From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 B65562E3B13; Tue, 15 Jul 2025 13:37:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752586655; cv=none; b=GoMZiuFEXdJU/1Erkcyi+k+ASZDBON/1CtbXKmfTFUGHxTOJ8S4zhzZTrHaFfdEYsyOD93JN9WczuH7cDA9ShOdUb2s+gR6PsFI4fl9Xs2aY3baBI9KraltgN+HEwkV4AOVRkx9HKOqS5Ywn3Oq0zi/SWfAXOhj38QqNEFkKgyc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752586655; c=relaxed/simple; bh=T35nPW0MydciyY67m6fyt3acuKE48fX+yZbF6qlYFT0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=u+Q0Mp/gr+rq8sqC0VkQOBDuP3owfFopRQ+D2EieE0F5zPYloPwkK7wIAImd1T9+BMjtPPF6WX5hDFfCb+beUhqRR6osod6pycVbgcO4eN77gAJvfgw36qtPDAIZ14s8vLJhZ01gDvngnDauHDtYNdit4uN8+D7IAMEBpnbZAkc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=GqnI77ak; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="GqnI77ak" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 465B3C4CEE3; Tue, 15 Jul 2025 13:37:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1752586655; bh=T35nPW0MydciyY67m6fyt3acuKE48fX+yZbF6qlYFT0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=GqnI77akZkQloOrSO5HvFx6GEJyt5R5T4peTwc2xAplV/gBNXkgsn2KNeuKkkRRFn who+idk4ioURZLf6qaZiBaL08gkk64fnNrnU5rlvG4MQuBb3it+5Cs3zrOKo44zu6+ YqIKiSdUX80yFclXAvERUfQi6zImolClNJ6KOyIE= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Georg Kohmann , Jakub Kicinski , WangYuli Subject: [PATCH 5.4 148/148] net: ipv6: Discard next-hop MTU less than minimum link MTU Date: Tue, 15 Jul 2025 15:14:30 +0200 Message-ID: <20250715130806.198532958@linuxfoundation.org> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20250715130800.293690950@linuxfoundation.org> References: <20250715130800.293690950@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Georg Kohmann commit 4a65dff81a04f874fa6915c7f069b4dc2c4010e4 upstream. When a ICMPV6_PKT_TOOBIG report a next-hop MTU that is less than the IPv6 minimum link MTU, the estimated path MTU is reduced to the minimum link MTU. This behaviour breaks TAHI IPv6 Core Conformance Test v6LC4.1.6: Packet Too Big Less than IPv6 MTU. Referring to RFC 8201 section 4: "If a node receives a Packet Too Big message reporting a next-hop MTU that is less than the IPv6 minimum link MTU, it must discard it. A node must not reduce its estimate of the Path MTU below the IPv6 minimum link MTU on receipt of a Packet Too Big message." Drop the path MTU update if reported MTU is less than the minimum link MTU. Signed-off-by: Georg Kohmann Signed-off-by: Jakub Kicinski Signed-off-by: WangYuli Signed-off-by: Greg Kroah-Hartman --- net/ipv6/route.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -2765,7 +2765,8 @@ static void __ip6_rt_update_pmtu(struct if (confirm_neigh) dst_confirm_neigh(dst, daddr); - mtu = max_t(u32, mtu, IPV6_MIN_MTU); + if (mtu < IPV6_MIN_MTU) + return; if (mtu >= dst_mtu(dst)) return;