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Miller" Cc: Kuniyuki Iwashima , Simon Horman , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH net-next 0/2] tcp: keep the route window on the SYN when SO_RCVBUF is set before connect Date: Sun, 11 Oct 2026 16:46:04 +0530 Message-ID: <20261011111606.14753-1-jain.sm@gmail.com> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit v1 was a single [PATCH net] with only the fix. Eric Dumazet pointed out that the changelog overstated the effect (TCP_WINDOW_CLAMP does not persist past the first data segments), that "no window scaling" was inaccurate (the option is still sent, with a shift of 0), and asked for a packetdrill test and for the series to target net-next. This v2 rewrites the changelog accordingly, leads with the common SO_RCVBUF-before-connect / listener case, adds a packetdrill test, and is based on net-next. Patch 1 is the fix: setsockopt(SO_RCVBUF) must not write tp->window_clamp while the socket is in TCP_CLOSE or TCP_LISTEN, so that tcp_connect_init() and tcp_openreq_init_rwin() still apply the route window metric (RTAX_WINDOW) and the defaults to the SYN / SYN-ACK window and window scale. Patch 2 adds a packetdrill test: with "window 4096" on the route to the peer and SO_RCVBUF set before connect(), the SYN must advertise the route-clamped window and window scale 0. On an unpatched net-next kernel the SYN carries win 65535, wscale 5; with patch 1 it carries win 2920, wscale 0. Changes since v1 (single [PATCH net]): - changelog: say the patch restores the SYN/SYN-ACK window and window scale, not a persistent clamp; note that since a2cbb1603943 tcp_measure_rcv_mss() recomputes window_clamp from sk_rcvbuf anyway. - changelog: "wscale 0 (option still sent, shift 0)" instead of "no window scaling"; lead with the SO_RCVBUF-before-connect / listener case. - add the packetdrill selftest (patch 2). - retarget from net to net-next. Shashank Mohan Jain (2): tcp: don't set window_clamp from SO_RCVBUF before the socket is connected selftests/net/packetdrill: test SO_RCVBUF before connect keeps route window net/ipv4/tcp.c | 8 ++++++ .../tcp_rcvbuf_before_connect_window.pkt | 27 +++++++++++++++++++ 2 files changed, 35 insertions(+) create mode 100644 tools/testing/selftests/net/packetdrill/tcp_rcvbuf_before_connect_window.pkt base-commit: d8674294aefef02266c4d47ad10131f1bffbe534 -- 2.43.0