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=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,USER_AGENT_GIT 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 BC9E2C33CAF for ; Thu, 23 Jan 2020 15:55:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9424D20704 for ; Thu, 23 Jan 2020 15:55:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=cloudflare.com header.i=@cloudflare.com header.b="nwkm0mz8" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728998AbgAWPzq (ORCPT ); Thu, 23 Jan 2020 10:55:46 -0500 Received: from mail-wr1-f66.google.com ([209.85.221.66]:36149 "EHLO mail-wr1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728901AbgAWPzn (ORCPT ); Thu, 23 Jan 2020 10:55:43 -0500 Received: by mail-wr1-f66.google.com with SMTP id z3so3666116wru.3 for ; Thu, 23 Jan 2020 07:55:40 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cloudflare.com; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=cTVNuQ7EbbdFeGuZ+T31KnByBM1u0Tx/L1PeHjvJyOM=; b=nwkm0mz8tVPRb9tnHZpAPlOfghqnYQpQQ5f7DjJV+FXIlzvdaGyRTaJBNuseuzcm4+ hz4bX7b153SoDTSLK+gXou4DWcQWDf618R8cewdOM7L4faO8BDRyhdb44kkU4LK2AHmO c0qDMWnor87nGeLKJG2+cJIMkzAgiwy/I3Aqo= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=cTVNuQ7EbbdFeGuZ+T31KnByBM1u0Tx/L1PeHjvJyOM=; b=Ns3gbbQhoHF/czRYn70NaxFdae//KTIU9h6MqMUMMLIqWoi+2UAHTpQw7DHWL/X+cy a6VKzoAuJGwOmukK2c6wiXUZBTBE4KkBDQ2DYnXeYL7iOTdv0Kb65YXsy4l09uVfeIT+ Mp35islS/O5ufrmDaD0PbX2n8hZwaevz3nHi2xwH1pUgjpyp2osximYUqkOEOTbqsXPn w+oGXb32CyAXB4X9rtE5Ekl1VyfF3vPLGu6m41IxhUw6HEionsaKzDJ0yRVjYI0VBreo zbDa2ruf2mfyVcjbBDyAHF9luKtHhIgOTxZUGxsnZmtPzNaprAa9x/rN/ZVsR+RIV+io rDxA== X-Gm-Message-State: APjAAAVefqdVYADn6pFVkh6snq90I6QAtbhYekqxL3awujtoHwR1OCQ3 1JTkm9zS1QtwH8zfyyFdODrsmw== X-Google-Smtp-Source: APXvYqzlts4QhlEzAWF7BL7PVZa2arGA7dpfBrE76w08gSalU/IXieor/jZXQRiZ24HTGXuLGO043g== X-Received: by 2002:a05:6000:1052:: with SMTP id c18mr17925717wrx.268.1579794939826; Thu, 23 Jan 2020 07:55:39 -0800 (PST) Received: from cloudflare.com ([176.221.114.230]) by smtp.gmail.com with ESMTPSA id s19sm3073497wmj.33.2020.01.23.07.55.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 23 Jan 2020 07:55:39 -0800 (PST) From: Jakub Sitnicki To: bpf@vger.kernel.org Cc: netdev@vger.kernel.org, kernel-team@cloudflare.com, John Fastabend , Lorenz Bauer , Martin Lau Subject: [PATCH bpf-next v4 03/12] net, sk_msg: Clear sk_user_data pointer on clone if tagged Date: Thu, 23 Jan 2020 16:55:25 +0100 Message-Id: <20200123155534.114313-4-jakub@cloudflare.com> X-Mailer: git-send-email 2.24.1 In-Reply-To: <20200123155534.114313-1-jakub@cloudflare.com> References: <20200123155534.114313-1-jakub@cloudflare.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org sk_user_data can hold a pointer to an object that is not intended to be shared between the parent socket and the child that gets a pointer copy on clone. This is the case when sk_user_data points at reference-counted object, like struct sk_psock. One way to resolve it is to tag the pointer with a no-copy flag by repurposing its lowest bit. Based on the bit-flag value we clear the child sk_user_data pointer after cloning the parent socket. The no-copy flag is stored in the pointer itself as opposed to externally, say in socket flags, to guarantee that the pointer and the flag are copied from parent to child socket in an atomic fashion. Parent socket state is subject to change while copying, we don't hold any locks at that time. This approach relies on an assumption that sk_user_data holds a pointer to an object aligned at least 2 bytes. A manual audit of existing users of rcu_dereference_sk_user_data