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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4D01BC6FD18 for ; Thu, 20 Apr 2023 03:30:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233398AbjDTDah (ORCPT ); Wed, 19 Apr 2023 23:30:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38074 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233076AbjDTDac (ORCPT ); Wed, 19 Apr 2023 23:30:32 -0400 Received: from smtp-fw-6002.amazon.com (smtp-fw-6002.amazon.com [52.95.49.90]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 27DA740D4 for ; Wed, 19 Apr 2023 20:30:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1681961431; x=1713497431; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=qnlhNfQD67yagxhtpdwnqtsh8YA4vw2SdZcU8Er9pVU=; b=G0pYeWxp1tYdd5obhSH1mme3ZHEvNqESxV6Dd5mgZlP2zXGTgt1YDvwe LSt0A2PrTBya6asEwbnYVun0mrAfAt80+jGHl0Cx62aj14aUC5mAXKd58 BO9rC7DdXOkKC1nitJ3FJms3fITd9UyUE/g7/UkzRqm+okKBZGiejQZIC Y=; X-IronPort-AV: E=Sophos;i="5.99,211,1677542400"; d="scan'208";a="320473140" Received: from iad12-co-svc-p1-lb1-vlan3.amazon.com (HELO email-inbound-relay-pdx-2b-m6i4x-f253a3a3.us-west-2.amazon.com) ([10.43.8.6]) by smtp-border-fw-6002.iad6.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Apr 2023 03:30:27 +0000 Received: from EX19MTAUWB002.ant.amazon.com (pdx1-ws-svc-p6-lb9-vlan2.pdx.amazon.com [10.236.137.194]) by email-inbound-relay-pdx-2b-m6i4x-f253a3a3.us-west-2.amazon.com (Postfix) with ESMTPS id D245580EF5; Thu, 20 Apr 2023 03:30:25 +0000 (UTC) Received: from EX19D004ANA001.ant.amazon.com (10.37.240.138) by EX19MTAUWB002.ant.amazon.com (10.250.64.231) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1118.25; Thu, 20 Apr 2023 03:30:25 +0000 Received: from 88665a182662.ant.amazon.com (10.106.100.17) by EX19D004ANA001.ant.amazon.com (10.37.240.138) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.1118.26; Thu, 20 Apr 2023 03:30:22 +0000 From: Kuniyuki Iwashima To: CC: , , , , , , , , Subject: Re: [PATCH v2 net] tcp/udp: Fix memleaks of sk and zerocopy skbs with TX timestamp. Date: Wed, 19 Apr 2023 20:30:13 -0700 Message-ID: <20230420033013.45693-1-kuniyu@amazon.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <6440a157b6113_128322942d@willemb.c.googlers.com.notmuch> References: <6440a157b6113_128322942d@willemb.c.googlers.com.notmuch> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-Originating-IP: [10.106.100.17] X-ClientProxiedBy: EX19D037UWB004.ant.amazon.com (10.13.138.84) To EX19D004ANA001.ant.amazon.com (10.37.240.138) Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org From: Willem de Bruijn Date: Wed, 19 Apr 2023 22:20:07 -0400 > Kuniyuki Iwashima wrote: > > From: Willem de Bruijn > > Date: Wed, 19 Apr 2023 13:50:47 -0400 > > > Kuniyuki Iwashima wrote: > > > > From: Willem de Bruijn > > > > Date: Wed, 19 Apr 2023 10:16:07 -0400 > > > > > Eric Dumazet wrote: > > > > > > On Tue, Apr 18, 2023 at 9:25 PM Kuniyuki Iwashima wrote: > > > > > > > > > > > > > > From: Eric Dumazet > > > > > > > Date: Tue, 18 Apr 2023 21:04:32 +0200 > > > > > > > > On Tue, Apr 18, 2023 at 8:44 PM Kuniyuki Iwashima wrote: > > > > > > > > > > > > > > > > > > From: Eric Dumazet > > > > > > > > > Date: Tue, 18 Apr 2023 20:33:44 +0200 > > > > > > > > > > On Tue, Apr 18, 2023 at 8:09 PM Kuniyuki Iwashima wrote: > > > > > > > > > > > > > > > > > > > > > > syzkaller reported [0] memory leaks of an UDP socket and ZEROCOPY > > > > > > > > > > > skbs. We can reproduce the problem with these sequences: > > > > > > > > > > > > > > > > > > > > > > sk = socket(AF_INET, SOCK_DGRAM, 