From patchwork Mon Apr 3 20:01:31 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: John Fastabend X-Patchwork-Id: 13198662 X-Patchwork-Delegate: bpf@iogearbox.net 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 30389C76188 for ; Mon, 3 Apr 2023 20:01:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232889AbjDCUB4 (ORCPT ); Mon, 3 Apr 2023 16:01:56 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41602 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232888AbjDCUBx (ORCPT ); Mon, 3 Apr 2023 16:01:53 -0400 Received: from mail-pl1-x62b.google.com (mail-pl1-x62b.google.com [IPv6:2607:f8b0:4864:20::62b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BDF383C23; Mon, 3 Apr 2023 13:01:49 -0700 (PDT) Received: by mail-pl1-x62b.google.com with SMTP id u10so29169400plz.7; Mon, 03 Apr 2023 13:01:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; t=1680552109; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=QZLeQQ1n11MV3iEBKLP57EKp7c8nx+XOI45qonfxXGc=; b=MBhewMzYx82iQuKQDSkHmEBnKLTn41YgPtjLB8ohxCAh79/Q5nlL8eqDK3ZgcYnaR7 IMP3QMLzroW+DzI6FDkDdF0STAJubL1oR1YnnudRYT9DEIAvlUvOiXQvCDmSxvNq0URl uv+8oueC2cJHEA0VLZxVsOMN5EpS4DXb8G999Z+lDauIndkzab1MUYIHPS7BvdSl2I8s tCAR6wreEKaqGtIKnhiC8CPG0Ac7sxtoTgMD326DtX+LOpqvMl3q+RKu4ruBcQMDourS 0wB7p5og+MZT3peBoirl9ym7pNRqYMYZVOEP6RFDdqGtweXdhveZbo6qgAdVenfi0mPU m26w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1680552109; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=QZLeQQ1n11MV3iEBKLP57EKp7c8nx+XOI45qonfxXGc=; b=gjFQYNSUCtNVjtLa/21en/9bHy+q5DhkAb/mMcS2HRgWkD45g/OygOYCMC7IX9hvet u8Tvi74lLZJ+Y12eaF55n/mHbTF3OKDbhRWuM3iq43dNVSMIvUtnAWuWXZnkDCznR2HI DTO3yZ42XFXNVzA6EQbNaNCLr4w/Xp7/utY1JeCc5lK6x0vrqf64h6e4FZxM0q6/VfFl o711p9e1cRhjTJb+XzwWQd29nMSMt/WjX4vqBzx76m7UmAL450aAFcoPzwNjQE5pe3qS vIUUgFu8TFa4hlG/Ju2DgrngCiPG1Xhm/qM1/7Av+F71iYSMqSVlS0gVJJAYJgYQDn/Z nqSg== X-Gm-Message-State: AAQBX9cEYp4OdaBoJWVDuAoX5sjK0eVP2RAH29ulc1C+fIaZH7Of+zPI a45BgTNl9emOBMmTJMV5b5U= X-Google-Smtp-Source: AKy350aC/YdyTSJvf1sGB4rOuNdfKg4ZKIASG06+/UfYjYLR05pVMD13bU/+F55HAoTnk9k+7AkPAw== X-Received: by 2002:a17:903:210a:b0:1a0:549d:39a1 with SMTP id o10-20020a170903210a00b001a0549d39a1mr215735ple.32.1680552109353; Mon, 03 Apr 2023 13:01:49 -0700 (PDT) Received: from localhost.localdomain ([2605:59c8:4c5:7110:3da7:5d97:f465:5e01]) by smtp.gmail.com with ESMTPSA id t18-20020a1709028c9200b0019c2b1c4db1sm6948835plo.239.2023.04.03.13.01.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 03 Apr 2023 13:01:48 -0700 (PDT) From: John Fastabend To: cong.wang@bytedance.com, jakub@cloudflare.com, daniel@iogearbox.net, lmb@isovalent.com, edumazet@google.com Cc: john.fastabend@gmail.com, bpf@vger.kernel.org, netdev@vger.kernel.org, ast@kernel.org, andrii@kernel.org, will@isovalent.com Subject: [PATCH bpf v3 05/12] bpf: sockmap, TCP data stall on recv before accept Date: Mon, 3 Apr 2023 13:01:31 -0700 Message-Id: <20230403200138.937569-6-john.fastabend@gmail.com> X-Mailer: git-send-email 2.33.0 In-Reply-To: <20230403200138.937569-1-john.fastabend@gmail.com> References: <20230403200138.937569-1-john.fastabend@gmail.