From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:60082 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727534AbeIMSvY (ORCPT ); Thu, 13 Sep 2018 14:51:24 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Eric Dumazet , Geoff Alexander , "David S. Miller" Subject: [PATCH 4.14 002/115] ipv4: tcp: send zero IPID for RST and ACK sent in SYN-RECV and TIME-WAIT state Date: Thu, 13 Sep 2018 15:30:22 +0200 Message-Id: <20180913131823.486289563@linuxfoundation.org> In-Reply-To: <20180913131823.327472833@linuxfoundation.org> References: <20180913131823.327472833@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: 4.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Eric Dumazet [ Upstream commit 431280eebed9f5079553daf003011097763e71fd ] tcp uses per-cpu (and per namespace) sockets (net->ipv4.tcp_sk) internally to send some control packets. 1) RST packets, through tcp_v4_send_reset() 2) ACK packets in SYN-RECV and TIME-WAIT state, through tcp_v4_send_ack() These packets assert IP_DF, and also use the hashed IP ident generator to provide an IPv4 ID number. Geoff Alexander reported this could be used to build off-path attacks. These packets should not be fragmented, since their size is smaller than IPV4_MIN_MTU. Only some tunneled paths could eventually have to fragment, regardless of inner IPID. We really can use zero IPID, to address the flaw, and as a bonus, avoid a couple of atomic operations in ip_idents_reserve() Signed-off-by: Eric Dumazet Reported-by: Geoff Alexander Tested-by: Geoff Alexander Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- net/ipv4/tcp_ipv4.c | 6 ++++++ 1 file changed, 6 insertions(+) --- a/net/ipv4/tcp_ipv4.c +++ b/net/ipv4/tcp_ipv4.c @@ -2468,6 +2468,12 @@ static int __net_init tcp_sk_init(struct if (res) goto fail; sock_set_flag(sk, SOCK_USE_WRITE_QUEUE); + + /* Please enforce IP_DF and IPID==0 for RST and + * ACK sent in SYN-RECV and TIME-WAIT state. + */ + inet_sk(sk)->pmtudisc = IP_PMTUDISC_DO; + *per_cpu_ptr(net->ipv4.tcp_sk, cpu) = sk; }