDPContextRequest and GTPPDUNotificationRequest. IE_CharginGatewayAddress defaults to length=4, so an ipv6_address is replaced by 127.0.0.1. 3GPP TS 29.060 sections 7.7.32 and 7.7.44 give Length 4 for IPv4 and 16 for IPv6.

This PR applies the IE_IP_Address design from #5278 to both IEs: one address MultipleTypeField, with ipv4_address and ipv6_address kept as deprecated names.

from scapy.all import raw, load_contrib
load_contrib("gtp")
from scapy.contrib.gtp import IE_GSNAddress, IE_CharginGatewayAddress
print(raw(IE_GSNAddress(ipv4_address="10.0.0.1")).hex(" "))
print(raw(IE_GSNAddress(ipv6_address="2001:db8::1")).hex(" "))
print(raw(IE_CharginGatewayAddress(ipv6_address="2001:db8::2")).hex(" "))

Before:

85 00 00
85 00 00
fb 00 04 7f 00 00 01

After:

85 00 04 0a 00 00 01
85 00 10 20 01 0d b8 00 00 00 00 00 00 00 00 00 00 00 01
fb 00 10 20 01 0d b8 00 00 00 00 00 00 00 00 00 00 00 02

tshark 4.6.9 decodes these addresses after the change and reports "unknown type or wrong length" for the GSN Address IEs before it. As with #5278, a Length other than 4 or 16 now reads that many octets into address, so the next IE stays aligned. Tests are added to test/contrib/gtp.uts.

This message was written with the help of AI (Claude Opus 5.5).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.16%. Comparing base (df72ff3) to head (b3ace4f).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5290      +/-   ##
==========================================
+ Coverage   80.07%   80.16%   +0.08%     
==========================================
  Files         375      375              
  Lines       98740    98752      +12     
==========================================
+ Hits        79065    79161      +96     
+ Misses      19675    19591      -84     

Files with missing lines	Coverage Δ
scapy/contrib/gtp.py	93.85% <100.00%> (+0.03%)	⬆️

... and 17 files with indirect coverage changes

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[gpotter2]

Thanks for the PR