From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lists1p.gnu.org (lists1p.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-ECDSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BCE54606A321 for ; Mon, 9 Nov 2026 15:52:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=QbJ4Y4pP Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1xQRet-0002Ju-BR; Mon, 09 Nov 2026 10:51:47 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1xQRej-0002JF-VT for qemu-devel@nongnu.org; Mon, 09 Nov 2026 10:51:37 -0500 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 1xQRef-0003wY-HK for qemu-devel@nongnu.org; Mon, 09 Nov 2026 10:51:36 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1794239492; 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=8qFJ5912sKHUz+BUOeTvZaGPgcR8ezIP40MkvtClxSc=; b=QbJ4Y4pPMnNTw0s1dv9STxN8BMeP15Xu1YlhtxnTdN6z/0b9GRhOVqBmf4nF/rbStD59oo 8TgeOuQfEVf8E+jNjD2a3MX2+/Dn+5T3piRfmG3m1JeP+xTz7/1is6tFv85Ti2gAGLSdid deFUL2AbaohvBvL8WyNRxDJ1cs32FP4= Received: from mx-prod-mc-03.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-678-3jZ9fS5LNvuflp1NW56Rgw-1; Mon, 09 Nov 2026 10:51:28 -0500 X-MC-Unique: 3jZ9fS5LNvuflp1NW56Rgw-1 X-Mimecast-MFC-AGG-ID: 3jZ9fS5LNvuflp1NW56Rgw_1794239486 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-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id A269E1955F7D; Mon, 9 Nov 2026 15:51:25 +0000 (UTC) Received: from localhost (headnet04.pony-001.prod.iad2.dc.redhat.com [10.2.32.116]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id AB7B030000E5; Mon, 9 Nov 2026 15:51:24 +0000 (UTC) Date: Mon, 9 Nov 2026 08:51:23 -0700 From: Stefan Hajnoczi To: Eric Blake Cc: qemu-devel@nongnu.org, qemu-stable@nongnu.org, berrange@redhat.com, qemu-block@nongnu.org, Feifan Qian , Haotian Jiang , Vladimir Sementsov-Ogievskiy Subject: Re: [PATCH v2 2/3] nbd/server: Reject rather than assert on non-compliant BLOCK_STATUS Message-ID: <20261109155123.GC429574@shajnocz.csb> References: <20261107225834.778738-5-eblake@redhat.com> <20261107225834.778738-7-eblake@redhat.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261107225834.778738-7-eblake@redhat.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Received-SPF: pass client-ip=170.10.133.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 5 X-Spam_score: 0.5 X-Spam_bar: / X-Spam_report: (0.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Archive: List-Post: List-Help: List-Subscribe: , Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org X-Spam-Status: No, score=-20.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Sat, Nov 07, 2026 at 04:54:37PM -0600, Eric Blake wrote: > The NBD spec is clear that a client must not send NBD_BLOCK_STATUS > requests to a server if it did not negotiate any metacontexts with > NBD_OPT_SET_META_CONTEXT. However, if the non-compliant client uses > NBD_OPT_EXTENDED_HEADERS and then passes in the relatively new > NBD_CMD_FLAG_PAYLOAD_LEN flag alongside an inappropriate block status > request, this was enough to trigger an assertion in qemu. > > If you do not use recommended practice to prevent untrusted clients > from connecting to QEMU's NBD server, then you are at risk of a denial > of service attack from a rogue client. Per our stated policy on flaws > triggered by network connections, this is considered a low-severity > security flaw, since it is trivial to avoid by using proper > configuration of TLS and x509 certificate authorization to reject > rogue clients; therefore, no CVE has been assigned yet. > > Fixes: 2dcbb11b ("nbd/server: Add FLAG_PAYLOAD support to CMD_BLOCK_STATUS", v8.2.0) > Reported-by: Feifan Qian > Reported-by: https://gitlab.com/qemu-project/qemu/-/work_items/3796 > CC: Haotian Jiang > CC: qemu-stable@nongnu.org > Signed-off-by: Eric Blake > --- > nbd/server.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) Reviewed-by: Stefan Hajnoczi