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 0F2BBC77B75 for ; Tue, 18 Apr 2023 19:25:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231539AbjDRTZ3 (ORCPT ); Tue, 18 Apr 2023 15:25:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42032 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229915AbjDRTZ2 (ORCPT ); Tue, 18 Apr 2023 15:25:28 -0400 Received: from smtp-fw-33001.amazon.com (smtp-fw-33001.amazon.com [207.171.190.10]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 96B1E10E2 for ; Tue, 18 Apr 2023 12:25:26 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1681845927; x=1713381927; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=rNijkR9wQIuH6LW1jzSRJ1IYqZy332VhSMO5uQJmubY=; b=o9BcNszWFg11vOMnDhXkXMrCxycj1WWTWvlbu0xSnkavk//CLKSkSP/E 8rj2wT6JHjF6vnQPrJsVg9Sj/7xs4Z+75FVbrmBLoHB5ROmDTofq0qG5i QH8FbrR2osAn7Wkg4K5jvjLNFCjJ5J6S9EkcJMzwU/RpOAQzptLWVu1zy 4=; X-IronPort-AV: E=Sophos;i="5.99,207,1677542400"; d="scan'208";a="278145411" Received: from iad12-co-svc-p1-lb1-vlan3.amazon.com (HELO email-inbound-relay-iad-1a-m6i4x-bbc6e425.us-east-1.amazon.com) ([10.43.8.6]) by smtp-border-fw-33001.sea14.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Apr 2023 19:25:21 +0000 Received: from EX19MTAUWC001.ant.amazon.com (iad12-ws-svc-p26-lb9-vlan3.iad.amazon.com [10.40.163.38]) by email-inbound-relay-iad-1a-m6i4x-bbc6e425.us-east-1.amazon.com (Postfix) with ESMTPS id 788A280E08; Tue, 18 Apr 2023 19:25:18 +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; Tue, 18 Apr 2023 19:25:17 +0000 Received: from 88665a182662.ant.amazon.com.com (10.106.101.27) 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; Tue, 18 Apr 2023 19:25:13 +0000 From: Kuniyuki Iwashima To: CC: , , , , , , , Subject: Re: [PATCH v2 net] tcp/udp: Fix memleaks of sk and zerocopy skbs with TX timestamp. Date: Tue, 18 Apr 2023 12:25:04 -0700 Message-ID: <20230418192504.98991-1-kuniyu@amazon.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-Originating-IP: [10.106.101.27] X-ClientProxiedBy: EX19D044UWA003.ant.amazon.com (10.13.139.43) To EX19D004ANA001.ant.amazon.com (10.37.240.138) Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org 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 ? > > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > index ef81452759be3fd251faaf76d89cfd002ee79256..f570e7c89248e2d9d9ab50c2e86ac7019b837484 > 100644 > --- a/net/core/skbuff.c > +++ b/net/core/skbuff.c > @@ -3606,14 +3606,24 @@ EXPORT_SYMBOL(skb_dequeue_tail); > * skb_queue_purge - empty a list > * @list: list to empty > * > - * Delete all buffers on an &sk_buff list. Each buffer is removed from > - * the list and one reference dropped. This function takes the list > - * lock and is atomic with respect to other list locking functions. > + * Delete all buffers on an &sk_buff list. > */ > void skb_queue_purge(struct sk_buff_head *list) > { > + struct sk_buff_head priv; > + unsigned long flags; > struct sk_buff *skb; > - while ((skb = skb_dequeue(list)) != NULL) > + > + if (skb_queue_empty_lockless(list)) > + return; > + > + __skb_queue_head_init(&priv); > + > + spin_lock_irqsave(&list->lock, flags); > + skb_queue_splice_init(list, &priv); > + spin_unlock_irqrestore(&list->lock, flags); > + > + while ((skb = __skb_dequeue(&priv)) != NULL) > kfree_skb(skb); > } > EXPORT_SYMBOL(skb_queue_purge);