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JackDoan
44dd2e9ca4
Multi-disciplinary correctness review of the batched tun / GSO-GRO / sendmmsg rework. Each fix has a regression test; the merged tree builds on linux/darwin/openbsd/windows/freebsd/netbsd, vets clean, passes the unit and e2e suites, and is -race clean. Critical: - C1 zero-length inner UDP datagram no longer panics the process (remote DoS): the UDP coalescer routes payLen==0 to passthrough instead of seeding a GSO slot, and WriteGSO skips empty payload iovecs as defense in depth. - C2 segmenter no longer corrupts inner headers when gsoSize < headerLen: the L3+L4 header is snapshotted once and each segment stamped from the copy, replacing the destructive overlapping in-place slide (SegmentTCP + SegmentUDP). High: - H1 applyOuterECN updates the IPv4 header checksum (RFC 1624 incremental) when folding outer CE into the inner ToS, so passthrough packets are no longer dropped by the peer stack. - H2 the GRO reject path caps the borrowed RX segment ([:n:n]) so a reject can no longer overrun into the next coalesced segment's Nebula header. Note: oversized ICMPv6 rejects that need >16B beyond the segment are now refused rather than sent under GRO (safe; see TOFIX.md for the scratch-buffer follow-up). - H3 WriteBatch falls back to per-packet WriteTo for a chunk when writeSockaddr fails, so one bad-family destination costs only its own packet, not the batch. - H4 UserDevice.Readers returns N distinct queue wrappers with private buffers (sharing the pipes) so concurrent readers no longer race/overwrite borrowed packet bytes. - H5 Poll.Close / Offload.Close no longer null t.fd (matching master's tunFile.Close), removing the data race with a concurrent readOne load. Medium/Low: - M1 the UDP GSO 127-segment gate moved from kernel >=5.5 to >=6.9 (the real UDP_MAX_SEGMENTS 64->128 threshold), avoiding EINVAL + per-packet fallback on 5.5-6.8 kernels. - M2 NewMultiQueueReader replays the offload mask newTun actually negotiated instead of the TSO-only mask, so adding a queue no longer disables USO device-wide; the advertised USO capability derives from the same mask. - M3 the shutdown eventfd is closed in pollQueueSet.Close / offloadQueueSet.Close (double-close guarded), fixing the per-lifecycle fd leak. - M4 dual-stack ECN selects the cmsg by address family, not socket family: RX parseRecvCmsg reads both IP_TOS and IPV6_TCLASS; TX writeEntryCmsg stamps IP_TOS for v4/v4-mapped dests and IPV6_TCLASS for v6 (on-host verified). - L1 newPoll no longer closes the fd on failure (matching newOffload), removing the double-close on QueueSet.Add error.