drsuapi: drop writeDSNAME structLen +2 cargo-cult#34
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MS-DRSR 4.1.4.1.1 specifies structLen as the exact byte size, rounded to a 4-byte boundary. Impacket carries a "+2" on top of the round-up that no part of the spec or wire trace justifies; AD is forgiving in practice but a stricter implementation could reject. Keep just the alignment round, drop the unexplained 2 extra bytes. This is the last open item from #32. Request-side change with no parser-side regression detection, so it was held out of #33 pending lab verification. Verified end-to-end against the GOAD lab (sevenkingdoms.local forest root + north.sevenkingdoms.local child domain): secretsdump --just-dc-ntlm exercises DsBind, DsDomainControllerInfo, DsCrackNames, and DsGetNCChanges in sequence and returns success on both domains. Output is byte-for-byte identical to the pre-fix dumps captured before removing the +2. Closes #32.
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Summary
Closes the final item from #32. MS-DRSR 4.1.4.1.1 specifies
structLenas the exact byte size of the DSNAME structure, rounded up to a 4-byte boundary. The previous code applied the round-up and then added 2 more bytes "per Impacket" — neither the spec nor the wire trace justifies the extra 2 bytes. AD is forgiving in practice but a stricter implementation could reject. With the+2in place the advertisedstructLenwas systematically congruent to 2 mod 4 (i.e. off the alignment) and 2 bytes larger than the actual serialized payload. The trailingwritten % 4round at the end ofwriteDSNAMEalready handles wire-side NDR alignment, so dropping the+2doesn't leave a gap.Verification
Item 3 was held out of #33 because it's request-side and there's no parser-side regression detection. Verified end-to-end against the GOAD lab:
sevenkingdoms.local, kingslanding @ 10.10.10.10) —secretsdump --just-dc-ntlmexercisesDsBind→DsDomainControllerInfo→DsCrackNames(viaGetDomainDN) →DsGetNCChanges. All four returned success; full account dump captured.north.sevenkingdoms.local, winterfell @ 10.10.10.11) — same four-RPC sequence, full dump captured.+2in place (the same dumps from drsuapi: tighten V6 parser allocations, fix RDN unescape, drop dead helper #33's lab pass).Test plan
go build ./...go vet ./pkg/dcerpc/drsuapi/...go test ./pkg/dcerpc/drsuapi/...secretsdump --just-dc-ntlmagainst forest root (sevenkingdoms.local)secretsdump --just-dc-ntlmagainst child domain (north.sevenkingdoms.local)Closes #32.