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 696B1C433FE for ; Sat, 19 Nov 2022 13:52:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232440AbiKSNwh (ORCPT ); Sat, 19 Nov 2022 08:52:37 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50652 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232246AbiKSNwg (ORCPT ); Sat, 19 Nov 2022 08:52:36 -0500 Received: from www262.sakura.ne.jp (www262.sakura.ne.jp [202.181.97.72]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 184612CDF8 for ; Sat, 19 Nov 2022 05:52:33 -0800 (PST) Received: from fsav314.sakura.ne.jp (fsav314.sakura.ne.jp [153.120.85.145]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id 2AJDqVaW002234; Sat, 19 Nov 2022 22:52:32 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav314.sakura.ne.jp (F-Secure/fsigk_smtp/550/fsav314.sakura.ne.jp); Sat, 19 Nov 2022 22:52:31 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/fsav314.sakura.ne.jp) Received: from [192.168.1.9] (M106072142033.v4.enabler.ne.jp [106.72.142.33]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id 2AJDqVps002229 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NO); Sat, 19 Nov 2022 22:52:31 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Message-ID: Date: Sat, 19 Nov 2022 22:52:30 +0900 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 6.3; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.5.0 Subject: Re: [PATCH net] l2tp: Don't sleep and disable BH under writer-side sk_callback_lock Content-Language: en-US To: Jakub Sitnicki , netdev@vger.kernel.org Cc: "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 References: <20221119130317.39158-1-jakub@cloudflare.com> From: Tetsuo Handa In-Reply-To: <20221119130317.39158-1-jakub@cloudflare.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org 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.