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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 88E91C433FE for ; Mon, 21 Nov 2022 09:03:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229664AbiKUJDl (ORCPT ); Mon, 21 Nov 2022 04:03:41 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53052 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229500AbiKUJDj (ORCPT ); Mon, 21 Nov 2022 04:03:39 -0500 Received: from mail-ed1-x532.google.com (mail-ed1-x532.google.com [IPv6:2a00:1450:4864:20::532]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CD2FF6DCCE for ; Mon, 21 Nov 2022 01:03:38 -0800 (PST) Received: by mail-ed1-x532.google.com with SMTP id l24so2703734edj.8 for ; Mon, 21 Nov 2022 01:03:38 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cloudflare.com; s=google; h=mime-version:message-id:in-reply-to:date:subject:cc:to:from :user-agent:references:from:to:cc:subject:date:message-id:reply-to; bh=UB1MfhNwZW6ubazXZ6eesXGjaNDuQLnoqWVlBtiJzkM=; b=fnLqr6bPx15rfA08GN5Fjlh4yXMkQEvaoc/8Cu/nADLEWKUGIPF1TqnCzFx8yEzr0Z S/Pr2VueriRrXfWEjKEzNSfh4MNPhtOeh9qFpIsDz111yURKJmVy0aA1qkcsplilUQUv AP9L1+4ZWQA5r6wVJZ2zqbf4G61QwYDNQYd54= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=mime-version:message-id:in-reply-to:date:subject:cc:to:from :user-agent:references:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=UB1MfhNwZW6ubazXZ6eesXGjaNDuQLnoqWVlBtiJzkM=; b=GeqHZI3XT8jBacpfx8MWK1DT0D/WtNjwWQ6e0hvVNzpxjjmyDwm12YWHmlzdq2Sl2M 9HLUTKzgfpr8St2uc/+rQH5xqdwgRNYSkInGvutoRl7EBvKd8e+NUvZRsvlKOFhcURjo j+mBqYBRQQY5jeDv2+L39mFQ6HxQkMx5Un5KYxuyycgOth3nltC6tAIQEdNLgu4kEU6h C5SPzrmneRiZSg/A5itxDyWmWseU6En+EQQkxp5WQgyxhGzxNhDbkdhOj2uGYc1CoES2 CruNfG/VT5EFV45HxdM6YoY8vVxoqSKfwmWqiLR5/YrOlEb4rpxgL3ROs9D5N0U7G+MR h1vw== X-Gm-Message-State: ANoB5pnOJXdFpCcSxHohquUIB+tv7sGZiNWW7PJOzLz01VQfqzdOjbNm g3kTnCdgoCweH+gmePVMazwXtA== X-Google-Smtp-Source: AA0mqf4mzAWbnCBclDcmi2quMF6lNU3kbfwzw/p9IK4AJtu+8fct5KB1i9cH7vzAd3fVDYvR6IMzxA== X-Received: by 2002:a05:6402:1015:b0:461:5f19:61da with SMTP id c21-20020a056402101500b004615f1961damr15235097edu.34.1669021417391; Mon, 21 Nov 2022 01:03:37 -0800 (PST) Received: from cloudflare.com (79.184.204.15.ipv4.supernova.orange.pl. [79.184.204.15]) by smtp.gmail.com with ESMTPSA id d12-20020a170906304c00b007b29a6bec28sm4772372ejd.27.2022.11.21.01.03.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 21 Nov 2022 01:03:37 -0800 (PST) References: <20221119130317.39158-1-jakub@cloudflare.com> User-agent: mu4e 1.6.10; emacs 27.2 From: Jakub Sitnicki To: Tetsuo Handa Cc: netdev@vger.kernel.org, "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Tom Parkin , syzbot+703d9e154b3b58277261@syzkaller.appspotmail.com, syzbot+50680ced9e98a61f7698@syzkaller.appspotmail.com, syzbot+de987172bb74a381879b@syzkaller.appspotmail.com Subject: Re: [PATCH net] l2tp: Don't sleep and disable BH under writer-side sk_callback_lock Date: Mon, 21 Nov 2022 10:00:58 +0100 In-reply-to: Message-ID: <87wn7o7k7r.fsf@cloudflare.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Sat, Nov 19, 2022 at 11:27 PM +09, Tetsuo Handa wrote: > On 2022/11/19 22:52, Tetsuo Handa wrote: >> On 2022/11/19 22:03, Jakub Sitnicki wrote: >>> When holding a reader-writer spin lock we cannot sleep. Calling >>> setup_udp_tunnel_sock() with write lock held violates this rule, because we >>> end up calling percpu_down_read(), which might sleep, as syzbot reports >>> [1]: >>> >>> __might_resched.cold+0x222/0x26b kernel/sched/core.c:9890 >>> percpu_down_read include/linux/percpu-rwsem.h:49 [inline] >>> cpus_read_lock+0x1b/0x140 kernel/cpu.c:310 >>> static_key_slow_inc+0x12/0x20 kernel/jump_label.c:158 >>> udp_tunnel_encap_enable include/net/udp_tunnel.h:187 [inline] >>> setup_udp_tunnel_sock+0x43d/0x550 net/ipv4/udp_tunnel_core.c:81 >>> l2tp_tunnel_register+0xc51/0x1210 net/l2tp/l2tp_core.c:1509 >>> pppol2tp_connect+0xcdc/0x1a10 net/l2tp/l2tp_ppp.c:723 >>> >>> Trim the writer-side critical section for sk_callback_lock down to the >>> minimum, so that it covers only operations on sk_user_data. >> >> This patch does not look correct. >> >> Since l2tp_validate_socket() checks that sk->sk_user_data == NULL with >> sk->sk_callback_lock held, you need to call rcu_assign_sk_user_data(sk, tunnel) >> before releasing sk->sk_callback_lock. >> > > Is it safe to temporarily set a dummy pointer like below? > If it is not safe, what makes assignments done by > setup_udp_tunnel_sock() safe? Yes, I think so. Great idea. I've used it in v2. We can check & assign sk_user_data under sk_callback_lock, and then just let setup_udp_tunnel_sock overwrite it with the same value, without holding the lock. I still think that it's best to keep the critical section as short as possible, though. [...]