0) > > > > > > > > > > > sk.setsockopt(SOL_SOCKET, SO_TIMESTAMPING, SOF_TIMESTAMPING_TX_SOFTWARE) > > > > > > > > > > > sk.setsockopt(SOL_SOCKET, SO_ZEROCOPY, 1) > > > > > > > > > > > sk.sendto(b'', MSG_ZEROCOPY, ('127.0.0.1', 53)) > > > > > > > > > > > sk.close() > > > > > > > > > > > > > > > > > > > > > > sendmsg() calls msg_zerocopy_alloc(), which allocates a skb, sets > > > > > > > > > > > skb->cb->ubuf.refcnt to 1, and calls sock_hold(). Here, struct > > > > > > > > > > > ubuf_info_msgzc indirectly holds a refcnt of the socket. When the > > > > > > > > > > > skb is sent, __skb_tstamp_tx() clones it and puts the clone into > > > > > > > > > > > the socket's error queue with the TX timestamp. > > > > > > > > > > > > > > > > > > > > > > When the original skb is received locally, skb_copy_ubufs() calls > > > > > > > > > > > skb_unclone(), and pskb_expand_head() increments skb->cb->ubuf.refcnt. > > > > > > > > > > > This additional count is decremented while freeing the skb, but struct > > > > > > > > > > > ubuf_info_msgzc still has a refcnt, so __msg_zerocopy_callback() is > > > > > > > > > > > not called. > > > > > > > > > > > > > > > > > > > > > > The last refcnt is not released unless we retrieve the TX timestamped > > > > > > > > > > > skb by recvmsg(). When we close() the socket holding such skb, we > > > > > > > > > > > never call sock_put() and leak the count, skb, and sk. > > > > > > > > > > > > > > > > > > > > > > To avoid this problem, we must (i) call skb_queue_purge() after > > > > > > > > > > > flagging SOCK_DEAD during close() and (ii) make sure that TX tstamp > > > > > > > > > > > skb is not queued when SOCK_DEAD is flagged. UDP lacks (i) and (ii), > > > > > > > > > > > and TCP lacks (ii). > > > > > > > > > > > > > > > > > > > > > > Without (ii), a skb queued in a qdisc or device could be put into > > > > > > > > > > > the error queue after skb_queue_purge(). > > > > > > > > > > > > > > > > > > > > > > sendmsg() /* return immediately, but packets > > > > > > > > > > > * are queued in a qdisc or device > > > > > > > > > > > */ > > > > > > > > > > > close() > > > > > > > > > > > skb_queue_purge() > > > > > > > > > > > __skb_tstamp_tx() > > > > > > > > > > > __skb_complete_tx_timestamp() > > > > > > > > > > > sock_queue_err_skb() > > > > > > > > > > > skb_queue_tail() > > > > > > > > > > > > > > > > > > > > > > Also, we need to check SOCK_DEAD under sk->sk_error_queue.lock > > > > > > > > > > > in sock_queue_err_skb() to avoid this race. > > > > > > > > > > > > > > > > > > > > > > if (!sock_flag(sk, SOCK_DEAD)) > > > > > > > > > > > sock_set_flag(sk, SOCK_DEAD) > > > > > > > > > > > skb_queue_purge() > > > > > > > > > > > > > > > > > > > > > > skb_queue_tail() > > > > > > > > > > > > > > > > > > > > > > [0]: > > > > > > > > > > > > > > > > > > > > > Fixes: f214f915e7db ("tcp: enable MSG_ZEROCOPY") > > > > > > > > > > > Fixes: b5947e5d1e71 ("udp: msg_zerocopy") > > > > > > > > > > > Reported-by: syzbot > > > > > > > > > > > Signed-off-by: Kuniyuki Iwashima > > > > > > > > > > > --- > > > > > > > > > > > v2: > > > > > > > > > > > * Move skb_queue_purge() after setting SOCK_DEAD in udp_destroy_sock() > > > > > > > > > > > * Check SOCK_DEAD in sock_queue_err_skb() with sk_error_queue.lock > > > > > > > > > > > * Add Fixes tag for TCP > > > > > > > > > > > > > > > > > > > > > > v1: https://lore.kernel.org/netdev/20230417171155.22916-1-kuniyu@amazon.com/ > > > > > > > > > > > --- > > > > > > > > > > > net/core/skbuff.c | 15 ++++++++++++--- > > > > > > > > > > > net/ipv4/udp.c | 5 +++++ > > > > > > > > > > > 2 files changed, 17 insertions(+), 3 