From nobody Mon Feb 9 14:38:09 2026 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) client-ip=208.118.235.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zohomail.com; spf=pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org Return-Path: Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) by mx.zohomail.com with SMTPS id 1510178498720559.2975805578801; Wed, 8 Nov 2017 14:01:38 -0800 (PST) Received: from localhost ([::1]:34091 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eCYPc-0008Mr-Vt for importer@patchew.org; Wed, 08 Nov 2017 17:01:33 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45847) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eCYLU-0004z8-KJ for qemu-devel@nongnu.org; Wed, 08 Nov 2017 16:57:17 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1eCYLT-0000UM-RA for qemu-devel@nongnu.org; Wed, 08 Nov 2017 16:57:16 -0500 Received: from mx1.redhat.com ([209.132.183.28]:52618) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1eCYLQ-0000Sm-7t; Wed, 08 Nov 2017 16:57:12 -0500 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 40117C04AC49; Wed, 8 Nov 2017 21:57:11 +0000 (UTC) Received: from red.redhat.com (ovpn-125-14.rdu2.redhat.com [10.10.125.14]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0D4315EE01; Wed, 8 Nov 2017 21:57:09 +0000 (UTC) From: Eric Blake To: qemu-devel@nongnu.org Date: Wed, 8 Nov 2017 15:56:58 -0600 Message-Id: <20171108215703.9295-3-eblake@redhat.com> In-Reply-To: <20171108215703.9295-1-eblake@redhat.com> References: <20171108215703.9295-1-eblake@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.31]); Wed, 08 Nov 2017 21:57:11 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.132.183.28 Subject: [Qemu-devel] [PATCH v2 2/7] nbd-client: Refuse read-only client with BDRV_O_RDWR X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, vsementsov@virtuozzo.com, qemu-block@nongnu.org, qemu-stable@nongnu.org, Max Reitz , pbonzini@redhat.com Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail: RSF_0 Z_629925259 SPT_0 Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" The NBD spec says that clients should not try to write/trim to an export advertised as read-only by the server. But we failed to check that, and would allow the block layer to use NBD with BDRV_O_RDWR even when the server is read-only, which meant we were depending on the server sending a proper EPERM failure for various commands, and also exposes a leaky abstraction: using qemu-io in read-write mode would succeed on 'w -z 0 0' because of local short-circuiting logic, but 'w 0 0' would send a request over the wire (where it then depends on the server, and fails at least for qemu-nbd but might pass for other NBD implementations). With this patch, a client MUST request read-only mode to access a server that is doing a read-only export, or else it will get a message like: can't open device nbd://localhost:10809/foo: request for write access confl= icts with read-only export It is no longer possible to even attempt writes over the wire (including the corner case of 0-length writes), because the block layer enforces the explicit read-only request; this matches the behavior of qcow2 when backed by a read-only POSIX file. Fix iotest 147 to comply with the new behavior (since nbd-server-add defaults to a read-only export, we must tell blockdev-add to set up a read-only client). CC: qemu-stable@nongnu.org Signed-off-by: Eric Blake Reviewed-by: Vladimir Sementsov-Ogievskiy --- v2: retitle; require explicit read-only request, rather than magically setting it (includes iotest fallout) [Kevin] --- block/nbd-client.c | 9 +++++++++ tests/qemu-iotests/147 | 1 + 2 files changed, 10 insertions(+) diff --git a/block/nbd-client.c b/block/nbd-client.c index de6c153328..daa4392531 100644 --- a/block/nbd-client.c +++ b/block/nbd-client.c @@ -697,6 +697,7 @@ int nbd_client_co_pwritev(BlockDriverState *bs, uint64_= t offset, .len =3D bytes, }; + assert(!(client->info.flags & NBD_FLAG_READ_ONLY)); if (flags & BDRV_REQ_FUA) { assert(client->info.flags & NBD_FLAG_SEND_FUA); request.flags |=3D NBD_CMD_FLAG_FUA; @@ -717,6 +718,7 @@ int nbd_client_co_pwrite_zeroes(BlockDriverState *bs, i= nt64_t offset, .len =3D bytes, }; + assert(!(client->info.flags & NBD_FLAG_READ_ONLY)); if (!(client->info.flags & NBD_FLAG_SEND_WRITE_ZEROES)) { return -ENOTSUP; } @@ -756,6 +758,7 @@ int nbd_client_co_pdiscard(BlockDriverState *bs, int64_= t offset, int bytes) .len =3D bytes, }; + assert(!(client->info.flags & NBD_FLAG_READ_ONLY)); if (!(client->info.flags & NBD_FLAG_SEND_TRIM)) { return 0; } @@ -814,6 +817,12 @@ int nbd_client_init(BlockDriverState *bs, logout("Failed to negotiate with the NBD server\n"); return ret; } + if (client->info.flags & NBD_FLAG_READ_ONLY && + !bdrv_is_read_only(bs)) { + error_setg(errp, + "request for write access conflicts with read-only expo= rt"); + return -EACCES; + } if (client->info.flags & NBD_FLAG_SEND_FUA) { bs->supported_write_flags =3D BDRV_REQ_FUA; bs->supported_zero_flags |=3D BDRV_REQ_FUA; diff --git a/tests/qemu-iotests/147 b/tests/qemu-iotests/147 index db34838cd0..90f40ed245 100755 --- a/tests/qemu-iotests/147 +++ b/tests/qemu-iotests/147 @@ -43,6 +43,7 @@ class NBDBlockdevAddBase(iotests.QMPTestCase): 'driver': 'raw', 'file': { 'driver': 'nbd', + 'read-only': True, 'server': address } } if export is not None: --=20 2.13.6