mirror of
https://github.com/soypat/lneto.git
synced 2026-07-26 10:38:47 +00:00
Pat Whittingslow
faae7ab076
* fix for #58 * add fixes for both retransmit and fuzz failure found * fix infinite challenge ack due to RST+SYN+FIN corrupt packet in SYNRCV state * fuzz: previous recovery ack path led to infinite transmit * fuzz: calculate CRCs when fuzzing to reduce search space to non-CRC error cases * add local fuzz corpus to tests * add more cases to fuzz corpus
121 lines
3.3 KiB
Go
121 lines
3.3 KiB
Go
package tcp
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func (tcb *ControlBlock) rcvListen(seg Segment) (pending Flags, err error) {
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switch {
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case !seg.Flags.HasAll(FlagSYN):
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err = errExpectedSYN
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}
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if err != nil {
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return 0, err
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}
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// Initialize all connection state:
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tcb.resetSnd(tcb.snd.ISS, seg.WND)
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tcb.resetRcv(tcb.rcv.WND, seg.SEQ)
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// We must respond with SYN|ACK frame after receiving SYN in listen state (three way handshake).
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tcb.pending[0] = synack
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tcb._state = StateSynRcvd
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return synack, nil
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}
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func (tcb *ControlBlock) rcvSynSent(seg Segment) (pending Flags, err error) {
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hasSyn := seg.Flags.HasAny(FlagSYN)
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hasAck := seg.Flags.HasAny(FlagACK)
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switch {
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case !hasSyn:
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err = errExpectedSYN
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case hasAck && seg.ACK != tcb.snd.UNA+1:
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err = errBadSegack
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}
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if err != nil {
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return 0, err
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}
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if hasAck {
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tcb._state = StateEstablished
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pending = FlagACK
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tcb.resetRcv(tcb.rcv.WND, seg.SEQ)
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} else {
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// Simultaneous connection sync edge case.
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pending = synack
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tcb._state = StateSynRcvd
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tcb.resetSnd(tcb.snd.ISS, seg.WND)
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tcb.resetRcv(tcb.rcv.WND, seg.SEQ)
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}
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return pending, nil
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}
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func (tcb *ControlBlock) rcvSynRcvd(seg Segment) (pending Flags, err error) {
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switch {
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case !seg.Flags.HasAll(FlagACK):
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// RFC 9293 §3.10.7.4 step 5: "If the ACK bit is off, drop the segment and return."
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err = errBadSegack
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case seg.ACK != tcb.snd.UNA+1:
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err = errBadSegack
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}
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if err != nil {
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return 0, err
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}
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tcb._state = StateEstablished
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return 0, nil
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}
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func (tcb *ControlBlock) rcvEstablished(seg Segment) (pending Flags, err error) {
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flags := seg.Flags
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dataToAck := seg.DATALEN > 0
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hasFin := flags.HasAny(FlagFIN)
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if dataToAck || hasFin {
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pending = FlagACK
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if hasFin {
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// See Figure 5: TCP Connection State Diagram of RFC 9293.
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tcb._state = StateCloseWait
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// RFC 9293 §3.5: CLOSE-WAIT allows local side to continue sending.
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// Do NOT auto-queue FIN here; user must call Close() explicitly.
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}
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}
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return pending, nil
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}
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func (tcb *ControlBlock) rcvFinWait1(seg Segment) (pending Flags, err error) {
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flags := seg.Flags
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hasFin := flags&FlagFIN != 0
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hasAck := flags&FlagACK != 0
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switch {
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case hasFin && hasAck && seg.ACK == tcb.snd.NXT:
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// Special case: Server sent a FINACK response to our FIN so we enter TimeWait directly.
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// We have to check ACK against send NXT to avoid simultaneous close sequence edge case.
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tcb._state = StateTimeWait
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case hasFin:
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tcb._state = StateClosing
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case hasAck && seg.ACK == tcb.snd.NXT:
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// RFC 9293 §3.10.7.4 step 5: enter FIN-WAIT-2 only if the FIN is now acknowledged.
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tcb._state = StateFinWait2
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case hasAck:
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// Partial ACK: acknowledges data but not the FIN. Stay in FIN-WAIT-1.
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default:
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return 0, errFinwaitExpectedACK
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}
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// Only queue ACK when there is data or FIN to acknowledge.
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// Bare ACKs must not elicit an ACK response; doing so creates an
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// infinite ACK ping-pong when the peer sends challenge ACKs.
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if seg.DATALEN > 0 || hasFin {
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pending = FlagACK
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}
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return pending, nil
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}
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func (tcb *ControlBlock) rcvFinWait2(seg Segment) (pending Flags, err error) {
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if seg.Flags.HasAny(FlagFIN) {
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tcb._state = StateTimeWait
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return FlagACK, nil
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}
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// Bare ACKs and data are valid in FIN-WAIT-2 per RFC 9293 §3.10.7.4.
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// The remote side hasn't closed yet; it may still send data.
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if seg.DATALEN > 0 {
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return FlagACK, nil
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}
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return 0, nil
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}
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