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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 89241C3DA7F for ; Wed, 7 Aug 2024 18:30:12 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1sblPs-0004sR-F4; Wed, 07 Aug 2024 14:29:44 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1sblPp-0004em-C6 for qemu-devel@nongnu.org; Wed, 07 Aug 2024 14:29:41 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1sblPm-00063M-Rp for qemu-devel@nongnu.org; Wed, 07 Aug 2024 14:29:40 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1723055377; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=V3DL5fY+1h4XM5i3gTPixbwdC4381vvzw/q4aERMqgo=; b=VwE5pWycoam5Udi+mGVj/JgTEB4npuEl9jegW8jk57+uehfw1uvRk5zs5FAw/vcf53xaIa Hf1TGN3mFOXX+wEK8Lcloh/pEy3EhMT/jTWNKphxfyiHGbOpUSbUzTb2r5X4XKR2V/eS9p bzg7oNaG3NNDZ0xIZWsoqz+bYnYQTeE= Received: from mx-prod-mc-02.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-370-CGHjcbBUPOi7e2cBnc0s9Q-1; Wed, 07 Aug 2024 14:29:34 -0400 X-MC-Unique: CGHjcbBUPOi7e2cBnc0s9Q-1 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id D95C41955D5E; Wed, 7 Aug 2024 18:29:32 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.79]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 149513000199; Wed, 7 Aug 2024 18:29:28 +0000 (UTC) Date: Wed, 7 Aug 2024 19:29:25 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Eric Blake Cc: qemu-devel@nongnu.org, kwolf@redhat.com, hreitz@redhat.com, qemu-block@nongnu.org, den@virtuozzo.com, andrey.drobyshev@virtuozzo.com, alexander.ivanov@virtuozzo.com, vsementsov@yandex-team.ru Subject: Re: [PATCH v4 5/7] nbd/server: CVE-2024-7409: Close stray client sockets at shutdown Message-ID: References: <20240807174943.771624-9-eblake@redhat.com> <20240807174943.771624-14-eblake@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20240807174943.771624-14-eblake@redhat.com> User-Agent: Mutt/2.2.12 (2023-09-09) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.144, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Wed, Aug 07, 2024 at 12:43:31PM -0500, Eric Blake wrote: > A malicious client can attempt to connect to an NBD server, and then > intentionally delay progress in the handshake, including if it does > not know the TLS secrets. Although this behavior can be bounded by > the max-connections parameter, the QMP nbd-server-start currently > defaults to unlimited incoming client connections. Worse, if the > client waits to close the socket until after the QMP nbd-server-stop > command is executed, qemu will then SEGV when trying to dereference > the NULL nbd_server global which is no longer present, which amounts > to a denial of service attack. If another NBD server is started > before the malicious client disconnects, I cannot rule out additional > adverse effects when the old client interferes with the connection > count of the new server. > > For environments without this patch, the CVE can be mitigated by > ensuring (such as via a firewall) that only trusted clients can > connect to an NBD server. Note that using frameworks like libvirt > that ensure that TLS is used and that nbd-server-stop is not executed > while any trusted clients are still connected will only help if there > is also no possibility for an untrusted client to open a connection > but then stall on the NBD handshake. > > Given the previous patches, it would be possible to guarantee that no > clients remain connected by having nbd-server-stop sleep for longer > than the default handshake deadline before finally freeing the global > nbd_server object, but that could make QMP non-responsive for a long > time. So intead, this patch fixes the problem by tracking all client > sockets opened while the server is running, and forcefully closing any > such sockets remaining without a completed handshake at the time of > nbd-server-stop, then waiting until the coroutines servicing those > sockets notice the state change. nbd-server-stop now has a second > AIO_WAIT_WHILE_UNLOCKED (the first is indirectly through the > blk_exp_close_all_type() that disconnects all clients that completed > handshakes), but forced socket shutdown is enough to progress the > coroutines and quickly tear down all clients before the server is > freed, thus finally fixing the CVE. > > This patch relies heavily on the fact that nbd/server.c guarantees > that it only calls nbd_blockdev_client_closed() from the main loop > (see the assertion in nbd_client_put() and the hoops used in > nbd_client_put_nonzero() to achieve that); if we did not have that > guarantee, we would also need a mutex protecting our accesses of the > list of connections to survive re-entrancy from independent iothreads. > > Although I did not actually try to test old builds, it looks like this > problem has existed since at least commit 862172f45c (v2.12.0, 2017) - > even back when that patch started using a QIONetListener to handle > listening on multiple sockets, nbd_server_free() was already unaware > that the nbd_blockdev_client_closed callback can be reached later by a > client thread that has not completed handshakes (and therefore the > client's socket never got added to the list closed in > nbd_export_close_all), despite that patch intentionally tearing down > the QIONetListener to prevent new clients. > > Reported-by: Alexander Ivanov > Fixes: CVE-2024-7409 > Signed-off-by: Eric Blake > --- > blockdev-nbd.c | 35 ++++++++++++++++++++++++++++++++++- > 1 file changed, 34 insertions(+), 1 deletion(-) Reviewed-by: Daniel P. Berrangé With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|