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[2604:1380:1:3600::1]) by mx.google.com with ESMTPS id y200si3448210wmc.65.2021.09.28.12.51.03 for (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Tue, 28 Sep 2021 12:51:03 -0700 (PDT) Received-SPF: pass (google.com: domain of mptcp+bounces-2079-wpasupplicant.patchew=gmail.com@lists.linux.dev designates 2604:1380:1:3600::1 as permitted sender) client-ip=2604:1380:1:3600::1; Authentication-Results: mx.google.com; dkim=pass header.i=@redhat.com header.s=mimecast20190719 header.b=dNr8PEoh; spf=pass (google.com: domain of mptcp+bounces-2079-wpasupplicant.patchew=gmail.com@lists.linux.dev designates 2604:1380:1:3600::1 as permitted sender) smtp.mailfrom="mptcp+bounces-2079-wpasupplicant.patchew=gmail.com@lists.linux.dev"; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.subspace.kernel.org (wormhole.subspace.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ewr.edge.kernel.org (Postfix) with ESMTPS id 28FFB1C0BF5 for ; Tue, 28 Sep 2021 19:51:02 +0000 (UTC) Received: from localhost.localdomain (localhost.localdomain [127.0.0.1]) by smtp.subspace.kernel.org (Postfix) with ESMTP id CE1823FCB; Tue, 28 Sep 2021 19:51:00 +0000 (UTC) X-Original-To: mptcp@lists.linux.dev Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EA51B2FAF for ; Tue, 28 Sep 2021 19:50:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1632858657; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=DiaF37ZC9mTxVdpV8bMf6kvgWqnK1qThZoamW6jQjJc=; b=dNr8PEohtMiPpxTeT61esaIomba6JpiKIusawCA4viEhL/EO/zqy3HVkmOfaMSB5IrQGvB bnIWBX/O/XcNx8/Ecnu1IFnZ9it/9hfBeADNY6uhBMl5ADEfIbwTtV2opfs12rB2wASkN7 qnkYHWHPxeLjTPnj0D8LEKRe73Ce110= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-529-1mJwvhBaPfWwW0X9XUZY2w-1; Tue, 28 Sep 2021 15:50:56 -0400 X-MC-Unique: 1mJwvhBaPfWwW0X9XUZY2w-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 4F9A61054F92 for ; Tue, 28 Sep 2021 19:50:55 +0000 (UTC) Received: from gerbillo.redhat.com (unknown [10.39.192.59]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7D3FC19C79; Tue, 28 Sep 2021 19:50:54 +0000 (UTC) From: Paolo Abeni To: mptcp@lists.linux.dev Cc: fwestpha@redhat.com Subject: [PATCH v3 mptcp-net] mptcp: fix possible stall on recvmsg() Date: Tue, 28 Sep 2021 21:50:47 +0200 Message-Id: Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=pabeni@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" recvmsg() can enter an infinite loop if the caller provides the MSG_WAITALL, the data present in the receive queue is not sufficient to fulfill the request and no more data is received by the peer. When the above happens, mptcp_wait_data() will always return with no wait, as the MPTCP_DATA_READY flag checked by such function is set and never cleared in such code path. Leveraging the above syzbot was able to trigger an RCU stall: rcu: INFO: rcu_preempt self-detected stall on CPU rcu: 0-...!: (10499 ticks this GP) idle=3D0af/1/0x4000000000000000 softi= rq=3D10678/10678 fqs=3D1 (t=3D10500 jiffies g=3D13089 q=3D109) rcu: rcu_preempt kthread starved for 10497 jiffies! g13089 f0x0 RCU_GP_WAIT= _FQS(5) ->state=3D0x0 ->cpu=3D1 rcu: Unless rcu_preempt kthread gets sufficient CPU time, OOM is now exp= ected behavior. rcu: RCU grace-period kthread stack dump: task:rcu_preempt state:R running task stack:28696 pid: 14 ppid: = 2 flags:0x00004000 Call Trace: context_switch kernel/sched/core.c:4955 [inline] __schedule+0x940/0x26f0 kernel/sched/core.c:6236 schedule+0xd3/0x270 kernel/sched/core.c:6315 schedule_timeout+0x14a/0x2a0 kernel/time/timer.c:1881 rcu_gp_fqs_loop+0x186/0x810 kernel/rcu/tree.c:1955 rcu_gp_kthread+0x1de/0x320 kernel/rcu/tree.c:2128 kthread+0x405/0x4f0 kernel/kthread.c:327 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295 rcu: Stack dump where RCU GP kthread last ran: Sending NMI from