From patchwork Fri Apr 7 17:16:47 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: John Fastabend X-Patchwork-Id: 13205139 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 CF73BC77B6C for ; Fri, 7 Apr 2023 17:17:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230141AbjDGRRR (ORCPT ); Fri, 7 Apr 2023 13:17:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50986 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230113AbjDGRRP (ORCPT ); Fri, 7 Apr 2023 13:17:15 -0400 Received: from mail-pl1-x633.google.com (mail-pl1-x633.google.com [IPv6:2607:f8b0:4864:20::633]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7992BC162; Fri, 7 Apr 2023 10:17:06 -0700 (PDT) Received: by mail-pl1-x633.google.com with SMTP id ji2so909770plb.0; Fri, 07 Apr 2023 10:17:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; t=1680887825; x=1683479825; 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=htPOUzZg3EbALPZe7sbvBzrXy4PK3k2mTymzW6/vNDafX8FVsPkPr6PXbNd4r+rs3W 3q05ZvBXCgo1W+cVeQnJvtarLTlGQzQ3ZTWd3UUYNmTtPuzMiDN2DC+v3abd8F+PUAEO vnFATCCyU1UuWO/cCQz38GtDrxnlYU3Y8c4FYwCwEIlcr8dOmO5QPN9MmVi/SNfAsNAh aKjwFD/LuWxhmk50g/JiwkDxx2eTRa95z1XpgGWuxPRSgZwSOy5kRLIOVwl7W/yMDn2z jsUOb2IbCVfPJNyD10ZR18vcwPvhs9rjk4lCUe4a+O8qWMR/BOlnQseFNNPKsWl+FF9r cAMg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1680887825; x=1683479825; 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=ae7L+ibRLN1sSqdeIlC10MYBQZ+SiaJNUHRrURMM3MWEd1JdYprTCqDzyhipV+SkNj WBRThZklru1h0qKn1a5L3VyWVRjopGvdq5g6fAo0rpxf1kYkz0xVbW4fII8OcQsb1WZx bq3rBSNLMKEwbLAmw7hmKE+MWvy8BzM4fCVwJLCDJRXKMe4B/mvT1qC+t3kqMCfXDM8G mQpVDFJhTRIVeWqHHate6TgAEuJMsmTIYj9KktcvI+sOi3inP0n33OQUVaPCcSPUtZR3 SJfZRdpEeLQqSzWK7+ggThQ9IjGrWYV5SeE2rrWlN5GrGyDGnD0rxffwgEyFHteu3yeo bjxg== X-Gm-Message-State: AAQBX9eDYVQESFXDIdh2+jUSp6sOQrzbtk6RRA0y2qXRq4ffjrkbpSED ZR1vW0K+2uiRXEtGidKvx9o= X-Google-Smtp-Source: AKy350aZQlqmtvZKn55SNFrf+oONpzetl3QvDZxtq2RsAWHpPax/XKzzmBBZNTUQX3UrgdfAKSRvaQ== X-Received: by 2002:a17:902:7593:b0:1a5:dfd:d167 with SMTP id j19-20020a170902759300b001a50dfdd167mr3248454pll.8.1680887825511; Fri, 07 Apr 2023 10:17:05 -0700 (PDT) Received: from john.lan ([98.97.116.126]) by smtp.gmail.com with ESMTPSA id p1-20020a1709028a8100b0019b0937003esm3185425plo.150.2023.04.07.10.17.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 07 Apr 2023 10:17:05 -0700 (PDT) From: John Fastabend To: 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 v6 05/12] bpf: sockmap, TCP data stall on recv before accept Date: Fri, 7 Apr 2023 10:16:47 -0700 Message-Id: <20230407171654.107311-6-john.fastabend@gmail.com> X-Mailer: git-send-email 2.33.0 In-Reply-To: <20230407171654.107311-1-john.fastabend@gmail.com> References: <20230407171654.107311-1-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 Reviewed-by: Jakub Sitnicki --- 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