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 0CF8EC77B73 for ; Wed, 19 Apr 2023 17:08:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233376AbjDSRI5 (ORCPT ); Wed, 19 Apr 2023 13:08:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33898 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230073AbjDSRI4 (ORCPT ); Wed, 19 Apr 2023 13:08:56 -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 67344A247 for ; Wed, 19 Apr 2023 10:07:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1681924069; x=1713460069; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=BIghVi7DSpnnR8kVK+iRLxGDPQRkzIFIplqL99xh65w=; b=a61llMJkzqsgidmAttkaVTvCv0haZ43vDRMqOe9Pjnud3cEhqvWJp5z4 CKde9Xjp2YTEYl4ms8bMPvMlf1YkdkRnda0CpmDnjxABNh9TCyt+PvUhl 9x168YDNG+i+1Yn1Qh6JBrS/dn2fmqLlwYzSz3nXi5h+Zt4l9WVtMt61L U=; X-IronPort-AV: E=Sophos;i="5.99,208,1677542400"; d="scan'208";a="320258658" Received: from iad12-co-svc-p1-lb1-vlan3.amazon.com (HELO email-inbound-relay-iad-1a-m6i4x-47cc8a4c.us-east-1.amazon.com) ([10.43.8.6]) by smtp-border-fw-6002.iad6.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Apr 2023 17:07:45 +0000 Received: from EX19MTAUWC001.ant.amazon.com (iad12-ws-svc-p26-lb9-vlan2.iad.amazon.com [10.40.163.34]) by email-inbound-relay-iad-1a-m6i4x-47cc8a4c.us-east-1.amazon.com (Postfix) with ESMTPS id EC110160A81; Wed, 19 Apr 2023 17:07:42 +0000 (UTC) Received: from EX19D004ANA001.ant.amazon.com (10.37.240.138) by EX19MTAUWC001.ant.amazon.com (10.250.64.174) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1118.25; Wed, 19 Apr 2023 17:07:39 +0000 Received: from 88665a182662.ant.amazon.com (10.187.170.33) by EX19D004ANA001.ant.amazon.com (10.37.240.138) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1118.26; Wed, 19 Apr 2023 17:07:36 +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 10:07:26 -0700 Message-ID: <20230419170727.29740-1-kuniyu@amazon.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <643ff7a7a551f_38347529475@willemb.c.googlers.com.notmuch> References: <643ff7a7a551f_38347529475@willemb.c.googlers.com.notmuch> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-Originating-IP: [10.187.170.33] X-ClientProxiedBy: EX19D040UWB003.ant.amazon.com (10.13.138.8) 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 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<--- > > > I suggest we generalize fix that went in this patch : > > > > dd4f10722aeb10f4f582948839f066bebe44e5fb net: fix socket refcounting > > in skb_complete_wifi_ack() > > > > Instead of adding yet another rule about a queue lock, and a socket > > flag, this would keep things tied to sk_refcnt. > > > > Also I do not think TCP has an issue, please take a look at > > > > [1] > > commit e0c8bccd40fc1c19e1d246c39bcf79e357e1ada3 net: stream: purge > > sk_error_queue in sk_stream_kill_queues() > > > > (A leak in TCP would be caught in a few hours by syzbot really) I have tested TCP before posting v1 and found this skb_queue_purge() was to prevent the same issue, but Willem's point sounds reasonable that packets queued in qdisc or device could be put in the error queue after close() completes. That's why I mentioned TCP since v2.