CPU 0 to CPUs 1: NMI backtrace for cpu 1 CPU: 1 PID: 8510 Comm: syz-executor827 Not tainted 5.15.0-rc2-next-20210920= -syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Goo= gle 01/01/2011 RIP: 0010:bytes_is_nonzero mm/kasan/generic.c:84 [inline] RIP: 0010:memory_is_nonzero mm/kasan/generic.c:102 [inline] RIP: 0010:memory_is_poisoned_n mm/kasan/generic.c:128 [inline] RIP: 0010:memory_is_poisoned mm/kasan/generic.c:159 [inline] RIP: 0010:check_region_inline mm/kasan/generic.c:180 [inline] RIP: 0010:kasan_check_range+0xc8/0x180 mm/kasan/generic.c:189 Code: 38 00 74 ed 48 8d 50 08 eb 09 48 83 c0 01 48 39 d0 74 7a 80 38 00 74 = f2 48 89 c2 b8 01 00 00 00 48 85 d2 75 56 5b 5d 41 5c c3 <48> 85 d2 74 5e 4= 8 01 ea eb 09 48 83 c0 01 48 39 d0 74 50 80 38 00 RSP: 0018:ffffc9000cd676c8 EFLAGS: 00000283 RAX: ffffed100e9a110e RBX: ffffed100e9a110f RCX: ffffffff88ea062a RDX: 0000000000000001 RSI: 0000000000000008 RDI: ffff888074d08870 RBP: ffffed100e9a110e R08: 0000000000000001 R09: ffff888074d08877 R10: ffffed100e9a110e R11: 0000000000000000 R12: ffff888074d08000 R13: ffff888074d08000 R14: ffff888074d08088 R15: ffff888074d08000 FS: 0000555556d8e300(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000 S: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000020000180 CR3: 0000000068909000 CR4: 00000000001506e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: instrument_atomic_read_write include/linux/instrumented.h:101 [inline] test_and_clear_bit include/asm-generic/bitops/instrumented-atomic.h:83 [in= line] mptcp_release_cb+0x14a/0x210 net/mptcp/protocol.c:3016 release_sock+0xb4/0x1b0 net/core/sock.c:3204 mptcp_wait_data net/mptcp/protocol.c:1770 [inline] mptcp_recvmsg+0xfd1/0x27b0 net/mptcp/protocol.c:2080 inet6_recvmsg+0x11b/0x5e0 net/ipv6/af_inet6.c:659 sock_recvmsg_nosec net/socket.c:944 [inline] ____sys_recvmsg+0x527/0x600 net/socket.c:2626 ___sys_recvmsg+0x127/0x200 net/socket.c:2670 do_recvmmsg+0x24d/0x6d0 net/socket.c:2764 __sys_recvmmsg net/socket.c:2843 [inline] __do_sys_recvmmsg net/socket.c:2866 [inline] __se_sys_recvmmsg net/socket.c:2859 [inline] __x64_sys_recvmmsg+0x20b/0x260 net/socket.c:2859 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x44/0xae RIP: 0033:0x7fc200d2dc39 Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 41 15 00 00 90 48 89 f8 48 89 f7 = 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff f= f 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007ffc5758e5a8 EFLAGS: 00000246 ORIG_RAX: 000000000000012b RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007fc200d2dc39 RDX: 0000000000000002 RSI: 00000000200017c0 RDI: 0000000000000003 RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000f0b5ff R10: 0000000000000100 R11: 0000000000000246 R12: 0000000000000003 R13: 00007ffc5758e5d0 R14: 00007ffc5758e5c0 R15: 0000000000000003 Fix the issue replacing the MPTCP_DATA_READY bit with direct inspection of the msk receive queue. Reported-and-tested-by: syzbot+3360da629681aa0d22fe@syzkaller.appspotmail.c= om Fixes: 7a6a6cbc3e59 ("mptcp: recvmsg() can drain data from multiple subflow= ") Signed-off-by: Paolo Abeni Reviewed-by: Mat Martineau --- v2 -> v3: - added more descriptive comment in mptcp_check_readable() - Mat v1 -> v2: - instead of do more fiddling with the DATA_READY bit, just check sk_receive_queue --- net/mptcp/protocol.c | 55 ++++++++++++-------------------------------- 1 file changed, 15 insertions(+), 40 deletions(-) diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c index e5df0b5971c8..27b1f059dc93 100644 --- a/net/mptcp/protocol.c +++ b/net/mptcp/protocol.c @@ -528,7 +528,6 @@ static bool mptcp_check_data_fin(struct sock *sk) =20 sk->sk_shutdown |=3D RCV_SHUTDOWN; smp_mb__before_atomic(); /* SHUTDOWN must be visible first */ - set_bit(MPTCP_DATA_READY, &msk->flags); =20 switch (sk->sk_state) { case TCP_ESTABLISHED: @@ -742,10 +741,9 @@ void mptcp_data_ready(struct sock *sk, struct sock *ss= k) =20 /* Wake-up the reader only for in-sequence data */ mptcp_data_lock(sk); - if (move_skbs_to_msk(msk, ssk)) { - set_bit(MPTCP_DATA_READY, &msk->flags); + if (move_skbs_to_msk(msk, ssk)) sk->sk_data_ready(sk); - } + mptcp_data_unlock(sk); } =20 @@ -847,7 +845,6 @@ static void mptcp_check_for_eof(struct mptcp_sock *msk) sk->sk_shutdown |=3D RCV_SHUTDOWN; =20 smp_mb__before_atomic(); /* SHUTDOWN must be visible first */ - set_bit(MPTCP_DATA_READY, &msk->flags); sk->sk_data_ready(sk); } =20 @@ -1759,21 +1756,6 @@ static int mptcp_sendmsg(struct sock *sk, struct msg= hdr *msg, size_t len) return copied ? : ret; } =20 -static void mptcp_wait_data(struct sock *sk, long *timeo) -{ - DEFINE_WAIT_FUNC(wait, woken_wake_function); - struct mptcp_sock *msk =3D mptcp_sk(sk); - - add_wait_queue(sk_sleep(sk), &wait); - sk_set_bit(SOCKWQ_ASYNC_WAITDATA, sk); - - sk_wait_event(sk, timeo, - test_bit(MPTCP_DATA_READY, &msk->flags), &wait); - - sk_clear_bit(SOCKWQ_ASYNC_WAITDATA, sk); - remove_wait_queue(sk_sleep(sk), &wait); -} - static int __mptcp_recvmsg_mskq(struct mptcp_sock *msk, struct msghdr *msg, size_t len, int flags, @@ -2077,19 +2059,7 @@ static int mptcp_recvmsg(struct sock *sk, struct msg= hdr *msg, size_t len, } =20 pr_debug("block timeout %ld", timeo); - mptcp_wait_data(sk, &timeo); - } - - if (skb_queue_empty_lockless(&sk->sk_receive_queue) && - skb_queue_empty(&msk->receive_queue)) { - /* entire backlog drained, clear DATA_READY. */ - clear_bit(MPTCP_DATA_READY, &msk->flags); - - /* .. race-breaker: ssk might have gotten new data - * after last __mptcp_move_skbs() returned false. - */ - if (unlikely(__mptcp_move_skbs(msk))) - set_bit(MPTCP_DATA_READY, &msk->flags); + sk_wait_data(sk, &timeo, NULL); } =20 out_err: @@ -2098,9 +2068,9 @@ static int mptcp_recvmsg(struct sock *sk, struct msgh= dr *msg, size_t len, tcp_recv_timestamp(msg, sk, &tss); } =20 - pr_debug("msk=3D%p data_ready=3D%d rx queue empty=3D%d copied=3D%d", - msk, test_bit(MPTCP_DATA_READY, &msk->flags), - skb_queue_empty_lockless(&sk->sk_receive_queue), copied); + pr_debug("msk=3D%p rx queue empty=3D%d:%d copied=3D%d", + msk, skb_queue_empty_lockless(&sk->sk_receive_queue), + skb_queue_empty(&msk->receive_queue), copied); if (!(flags & MSG_PEEK)) mptcp_rcv_space_adjust(msk, copied); =20 @@ -2368,7 +2338,6 @@ static void mptcp_check_fastclose(struct mptcp_sock *= msk) inet_sk_state_store(sk, TCP_CLOSE); sk->sk_shutdown =3D SHUTDOWN_MASK; smp_mb__before_atomic(); /* SHUTDOWN must be visible first */ - set_bit(MPTCP_DATA_READY, &msk->flags); set_bit(MPTCP_WORK_CLOSE_SUBFLOW, &msk->flags); =20 mptcp_close_wake_up(sk); @@ -3385,8 +3354,14 @@ static int mptcp_stream_accept(struct socket *sock, = struct socket *newsock, =20 static __poll_t mptcp_check_readable(struct mptcp_sock *msk) { - return test_bit(MPTCP_DATA_READY, &msk->flags) ? EPOLLIN | EPOLLRDNORM : - 0; + /* Concurrent splices from sk_receive_queue into receive_queue will + * always show at least one non-empty queue when checked in this order. + */ + if (skb_queue_empty_lockless(&((struct sock *)msk)->sk_receive_queue) && + skb_queue_empty_lockless(&msk->receive_queue)) + return 0; + + return EPOLLIN | EPOLLRDNORM; } =20 static __poll_t mptcp_check_writeable(struct mptcp_sock *msk) @@ -3421,7 +3396,7 @@ static __poll_t mptcp_poll(struct file *file, struct = socket *sock, state =3D inet_sk_state_load(sk); pr_debug("msk=3D%p state=3D%d flags=3D%lx", msk, state, msk->flags); if (state =3D=3D TCP_LISTEN) - return mptcp_check_readable(msk); + return test_bit(MPTCP_DATA_READY, &msk->flags) ? EPOLLIN | EPOLLRDNORM := 0; =20 if (state !=3D TCP_SYN_SENT && state !=3D TCP_SYN_RECV) { mask |=3D mptcp_check_readable(msk); --=20 2.26.3