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 D4C23C77B72 for ; Tue, 18 Apr 2023 01:24:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229946AbjDRBYp (ORCPT ); Mon, 17 Apr 2023 21:24:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44282 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229687AbjDRBYn (ORCPT ); Mon, 17 Apr 2023 21:24:43 -0400 Received: from smtp-fw-80007.amazon.com (smtp-fw-80007.amazon.com [99.78.197.218]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 736A644AB for ; Mon, 17 Apr 2023 18:24:39 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1681781080; x=1713317080; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=mqODA4ZqlVeCeGvY+5HNbSlv13C7snY1bZz/qMjmvfM=; b=ttxGIslFGo2csKudXQu8X8LZsdRi1uIrBWN0ml1a31EB+yg/i5lkUo+l Xc6VpARCEDsASdDV4sd61qMKQ3sfK4b0UBP6+4uQsCI8BX7M8kPK+XDp4 kyGsHFDYi/r56tm6rYf9J596eP5ieE8X5ZMOhA0q+iJadt8i4fVO2jUSQ Q=; X-IronPort-AV: E=Sophos;i="5.99,205,1677542400"; d="scan'208";a="205436333" Received: from pdx4-co-svc-p1-lb2-vlan3.amazon.com (HELO email-inbound-relay-iad-1box-1dm6-7f722725.us-east-1.amazon.com) ([10.25.36.214]) by smtp-border-fw-80007.pdx80.corp.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Apr 2023 01:24:36 +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-1box-1dm6-7f722725.us-east-1.amazon.com (Postfix) with ESMTPS id 6087480D38; Tue, 18 Apr 2023 01:24:33 +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 01:24:32 +0000 Received: from 88665a182662.ant.amazon.com (10.94.51.151) 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 01:24:29 +0000 From: Kuniyuki Iwashima To: CC: , , , , , , , , Subject: RE: [PATCH v1 net] udp: Fix memleaks of sk and zerocopy skbs with TX timestamp. Date: Mon, 17 Apr 2023 18:24:21 -0700 Message-ID: <20230418012421.86283-1-kuniyu@amazon.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <643de9b9bc7d4_2f58012942e@willemb.c.googlers.com.notmuch> References: <643de9b9bc7d4_2f58012942e@willemb.c.googlers.com.notmuch> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-Originating-IP: [10.94.51.151] X-ClientProxiedBy: EX19D040UWA002.ant.amazon.com (10.13.139.113) 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: Mon, 17 Apr 2023 20:52:09 -0400 > Kuniyuki Iwashima wrote: > > From: Willem de Bruijn > > Date: Mon, 17 Apr 2023 19:28:25 -0400 > > > Kuniyuki Iwashima wrote: > > > > From: Willem de Bruijn > > > > Date: Mon, 17 Apr 2023 17:53:33 -0400 > > > > > Kuniyuki Iwashima wrote: > > > > > > From: Willem de Bruijn > > > > > > Date: Mon, 17 Apr 2023 16:36:20 -0400 > > > > > > > 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 call skb_queue_purge() while we close() > > > > > > > > UDP sockets. > > > > > > > > > > > > > > > > Note that TCP does not have this problem because skb_queue_purge() is > > > > > > > > called by sk_stream_kill_queues() during close(). > > > > > > > > > > > > > > Thanks for the clear description. > > > > > > > > > > > > > > So the issue is that the tx timestamp notification is still queued on > > > > > > > the error queue and this is not freed on socket destruction. > > > > > > > > > > > > > > That surprises me. The error definitely needs to be purged on socket > > > > > > > destruction. And it is, called in inet_sock_destruct, which is called > > > > > > > udp_destruct_sock. > > > > > > > > > > > > > > The issue here is that there is a circular dependency, where the > > > > > > > sk_destruct is not called until the ref count drops to zero? > > > > > > > > > > > > Yes, right. > > > > > > > > > > > > > > > > > > > > sk_stream_kill_queues is called from inet_csk_destroy_sock, from > > > > > > > __tcp_close (and thus tcp_prot.close) among others. > > > > > > > > > > > > > > purging the error queue for other sockets on .close rather than > > > > > > > .destroy sounds good to me. > > > > > > > > > > > > > > But SOF_TIMESTAMPING_TX_SOFTWARE and MSG_ZEROCOPY are not limited to > > > > > > > TCP and UDP. So we probably need this in a more protocol independent > > > > > > > close. > > > > > > > > > > > > At least, we limit SO_ZEROCOPY to TCP, UDP and RDS for now. Also, RDS > > > > > > seems to just use TCP. [0] > > > > > > > > > > > > ---8<--- > > > > > > case SO_ZEROCOPY: > > > > > > if (sk->sk_family == PF_INET || sk->sk_family == PF_INET6) { > > > > > > if (!