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net A common mechanism to put a TCP socket into the sockmap is to hook the BPF_SOCK_OPS_{ACTIVE_PASSIVE}_ESTABLISHED_CB event with a BPF program that can map the socket info to the correct BPF verdict parser. When the user adds the socket to the map the psock is created and the new ops are assigned to ensure the verdict program will 'see' the sk_buffs as they arrive. Part of this process hooks the sk_data_ready op with a BPF specific handler to wake up the BPF verdict program when data is ready to read. The logic is simple enough (posted here for easy reading) static void sk_psock_verdict_data_ready(struct sock *sk) { struct socket *sock = sk->sk_socket; if (unlikely(!sock || !sock->ops || !sock->ops->read_skb)) return; sock->ops->read_skb(sk, sk_psock_verdict_recv); } The oversight here is sk->sk_socket is not assigned until the application accepts() the new socket. However, its entirely ok for the peer application to do a connect() followed immediately by sends. The socket on the receiver is sitting on the backlog queue of the listening socket until its accepted and the data is queued up. If the peer never accepts the socket or is slow it will eventually hit data limits and rate limit the session. But, important for BPF sockmap hooks when this data is received TCP stack does the sk_data_ready() call but the read_skb() for this data is never called because sk_socket is missing. The data sits on the sk_receive_queue. Then once the socket is accepted if we never receive more data from the peer there will be no further sk_data_ready calls and all the data is still on the sk_receive_queue(). Then user calls recvmsg after accept() and for TCP sockets in sockmap we use the tcp_bpf_recvmsg_parser() handler. The handler checks for data in the sk_msg ingress queue expecting that the BPF program has already run from the sk_data_ready hook and enqueued the data as needed. So we are stuck. To fix do an unlikely check in recvmsg handler for data on the sk_receive_queue and if it exists wake up data_ready. We have the sock locked in both read_skb and recvmsg so should avoid having multiple runners. Fixes: 04919bed948dc ("tcp: Introduce tcp_read_skb()") Signed-off-by: John Fastabend --- net/ipv4/tcp_bpf.c | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c index 804bd0c247d0..ae6c7130551c 100644 --- a/net/ipv4/tcp_bpf.c +++ b/net/ipv4/tcp_bpf.c @@ -212,6 +212,26 @@ static int tcp_bpf_recvmsg_parser(struct sock *sk, return tcp_recvmsg(sk, msg, len, flags, addr_len); lock_sock(sk); + + /* We may have received data on the sk_receive_queue pre-accept and + * then we can not use read_skb in this context because we haven't + * assigned a sk_socket yet so have no link to the ops. The work-around + * is to check the sk_receive_queue and in these cases read skbs off + * queue again. The read_skb hook is not running at this point because + * of lock_sock so we avoid having multiple runners in read_skb. + */ + if (unlikely(!skb_queue_empty(&sk->sk_receive_queue))) { + tcp_data_ready(sk); + /* This handles the ENOMEM errors if we both receive data + * pre accept and are already under memory pressure. At least + * let user no to retry. + */ + if (unlikely(!skb_queue_empty(&sk->sk_receive_queue))) { + copied = -EAGAIN; + goto out; + } + } + msg_bytes_ready: copied = sk_msg_recvmsg(sk, psock, msg, len, flags); /* The typical case for EFAULT is the socket was gracefully