deletions(-) > > > > > > > > > > > > > > > > > > > > > > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > > > > > > > > > > > index 4c0879798eb8..287b834df9c8 100644 > > > > > > > > > > > --- a/net/core/skbuff.c > > > > > > > > > > > +++ b/net/core/skbuff.c > > > > > > > > > > > @@ -4979,6 +4979,8 @@ static void skb_set_err_queue(struct sk_buff *skb) > > > > > > > > > > > */ > > > > > > > > > > > int sock_queue_err_skb(struct sock *sk, struct sk_buff *skb) > > > > > > > > > > > { > > > > > > > > > > > + unsigned long flags; > > > > > > > > > > > + > > > > > > > > > > > if (atomic_read(&sk->sk_rmem_alloc) + skb->truesize >= > > > > > > > > > > > (unsigned int)READ_ONCE(sk->sk_rcvbuf)) > > > > > > > > > > > return -ENOMEM; > > > > > > > > > > > @@ -4992,9 +4994,16 @@ int sock_queue_err_skb(struct sock *sk, struct sk_buff *skb) > > > > > > > > > > > /* before exiting rcu section, make sure dst is refcounted */ > > > > > > > > > > > skb_dst_force(skb); > > > > > > > > > > > > > > > > > > > > > > - skb_queue_tail(&sk->sk_error_queue, skb); > > > > > > > > > > > - if (!sock_flag(sk, SOCK_DEAD)) > > > > > > > > > > > - sk_error_report(sk); > > > > > > > > > > > + spin_lock_irqsave(&sk->sk_error_queue.lock, flags); > > > > > > > > > > > + if (sock_flag(sk, SOCK_DEAD)) { > > > > > > > > > > > > > > > > > > > > SOCK_DEAD is set without holding sk_error_queue.lock, so I wonder why you > > > > > > > > > > want to add a confusing construct. > > > > > > > > > > > > > > > > > > > > Just bail early ? > > > > > > > > > > > > > > > > > > > > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > > > > > > > > > > index ef81452759be3fd251faaf76d89cfd002ee79256..fda05cb44f95821e98f8c5c05fba840a9d276abb > > > > > > > > > > 100644 > > > > > > > > > > --- a/net/core/skbuff.c > > > > > > > > > > +++ b/net/core/skbuff.c > > > > > > > > > > @@ -4983,6 +4983,9 @@ int sock_queue_err_skb(struct sock *sk, struct > > > > > > > > > > sk_buff *skb) > > > > > > > > > > (unsigned int)READ_ONCE(sk->sk_rcvbuf)) > > > > > > > > > > return -ENOMEM; > > > > > > > > > > > > > > > > > > > > + if (sock_flag(sk, SOCK_DEAD)) > > > > > > > > > > + return -EINVAL; > > > > > > > > > > + > > > > > > > > > > > > > > > > > > Isn't it possible that these sequences happen > > > > > > > > > > > > > > > > > > close() > > > > > > > > > sock_set_flag(sk, SOCK_DEAD); > > > > > > > > > skb_queue_purge(&sk->sk_error_queue) > > > > > > > > > > > > > > > > > > between the skb_queue_tail() below ? (2nd race mentioned in changelog) > > > > > > > > > > > > > > > > > > I thought we can guarantee the ordering by taking the same lock. > > > > > > > > > > > > > > > > > > > > > > > > > This is fragile. > > > > > > > > > > > > > > Yes, but I didn't have better idea to avoid the race... > > > > > > > > > > > > > > > > > > > > > > > We could very well rewrite skb_queue_purge() to not acquire the lock > > > > > > > > in the common case. > > > > > > > > I had the following in my tree for a while, to avoid many atomic and > > > > > > > > irq masking operations... > > > > > > > > > > > > > > Cool, and it still works with my patch, no ? > > > > > > > > > > > > > > > > > > > > > > > > > Really the only thing that ensures a race is not possible is the > > > > > > typical sk_refcnt acquisition. > > > > > > > > > > > > But I do not see why an skb stored in error_queue should keep the > > > > > > refcnt on the socket. > > > > > > This seems like a chicken and egg problem, and caused various issues > > > > > > in the past, > > > > > > see for instance [1] > > > > > > > > > > > > We better make sure error queue is