From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DEA5FC433DF for ; Wed, 1 Jul 2020 12:19:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BBAD620760 for ; Wed, 1 Jul 2020 12:19:49 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.b="sG39cyUa" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730562AbgGAMTq (ORCPT ); Wed, 1 Jul 2020 08:19:46 -0400 Received: from mail.efficios.com ([167.114.26.124]:50208 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730063AbgGAMTq (ORCPT ); Wed, 1 Jul 2020 08:19:46 -0400 Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id A354A2CD6E7; Wed, 1 Jul 2020 08:19:42 -0400 (EDT) Received: from mail.efficios.com ([127.0.0.1]) by localhost (mail03.efficios.com [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id 2FJk1-xrNm4E; Wed, 1 Jul 2020 08:19:42 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id 4A8AD2CD572; Wed, 1 Jul 2020 08:19:42 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com 4A8AD2CD572 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1593605982; bh=YXoF5PUmxWXzp2LmHg4Wgh13FE3P4zYYtwXrHzfqq3Y=; h=Date:From:To:Message-ID:MIME-Version; b=sG39cyUal96uC6mVyehepRr4pm1czvIHFsUGOd53n/dOX2qwq+HAY1AYOll43FKKK aLuZoGCMngJoRBScUGKntC5NT2sInb2Eh8EG2FT8QXfZVR4/kojqte6y6KA83fzKVL WFgTHC3EULUyItFTiDhFMGZgVgN9jjWwoNoge6dDRMkSxcq/587EsdxMPEJi9RtYul PPSZGqHYpt3+gngE0EmiaxVZr6Gx1mJQeLWvBcW2zWhTOWd/bZ9RyHfuA9YUMzNiNU nW+fcJm7c+MLyrTZaCM/0+juW8g5yPVmeI9N43OiiPOGCGvDyxqG6ceJ2/RfFq/OlS K5lGL6JG5BUow== X-Virus-Scanned: amavisd-new at efficios.com Received: from mail.efficios.com ([127.0.0.1]) by localhost (mail03.efficios.com [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id 8b3X4FPEW-Fj; Wed, 1 Jul 2020 08:19:42 -0400 (EDT) Received: from mail03.efficios.com (mail03.efficios.com [167.114.26.124]) by mail.efficios.com (Postfix) with ESMTP id 3BB862CD987; Wed, 1 Jul 2020 08:19:42 -0400 (EDT) Date: Wed, 1 Jul 2020 08:19:42 -0400 (EDT) From: Mathieu Desnoyers To: Eric Dumazet Cc: Herbert Xu , "David S. Miller" , Linus Torvalds , linux-kernel , netdev , Yuchung Cheng , Jonathan Rajotte-Julien Message-ID: <338284155.18826.1593605982156.JavaMail.zimbra@efficios.com> In-Reply-To: References: <20200701020211.GA6875@gondor.apana.org.au> <20200701022241.GA7167@gondor.apana.org.au> <20200701025843.GA7254@gondor.apana.org.au> Subject: Re: [regression] TCP_MD5SIG on established sockets MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [167.114.26.124] X-Mailer: Zimbra 8.8.15_GA_3945 (ZimbraWebClient - FF77 (Linux)/8.8.15_GA_3928) Thread-Topic: TCP_MD5SIG on established sockets Thread-Index: DVmdKoIdfg8hNWwm7FgIos17cuNI0g== Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org ----- On Jun 30, 2020, at 11:36 PM, Eric Dumazet edumazet@google.com wrote: > On Tue, Jun 30, 2020 at 7:59 PM Herbert Xu wrote: >> >> On Tue, Jun 30, 2020 at 07:30:43PM -0700, Eric Dumazet wrote: >> > >> > I made this clear in the changelog, do we want comments all over the places ? >> > Do not get me wrong, we had this bug for years and suddenly this is a >> > big deal... >> >> I thought you were adding a new pair of smp_rmb/smp_wmb. If they >> already exist in the code then I agree it's not a big deal. But >> adding a new pair of bogus smp_Xmb's is bad for maintenance. >> > > If I knew so many people were excited about TCP / MD5, I would have > posted all my patches on lkml ;) > > Without the smp_wmb() we would still need something to prevent KMSAN > from detecting that we read uninitialized bytes, > if key->keylen is increased. (initial content of key->key[] is garbage) > > Something like this : The approach below looks good to me, but you'll also need to annotate both tcp_md5_hash_key and tcp_md5_do_add with __no_kcsan or use data_race(expr) to let the concurrency sanitizer know that there is a known data race which is there on purpose (triggered by memcpy in tcp_md5_do_add and somewhere within crypto_ahash_update). See Documentation/dev-tools/kcsan.rst for details. Thanks, Mathieu > > diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c > index > f111660453241692a17c881dd6dc2910a1236263..c3af8180c7049d5c4987bf5c67e4aff2ed6967c9 > 100644 > --- a/net/ipv4/tcp.c > +++ b/net/ipv4/tcp.c > @@ -4033,11 +4033,9 @@ EXPORT_SYMBOL(tcp_md5_hash_skb_data); > > int tcp_md5_hash_key(struct tcp_md5sig_pool *hp, const struct > tcp_md5sig_key *key) > { > - u8 keylen = key->keylen; > + u8 keylen = READ_ONCE(key->keylen); /* paired with > WRITE_ONCE() in tcp_md5_do_add */ > struct scatterlist sg; > > - smp_rmb(); /* paired with smp_wmb() in tcp_md5_do_add() */ > - > sg_init_one(&sg, key->key, keylen); > ahash_request_set_crypt(hp->md5_req, &sg, NULL, keylen); > return crypto_ahash_update(hp->md5_req); > diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c > index > 99916fcc15ca0be12c2c133ff40516f79e6fdf7f..0d08e0134335a21d23702e6a5c24a0f2b3c61c6f > 100644 > --- a/net/ipv4/tcp_ipv4.c > +++ b/net/ipv4/tcp_ipv4.c > @@ -1114,9 +1114,13 @@ int tcp_md5_do_add(struct sock *sk, const union > tcp_md5_addr *addr, > /* Pre-existing entry - just update that one. */ > memcpy(key->key, newkey, newkeylen); > > - smp_wmb(); /* pairs with smp_rmb() in tcp_md5_hash_key() */ > + /* Pairs with READ_ONCE() in tcp_md5_hash_key(). > + * Also note that a reader could catch new key->keylen value > + * but old key->key[], this is the reason we use __GFP_ZERO > + * at sock_kmalloc() time below these lines. > + */ > + WRITE_ONCE(key->keylen, newkeylen); > > - key->keylen = newkeylen; > return 0; > } > > @@ -1132,7 +1136,7 @@ int tcp_md5_do_add(struct sock *sk, const union > tcp_md5_addr *addr, > rcu_assign_pointer(tp->md5sig_info, md5sig); > } > > - key = sock_kmalloc(sk, sizeof(*key), gfp); > + key = sock_kmalloc(sk, sizeof(*key), gfp | __GFP_ZERO); > if (!key) > return -ENOMEM; > if (!tcp_alloc_md5sig_pool()) { -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com