[PATCH v2 0/2] tcp: exclude old ACKs from fast path

[Inbal Schussheim]

Exclude ACKs outside [SND.UNA, SND.NXT] from TCP header prediction so
that they fall through to the slow path, where ACK
validation is applied.

Add a packetdrill test for a data segment carrying an
excessively old ACK. The test fails on the unpatched kernel and passes
with the fix.

Changes in v2:

- Exclude all ACKs before SND.UNA from header prediction instead of
  duplicating old-ACK validation in the fast path.
- Cover pure ACKs as well as data-carrying segments.
- Let the existing slow path handle validation and challenge ACKs.
- Remove the packetdrill reproducer from the commit message; add the
  packetdrill test separately.

Inbal Schussheim (2):
  tcp: exclude old ACKs from tcp fast path
  selftests: net: packetdrill: test exclusion of old ACK from TCP fast
    path

 net/ipv4/tcp_input.c                          |  2 +-
 .../tcp_rfc5961_reject-old-ack.pkt            | 23 +++++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/net/packetdrill/tcp_rfc5961_reject-old-ack.pkt

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2.43.0