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=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 5A2B3C388F2 for ; Tue, 3 Nov 2020 04:12:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E5C1E22245 for ; Tue, 3 Nov 2020 04:12:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="GzpY15iF" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725953AbgKCEMx (ORCPT ); Mon, 2 Nov 2020 23:12:53 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:44675 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725940AbgKCEMw (ORCPT ); Mon, 2 Nov 2020 23:12:52 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1604376770; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=NgYZUQ3WOulleStwOp1G16UNxwlI9rafuhu3xgy1Db0=; b=GzpY15iFWS3+j8BQSdvHp0qdYSkCffoeA9tBRC90ESZhoFgVR4uRgI2GyBj2nU76aparxT z/xlkpnGqRPLVv1eCz+RLcXH5T4yb19VIQGh1oPzjrWI+wEkx3a5r6g1JiXeaRm0YiJqJU ihUO4CDT+CqvCCuz2FuNhR1KbLR6k14= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-7-EB9aRCxWMfK-qixqLQiAeQ-1; Mon, 02 Nov 2020 23:12:49 -0500 X-MC-Unique: EB9aRCxWMfK-qixqLQiAeQ-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D81868030AE; Tue, 3 Nov 2020 04:12:47 +0000 (UTC) Received: from T590 (ovpn-12-125.pek2.redhat.com [10.72.12.125]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8D56E672C0; Tue, 3 Nov 2020 04:12:37 +0000 (UTC) Date: Tue, 3 Nov 2020 12:12:15 +0800 From: Ming Lei To: xiubli@redhat.com Cc: josef@toxicpanda.com, axboe@kernel.dk, nbd@other.debian.org, linux-block@vger.kernel.org, jdillama@redhat.com, mgolub@suse.de Subject: Re: [PATCH v2 1/2] nbd: fix use-after-freed crash for nbd->recv_workq Message-ID: <20201103041215.GD25186@T590> References: <20201103030758.317781-1-xiubli@redhat.com> <20201103030758.317781-2-xiubli@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201103030758.317781-2-xiubli@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Mon, Nov 02, 2020 at 10:07:57PM -0500, xiubli@redhat.com wrote: > From: Xiubo Li > > The crash call trace: > > <6>[ 1012.319386] block nbd1: NBD_DISCONNECT > <1>[ 1012.319437] BUG: kernel NULL pointer dereference, address: 0000000000000020 > <1>[ 1012.319439] #PF: supervisor write access in kernel mode > <1>[ 1012.319441] #PF: error_code(0x0002) - not-present page > <6>[ 1012.319442] PGD 0 P4D 0 > <4>[ 1012.319448] Oops: 0002 [#1] SMP NOPTI > <4>[ 1012.319454] CPU: 9 PID: 25111 Comm: rbd-nbd Tainted: G E 5.9.0+ #6 > [...] > <4>[ 1012.319505] PKRU: 55555554 > <4>[ 1012.319506] Call Trace: > <4>[ 1012.319560] flush_workqueue+0x81/0x440 > <4>[ 1012.319598] nbd_disconnect_and_put+0x50/0x70 [nbd] > <4>[ 1012.319607] nbd_genl_disconnect+0xc7/0x170 [nbd] > <4>[ 1012.319627] genl_rcv_msg+0x1dd/0x2f9 > <4>[ 1012.319642] ? genl_start+0x140/0x140 > <4>[ 1012.319644] netlink_rcv_skb+0x49/0x110 > <4>[ 1012.319649] genl_rcv+0x24/0x40 > <4>[ 1012.319651] netlink_unicast+0x1a5/0x280 > <4>[ 1012.319653] netlink_sendmsg+0x23d/0x470 > <4>[ 1012.319667] sock_sendmsg+0x5b/0x60 > <4>[ 1012.319676] ____sys_sendmsg+0x1ef/0x260 > <4>[ 1012.319679] ? copy_msghdr_from_user+0x5c/0x90 > <4>[ 1012.319680] ? ____sys_recvmsg+0xa5/0x180 > <4>[ 1012.319682] ___sys_sendmsg+0x7c/0xc0 > <4>[ 1012.319683] ? copy_msghdr_from_user+0x5c/0x90 > <4>[ 1012.319685] ? ___sys_recvmsg+0x89/0xc0 > <4>[ 1012.319692] ? __wake_up_common_lock+0x87/0xc0 > <4>[ 1012.319715] ? __check_object_size+0x46/0x173 > <4>[ 1012.319727] ? _copy_to_user+0x22/0x30 > <4>[ 1012.319729] ? move_addr_to_user+0xc3/0x100 > <4>[ 1012.319731] __sys_sendmsg+0x57/0xa0 > <4>[ 1012.319744] do_syscall_64+0x33/0x40 > <4>[ 1012.319760] entry_SYSCALL_64_after_hwframe+0x44/0xa9 > <4>[ 1012.319780] RIP: 0033:0x7f5baa8e3ad5 > > In case the reference of nbd->config has reached zero and the > related resource has been released, if another process tries to > send the DISCONENCT cmd by using the netlink, it will potentially > crash like this. > > Signed-off-by: Xiubo Li > --- > drivers/block/nbd.c | 25 ++++++++++++++++++++----- > 1 file changed, 20 insertions(+), 5 deletions(-) > > diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c > index f46e26c9d9b3..3bb8281bb753 100644 > --- a/drivers/block/nbd.c > +++ b/drivers/block/nbd.c > @@ -2003,16 +2003,31 @@ static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info) > > static void nbd_disconnect_and_put(struct nbd_device *nbd) > { > + bool flush = true; > + > mutex_lock(&nbd->config_lock); > nbd_disconnect(nbd); > nbd_clear_sock(nbd); > - mutex_unlock(&nbd->config_lock); > /* > - * Make sure recv thread has finished, so it does not drop the last > - * config ref and try to destroy the workqueue from inside the work > - * queue. > + * In very rare case that the nbd->recv_workq may already have been > + * released by the recv_work(). > */ > - flush_workqueue(nbd->recv_workq); > + if (likely(!nbd->recv_workq)) It is actually unlikely, but doesn't make any sense to annotate the check since it isn't fast path, so please remove it. > + refcount_inc(&nbd->config_refs); > + else > + flush = false; > + mutex_unlock(&nbd->config_lock); > + > + if (flush) { > + /* > + * Make sure recv thread has finished, so it does not drop > + * the last config ref and try to destroy the workqueue > + * from inside the work queue. > + */ > + flush_workqueue(nbd->recv_workq); > + nbd_config_put(nbd); > + } > + > if (test_and_clear_bit(NBD_RT_HAS_CONFIG_REF, > &nbd->config->runtime_flags)) > nbd_config_put(nbd); The approach is fine, and the reason is that nbd_disconnect_and_put() still can be called via netlink when the nbd device has been closed: Once the above likely() is removed, feel free to add: Reviewed-by: Ming Lei Thanks, Ming