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 1BB40C77B75 for ; Tue, 18 Apr 2023 00:52:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229830AbjDRAwO (ORCPT ); Mon, 17 Apr 2023 20:52:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59172 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229477AbjDRAwN (ORCPT ); Mon, 17 Apr 2023 20:52:13 -0400 Received: from mail-qv1-xf31.google.com (mail-qv1-xf31.google.com [IPv6:2607:f8b0:4864:20::f31]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7E5B219A4 for ; Mon, 17 Apr 2023 17:52:11 -0700 (PDT) Received: by mail-qv1-xf31.google.com with SMTP id ok10so5441972qvb.11 for ; Mon, 17 Apr 2023 17:52:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20221208; t=1681779130; x=1684371130; h=content-transfer-encoding:mime-version:subject:references :in-reply-to:message-id:cc:to:from:date:from:to:cc:subject:date :message-id:reply-to; bh=4yI+nvZfbbsJilJ1YN/9fEAAljV/0ucDcMXVACNA/6A=; b=fEHTsyWZ14E9XQXHjLcgnBv159Zftzay9xo/uIX+H5Hz5tRUP/sefdOh9KKG7orENo lOo58wrt2vKWMxPuaalebGbNGw37byrZJzupKgXJwlAqJFdYo9nDPR/CGvrsTULxQZqE auyOT+FRfjyqvtGm/kSWpW0XIQFffd4DfMMT+Om+QbZqAdutPKK5Q6OEpVL0Id8mR5cO 1Mz8rQgYvDkQLWx5TK5isRBlKK2RA9us60K53YT3XquiersNlGeRSGuFz0jLO4uw+0x8 Qdfj5B6q5vK8agvf9dMsD6Dk5oWhScptFatlnj8wk4+BjgtnPIxYxSpRyx8lQa3CpM9V mq3g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1681779130; x=1684371130; h=content-transfer-encoding:mime-version:subject:references :in-reply-to:message-id:cc:to:from:date:x-gm-message-state:from:to :cc:subject:date:message-id:reply-to; bh=4yI+nvZfbbsJilJ1YN/9fEAAljV/0ucDcMXVACNA/6A=; b=PqAhCGj+Cv0JUCkJxpeTnI48Hs8P1wzHnkcPhm7F+9wHsmDoJ20x4thLdVvU6rP1FZ JSdYL8+efYJNO6qS3bYG+CpReMvi6teux5EFDuSGy7ihFb+juGeH1l+uE6hboSZw76r3 2n2MrpZoD3N1NIdLwuFRR7kzjivwxcUu+scho+0GwDoAzxbxygbZ3+eisv/oH2vIroS7 Zf6ZNPBbBB2mIRy9mPB+nZuUkjUBAEk5MnHPGagS1QqUMJuT8yOceGcf6uiNq6eBHPo9 P1sr79AcQLeRFCdpByMhGaY2l/UXKOKxRaivTEEo/OrYgUtNgynBeG88Y9P4yqRxKRNM KDXQ== X-Gm-Message-State: AAQBX9dJTEdWseZoQJMv7Q+vMRoEOL+vDgsw9FhRL+cMU4M/l8Jw0rOk LoQgLo/3SlkDwLIeTvCzfHo= X-Google-Smtp-Source: AKy350Zy3vRriyxR0LQlISBeZZUveq7xhAHVRw1EiilqoTjaBPJShb+8ue1E26Eud18aCqf2vwdQbA== X-Received: by 2002:a05:6214:62b:b0:5e9:2bad:c8fa with SMTP id a11-20020a056214062b00b005e92badc8famr18044868qvx.33.1681779130425; Mon, 17 Apr 2023 17:52:10 -0700 (PDT) Received: from localhost (240.157.150.34.bc.googleusercontent.com. [34.150.157.240]) by smtp.gmail.com with ESMTPSA id qf7-20020a0562144b8700b005ef5f7c1ae1sm2266589qvb.105.2023.04.17.17.52.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 Apr 2023 17:52:10 -0700 (PDT) Date: Mon, 17 Apr 2023 20:52:09 -0400 From: Willem de Bruijn To: Kuniyuki Iwashima , willemdebruijn.kernel@gmail.com Cc: davem@davemloft.net, edumazet@google.com, kuba@kernel.org, kuni1840@gmail.com, kuniyu@amazon.com, netdev@vger.kernel.org, pabeni@redhat.com, syzkaller@googlegroups.com, willemb@google.com Message-ID: <643de9b9bc7d4_2f58012942e@willemb.c.googlers.com.notmuch> In-Reply-To: <20230417235308.79619-1-kuniyu@amazon.com> References: <643dd619d3bf3_2db9242942c@willemb.c.googlers.com.notmuch> <20230417235308.79619-1-kuniyu@amazon.com> Subject: RE: [PATCH v1 net] udp: Fix memleaks of sk and zerocopy skbs with TX timestamp. Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org 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. > ---8<--- > index de4b528522bb..98505e66262e 100644 > --- a/include/net/udp.h > +++ b/include/net/udp.h > @@ -195,7 +195,16 @@ void udp_lib_rehash(struct sock *sk, u16 new_hash); > > static inline void udp_lib_close(struct sock *sk, long timeout) > { > + sock_hold(sk); > + > sk_common_release(sk); > + > + /* 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); > + > + sock_put(sk); > } > > int udp_lib_get_port(struct sock *sk, unsigned short snum, > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > index 4c0879798eb8..628eaee1815c 100644 > --- a/net/core/skbuff.c > +++ b/net/core/skbuff.c > @@ -4992,9 +4992,10 @@ 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)) > + if (!sock_flag(sk, SOCK_DEAD)) { > + skb_queue_tail(&sk->sk_error_queue, skb); > sk_error_report(sk); > + } > return 0; > } > EXPORT_SYMBOL(sock_queue_err_skb); > ---8<--- > > > > > > > > > > > > > > > Unfortunately even the sock_set_flag(sk, SOCK_DEAD) is not sufficient > > > > to ensure that no tx completions are subsequently queued for packets > > > > that are in transmission. sk_common_release has a comment > > > > > > > > * receive queue, but transmitted packets will delay socket destruction > > > > * until the last reference will be released. > > > > */ > > > > > > > > This should equally apply to TCP. Evidentlly it is not a problem > > > > there. I don't entirely follow yet how this is avoided. > > > > > > TCP stops timers and clears write queue before sk_stream_kill_queues(), > > > so I think concurrent TX is not fired when we purging error queues. > > > > > > - inet_csk_destroy_sock > > > - sk->sk_prot->destroy / tcp_v4_destroy_sock > > > - tcp_clear_xmit_timers > > > - inet_csk_clear_xmit_timers > > > - tcp_write_queue_purge > > > - sk_stream_kill_queues > > > > > > > Interesting. Same point with packets currently being transmitted by > > the device. > > > > > > > > > > MSG_ZEROCOPY notifications are not queued if SOCK_DEAD (first branch > > > > in __msg_zerocopy_callback). Perhaps we need the same in > > > > sock_queue_err_skb?