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 03C26606A31C for ; Mon, 9 Nov 2026 13:59:01 +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=HtBYRDsK Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1xQPtG-0005CH-Hz; Mon, 09 Nov 2026 08:58:30 -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 1xQPt6-00052n-Fa for qemu-devel@nongnu.org; Mon, 09 Nov 2026 08:58:20 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1xQPt3-0007IH-Ce for qemu-devel@nongnu.org; Mon, 09 Nov 2026 08:58:20 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1794232695; 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=aeormPUN+IE5IR9JK1OrZdmwByJz1Sup5ujeu3UnUpA=; b=HtBYRDsKL67pYsMB5FHCmxWs4Bk9zaaOdp6T5U+0nGRqPS9PzvZnQJrzqq550804qXdG2i 3pGjHUovBYBrTOWA0JfdLKQ+l5eo0XvQpJE7J0rWw+Ij+uaLGRgZcSz5lIJcZdkLN6jcGG ZFmB5dFBtTJfY3H3aVSMda2QIulds6U= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-687-OOtiTlRtNQaaiiH2IV6ckg-1; Mon, 09 Nov 2026 08:58:10 -0500 X-MC-Unique: OOtiTlRtNQaaiiH2IV6ckg-1 X-Mimecast-MFC-AGG-ID: OOtiTlRtNQaaiiH2IV6ckg_1794232688 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (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-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 09A9F1800637; Mon, 9 Nov 2026 13:57:56 +0000 (UTC) Received: from redhat.com (headnet04.pony-001.prod.iad2.dc.redhat.com [10.2.32.116]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 8112F18004F5; Mon, 9 Nov 2026 13:57:53 +0000 (UTC) Date: Mon, 9 Nov 2026 07:57:50 -0600 From: Eric Blake To: qemu-devel@nongnu.org Cc: 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: 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> User-Agent: NeoMutt/20260616 X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 Received-SPF: pass client-ip=170.10.129.124; envelope-from=eblake@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 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_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=unavailable 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=-22.3 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,USER_AGENT_SANE_1 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. CVE-2026-124559 has been assigned; I'll update the commit message accordingly before the pull request, if no other changes in the series are requested. > > 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(-) > > diff --git a/nbd/server.c b/nbd/server.c > index e6c47f8c2e3..bc37cbcb338 100644 > --- a/nbd/server.c > +++ b/nbd/server.c > @@ -2584,12 +2584,12 @@ nbd_co_block_status_payload_read(NBDClient *client, NBDRequest *request, > return -EINVAL; > } > > - assert(client->contexts.exp == client->exp); > nr_bitmaps = client->exp->nr_export_bitmaps; > request->contexts = g_new0(NBDMetaContexts, 1); > request->contexts->exp = client->exp; > > - if (payload_len % sizeof(uint32_t) || > + if (!client->contexts.count || > + payload_len % sizeof(uint32_t) || > payload_len < sizeof(NBDBlockStatusPayload) || > payload_len > (sizeof(NBDBlockStatusPayload) + > sizeof(id) * client->contexts.count)) { > -- > 2.56.0 > > -- Eric Blake, Principal Software Engineer Red Hat, Inc. 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