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=ham 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 10494C34048 for ; Tue, 18 Feb 2020 17:10:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DC3FE208C4 for ; Tue, 18 Feb 2020 17:10:32 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=cloudflare.com header.i=@cloudflare.com header.b="BOI5Ve+9" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726707AbgBRRKc (ORCPT ); Tue, 18 Feb 2020 12:10:32 -0500 Received: from mail-wm1-f66.google.com ([209.85.128.66]:35235 "EHLO mail-wm1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726764AbgBRRKb (ORCPT ); Tue, 18 Feb 2020 12:10:31 -0500 Received: by mail-wm1-f66.google.com with SMTP id b17so3790481wmb.0 for ; Tue, 18 Feb 2020 09:10:30 -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=iErDGLeYzQHnDlu4pDhNRNJjWqR/EZKacma+vcdQIyM=; b=BOI5Ve+9dtgcPUmQGJFEL+0FnLXwb5Ls+ycGUCSxYlY9RDNy7w/+CX7t7HvNDt0/oH 8+A17ZgCbRHkVGC0bIZ/GC3KnYaIpGGz9+V9fQfKu6xZtHpEoyxc3HjZNdZew8+2c8Bn O61RNqcExdy2f3met7mmjbKLqR1LmiJA3oQG4= 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=iErDGLeYzQHnDlu4pDhNRNJjWqR/EZKacma+vcdQIyM=; b=gDlGpN/fswp0lbSXH0LB4MFpN3IFxxbp9XLQJ63TEIixYgdalw1l+4zLm3uHnTkM8c DJm+bAvqBGaFcGRuOP0pXVLVKTYEjr3InLsG0CzXlmXI79kMwhcXJO+kS8rVixnMnejQ z/ZtAPfP0oyZLlv7U4z3UupycvwxTUsiSZsTikMm039ueW8Osl6XOx41DqvvWFvCoUzY LiqpCuY90wqSpVBbaN9HS4T6nAQW0p4GA109pajyyakD4z+q80+xZNVbFvO5lkohNRGR QmodhOC6M0Ajd7moeRAh7FjVLUUQEo2dB9a4HVJ0M19S7QdBIgBUzogzoTH/L6pyxqls 8Wkg== X-Gm-Message-State: APjAAAV2fTqLFoYTn5LcjsvSNeEgy8EpnLL4V73KfR/+ByRQ3pqai1/y uLVc90oxn5YSAjJ1cwoJH7r6sK1UarPxhdfo X-Google-Smtp-Source: APXvYqxFVAw6+sSO8kt7A/AIspyaCYt9Q/MZ2kHza1B+4Y9SjghpS8Psc5P5QwZBwc1GehjaBfbeIQ== X-Received: by 2002:a05:600c:291d:: with SMTP id i29mr4320406wmd.39.1582045829059; Tue, 18 Feb 2020 09:10:29 -0800 (PST) Received: from cloudflare.com ([88.157.168.82]) by smtp.gmail.com with ESMTPSA id g19sm3572281wmh.36.2020.02.18.09.10.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 18 Feb 2020 09:10:28 -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 v7 02/11] net, sk_msg: Clear sk_user_data pointer on clone if tagged Date: Tue, 18 Feb 2020 17:10:14 +0000 Message-Id: <20200218171023.844439-3-jakub@cloudflare.com> X-Mailer: git-send-email 2.24.1 In-Reply-To: <20200218171023.844439-1-jakub@cloudflare.com> References: <20200218171023.844439-1-jakub@cloudflare.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@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 02162b0378f7..9f37fdfd15d4 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -502,10 +502,43 @@ 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 bf1173b93eda..e4af4dbc1c9e 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -1865,6 +1865,12 @@ 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