(sk_is_tcp(sk) || > > > > > > (sk->sk_type == SOCK_DGRAM && > > > > > > sk->sk_protocol == IPPROTO_UDP))) > > > > > > ret = -EOPNOTSUPP; > > > > > > } else if (sk->sk_family != PF_RDS) { > > > > > > ret = -EOPNOTSUPP; > > > > > > } > > > > > > if (!ret) { > > > > > > if (val < 0 || val > 1) > > > > > > ret = -EINVAL; > > > > > > else > > > > > > sock_valbool_flag(sk, SOCK_ZEROCOPY, valbool); > > > > > > } > > > > > > break; > > > > > > ---8<--- > > > > > > > > > > > > [0]: https://lore.kernel.org/netdev/cover.1518718761.git.sowmini.varadhan@oracle.com/ > > > > > > > > > > Good point, thanks. I used to experiment with more protocols, as can > > > > > be seen from msg_zerocopy.c. But those are thankfully not relevant. > > > > > > > > > > > > Thanks, > > > > > > Kuniyuki > > > > > > > > > > > > > > > > > > > > > > > > > > > [0]: > > > > > > > > BUG: memory leak > > > > > > > > unreferenced object 0xffff88800c6d2d00 (size 1152): > > > > > > > > comm "syz-executor392", pid 264, jiffies 4294785440 (age 13.044s) > > > > > > > > hex dump (first 32 bytes): > > > > > > > > 00 00 00 00 00 00 00 00 cd af e8 81 00 00 00 00 ................ > > > > > > > > 02 00 07 40 00 00 00 00 00 00 00 00 00 00 00 00 ...@............ > > > > > > > > backtrace: > > > > > > > > [<0000000055636812>] sk_prot_alloc+0x64/0x2a0 net/core/sock.c:2024 > > > > > > > > [<0000000054d77b7a>] sk_alloc+0x3b/0x800 net/core/sock.c:2083 > > > > > > > > [<0000000066f3c7e0>] inet_create net/ipv4/af_inet.c:319 [inline] > > > > > > > > [<0000000066f3c7e0>] inet_create+0x31e/0xe40 net/ipv4/af_inet.c:245 > > > > > > > > [<000000009b83af97>] __sock_create+0x2ab/0x550 net/socket.c:1515 > > > > > > > > [<00000000b9b11231>] sock_create net/socket.c:1566 [inline] > > > > > > > > [<00000000b9b11231>] __sys_socket_create net/socket.c:1603 [inline] > > > > > > > > [<00000000b9b11231>] __sys_socket_create net/socket.c:1588 [inline] > > > > > > > > [<00000000b9b11231>] __sys_socket+0x138/0x250 net/socket.c:1636 > > > > > > > > [<000000004fb45142>] __do_sys_socket net/socket.c:1649 [inline] > > > > > > > > [<000000004fb45142>] __se_sys_socket net/socket.c:1647 [inline] > > > > > > > > [<000000004fb45142>] __x64_sys_socket+0x73/0xb0 net/socket.c:1647 > > > > > > > > [<0000000066999e0e>] do_syscall_x64 arch/x86/entry/common.c:50 [inline] > > > > > > > > [<0000000066999e0e>] do_syscall_64+0x38/0x90 arch/x86/entry/common.c:80 > > > > > > > > [<0000000017f238c1>] entry_SYSCALL_64_after_hwframe+0x63/0xcd > > > > > > > > > > > > > > > > BUG: memory leak > > > > > > > > unreferenced object 0xffff888017633a00 (size 240): > > > > > > > > comm "syz-executor392", pid 264, jiffies 4294785440 (age 13.044s) > > > > > > > > hex dump (first 32 bytes): > > > > > > > > 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ > > > > > > > > 00 00 00 00 00 00 00 00 00 2d 6d 0c 80 88 ff ff .........-m..... > > > > > > > > backtrace: > > > > > > > > [<000000002b1c4368>] __alloc_skb+0x229/0x320 net/core/skbuff.c:497 > > > > > > > > [<00000000143579a6>] alloc_skb include/linux/skbuff.h:1265 [inline] > > > > > > > > [<00000000143579a6>] sock_omalloc+0xaa/0x190 net/core/sock.c:2596 > > > > > > > > [<00000000be626478>] msg_zerocopy_alloc net/core/skbuff.c:1294 [inline] > > > > > > > > [<00000000be626478>] msg_zerocopy_realloc+0x1ce/0x7f0 net/core/skbuff.c:1370 > > > > > > > > [<00000000cbfc9870>] __ip_append_data+0x2adf/0x3b30 net/ipv4/ip_output.c:1037 > > > > > > > > [<0000000089869146>] ip_make_skb+0x26c/0x2e0 net/ipv4/ip_output.c:1652 > > > > > > > > [<00000000098015c2>] udp_sendmsg+0x1bac/0x2390 net/ipv4/udp.c:1253 > > > > > > > > [<0000000045e0e95e>] inet_sendmsg+0x10a/0x150 net/ipv4/af_inet.c:819 > > > > > > > > [<000000008d31bfde>] sock_sendmsg_nosec net/socket.c:714 [inline] > > > > > > > > [<000000008d31bfde>] sock_sendmsg+0x141/0x190 net/socket.c:734 > > > > > > > > [<0000000021e21aa4>] __sys_sendto+0x243/0x360 net/socket.c:2117 > > > > > > > > [<00000000ac0af00c>] __do_sys_sendto net/socket.c:2129 [inline] > > > > > > > > [<00000000ac0af00c>] __se_sys_sendto net/socket.c:2125 [inline] > > > > > > > > [<00000000ac0af00c>] __x64_sys_sendto+0xe1/0x1c0 net/socket.c:2125 > > > > > > > > [<0000000066999e0e>] do_syscall_x64 arch/x86/entry/common.c:50 [inline] > > > > > > > > [<0000000066999e0e>] do_syscall_64+0x38/0x90 arch/x86/entry/common.c:80 > > > > > > > > [<0000000017f238c1>] entry_SYSCALL_64_after_hwframe+0x63/0xcd > > > > > > > > > > > > > > > > Fixes: b5947e5d1e71 ("udp: msg_zerocopy") > > > > > > > > Reported-by: syzbot > > > > > > > > Signed-off-by: Kuniyuki Iwashima > > > > > > > > --- > > > > > > > > include/net/udp.h | 5 +++++ > > > > > > > > 1 file changed, 5 insertions(+) > > > > > > > > > > > > > > > > diff --git a/include/net/udp.h b/include/net/udp.h > > > > > > > > index de4b528522bb..b9182f166b2f 100644 > > > > > > > > --- a/include/net/udp.h > > > > > > > > +++ b/include/net/udp.h > > > > > > > > @@ -195,6 +195,11 @@ void udp_lib_rehash(struct sock *sk, u16 new_hash); > > > > > > > > > > > > > > > > static inline void udp_lib_close(struct sock *sk, long timeout) > > > > > > > > { > > > > > > > > + /* A zerocopy skb has a refcnt of sk and may be > > > > > > > > + * put into sk_error_queue with TX timestamp > > > > > > > > + */ > > > > > > > > + skb_queue_purge(&sk->sk_error_queue); > > > > > > > > + > > > > > > > > sk_common_release(sk); > > > > > > > > } > > > > > > > > > > Does this leave a race, where another completion may be queued between > > > > > skb_queue_purge and the eventual sock_put in sk_common_release? > > > > > > > > I thought udp_send_skb() returns only after TX completion, and > > > > ->release() will never called while file is accessed by sendmsg(). > > > > > > udp_send_skb (and the sendmsg) syscall returns immediately sending > > > the packet. > > > > > > The packets I'm concerned about are those queued in a qdisc or the > > > device, waiting for a completion. > > > > Ah, I got your point. > > > > So, we need to make sure TX tstamp is not queued if SOCK_DEAD is > > flagged and we purge the queue only after marking SOCK_DEAD ? > > Exactly. Thanks for the sketch. > > Ideally without having to take an extra lock in the common path. > sk_commmon_release calls sk_prot->destroy == udp_destroy_sock, > which already sets SOCK_DEAD. > > Could we move the skb_queue_purge in there? That is also what > calls udp_flush_pending_frames. Yes, that makes sense. I was thinking if we need a memory barrier for SOCK_DEAD to sync with TX, which reads it locklessly. Maybe we should check SOCK_DEAD with sk->sk_error_queue.lock held ? And I forgot to return error from sock_queue_err_skb() to free skb in __skb_complete_tx_timestamp(). ---8<--- 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)) { + spin_unlock_irqrestore(&sk->sk_error_queue.lock, flags); + return -EINVAL; + } + __skb_queue_tail(&sk->sk_error_queue, skb); + spin_unlock_irqrestore(&sk->sk_error_queue.lock, flags); + + sk_error_report(sk); + return 0; } EXPORT_SYMBOL(sock_queue_err_skb); diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c index c605d171eb2d..7060a5cda711 100644 --- a/net/ipv4/udp.c +++ b/net/ipv4/udp.c @@ -2674,6 +2674,11 @@ void udp_destroy_sock(struct sock *sk) if (up->encap_enabled) static_branch_dec(&udp_encap_needed_key); } + + /* A zerocopy skb has a refcnt of sk and may be + * put into sk_error_queue with TX timestamp + */ + skb_queue_purge(&sk->sk_error_queue); } /* ---8<---