purged at socket dismantle (after > > > > > > refcnt reached 0) > > > > > > > > > > The problem here is that the timestamp queued on the error queue > > > > > holds a reference on a ubuf if MSG_ZEROCOPY and that ubuf holds an > > > > > sk_ref. > > > > > > > > > > The timestamped packet may contain packet contents, so the ubuf > > > > > ref is not superfluous. > > > > > > > > > > Come to think of it, we've always maintained that zerocopy packets > > > > > should not be looped to sockets where they can be queued indefinitely, > > > > > including packet sockets. > > > > > > > > > > If we enforce that for these tx timestamps too, then that also > > > > > solves this issue. > > > > > > > > > > A process that wants efficient MSG_ZEROCOPY will have to request > > > > > timestamping with SOF_TIMESTAMPING_OPT_TSONLY to avoid returning the > > > > > data along with the timestamp. > > > > > > > > Actually, my first attempt was similar to this that avoids skb_clone() > > > > silently if MSG_ZEROCOPY, but this kind of way could break users who > > > > were using tstamp and just added MSG_ZEROCOPY logic to their app, so > > > > I placed skb_queue_purge() during close(). > > > > > > > > ---8<--- > > > > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > > > > index eb7d33b41e71..9318b438888e 100644 > > > > --- a/net/core/skbuff.c > > > > +++ b/net/core/skbuff.c > > > > @@ -5135,7 +5149,7 @@ void __skb_tstamp_tx(struct sk_buff *orig_skb, > > > > if (!skb_may_tx_timestamp(sk, tsonly)) > > > > return; > > > > > > > > - if (tsonly) { > > > > + if (tsonly || skb_zcopy(orig_skb)) { > > > > #ifdef CONFIG_INET > > > > if ((sk->sk_tsflags & SOF_TIMESTAMPING_OPT_STATS) && > > > > sk_is_tcp(sk)) { > > > > ---8<--- > > > > > > Actually, the skb_clone in __skb_tstamp_tx should already release > > > the reference on the ubuf. > > > > > > With the same mechanism that we rely on for packet sockets, e.g., > > > in dev_queue_xmit_nit. > > > > > > skb_clone calls skb_orphan_frags calls skb_copy_ubufs for zerocopy > > > skbs. Which creates a copy of the data and calls skb_zcopy_clear. > > > > > > The skb that gets queued onto the error queue should not have a > > > reference on an ubuf: skb_zcopy(skb) should return NULL. > > > > Exactly, so how about this ? > > > > ---8<--- > > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > > index 768f9d04911f..0fa0b2ac7071 100644 > > --- a/net/core/skbuff.c > > +++ b/net/core/skbuff.c > > @@ -5166,6 +5166,9 @@ void __skb_tstamp_tx(struct sk_buff *orig_skb, > > if (!skb) > > return; > > > > + if (skb_zcopy(skb) && skb_copy_ubufs(skb, GFP_ATOMIC)) > > + return; > > + > > if (tsonly) { > > skb_shinfo(skb)->tx_flags |= skb_shinfo(orig_skb)->tx_flags & > > SKBTX_ANY_TSTAMP; > > ---8<--- > > > > What I meant was that given this I don't understand how a packet > with ubuf references gets queued at all. > > __skb_tstamp_tx does not queue orig_skb. It either allocates a new > skb or calls skb = skb_clone(orig_skb). > > That existing call internally calls skb_orphan_frags and > skb_copy_ubufs. No, skb_orphan_frags() does not call skb_copy_ubufs() here because msg_zerocopy_alloc() sets SKBFL_DONT_ORPHAN for orig_skb. So, we need to call skb_copy_ubufs() explicitly if skb_zcopy(skb). > > So the extra test should not be needed. Indeed I would be surprised if > this triggers: And this actually triggers. > > @@ -5164,6 +5164,8 @@ void __skb_tstamp_tx(struct sk_buff *orig_skb, > if (!skb) > return; > > + WARN_ON_ONCE(skb_zcopy(sbk)); > + > > if (tsonly) { > skb_shinfo(skb)->tx_flags |= skb_shinfo(orig_skb)->tx_flags & > SKBTX_ANY_TSTAMP;