helper confirms our assumption. Also, an RCU-protected sk_user_data is not likely to hold a pointer to a char value or a pathological case of "struct { char c; }". To be safe, warn when the flag-bit is set when setting sk_user_data to catch any future misuses. It is worth considering why clearing sk_user_data unconditionally is not an option. There exist users, DRBD, NVMe, and Xen drivers being among them, that rely on the pointer being copied when cloning the listening socket. Potentially we could distinguish these users by checking if the listening socket has been created in kernel-space via sock_create_kern, and hence has sk_kern_sock flag set. However, this is not the case for NVMe and Xen drivers, which create sockets without marking them as belonging to the kernel. Acked-by: John Fastabend Acked-by: Martin KaFai Lau Signed-off-by: Jakub Sitnicki --- include/net/sock.h | 37 +++++++++++++++++++++++++++++++++++-- net/core/skmsg.c | 2 +- net/core/sock.c | 6 ++++++ 3 files changed, 42 insertions(+), 3 deletions(-) diff --git a/include/net/sock.h b/include/net/sock.h index 0891c55f1e82..93e359a03174 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -518,10 +518,43 @@ enum sk_pacing { SK_PACING_FQ = 2, }; +/* Pointer stored in sk_user_data might not be suitable for copying + * when cloning the socket. For instance, it can point to a reference + * counted object. sk_user_data bottom bit is set if pointer must not + * be copied. + */ +#define SK_USER_DATA_NOCOPY 1UL +#define SK_USER_DATA_PTRMASK ~(SK_USER_DATA_NOCOPY) + +/** + * sk_user_data_is_nocopy - Test if sk_user_data pointer must not be copied + * @sk: socket + */ +static inline bool sk_user_data_is_nocopy(const struct sock *sk) +{ + return ((uintptr_t)sk->sk_user_data & SK_USER_DATA_NOCOPY); +} + #define __sk_user_data(sk) ((*((void __rcu **)&(sk)->sk_user_data))) -#define rcu_dereference_sk_user_data(sk) rcu_dereference(__sk_user_data((sk))) -#define rcu_assign_sk_user_data(sk, ptr) rcu_assign_pointer(__sk_user_data((sk)), ptr) +#define rcu_dereference_sk_user_data(sk) \ +({ \ + void *__tmp = rcu_dereference(__sk_user_data((sk))); \ + (void *)((uintptr_t)__tmp & SK_USER_DATA_PTRMASK); \ +}) +#define rcu_assign_sk_user_data(sk, ptr) \ +({ \ + uintptr_t __tmp = (uintptr_t)(ptr); \ + WARN_ON_ONCE(__tmp & ~SK_USER_DATA_PTRMASK); \ + rcu_assign_pointer(__sk_user_data((sk)), __tmp); \ +}) +#define rcu_assign_sk_user_data_nocopy(sk, ptr) \ +({ \ + uintptr_t __tmp = (uintptr_t)(ptr); \ + WARN_ON_ONCE(__tmp & ~SK_USER_DATA_PTRMASK); \ + rcu_assign_pointer(__sk_user_data((sk)), \ + __tmp | SK_USER_DATA_NOCOPY); \ +}) /* * SK_CAN_REUSE and SK_NO_REUSE on a socket mean that the socket is OK diff --git a/net/core/skmsg.c b/net/core/skmsg.c index ded2d5227678..eeb28cb85664 100644 --- a/net/core/skmsg.c +++ b/net/core/skmsg.c @@ -512,7 +512,7 @@ struct sk_psock *sk_psock_init(struct sock *sk, int node) sk_psock_set_state(psock, SK_PSOCK_TX_ENABLED); refcount_set(&psock->refcnt, 1); - rcu_assign_sk_user_data(sk, psock); + rcu_assign_sk_user_data_nocopy(sk, psock); sock_hold(sk); return psock; diff --git a/net/core/sock.c b/net/core/sock.c index 3953bb23f4d0..74662943af5c 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -1864,6 +1864,12 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority) goto out; } + /* Clear sk_user_data if parent had the pointer tagged + * as not suitable for copying when cloning. + */ + if (sk_user_data_is_nocopy(newsk)) + RCU_INIT_POINTER(newsk->sk_user_data, NULL); + newsk->sk_err = 0; newsk->sk_err_soft = 0; newsk->sk_priority = 0; -- 2.24.1