[openssl/openssl] b41c1b: quic: reject ACK of an unsent packet number

  Branch: refs/heads/openssl-3.5
  Home:   https://github.com/openssl/openssl
  Commit: b41c1bc191299c74949b631c54b376c2485b7855
      https://github.com/openssl/openssl/commit/b41c1bc191299c74949b631c54b376c2485b7855
  Author: Haiyang Huang <[email protected]>
  Date:   2026-08-11 (Tue, 11 Aug 2026)

  Changed paths:
    M ssl/quic/quic_ackm.c
    M ssl/quic/quic_rx_depack.c
    M test/quic_ackm_test.c
    M test/quic_multistream_test.c

  Log Message:
  -----------
  quic: reject ACK of an unsent packet number

ossl_ackm_on_rx_ack_frame() stored ack_ranges[0].end into
largest_acked_pkt[pkt_space] without checking it against the highest
packet number actually sent in that space. Because largest_acked_pkt
only ever increases and drives loss detection, an ACK acknowledging a
packet number that was never sent (up to 2**62 - 1) pins the value and
causes every in-flight and subsequently-sent packet to be declared lost,
permanently corrupting loss detection for the connection.

RFC 9000 s. 13.1 recommends treating an acknowledgment for a packet the
endpoint did not send as a connection error of type PROTOCOL_VIOLATION,
where it can be detected.

Reject any ACK whose largest acknowledged packet number exceeds the
highest packet number sent in that space; the bound, highest_sent, is
already tracked. The depacketiser raises PROTOCOL_VIOLATION when the ACK
manager rejects the frame.

Update the QUIC tests for the new behaviour: cases 7 and 8 now assert
rejection, case 14 covers the 2**62 - 1 boundary, two pre-existing
fixtures that acknowledged one packet past the highest sent are
corrected, and the "fictional PN" script now expects a PROTOCOL_VIOLATION
close.

Fixes: fa4e92a70a5f "QUIC ACK Manager, Statistics Manager and Congestion Control API"
Assisted-by: Claude:claude-opus-4.6

Reviewed-by: Saša Nedvědický <[email protected]>
Reviewed-by: Tomas Mraz <[email protected]>
MergeDate: Tue Jun 23 16:36:27 2026
Reviewed-by: Frederik Wedel-Heinen <[email protected]>
Reviewed-by: Nikola Pajkovsky <[email protected]>
(Merged from https://github.com/openssl/openssl/pull/32208)



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