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 X-Spam-Level: X-Spam-Status: No, score=-9.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B23BFC63777 for ; Mon, 16 Nov 2020 14:31:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6C53422409 for ; Mon, 16 Nov 2020 14:31:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=cloudflare.com header.i=@cloudflare.com header.b="maIsAJsZ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730197AbgKPObg (ORCPT ); Mon, 16 Nov 2020 09:31:36 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44718 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729232AbgKPObg (ORCPT ); Mon, 16 Nov 2020 09:31:36 -0500 Received: from mail-wm1-x343.google.com (mail-wm1-x343.google.com [IPv6:2a00:1450:4864:20::343]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D98D1C0613CF for ; Mon, 16 Nov 2020 06:31:35 -0800 (PST) Received: by mail-wm1-x343.google.com with SMTP id p22so23899507wmg.3 for ; Mon, 16 Nov 2020 06:31:35 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cloudflare.com; s=google; h=references:user-agent:from:to:cc:subject:in-reply-to:date :message-id:mime-version; bh=qMjDR0Ym+nhpvOJ6zJJnl+LYMN6YDDREpuIxO7AtctE=; b=maIsAJsZ9C5ds72BdFMn8SZrZag4sqWfO/sawEbHeTLRHGOCxsrX7qrwfnuNG1YA1j QZtGTqZB+Or9el/yGKjjvrccoBtEOZOyFIj2uWR0DabDfm6HTvCTdRnSue5wP33Spa0P i9O51hwM6xuwY4SCPNtQ+frLZ/lUKwXYB+8XA= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:references:user-agent:from:to:cc:subject :in-reply-to:date:message-id:mime-version; bh=qMjDR0Ym+nhpvOJ6zJJnl+LYMN6YDDREpuIxO7AtctE=; b=Va63WDIsps0i3XYUEUPlbhmv6D8aA6TRWVu20GZ/1AvNpUkW0PlYkpbeEDIbsYzGmO uBtWQ8ULidcGhhBqLJVV78DFhXInd5xRsKNKPs5qaizP22ScjrJY1R9IcHyLmB85d/Nm 3BZd9X/YoNf/+/5L7ykfWSttwqNeDGkovIVp+i6+yMBFdympJ9ITje4iDQrutScLsMSc YJ/x1ADtYILaSulThv97Vavnavj9vw1Tc5Ku4sYJVIfXqTZB925IP0Oo7WdvmNtUrAI9 xsR8J+RqM5n86b2AfeSjbaamRd4iC1UO+hKdM7sUpTJUT5nz27nHQHTfKvieAsC3qhmg 9AiA== X-Gm-Message-State: AOAM5323jcaR2QJy1OtZmA+/TUSCJ5TvrbHE9MkKT4tuP9xE+1hRWpd3 1J+zs5eRDcgNj+cYEKRzAlpO1Q== X-Google-Smtp-Source: ABdhPJwH2qVsIs/Q09LWrmiCrFI7JYrstrUAmtDXK2/+Vjjo5XitU8+h0y5abnzV1eFvxC7rtTQtig== X-Received: by 2002:a7b:c845:: with SMTP id c5mr15528327wml.135.1605537094497; Mon, 16 Nov 2020 06:31:34 -0800 (PST) Received: from cloudflare.com ([2a02:a310:c262:aa00:b35e:8938:2c2a:ba8b]) by smtp.gmail.com with ESMTPSA id u16sm22809008wrn.55.2020.11.16.06.31.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 16 Nov 2020 06:31:33 -0800 (PST) References: <160522352433.135009.15329422887113794062.stgit@john-XPS-13-9370> <160522367856.135009.17304729578208922913.stgit@john-XPS-13-9370> User-agent: mu4e 1.1.0; emacs 26.3 From: Jakub Sitnicki To: John Fastabend Cc: ast@kernel.org, daniel@iogearbox.net, bpf@vger.kernel.org, netdev@vger.kernel.org Subject: Re: [bpf PATCH v2 5/6] bpf, sockmap: Handle memory acct if skb_verdict prog redirects to self In-reply-to: <160522367856.135009.17304729578208922913.stgit@john-XPS-13-9370> Date: Mon, 16 Nov 2020 15:31:32 +0100 Message-ID: <87blfxweyj.fsf@cloudflare.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Fri, Nov 13, 2020 at 12:27 AM CET, John Fastabend wrote: > If the skb_verdict_prog redirects an skb knowingly to itself, fix your > BPF program this is not optimal and an abuse of the API please use > SK_PASS. That said there may be cases, such as socket load balancing, > where picking the socket is hashed based or otherwise picks the same > socket it was received on in some rare cases. If this happens we don't > want to confuse userspace giving them an EAGAIN error if we can avoid > it. > > To avoid double accounting in these cases. At the moment even if the > skb has already been charged against the sockets rcvbuf and forward > alloc we check it again and do set_owner_r() causing it to be orphaned > and recharged. For one this is useless work, but more importantly we > can have a case where the skb could be put on the ingress queue, but > because we are under memory pressure we return EAGAIN. The trouble > here is the skb has already been accounted for so any rcvbuf checks > include the memory associated with the packet already. This rolls > up and can result in unecessary EAGAIN errors in userspace read() > calls. > > Fix by doing an unlikely check and skipping checks if skb->sk == sk. > > Fixes: 51199405f9672 ("bpf: skb_verdict, support SK_PASS on RX BPF path") > Signed-off-by: John Fastabend > --- > net/core/skmsg.c | 17 +++++++++++------ > 1 file changed, 11 insertions(+), 6 deletions(-) > > diff --git a/net/core/skmsg.c b/net/core/skmsg.c > index 9aed5a2c7c5b..f747ee341fe8 100644 > --- a/net/core/skmsg.c > +++ b/net/core/skmsg.c > @@ -404,11 +404,13 @@ static struct sk_msg *sk_psock_create_ingress_msg(struct sock *sk, > { > struct sk_msg *msg; > > - if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf) > - return NULL; > + if (likely(skb->sk != sk)) { > + if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf) > + return NULL; > > - if (!sk_rmem_schedule(sk, skb, skb->truesize)) > - return NULL; > + if (!sk_rmem_schedule(sk, skb, skb->truesize)) > + return NULL; > + } > > msg = kzalloc(sizeof(*msg), __GFP_NOWARN | GFP_ATOMIC); > if (unlikely(!msg)) > @@ -455,9 +457,12 @@ static int sk_psock_skb_ingress(struct sk_psock *psock, struct sk_buff *skb) > * the BPF program was run initiating the redirect to the socket > * we will eventually receive this data on. The data will be released > * from skb_consume found in __tcp_bpf_recvmsg() after its been copied > - * into user buffers. > + * into user buffers. If we are receiving on the same sock skb->sk is > + * already assigned, skip memory accounting and owner transition seeing > + * it already set correctly. > */ > - skb_set_owner_r(skb, sk); > + if (likely(skb->sk != sk)) > + skb_set_owner_r(skb, sk); > return sk_psock_skb_ingress_enqueue(skb, psock, sk, msg); > } > I think all the added checks boil down to having: struct sock *sk = psock->sk; if (unlikely(skb->sk == sk)) return sk_psock_skb_ingress_self(psock, skb); ... on entry to sk_psock_skb_ingress().