[bIackr0se]

Description

A DAG Metric Container object of a type scapy has no class for (anything other than types 1 to 8) is read with the wrong header, and the objects after it are lost. Every routing metric or constraint object starts with Type, 16 bits of flags and a Length octet, then Length octets of body (RFC 6551, 2.1). DAGMCObjUnknown read a length octet right after Type, so it took the first flags octet as its length and the following object became part of its data or its payload.

DAGMCObjUnknown now subclasses DAGMCObj, so it has the common header, and its odata holds Length octets of body. olen is kept as a deprecated name of len. A built unknown object now writes the 4-octet header (09 00 00 02 ab cd for type 9 with body ab cd, where 09 02 ab cd was written before), and its default otype is the DAGMCObj default 0 instead of 3 (Hop Count, which has its own class).

from scapy.all import load_contrib
load_contrib("rpl")
load_contrib("rpl_metrics")
from scapy.contrib.rpl_metrics import RPLOptDAGMC
# Hop Count 3, an object of type 9 with an empty body, Link ETX 256
p = RPLOptDAGMC(bytes.fromhex("021003000002000309000000070000020100"))
print([o.name for o in p.options])

Before:

['Hop Count', 'Unknown DAGMC Object Option']

After:

['Hop Count', 'Unknown DAGMC Object Option', 'Link ETX']

tshark 4.6.9 decodes that container as the same three objects. With a non-empty unknown body, tshark reads the same 4-octet header but does not skip the body (the default branch of its metric loop does not advance), so the split there follows the RFC Length. A test is added to test/contrib/rpl.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 80.14%. Comparing base (0e2f6ba) to head (6fe6526).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5299      +/-   ##
==========================================
+ Coverage   80.06%   80.14%   +0.08%     
==========================================
  Files         375      375              
  Lines       98775    98776       +1     
==========================================
+ Hits        79083    79168      +85     
+ Misses      19692    19608      -84     

Files with missing lines	Coverage Δ
scapy/contrib/rpl_metrics.py	100.00% <100.00%> (+1.31%)	⬆️

... and 15 files with indirect coverage changes

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