From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-189.mta1.migadu.com (out-189.mta1.migadu.com [95.215.58.189]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E6BA22264D3 for ; Tue, 21 Apr 2026 01:41:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.189 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776735719; cv=none; b=VoP67WcjikvI7nUPL9hbM+Nd/P/UZKv88tvVQpDAM7VeYCHr0W3vh2wv3qqlKrNf/5Xz/c1wTusW6qAcP0yXize/cXt/Yyj+rVbxMqSNAf5adqy0mXnoxJC8PrCEWsc4gwA1qOUOUP6rO4TS4lKNOozlENglJIOIkex/3XB0HeQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776735719; c=relaxed/simple; bh=xGNRs67avlSqbJqN4bE6daG8ATvnj5UZMJz81YX4ITk=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=YYPIq33dcLDkmZ2OKnqn3rWBYPRe/f1tEhDWO6L+0walshcBZUaoLWZ+iIb5oSAdsjS0TA0nYcZexT6wRD7l8dfV6+EfiNjK5uDwcHnW9zDLOTZhcDoVJjonJ0xuYQIh9dhNo84oy0xNz3KDFGVFjnnIBBUaLtBSVM4j+zJtNY4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=lBWDuWed; arc=none smtp.client-ip=95.215.58.189 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="lBWDuWed" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1776735706; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=n9Wjds9gfYG9hcGpHzgc5qbfR/aZU4udFuWpgj4YHEY=; b=lBWDuWed/5BX3sZXNPoTGgjnSGrfjaNi2AOfMZq1gakbHN+gAhlq7lmRXJTaP91YDeqFxj ARbbJ1hvR4oqHzxVUTq2ClcvCP7lz423I7I1kii7xFpnbiypQgZma6qkmasz2HmJlkI6uW CBCRvdG20A/tIaohIaCzrUYYkLwI2P4= From: Jiayuan Chen To: netdev@vger.kernel.org Cc: Jiayuan Chen , Eric Dumazet , Neal Cardwell , Kuniyuki Iwashima , "David S. Miller" , David Ahern , Jakub Kicinski , Paolo Abeni , Simon Horman , Shuah Khan , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH net v2 0/2] tcp: symmetric challenge ACK for SEG.ACK > SND.NXT Date: Tue, 21 Apr 2026 09:40:59 +0800 Message-ID: <20260421014128.289362-1-jiayuan.chen@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT Commit 354e4aa391ed ("tcp: RFC 5961 5.2 Blind Data Injection Attack Mitigation") quotes RFC 5961 Section 5.2 in full, which requires that any incoming segment whose ACK value falls outside [SND.UNA - MAX.SND.WND, SND.NXT] MUST be discarded and an ACK sent back. Linux currently sends that challenge ACK only on the lower edge (SEG.ACK < SND.UNA - MAX.SND.WND); on the symmetric upper edge (SEG.ACK > SND.NXT) the segment is silently dropped with SKB_DROP_REASON_TCP_ACK_UNSENT_DATA. Patch 1 completes the mitigation by emitting a rate-limited challenge ACK on that branch, reusing tcp_send_challenge_ack() and honouring FLAG_NO_CHALLENGE_ACK for consistency with the lower-edge case. It also updates the existing tcp_ts_recent_invalid_ack.pkt selftest, which drives this exact path, to consume the new challenge ACK so bisect stays clean. Patch 2 adds a new packetdrill selftest that exercises RFC 5961 Section 5.2 on both edges of the acceptable window, filling a gap in the selftests tree (neither edge had dedicated coverage before). --- Changelog ========= v1 -> v2: - Add Reviewed-by tag. - Fold the tcp_ts_recent_invalid_ack.pkt update into patch 1 so that bisect stays clean and the fix is self-contained for backport. - Extend the new selftest to cover both edges of RFC 5961 Section 5.2 (SEG.ACK > SND.NXT and SEG.ACK < SND.UNA - MAX.SND.WND) in a single connection, and rename it to tcp_rfc5961_ack-out-of-window.pkt. Neither edge had explicit packetdrill coverage before. v1: https://lore.kernel.org/netdev/20260420025428.101192-1-jiayuan.chen@linux.dev/ Jiayuan Chen (2): tcp: send a challenge ACK on SEG.ACK > SND.NXT selftests/net: packetdrill: cover RFC 5961 5.2 challenge ACK on both edges net/ipv4/tcp_input.c | 10 ++-- .../tcp_rfc5961_ack-out-of-window.pkt | 46 +++++++++++++++++++ .../packetdrill/tcp_ts_recent_invalid_ack.pkt | 4 +- 3 files changed, 56 insertions(+), 4 deletions(-) create mode 100644 tools/testing/selftests/net/packetdrill/tcp_rfc5961_ack-out-of-window.pkt -- 2.43.0