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Mon, 21 Sep 2026 15:26:20 -0700 (PDT) Received: from com-94485.corp.openai.org ([199.47.143.14]) by smtp.gmail.com with ESMTPSA id af79cd13be357-93c19bc6f4bsm30675085a.44.2026.09.21.15.26.18 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Mon, 21 Sep 2026 15:26:20 -0700 (PDT) From: Jeff Jo To: netdev@vger.kernel.org Cc: edumazet@google.com, ncardwell@google.com, kuniyu@google.com, davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, shuah@kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH net 2/2] selftests: net: check timestamp echo after an old ACK Date: Mon, 21 Sep 2026 15:26:12 -0700 Message-ID: <20260921222609.50824-6-jeffjo@openai.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260921222609.50824-4-jeffjo@openai.com> References: <20260921222609.50824-4-jeffjo@openai.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Add a regression test for a gap-filling packet whose acknowledgment has become old. Linux first sends data to the peer. Deliver two peer data packets out of order: the later packet acknowledges Linux's data, while the delayed packet still carries the earlier acknowledgment. Require the final reply to echo the delayed packet's timestamp. Use a large jump in peer timestamps to represent the idle interval. The test checks the echo directly, without waiting for that interval and without packet loss or retransmission. Packetdrill does not currently compare the timestamp-echo field (TSecr), so the packet script alone can pass on a broken kernel. Add a shell wrapper to check all four outgoing timestamp echoes in packetdrill's output. Register the wrapper as the runnable test and keep the packet script as a supporting file. Run the test in a separate network namespace for each of IPv4, IPv6 and IPv4-mapped IPv6. Assisted-by: LLM Signed-off-by: Jeff Jo --- .../selftests/net/packetdrill/Makefile | 5 +- .../net/packetdrill/tcp_old_ack_ts.pkt | 23 ++++++++ .../net/packetdrill/tcp_old_ack_ts.sh | 57 +++++++++++++++++++ 3 files changed, 84 insertions(+), 1 deletion(-) create mode 100644 tools/testing/selftests/net/packetdrill/tcp_old_ack_ts.pkt create mode 100755 tools/testing/selftests/net/packetdrill/tcp_old_ack_ts.sh diff --git a/tools/testing/selftests/net/packetdrill/Makefile b/tools/testing/selftests/net/packetdrill/Makefile index ff54641493e9..4695d8258aa1 100644 --- a/tools/testing/selftests/net/packetdrill/Makefile +++ b/tools/testing/selftests/net/packetdrill/Makefile @@ -7,6 +7,9 @@ TEST_INCLUDES := \ ../../kselftest/ktap_helpers.sh \ # end of TEST_INCLUDES -TEST_PROGS := $(wildcard *.pkt) +# This fixture requires its wrapper to validate outbound timestamp echoes. +TEST_PROGS := $(filter-out tcp_old_ack_ts.pkt,$(wildcard *.pkt)) +TEST_PROGS += tcp_old_ack_ts.sh +TEST_FILES := tcp_old_ack_ts.pkt include ../../lib.mk diff --git a/tools/testing/selftests/net/packetdrill/tcp_old_ack_ts.pkt b/tools/testing/selftests/net/packetdrill/tcp_old_ack_ts.pkt new file mode 100644 index 000000000000..d13f5ea4ac12 --- /dev/null +++ b/tools/testing/selftests/net/packetdrill/tcp_old_ack_ts.pkt @@ -0,0 +1,23 @@ +// SPDX-License-Identifier: GPL-2.0 +// Run through tcp_old_ack_ts.sh: packetdrill alone does not check TSecr. +// An out-of-order segment advances SND.UNA. The gap filler still carries +// its original, older ACK; accepting its data must refresh TS.Recent. +--tcp_ts_tick_usecs=1000 + +`./defaults.sh` + +0.000 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3 ++0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0 ++0 bind(3, ..., ...) = 0 ++0 listen(3, 1) = 0 +0.100 < S 0:0(0) win 20000 ++0 > S. 0:0(0) ack 1 +0.200 < . 1:1(0) ack 1 win 20000 ++0 accept(3, ..., ...) = 4 +0.300 write(4, ..., 17) = 17 ++0 > P. 1:18(17) ack 1 +0.310 < P. 18:35(17) ack 18 win 20000 ++0 > . 18:18(0) ack 1 +0.320 < P. 1:18(17) ack 1 win 20000 ++0 > . 18:18(0) ack 35 ++0 read(4, ..., 34) = 34 diff --git a/tools/testing/selftests/net/packetdrill/tcp_old_ack_ts.sh b/tools/testing/selftests/net/packetdrill/tcp_old_ack_ts.sh new file mode 100755 index 000000000000..4c4534a81e78 --- /dev/null +++ b/tools/testing/selftests/net/packetdrill/tcp_old_ack_ts.sh @@ -0,0 +1,57 @@ +#!/bin/bash +# SPDX-License-Identifier: GPL-2.0 + +cd "$(dirname "$(realpath "$0")")" || exit 1 +source ../../kselftest/ktap_helpers.sh + +if ! command -v packetdrill >/dev/null; then + ktap_skip_all "packetdrill not found in PATH" + exit "$KSFT_SKIP" +fi + +log=$(mktemp) || exit "$KSFT_FAIL" +trap 'rm -f "$log"' EXIT +optargs=() +if [[ -n "${KSFT_MACHINE_SLOW}" ]]; then + optargs+=(--tolerance_usecs=14000) +fi + +ktap_print_header +ktap_set_plan 3 + +for family in ipv4 ipv6 ipv4-mapped-ipv6; do + mtu=1500 + [[ "$family" == ipv6 ]] && mtu=1520 + if ! unshare -n packetdrill --verbose --ip_version="$family" \ + --mtu="$mtu" "${optargs[@]}" tcp_old_ack_ts.pkt >"$log" 2>&1; then + sed 's/^/# /' "$log" + ktap_test_fail "$family: packetdrill" + continue + fi + + # Packetdrill checks packet structure and timing but ignores outbound + # TSecr. Require all four observed echoes, including the gap-filling ACK. + if awk ' + /outbound sniffed packet:/ { + count++ + if (!match($0, /ecr [0-9]+/)) { + bad = 1 + next + } + echoes = echoes (count == 1 ? "" : ",") \ + substr($0, RSTART + 4, RLENGTH - 4) + } + END { + if (bad || count != 4 || echoes != "900,1000,1000,301000") { + print "# unexpected timestamp echoes: " echoes + exit 1 + } + }' "$log"; then + ktap_test_pass "$family" + else + sed 's/^/# /' "$log" + ktap_test_fail "$family: timestamp echo" + fi +done + +ktap_finished -- 2.55.0